Tesi: "High-Frequency RADARs"

1

Woodfield, Emma Elizabeth. "Studies of nightside spectral with behaviour from coherent high frequency radars". Thesis, University of Leicester, 2002. http://hdl.handle.net/2381/30664.

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The work presented in this thesis is aimed to improving our understanding of the HF Doppler spectral width parameter and how it can be used to identify ionospheric and magnetospheric boundaries, specifically the use of the frequently observed gradient between high (>200 m s-1) and low (<200 m s-1) spectral width. Locating the boundaries between regions is important to the study of how the magnetosphere responds to the solar wind and interplanetary magnetic field conditions. Three case studies and a statistical investigation are presented herein which investigate the nature of these regions. Data from the Co-operative U.K. Twin Located Auroral Sounding System (CUTLASS) HF radars and the European Incoherent SCATter (EISCAT) radars from the primary observations. The cases presented show that high spectral width can be observed both on open and closed magnetic field lines, and that there is a relationship between elevated electron temperature and high spectral width (although the reverse is not true) which appears to be restricted to the post 0300 MLT nightside region. The data also show that high spectral widths can be associated with both single- and multiple-peak HF spectra. The statistical study compares three years of data from the CUTLASS radars and the Syowa East radar (part of the Super Dual Auroral Radar Network, SuperDARN), magnetically conjugate to Iceland East. It is found that the mean spectral width is dependent on latitude, magnetic local time (MLT) and season. The data from the two hemispheres show similar dependence on these factors, although the Syowa East spectral widths are larger in general (instrumental variations are discounted). These results suggest that the physical mechanism(s) creating the high spectral widths must work both on open and closed field lines, be dependent upon latitude and MLT, and be less prevalent (or attenuated) in summer months.

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2

Burger, Johann. "High frequency surface wave radar demonstrator". Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29408.

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High Frequency Surface Wave Radar (HFSWR) is used around the globe for the mapping of sea currents and coastal monitoring of the Exclusive Economic Zone. Decision to build an HF radar at the University of Cape Town (UCT) was made by Daniel O’Hagan and Andrew Wilkinson in February 2015 immediately after seeing a demonstration of the CODAR system at IMT. Their intention was subsequently discussed at several meetings, including a South African Radar Interest Group (SARIG) meeting and one at IMT in order to gauge interest and raise funding. There was both interest (mainly for ocean current monitoring) and scepticism (expressed by CSIR and SARIG members) of the value of HF radar for ship monitoring. This reports the design, construction, test, and evaluation of the UCT HFSWR demonstrator. A modular approach was taken in its design and construction making it easy to replicate and upscale. A pillar of this work is to prove the feasibility of a software defined radar (SDR) based HF radar demonstrator. Every part of the demonstrator was designed and constructed from scratch as UCT had no prior HF activities, and therefore no legacy antennas or components to utilise. A low-cost RF frontend follows the HF antennas, which were also designed for this project. Combined with an SDR platforn known as the Red Pitaya (RP), a complete HF radar demonstrator was assembled and trials were conducted at the UCT rugby field and at the IMT facilities in Simon’s Town. A preliminary assessment of the results reveal the effects of Bragg resonance scatter and detection of two stationary targets (mountains) distinguishable by both range and azimuth. This assessment of the results indicates that the demonstrator is operational.

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3

Middleditch, Andrew. "Spectral analysis in high frequency radar oceanography". Thesis, University of Sheffield, 2006. http://etheses.whiterose.ac.uk/3590/.

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High Frequency radar systems provide a unique opportunity to measure evolving littoral oceanic dynamics at high temporal and spatial resolution. Backscattered electromagnetic signals from ocean waves are modulated by Bragg resonant scattering. A perturbation analysis yields an expression for the spectral content of radar signals which can be exploited to provide estimates of oceanographic parameters: the radial component of surface current can be extracted from the frequency locations of the first order peaks; the ocean wave directional spectrum is related to the second order continuum via a non-linear integral equation. The periodogram, based on a Fourier decomposition of radax data, is the standard method used to derive frequency spectra. Limitations in this approach, caused by inhomogeneities in the underlying ocean field, are investigated. An instantaneous frequency technique is proposed in this thesis which mitigates the spectral distortion by demodulating the backscattered radax signals -a filtering procedure is developed which measures the temporally varying Bragg components. Alternative spectral techniques are analysed in order to validate the filter: an autoregressive paxa, metric modelling approach and an eigendecomposition method. The filter is evaluated, using radar and in situ data, which establishes its potential for ocean remote sensing. Significant improvements in the quantity and accuracy of wave measurements are demonstrated. Properties and constraints of the filter are derived using simulated data. Finally, the generic structure of the extracted instantaneous frequency signals is investigated and related to oceanographic processes.

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4

Paulose, Abraham Thomas. "High radar resolution with the step frequency waveform". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA284611.

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5

Warren, Craig. "Numerical modelling of high-frequency ground-penetrating radar antennas". Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/4074.

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Ground-Penetrating Radar (GPR) is a non-destructive electromagnetic investigative tool used in many applications across the fields of engineering and geophysics. The propagation of electromagnetic waves in lossy materials is complex and over the past 20 years, the computational modelling of GPR has developed to improve our understanding of this phenomenon. This research focuses on the development of accurate numerical models of widely-used, high-frequency commercial GPR antennas. High-frequency, highresolution GPR antennas are mainly used in civil engineering for the evaluation of structural features in concrete i. e., the location of rebars, conduits, voids and cracking. These types of target are typically located close to the surface and their responses can be coupled with the direct wave of the antenna. Most numerical simulations of GPR only include a simple excitation model, such as an infinitesimal dipole, which does not represent the actual antenna. By omitting the real antenna from the model, simulations cannot accurately replicate the amplitudes and waveshapes of real GPR responses. Numerical models of a 1.5 GHz Geophysical Survey Systems, Inc. (GSSI) antenna and a 1.2 GHz MALÅ GeoScience (MALÅ) antenna have been developed. The geometry of antennas is often complex with many fine features that must be captured in the numerical models. To visualise this level of detail in 3d, software was developed to link Paraview—an open source visualisation application which uses the Visualisation Toolkit (VTK)—with GprMax3D—electromagnetic simulation software based on the Finite-Difference Time-Domain (FDTD) method. Certain component values from the real antennas that were required for the models could not be readily determined due to commercial sensitivity. Values for these unknown parameters were found by implementing an optimisation technique known as Taguchi’s method. The metric used to initially assess the accuracy of the antenna models was a cross-corellation of the crosstalk responses from the models with the crosstalk responses measured from the real antennas. A 98 % match between modelled and real crosstalk responses was achieved. Further validation of the antenna models was undertaken using a series of laboratory experiments where oil-in-water (O/W) emulsions were created to simulate the electrical properties of real materials. The emulsions provided homogeneous liquids with controllable permittivity and conductivity and enabled different types of targets, typically encountered with GPR, to be tested. The laboratory setup was replicated in simulations which included the antenna models and an excellent agreement was shown between the measured and modelled data. The models reproduced both the amplitude and waveshape of the real responses whilst B-scans showed that the models were also accurately capturing effects, such as masking, present in the real data. It was shown that to achieve this accuracy, the real permittivity and conductivity profiles of materials must be correctly modelled. The validated antenna models were then used to investigate the radiation dynamics of GPR antennas. It was found that the shape and directivity of theoretically predicted far-field radiation patterns differ significantly from real antenna patterns. Being able to understand and visualise in 3d the antenna patterns of real GPR antennas, over realistic materials containing typical targets, is extremely important for antenna design and also from a practical user perspective.

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6

Svensson, Johan. "High Resolution Frequency Estimation in an FMCW Radar Application". Thesis, Linköpings universitet, Reglerteknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-148526.

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FMCW radars are widely used in the process industry for range estimation, usu- ally for estimating the liquid level in a tank. Since the tank system, often is an automatically controlled system, reliable estimates of the surface level are re- quired, e.g. to avoid the tank from pouring over or become empty. The goal of this thesis is to investigate methods which can distinguish fre- quencies closer to each other than the FFT resolution limit. Two properties are of interest, the accuracy and the resolution performance. Three such methods have been evaluated: one that tries to compensate for the leakage and interference of close frequencies, one subspace-based method and one deconvolution method. The deconvolution is performed with the iterative Lucy Richardson algorithm. The methods are evaluated against each other and against a typical FFT based algorithm. The methods sensitivity to amplitude differences is examined together with the robustness against noise and disturbances which appear due to imperfections in the radar unit. The deconvolution algorithm is the one that performs the best. The subspace-based method SURE requires prior knowledge of the number of ingoing frequencies which is difficult to know for real data from an FMCW radar. The leakage compensation method main weakness is the influence of the phase difference between close frequencies. The deconvolution algorithm is evaluated on some real data, and it is proven that it has better resolution performance than the FFT. However, the accuracy of the estimates are dependent on the number of iterations used. With a large num- ber of iterations, the algorithm finds peaks with small amplitude nearby the large peaks and they will thus interact and hence contribute to a worse accuracy even in the undisturbed case. If too few iterations are used in the deconvolution algo- rithm the resolution performance is about the same as the FFT algorithm. With a suitable choice of iterations about 40–50 mm, extra of continuous measurements are achieved. However, the estimation error of the gained resolution can in the worst case be about 40–50 mm.

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7

Green, Sean David. "Improving the range information of high frequency over-the-horizon skywave radar". Thesis, University of Sheffield, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268265.

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8

Delgado, Raymond R. "Mapping coastal surface winds in Monterey Bay using high frequency radar". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1999. http://handle.dtic.mil/100.2/ADA362924.

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Thesis (M.S. in Meteorology and M.S. in Physical Oceanography) Naval Postgraduate School, March 1999.
"March 1999". Thesis advisor(s): Jeffrey D. Paduan, Carlyle H. Wash. Includes bibliographical references (p. 121-122). Also available online.

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9

Chang, Paul Chinling. "Near zone radar imaging and feature capture of building interiors". Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1197399599.

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10

Palmer, David J. "Topside sounding on a microsatellite". Thesis, University of Surrey, 1997. http://epubs.surrey.ac.uk/844211/.

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An ionospheric topside sounder is a high frequency radar system that is located above the ionosphere, ideally on-board a polar orbiting satellite to provide global coverage. The previous eight satellite sounders have measured the critical frequency of the F2 ionosphere region using traditional swept frequency methods. The most expensive part of these missions however is considered to be the large network of ground support stations required for collecting and processing data. This information has been invaluable in improving our global understanding of the upper ionosphere and the accuracy of critical frequency maps used by HF radio engineers to calculate communications routes and the optimum frequencies for early warning OTH radars. A new technique for the direct detection of critical frequency has been developed, which is called the 'Dispersion Method'. Real data from previous sounders is used in the development and verification of this method. This sounder will not only provide traditional lonograms but detects critical frequency and spread echoes directly from the dispersion of a returning radar pulse. This new method does not use traditional lonograms with their inherent processing complexity and is an order faster than any previous sounder. The 'Dispersion Method' therefore resolves the problems encountered with the past topside sounder missions and produces large quantities of real time data autonomously when required. Previous sounding satellites had little memory capacity, no on-board processing capability, required large antennas and transmitters on satellites with a mass of between 150 and 250 kg. This meant power requirements of about 60 watts per orbit average. A feasibility study to place a third generation topside sounder into low Earth orbit on a 50 kg microsatellite with an orbit average power capacity of only 20 watts has been successfully completed.

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11

Kim, Kyung Cheol. "Calibration and validation of high frequency radar for ocean surface current mapping". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Jun%5FKim.pdf.

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12

Schmid, Robert L. "High-frequency silicon-germanium reconfigurable circuits for radar, communication, and radiometry applications". Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/54838.

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The objective of the proposed research is to create new reconfigurable RF and millimeter-wave circuit topologies that enable significant systems benefits. The market of RF systems has long evolved under a paradigm where once a system is built, performance cannot be changed. Companies have recognized that building flexibility into RF systems and providing mechanisms to reconfigure the RF performance can enable significant benefits, including: the ability support multiple modulation schemes and standards, the reduction of product size and overdesign, the ability to adapt to environmental conditions, the improvement in spectrum utilization, and the ability to calibrate, characterize, and monitor system performance. This work demonstrates X-band LNA designs with the ability to change the frequency of operation, improve linearity, and digitally control the tradeoff between performance and power dissipation. At W-band frequencies, a novel device configuration is developed, which significantly improves state-of-the-art silicon-based switch performance. The excellent switch performance is leveraged to address major issues in current millimeter-wave systems. A front-end built-in-self-test switch topology is developed to facilitate the characterization of millimeter-wave transceivers without expensive millimeter-wave equipment. A highly integrated Dicke radiometer is also created to enable sensitive measurements of thermal noise.

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13

Everaere, Etienne. "Polarimetry in Bistatic Configuration for Ultra High Frequency Radar Measurements on Forest Environment". Palaiseau, Ecole polytechnique, 2015. https://theses.hal.science/tel-01199522/document.

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Les systèmes radar permettent de couvrir de larges zones et grâce à la capacité qu’ont les ondes électromagnétiques qu’ils utilisent de passer à travers les milieux, le radar est un des outils les plus approprié pour la télédétection dans la forêt. Mais pour une utilisation efficace, il est important de choisir de bonne conﬁguration d’acquisition. À trop haute fréquence l’onde ne pénètre pas, c’est pourquoi nous limitons notre étude aux bandes UHF, P et L. De plus, un système radar qui utilise une diversité de polarisations d’émission et de réception peut récolter plus d’information de la scène, car la polarisation est sensible à la structure de la forêt. Avec un récepteur radar dissocié de l’émetteur, la polarimétrie a encore plus de potentiel car la symétrie entre les trajets aller et retour du monostatique est évité. Le but de cette thèse est d’anticiper des mesures réelles bistatiques en bande P sur la forêt. Cela permet de donner des paramètres clés pour choisir la meilleure conﬁguration que ce soit pour une application dans l’inversion des paramètres physiques de la forêt ou la détection d’objets artiﬁciels dans la forêt. La solution que nous proposons consiste en l’utilisation d’un polarimètre à l’échelle optique et qui permet de faire des mesures sur un ensemble de conﬁgurations bistatiques à la fois. Les scènes utilisées sont constituées de nanotubes de carbone qui reproduisent les caractéristiques structurelles et diélectriques de forêts de troncs à l’échelle radar. Nous démontrons que ces mesures peuvent être utilisées pour anticiper la mesure bistatique radar mais elles permettent également la validation des codes de simulation existants. Le code COBISMO développé pour le radar peut reproduire les mesures de nanotubes. En utilisant les résultats de comparaison, le code de simulation est ensuite appliqué pour étudier les conﬁgurations et les polarisations les plus à même de retrouver l’orientation des branches et pour la détection sous le couvert forestier
Due to penetration capabilities of electromagnetic waves and the possibility to cover large areas, radar is one of the most appropriate tool for remote sensing of forest. To use radar images for forestry, it is crucial to select and optimize the best conﬁgurations of acquisition. If the frequency is too high, no penetration occurs and only the top leafs will play a role in the scattering events. Large wavelengths used in radar are more able to penetrate the forest elements and to interact also with the ground below. For this reason, we limit this thesis to the use of UHF, P-band and L-band. By emitting and receiving several couples of polarizations, several images can be collected. The polarimetry is sensitive the structure information and consequently, it can bring a diversity of information. A radar system which comprises a transmitter and receiver which are spatially separated is an opportunity to supply additional information to classical polarimetric radar, because it breaks symmetry observed in the monostatic case. The aim of the thesis is to anticipate real P-band bistatic radar measurements on forest and to give keys to choose more appropriate conﬁguration for a given application: physical parameter retrieval or target detection. The solution we propose is to construct an optical scale device that is full polarimetric and that handle the bistatic conﬁgurations, and to measure scene having a structure comparable to a real forest. We demonstrate that the optical scale measurement can be used to anticipate polarimetric behavior of forest and jointly to validate our simulation code. Polarization and conﬁguration are studied to discriminate branch orientation and to detect man-made objects in the forest

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14

Streed, Daniel H. "High-frequency meteorological phenomena observed with the Naval Postgraduate School's UHF Doppler Wind Profiler". Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA243762.

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Thesis (M.S. in Meteorology and Physical Oceanography)--Naval Postgraduate School, December 1990.
Thesis Advisor(s): Nuss, Wendell A. Second Reader: Wash, C. H. "December 1990." Description based on title screen as viewed on March 30, 2010. DTIC Descriptor(s): Marine Meteorology, Meteorological Radar, Wind, Specifications, Comparison, Doppler Radar, Accuracy, Theses, Meteorological Data, Time, Short Range(Time), Reliability, Profiles, Scale, Data Acquisition, California, Inversion, Statistical Analysis, Meteorological Phenomena, Radiosondes, Schools, Ultrahigh Frequency, High Frequency, Contracts. DTIC Identifier(s): Wind Profilers. Author(s) subject terms: Doppler Wind Profiler, Wind Profiler, Doppler Radar. Includes bibliographical references (p. 115-117). Also available in print.

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15

Sova, Markus Gintas. "The sampling variability and the validation of high frequency radar measurements of the sea surface". Thesis, University of Sheffield, 1995. http://etheses.whiterose.ac.uk/12786/.

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Remote sensing is becoming an increasingly important tool for ocean wave measurement, and over the past decade much progress has been made in the development of the wave measuring capabilities of HF (High Frequency) radar. This system is able to make detailed and near continuous observations of the sea surface over a wide area. However, because the mathematics of the data extraction process is rather difficult, the statistical properties of the observed data have to date been poorly understood. In this study, the approximate sampling distributions of a variety of measurements from HF radar (including significant waveheight, mean wave period, wind direction, and various spectral parameters) are derived in terms of quantities that are either known or estimable. The resulting confidence intervals are, in the case of significant waveheight and mean wave period, of comparable width to those obtained from the corresponding NURWEC2 (Netherlands UK Radar Wave buoy Experimental Comparison) wave buoy measurements, and in the case of spectral power, they are narrower. Furthermore, methods are derived by which such radar measurements may be compared with their corresponding wave buoy measurements in a statistically valid manner, and their relative biases estimated. These methods are then applied to data taken during the NURWEC2 field trial, which suggest that the radars and the wave buoy show good correspondence for measurements of significant waveheight and of spectral power (over 85 - 125mHz - the frequencies with most wave power, and hence those of most importance). There is also a fair correspondence for mean period measurements in the range 6.8 - 11.0secs. Spectral mean direction shows good correspondence over 85 - 155mHz over the somewhat limited directional range (i. e. as observed during the NURWEC2 storm) of the data.

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16

Bourg, Natacha. "Interactions between boundary currents, fronts and eddies in the Northern Current and the East Australian Current. : Transport dynamics and application to the journey of Physalia spp". Electronic Thesis or Diss., Toulon, 2024. http://www.theses.fr/2024TOUL0001.

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Les courants de bords, caractérisés par de fortes vitesses et de nombreuses interactions dynamiques avec les marges continentales, sont les principaux moteurs de la variabilité océanique dans les régions côtières qu’ils traversent. La première partie de cette thèse se concentre sur les observations Radar Haute-Fréquence du Courant Nord dans la Méditerranée Nord-Occidentale et du courant est-australien dans l’océan Pacifique Sud. Nous étudions la variabilité saisonnière et interannuelle du courant et le développement de tourbillons de (sous) méso-échelle dans le système du Courant Nord. Concernant le courant est-Australien, nous examinons plus particulièrement sa dynamique de séparation, ses caractéristiques frontales et son impact sur la concentration de chlorophylle-a en surface.Les courants de bord, de par leur grande étendue et leur position le long du plateau continental,sont importants car ils agissent à la fois comme des barrières et des courroies de transport de matière passive. La deuxième partie se concentre sur Physalia spp., un organisme urticant pseudo-passif flottant à la surface de l’océan qui atteint régulièrement les côtes australiennes. Nous avons pu estimer l’impact relatif des variables météo-marines sur leur échouage. A partir d’expériences en laboratoire, nous établissons une paramétrisation de la dérive de maquettes 3D de Physalia spp. induite par le vent. Ce résultat,intégré dans une modélisation de suivi lagrangien selon des scénarios typiques du courant est-Australien nous permet de déterminer l’influence cumulée du vent et du courant sur les trajectoires des Physalia spp. Les résultats présentés dans cette thèse contribuent à la connaissance de deux courants de bord, caractérisés par des échelles et des modes de variabilité différents, et illustrent leur rôle dans le transport de matière passive à travers l’étude de la dérive de Physalia spp
Boundary currents, characterized by strong velocities and dynamic interactions with continental margins are the main drivers of ocean variability in the adjacent coastal regions. The first part of the thesis focuses on High-Frequency RADAR observations of the Northern Current in the North Western Mediterranean Sea and of the East Australian Current in the South Pacific Ocean. In the Northern Current system, we investigate the seasonal and inter-annual variability of the current and the occurrence of (sub) mesoscale eddies, while we focus on the study of the separation dynamics of the East Australian Current, its frontal characteristics and overall impact on surface chlorophyll-a concentration. Boundary currents, by their spatial extent and position along the continental shelf, are important in acting both as barriers and conveyers of transport of passive matter. The second part of the thesis focuses on Physalia spp., a pseudo-passive stinging organism floating at the ocean surface which regularly reaches Australian shores. We are able to estimate the relative impact of atmospheric and oceanic variables on Physalia spp. beaching. From laboratory experiments, we establish a parametrization of the wind-induced drift of 3D-printed replicas of Physalia spp. This result is then incorporated into a Lagrangian tracking model based on the most recurrent East Australian Current separation scenarios to assess the combined effects of winds and currents on the pathways of Physalia spp. The results presented in this thesis contribute to the knowledge of two boundary currrents characterized by different scales and modes of variability, giving insights in their role in transport of passive material through the study of Physalia spp journey

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17

Toh, Kwang Yong Daniel. "Evaluation of surface current mapping performance by SeaSonde High Frequency radar through simulations". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Dec%5FToh.pdf.

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18

Kouteas, Dimitrios. "Investigation of high frequency ship radar cross section reduction by means of shaping". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1998. http://handle.dtic.mil/100.2/ADA351615.

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Thesis (M.S. in Electrical Engineering and M.S. in Applied Physics) Naval Postgraduate School, September 1998.
Thesis advisor(s): David C. Jenn, David D. Cleary. "September 1998." Includes bibliographical references (p. 101-102). Also available in print.

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19

Buyukpapuscu, Suleyman Olcay. "System Identification With Particular Interest On The High Frequency Radar Under Ionospheric Disturbances". Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608166/index.pdf.

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We have been actively involved in the research and management activities of European Co-Operation in the Field of Scientific and Technical Research (EU COST) actions such as COST 238 Prediction and Retrospective Ionospheric Modeling over Europe (PRIME), COST 251 Improved Quality of Service in Ionospheric Telecommunication System Planning and Operation, COST 271 Effects of the Upper Atmosphere on Terrestrial and Earth-Space Communications, COST 296 Mitigation of Ionospheric Effects on Radio Systems (MIERS) and COST 724 Developing the Scientific Basis for Monitoring, Modeling and Predicting Space Weather. In this thesis High Frequency (3-30 MHz) (HF) radar system under ionospheric disturbances has been identified globally and some operational suggestions have been presented. The use of HF radar system is considered from the identification of ionospheric propagation medium point of view. Doppler velocity is considered as the characteristic parameter of the propagation medium. ap index is chosen as the parameter for disturbance characterization due to geomagnetic storms in the ionosphere. The main difficulty is the scarcity of data, which is rare and confidential. Therefore semi-synthetic data are generated. Dependence of Doppler velocity and group range of the echo signal on ap index is examined and some details of dependence are studied and demonstrated. Thus, effects of space weather on the ionosphere and as a result on HF radar wave propagation are displayed. These results are examples of system identification. This can be used in communication system planning and operation.

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20

Kim, Sung Yong. "Coastal ocean studies in southern San Diego using high-frequency radar derived surface currents". Diss., [La Jolla, Calif.] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3344796.

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Thesis (Ph. D.)--University of California, San Diego, 2009.
Title from first page of PDF file (viewed April 16, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 179-188).

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21

Hickey, Kenneth J. "Ocean surface current estimation using a long-range, single-station, high-frequency ground wave radar". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0008/MQ42394.pdf.

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22

Vicente, Ricardo Miguel F. P. "Characterization of Synthetic Aperture Radar Image Features of the Ocean as a Function of Wind Speed and High Frequency Radar Products". Thesis, Monterey, California. Naval Postgraduate School, 2012. http://hdl.handle.net/10945/7424.

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High-definition source images for those used in this document are available here: http://hdl.handle.net/10945/13822
Approved for public release, distribution unlimited
Assessment of coastal ocean conditions is valuable for both military and civilian operations. Remote sensing of those conditions can be even more valuable, particularly in the case of all-weather sensor types. The potential for better understanding of ocean conditions through the combination of remote sensing results was recognized here with the focus on SAR imagery and High Frequency (HF) radar-derived surface currents. The hypothesis that combining remote sensing products may improve results was tested using SAR imagery and available HF radar surface current maps along central California. Data were obtained from 2007-2010 when the network of HF radar stations was operating relatively continuously. Over the same time period, 780 archived SAR images were identified and, of those, 31 images were chosen for detailed assessment by identifying representative images under weak, moderate, and strong wind conditions. As expected, wind strength played a dominant role in determining the physical processes visible in the SAR imagery. Moderate wind speed of 24 m/s exhibited the most obvious ocean-related processes and the best correlation with features in the HF radar surface current maps. Surprising is the discovery that oceanographic features in the SAR imagery represent recent history of tracer advection over hours to days. As such, individual hourly, surface-current snapshots are not, perhaps, the best product for comparing with those features. Features in the daily-average currents, for example, appear more highly correlated with features in SAR imagery under moderate wind conditions.

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23

Chen, Tingsu. "CMOS High Frequency Circuits for Spin Torque Oscillator Technology". Licentiate thesis, KTH, Integrerade komponenter och kretsar, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-139588.

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Spin torque oscillator (STO) technology has a unique blend of features, including but not limited to octave tunability, GHz operating frequency, and nanoscaled size, which makes it highly suitable for microwave and radar applications. This thesis studies the fundamentals of STOs, utilizes the state-of-art STO's advantages, and proposes two STO-based microwave systems targeting its microwave applications and measurement setup, respectively. First, based on an investigation of possible STO applications, the magnetic tunnel junction (MTJ) STO shows a great suitability for microwave oscillator in multi-standard multi-band radios. Yet, it also imposes a large challenge due to its low output power, which limits it from being used as a microwave oscillator. In this regard, different power enhancement approaches are investigated to achieve an MTJ STO-based microwave oscillator. The only possible approach is to use a dedicated CMOS wideband amplifier to boost the output power of the MTJ STO. The dedicated wideband amplifier, containing a novel Balun-LNA, an amplification stage and an output buffer, is proposed, analyzed, implemented, measured and used to achieve the MTJ STO-based microwave oscillator. The proposed amplifier core consumes 25.44 mW from a 1.2 V power supply and occupies an area of 0.16 mm2 in a 65 nm CMOS process. The measurement results show a S21 of 35 dB, maximum NF of 5 dB, bandwidth of 2 GHz - 7 GHz. This performance, as well as the measurement results of the proposed MTJ STO-based microwave oscillator, show that this microwave oscillator has a highly-tunable range and is able to drive a PLL. The second aspect of this thesis, firstly identifies the major difficulties in measuring the giant magnetoresistance (GMR) STO, and hence studying its dynamic properties. Thereafter, the system architecture of a reliable GMR STO measurement setup, which integrates the GMR STO with a dedicated CMOS high frequency IC to overcome these difficulties in precise characterization of GMR STOs, is proposed. An analysis of integration methods is given and the integration method based on wire bonding is evaluated and employed, as a first integration attempt of STO and CMOS technologies. Moreover, a dedicated high frequency CMOS IC, which is composed of a dedicated on-chip bias-tee, ESD diodes, input and output networks, and an amplification stage for amplifying the weak signal generated by the GMR STO, is proposed, analyzed, developed, implemented and measured. The proposed dedicated high frequency circuits for GMR STO consumes 14.3 mW from a 1.2 V power supply and takes a total area of 0.329 mm2 in a 65 nm CMOS process. The proposed on-chip bias-tee presents a maximum measured S12 of -20 dB and a current handling of about 25 mA. Additionally, the proposed dedicated IC gives a measured gain of 13 dB with a bandwidth of 12.5 GHz - 14.5 GHz. The first attempt to measure the (GMR STO+IC) pair presents no RF signal at the output. The possible cause and other identified issues are given.

QC 20140114

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24

Enriquez, Andres E. "An investigation of surface current patterns related to upwelling in Monterey Bay, using high frequency radar". Thesis, Monterey, California. Naval Postgraduate School, 2004. http://hdl.handle.net/10945/1595.

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Approved for public release; distribution is unlimited
High Frequency (HF) radar backscatter instruments are under development and testing in the marine science and defense science communities for their abilities to remotely sense surface parameters in the coastal ocean over large areas. In the Navy context, the systems provide real-time mapping of ocean surface currents and waves critical to characterization and forecasting of the battlespace environment. In this study, HF radar, aircraft and satellite information were used to investigate and describe surface current in Monterey Bay, California, for a period of ten months, from June 01st, 2003 to March 31st, 2004. A network of five CODAR-type HF radar instruments measured hourly surface currents over the bay. The measurements were averaged over one-hour intervals and total surface velocities were mapped on a grid in the Monterey Bay. From the M1 Buoy located in the middle of the bay, an uninterrupted time series of wind intensity and direction was obtained for the whole period. Major upwelling events were observed during the period of June 14 to June 27, July 4 to July 19, August 8 to August 18 and other upwelling events were observed until late October. These periods of upwelling favorable winds are common during summer with durations of 10 to 20 days. Often they are interrupted by periods of relaxation state of just a few days as the winds veer to the northwest or northeast. Cyclonic circulation cells are developed on shore during upwelling conditions and an anticyclonic circulation in the middle of the bay is observed when the wind shifts to the southwest producing a strong flow out of the bay close to the coastline off Point PioÌ¨s. Downwelling conditions are much common less than upwelling, with occurrences during winter and early fall storms with events lasting between two to five days. When the wind blows to the northeast with an intensity of 4 m/s or more for more than 12 hours, a well developed anticyclonic gyre forms in the middle of the bay. This is associated with a strong current, 35 to 40 cm/s, which flushes out in the southern part of the bay close to the coast off Point PioÌ¨s. This flow reverses when the winds veer to the southwest and enter into the Bay with less intensity.
First Lieutenant, Chilean Navy

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25

Wright, George C. "Validation of high frequency radar used in ocean surface current mapping via in-situ drifting buoys". Thesis, Monterey, Calif. : Naval Postgraduate School, 2008. http://edocs.nps.edu/npspubs/scholarly/theses/2008/Sept/08Sep%5FWright.pdf.

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Thesis (M.S. in Physical Oceanography)--Naval Postgraduate School, September 2008.
Thesis Advisor(s): Paduan, Jeffrey D. "September 2008." Description based on title screen as viewed on November 4, 2008. Includes bibliographical references (p. 85-86). Also available in print.

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26

Enriquez, Andres. "An investigation of surface current patterns related to upwelling in Monterey Bay, using high frequency radar /". Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Jun%5FEnriquez.pdf.

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27

Wang, Wei. "Signal processing methods to improve ocean surface wave estimation from a high frequency surface wave radar". Thesis, University of Sheffield, 2011. http://etheses.whiterose.ac.uk/1996/.

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High frequency surface wave radars are operated as a remote sensor to measure ocean surface parameters to ranges exceeding 200-300 km from the coastline. The Bragg peaks in the power spectrum of backscattered radar electromagnetic signals from ocean waves reveal the Bragg resonant effect and the second order continuum reflect a hydrodynamic and electromagnetic modulation on the radio waves from the ocean waves. The power spectrum is thus utilized to invert the ocean wave directional spectrum by a non-linear integral equation. Further integrations of the ocean wave directional spectrum yield the estimates of wave parameters: significant waveheight, mean wave period, mean direction, directional spread, etc. Beside sea echoes, non-sea echoes or interferences (collectively termed ‘clutter'), are also received by radar antenna receivers and included in the power spectrum. Clutters which occupy the second order continuum are treated as sea echoes in the inverse algorithm and cause inaccurate estimation of the ocean wave directional spectrum. Thus clutter mitigation is the main purpose of this thesis and is intensively investigated. A three-step image processing approach is proposed in this thesis which could mitigate visible clutters, e.g. radio frequency interferences and ionospheric interferences, and also invisible clutters. The kernel implements a decomposition of the mixture space and then a projection of the mixture space into a desired subspace. In addition to this main approach, various signal processing methods are also investigated for improving the wave estimates, e.g. wavelet analysis, AR modeling, adaptive filtering algorithm. The clutter mitigation scheme is validated by operational use on a whole month of Pisces data and exhibits some improvements in the accuracy of wave estimates. To aid the operational use, a statistical pattern recognition method is also developed. Finally, the best schemes are chained together for a sequential operational use in terms of providing better wave estimation.

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28

Malan, Frederich T. "Reduction of the antenna coupling in a bi-static, FM-CW radar system". Thesis, Stellenbosch : Stellenbosch University, 2011. http://hdl.handle.net/10019.1/18029.

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Thesis (MScEng)--Stellenbosch University, 2011.
ENGLISH ABSTRACT: A well-known problem with FM-CW radar systems is the leakage of transmitter power into the receiver which leads to the making of close-in targets, and can severely limit the system dynamic range performance. This thesis considers two solutions to this radar system problem for a low frequency radar operating in the VHF band. The first method to suppress coupling is using separate transmit and receive antennas designed in such a way as to reduce coupling between them. The second is to design a negative feedback loop as part of the radar receiver where the feedback loop adaptively reduces the amount of transmitter leakage through to the receiver. This project details the realisation of these two solutions. A number of antenna designs are modelled in software and simulated to determine their characteristics of which the transmit-to-receive coupling is the key parameter. As no low coupling configuration could be found a simple configuration is chosen and practical measurements are taken. These antennas are then used in the radar system that is to be built. An FM-CW radar system is designed and simulated using software with a negative feedback loop being designed and implemented into the radar simulation. A practical radar system is then made inclusive of the feedback loop. Measurements are then taken to determine the efficacy of the feedback loop.
AFRIKAANSE OPSOMMING: ŉ Bekende probleem met FM-CW radar stelsels is die lekkasie van versender krag tot in die ontvanger wat lei tot die maak van nabye teikens en kan die stelsel se dinamiese sendbereik steng beperk. Hierdie tesis oorweeg twee oplossings tot hierdie probleem vir ŉ lae frekwensie radar wat in die VHF band werk. Die eerste metode wat na gekyk word om die koppeling te onderdruk is om die twee antennas van die radar stelsel so te ontwerp sodat die hoeveelheid koppeling tussen hulle verminder is. Die tweede is om ŉ negatiewe terugvoerlus as deel van die ontvanger te ontwerp. Hierdie terugvoerlus sal die versender lekkasie sein aanpassend in die ontvanger verminder. In hierdie projek word die realisering van bogenoemde oplossings uiteengeset. ŉ Paar verskillende antenna ontwerpe word gemodelleer in sagteware en word gesimuleer om hul karakteristieke te bepaal. Die belangrikste van hierdie faktore is die versender na ontvanger koppeling. Sienend dat geen ontwerp met ŉ lae genoeg koppeling gevind kon word nie, is ŉ eenvoudige ontwerp gekies en praktiese metings daarvan geneem. Hierdie antennas word dan gebruik in die radar stelsel wat gebou sal word. ŉ FM-CW radar stelsel word ontwerp en gesimuleer in sagteware. Die negatiewe terugvoerlus word ook ontwerp en geïmplementeer in die radar simulasie. ŉ Praktiese radar stelsel word dan gemaak insluitend die terugvoerlus. Metings word dan geneem om die effektiwiteit daarvan te bepaal.

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29

Fox, Alan David. "The use of high-frequency radar to study surface currents associated with a shelf sea frontal system". Thesis, Bangor University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316344.

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30

Lim, Kian Guan. "Battle damage assessment using inverse synthetic aperture radar (ISAR)". Thesis, Monterey, California. Naval Postgraduate School, 2004. http://hdl.handle.net/10945/1223.

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Approved for public release; distribution in unlimited.
An imaging radar, like ISAR, offers a combatant the capability to perform long range surveillance with high quality imagery for positive target identification. Extending this attractive feature to the battle damage assessment problem (BDA) gives the operator instant viewing of the target's behavior when it is hit. As a consequence, immediate and decisive action can be quickly taken (if required). However, the conventional Fourier processing adopted by most ISAR systems does not provide adequate time resolution to capture the target's dynamic responses during the hit. As a result, the radar image becomes distorted. To improve the time resolution, time-frequency transform (TFT) methods of ISAR imaging have been proposed. Unlike traditional Fourier-based processing, TFT's allows variable time resolution of the entire event that falls within the ISAR coherent integration period to be extracted as part of the imaging process. We have shown in this thesis that the use of linear Short Time-Frequency Transforms allows the translational response of the aircraft caused by a blast force to be clearly extracted. The TFT extracted images not only tell us how the aircraft responds to a blast effect but also provides additional information about the cause of image distortion in the traditional ISAR display.

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31

Saleh, Mahdi. "Contributions to High Range Resolution Radar Waveforms : Design of Complete Processing Chains of Various Intra-Pulse Modulated Stepped-Frequency Waveforms". Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0024.

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Dans divers systèmes radar, un grand intérêt a été porté à la sélection d’une forme d’onde et à la conception d’une chaîne de traitement complète, de l’émetteur au récepteur, afin d’obtenir un profil distance haute résolution (HRRP, acronyme de High Range Resolution Profile en anglais). Au cours des dernières décennies, les concepteurs d’algorithmes de traitement du signal radar ont concentré leur attention sur différentes formes d’onde telles que les techniques de compression d’impulsion et les systèmes à bande synthétique (SF acronyme de stepped frequency, en anglais).D’une part, trois types de formes d’onde de compression d’impulsions large bande ont été proposés dans la littérature : la forme d’onde modulée linéairement en fréquence (Linear Frequency Modulation), celle à codes de phase (Phase Coded) et la forme d’onde modulé non linéairement en fréquence (Non Linear Frequency Modulation). Ces approches sont très populaires, mais elles requièrent une fréquence d’échantillonnage généralement élevée au niveau du récepteur, et par voie de conséquence un convertisseur analogique-numérique coûteux. De plus, les formes d’onde PC et NLFM peuvent être préférables dans certaines applications à haute résolution, car elles conduisent à de meilleurs PSLR et ISLR que ceux obtenus avec la forme d’onde LFM.D’autre part, lorsqu’il s’agit de schémas SF, une fréquence d’échantillonnage moins élevée peut être envisagée, ce qui permet d’utiliser un CAN meilleur marché.Ces deux approches peuvent être combinées pour tirer avantage des deux familles. Bien que la combinaison standard mène à l’exploitation d’un CAN bon marché, les performances en termes de PSLR et ISLR ne sont pas nécessairement adaptées. Comme le PSLR et l’ISLR ont une grande influence sur la probabilité de détection et la probabilité de fausse alarme, notre objectif est de trouver des solutions alternatives. Ainsi, notre contribution dans ce mémoire de thèse consiste à proposer deux nouvelles chaînes de traitement, de l’émetteur au récepteur :1) Dans la première approche, le spectre de la forme d’onde à large bande est décomposé en un nombre prédéterminé de portions. Puis, les versions temporelles de ces dernières sont successivement transmises. Le signal reçu est alors traité soit en utilisant un algorithme FD (pour Frequency domain en anglais) modifié, soit un algorithme de reconstruction de forme d’onde réalisé directement dans le domaine temporel (TWR pour time wave reconstruction). Dans cette thèse, les formes d’ondes PC et NLFM ont été sélectionnées. Une étude comparative est alors menée entre les différentes chaînes de traitement, de l’émetteur au récepteur, que l’on peut constituer. Nos simulations montrent que les performances obtenues à partir de l’algorithme TWR sont le plus souvent meilleures que celles de l’algorithme FD modifié. La contre-partie est une augmentation du coût calculatoire. De plus, que ce soit avec une forme d’onde PC ou NLFM, l’approche présentée fournit de meilleurs résultats en termes de PSLR et ISLR que les formes d’onde SF classiques.2) La seconde démarche proposée consiste à approximer une forme d’onde NLFM à large bande par une forme d’onde LFM par morceaux, puis de la combiner avec une approche de type SF. Cela donne lieu à une forme d’onde combinant SF et un train d’impulsions LFM ayant différentes durées et largeurs de bande. La sélection des paramètres de cette forme d’onde est faite en minimisant un critère multi-objectif, tenant compte du PSLR, de l’ISLR et de la résolution distance. Cette estimation est opérée par algorithmes génétiques. Selon les poids utilisés dans le critère multi-objectif et le nombre d’impulsions LFM pris en compte, les performances des les formes d’onde résultantes varient.Une annexe est en outre fournie qui présente des travaux complémentaires sur la comparaison de modèles à partir de la divergence de Jeffreys
In various radar systems, a great deal of interest has been paid to selecting a waveformand designing a whole processing chain from the transmitter to the receiver toobtain the high range resolution profile (HRRP). For the last decades, radar designershave focused their attentions on different waveforms such as the pulse compressionwaveforms and the stepped frequency (SF) waveform:On the one hand, three different types of wide-band pulse compression waveforms havebeen proposed: the linear frequency modulation (LFM) waveform, the phase coded(PC) waveform, and the non-linear frequency modulation (NLFM) waveform. They arevery popular but the sampling frequency at the receiver is usually large. This hence requiresan expensive analog-to-digital convertor (ADC). In addition, the PC and NLFMwaveforms may be preferable in some high range resolution applications since they leadto peak sidelobe ratio (PSLR) and integrated sidelobe ratio (ISLR) better than the onesobtained with the LFM waveform.On the other hand, when dealing with SF waveforms, a small sampling frequency canbe considered, making it possible to use a cheap ADC.Pulse compression and SF waveforms can be combined to take advantage of both. Althoughthe standard combination of PC or NLFM with SF leads to the exploitation ofa cheap ADC, the performance of the PC waveform or NLFM waveform in terms ofPSLR and ISLR cannot be attained. As the PSLR and the ISLR have a great influenceon the probability of detection and probability of false alarm, our purpose in the PhDdissertation is to present two new processing chains, from the transmitter to the receiver:1) In the first approach, the spectrum of a wide-band pulse compression pulse is splitinto a predetermined number of portions. Then, the time-domain transformedversions of these various portions are transmitted. At the receiver, the receivedechoes can be either processed with a modified FD algorithm or a novel timewaveformreconstruction (TWR) algorithm. A comparative study is carried outbetween the different processing chains, from the transmitter to the receiver, thatcan be designed. Our simulations show that the performance in terms of PSLRand ISLR obtained with the TWR algorithm is better than that of the modified FDalgorithm for a certain number of portions. This comes at the expense of an additionalcomputational cost. Moreover, whatever the pulse compression used, the approach we present outperforms the standard SF waveforms in terms of PSLRand ISLR.2) In the second approach, we suggest approximating the wide-band NLFM by apiecewise linear waveform and then using it in a SF framework. Thus, a variablechirp rate SF-LFM waveform is proposed where SF is combined with a train ofLFM pulses having different chirp rates with different durations and bandwidths.The parameters of the proposed waveform are derived from the wide-band NLFMwaveform. Then, their selection is done by considering a multi-objective optimization issue taking into account the PSLR, the ISLR and the range resolution.The latter is addressed by using a genetic algorithm. Depending on the weightsused in the multi-objective criterion and the number of LFM pulses that is considered, the performance of the resulting waveforms vary.An appendix is finally provided in which additional works are presented dealing withmodel comparison based on Jeffreys divergence

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32

Menon, K. Rajalakshmi. "Application Of High Frequency Natural Resonances Extracted From Electromagnetic Scattering Response For Discrimination Of Radar Targets With Minor Variations". Thesis, Indian Institute of Science, 2001. https://etd.iisc.ac.in/handle/2005/159.

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Abstract (sommario):

Radars, as the name suggests, were traditionally used for Radio Detection and Ranging. Nevertheless, advances in high resolution electromagnetic simulations, Ultra Wide-Band sources, signal processing and computer technologies have resulted in a possible perception of radars as sensors for target discrimination. In this thesis, the feasibility of discrimination between targets even with minor variations in structure and material composition on the basis of radar echoes is effectively demonstrated. It is well-known that the echoes from any target are affected by its natural frequencies which are dependent only on the shape and material composition of the target, and independent of the aspect angle or the incident waveform. The E-pulse technique is based on the fact that incident waveforms can be designed that uniquely annihilate the echoes from chosen regions of a target, and forms the basis of the method of discrimination proposed in this thesis. Earlier methods reported in the literature, effectively discriminated only between different classes of targets with substantial variations in the overall dimensions of the body. Discrimination of targets of the same class with a minor structural modification or with a material coating on specific areas was rather difficult. This thesis attempts and successfully validates a method which comprehensively addresses this problem. The key idea of this method is to use the higher frequency resonances (which characterise the finer details of a target) in the E-pulse technique. An obviously important aspect of target discrimination is therefore that of precisely estimating the natural frequencies for each target and understanding the changes in these frequencies, and their associations with the changes in structure and material composition. Current approaches to determine these frequencies are either based In the time or frequency domains. While the latter approach comprises the computation of the roots of a related determinantal equation, in the time domain, the natural frequencies are extracted from the response of a target to an impulse. Such a response can either be generated from actual experiments or by simulating the scattering response using Computational Electromagnetic (CEM) techniques. In this work, the impulse response is obtained from the frequency response of the scatterers in the frequency range of interest. Since no single CEM technique can effectively cover the entire range of frequencies needed for the E-Pulse synthesis. The Method of Moments and Physical Optics have been used for low and high frequency scattering respectively. The results obtained using the latter technique are validated by comparing with those obtained using Method of Moments at the transition frequencies and Geometrical Theory of Diffraction (GTD). The natural frequencies (i.e., poles of a corresponding transfer function) are extracted from the impulse response using Prony's algorithm. One of the parameters in this method is the number of such poles (i.e.. the order of the transfer function) present in the response, and the accuracy of the computed pole values depends on this assumed order. Here, the Hankel singular values of a transfer function is used to estimate the number of poles. This in turn implies that a specific norm of the error between a transfer function corresponding to the frequency response generated earlier, and a transfer function with an assumed order obtained using Prony's method is minimised. In the thesis, a wide range of target shapes are considered for purposes of illustration: wires, cylinders, spheres, plates and complex bodies such as aircraft, and the discrimination capability is demonstrated by introducing minor perturbations in their shape and/or material composition. .The following cases are considered here: (a) Wires: Conducting wires with a protrusion in one segment; conducting wire from another coated with a dielectric in a segment, (b) Cylinders: Conducting cylinders with one perturbed; conducting cylinders with a portion scrapped off in the middle, (c) Plates: Conducting plates with a elongation on one comer; conducting plate with another one with a hole in the centre, (d) Spheres: Conducting spheres with different radii; conducting spheres with Radar Absorbing Material coated spheres with different coating thickness; conducting spheres with chiral coated spheres with varying coating thickness, (e) Aircraft: Canonical model of MiG-29 aircraft from a similar one with stores placed under the wing.

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33

Menon, K. Rajalakshmi. "Application Of High Frequency Natural Resonances Extracted From Electromagnetic Scattering Response For Discrimination Of Radar Targets With Minor Variations". Thesis, Indian Institute of Science, 2001. http://hdl.handle.net/2005/159.

Testo completo

Abstract (sommario):

Radars, as the name suggests, were traditionally used for Radio Detection and Ranging. Nevertheless, advances in high resolution electromagnetic simulations, Ultra Wide-Band sources, signal processing and computer technologies have resulted in a possible perception of radars as sensors for target discrimination. In this thesis, the feasibility of discrimination between targets even with minor variations in structure and material composition on the basis of radar echoes is effectively demonstrated. It is well-known that the echoes from any target are affected by its natural frequencies which are dependent only on the shape and material composition of the target, and independent of the aspect angle or the incident waveform. The E-pulse technique is based on the fact that incident waveforms can be designed that uniquely annihilate the echoes from chosen regions of a target, and forms the basis of the method of discrimination proposed in this thesis. Earlier methods reported in the literature, effectively discriminated only between different classes of targets with substantial variations in the overall dimensions of the body. Discrimination of targets of the same class with a minor structural modification or with a material coating on specific areas was rather difficult. This thesis attempts and successfully validates a method which comprehensively addresses this problem. The key idea of this method is to use the higher frequency resonances (which characterise the finer details of a target) in the E-pulse technique. An obviously important aspect of target discrimination is therefore that of precisely estimating the natural frequencies for each target and understanding the changes in these frequencies, and their associations with the changes in structure and material composition. Current approaches to determine these frequencies are either based In the time or frequency domains. While the latter approach comprises the computation of the roots of a related determinantal equation, in the time domain, the natural frequencies are extracted from the response of a target to an impulse. Such a response can either be generated from actual experiments or by simulating the scattering response using Computational Electromagnetic (CEM) techniques. In this work, the impulse response is obtained from the frequency response of the scatterers in the frequency range of interest. Since no single CEM technique can effectively cover the entire range of frequencies needed for the E-Pulse synthesis. The Method of Moments and Physical Optics have been used for low and high frequency scattering respectively. The results obtained using the latter technique are validated by comparing with those obtained using Method of Moments at the transition frequencies and Geometrical Theory of Diffraction (GTD). The natural frequencies (i.e., poles of a corresponding transfer function) are extracted from the impulse response using Prony's algorithm. One of the parameters in this method is the number of such poles (i.e.. the order of the transfer function) present in the response, and the accuracy of the computed pole values depends on this assumed order. Here, the Hankel singular values of a transfer function is used to estimate the number of poles. This in turn implies that a specific norm of the error between a transfer function corresponding to the frequency response generated earlier, and a transfer function with an assumed order obtained using Prony's method is minimised. In the thesis, a wide range of target shapes are considered for purposes of illustration: wires, cylinders, spheres, plates and complex bodies such as aircraft, and the discrimination capability is demonstrated by introducing minor perturbations in their shape and/or material composition. .The following cases are considered here: (a) Wires: Conducting wires with a protrusion in one segment; conducting wire from another coated with a dielectric in a segment, (b) Cylinders: Conducting cylinders with one perturbed; conducting cylinders with a portion scrapped off in the middle, (c) Plates: Conducting plates with a elongation on one comer; conducting plate with another one with a hole in the centre, (d) Spheres: Conducting spheres with different radii; conducting spheres with Radar Absorbing Material coated spheres with different coating thickness; conducting spheres with chiral coated spheres with varying coating thickness, (e) Aircraft: Canonical model of MiG-29 aircraft from a similar one with stores placed under the wing.

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34

Gill, Eric William. "The scattering of high frequency electromagnetic radiation from the ocean surface : an analysis based on a bistatic ground wave radar configuration /". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0003/NQ42476.pdf.

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35

REYES, SUAREZ NYDIA CATALINA. "Surface Circulation Structures in the Malta Sicily Channel derived from HF radar and altimetry: Estimation, validation and analysis". Doctoral thesis, Università degli Studi di Trieste, 2018. http://hdl.handle.net/11368/2922575.

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Il Canale Malta e Sicilia fa parte del sistema di canali della Sicilia, dove avvengono gli scambi idrici e le proprietà termoaline tra i bacini del Mediterraneo orientale e occidentale; allo stesso tempo questo scambio influenza i processi biologici ed è rilevante dal punto di vista produttivo e ambientale. Un campo geostrofico è stato calcolato da dati AVISO di Absolute dynamic topography, quei set di dati includono MADT a partire da Gennaio 1993 a Dicembre 2015. D'altra parte, i campi di vento vanno da Gennaio 1988 a Dicembre 2011 dal CCMP (Cross-Calibrated Multi-Platform wind vector analysis) sono stati ottenuti per vedere l'influenza del vento nella zona. La validazione e quindi l'analisi della circolazione superficiale è stata effettuata utilizzando stime del campo di velocità da dati radar ad alta frequenza da Agosto 2012 a Gennaio 2015 (una serie di tre radar CODAR tra Malta e Sicilia, nell'ambito del progetto CALYPSO). CCMP v2 da Agosto 2012 a Gennaio 2015, clorofilla satellitale, temperatura superficiale del mare e drifter sono stati utilizzati per la validazione dei dati radar ad alta frequenza. Questi set di dati ci hanno aiutato a identificare le principali strutture di circolazione superficiale che sono fondamentali per la comprensione delle dinamiche di circolazione nel Canale di Malta e Sicilia.
The Malta Sicily Channel makes part of the Sicily channel system, where water exchanges and thermohaline properties between the Eastern and Western Mediterranean basins takes place; at the same time this exchange influences the biological processes and it is relevant from the productive and environmental point of view. A geostrophic current field was com- puted out from AVISO Absolute dynamic topography product, those data sets include MADT starting from January 1993 to December 2015. On the other hand, wind fields spanning from January 1988 to December 2011 from the CCMP (Cross-Calibrated Multi-Platform wind vector analysis) were obtained to see the influence of the wind in the area. Validation and then analysis of the surface circulation was made using estimates of the velocity field from High frequency radar data spanning from August 2012 to January 2015 (a three array of CODAR HF-radars between Malta and Sicily, under the CALYPSO project). CCMP v2 from August 2012 to January 2015 were used for the high frequency radar validation as well as satellite chlorophyll, sea surface temperature and drifters. These datasets helped us to identify the main surface circulation structures which are fundamental for the understanding of the Malta Sicily Channel circulation dynamics.

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36

Wang, Weili. "Remote sensing of swell and currents in coastal zone by HF radar". Thesis, Toulon, 2015. http://www.theses.fr/2015TOUL0011/document.

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L’environnement maritime du littoral implique de nombreux processus complexes, mais le manque de données en haute résolution couvrant une large zone sur une longue période est souvent l’obstacle principal à des recherches plus approfondies. Le radar haute-fréquence (HF) est un moyen de faire de la télédétection afin d’obtenir pratiquement en temps réel de l’information sur la surface de la mer et sur une large zone. Ainsi l’étude de l’inversion des paramètres marins à partir de données issues de radars HF est réellement porteuse de sens. Cette thèse fait l’usage d’un jeu de données collectées durant 13 mois par deux réseaux de radar HF à commande de phase pour étudier les caractéristiques de signaux d’échos de la mer, étudier les données à traiter et les méthodes d’inversion, calculer les paramètres de la surface de la mer et évaluer la précision de l’inversion radar des paramètres de la houle.Cette thèse se réfère à l’onde de sol radar HF, dont les ondes radio interagissent avec l’océan du fait de la diffraction de résonance de Bragg. Nous passons en revue l’historique et les applications du radar HF. Nous rappelons les bases de la théorie des ondes électromagnétiques. Nous décrivons les principes d’inversion des courants de surface de la mer, direction du vent et paramètres de houles. La faisabilité de l’inversion de paramètres de houle est examinée. A partir de l’analyse théorique et des études statistiques de nombreux échantillons de données, cette thèse propose une série de méthodes sur le traitement du signal brut et le contrôle de qualité, ce qui inclut la détermination du niveau de bruit, le moyennage des données dans l’espace et le temps, l’identification correcte des pics spectraux, le seuil de largeur de pic, etc. Respectant les caractéristiques de différents processus physiques, les inversions de courant et de vent utilisent des spectres collectés toutes les 20 minutes ; l’inversion des paramètres de houle utilise des spectres moyennés sur 1 heure. Les statistiques des spectres utilisés pour le calcul des paramètres de houle sont présentées pour chacune des stations. Un ensemble de programme efficaces de calculs automatiques avec une complexité algorithme réduite sont développés pour réaliser le traitement et en tirer les paramètres marins.Les vitesses de courants radiales sont obtenues à partir d’une unique station radar. Les champs de vecteurs de courants sont obtenus en combinant chaque station. On montre une année de débit moyen dans la mer d’Iroise, ainsi que le calcul de la vorticité et de la divergence. On étudie un ensemble de données d’un mois du radar SeaSonde de Qingdao. Les schémas de débit moyen, ainsi que la vorticité et la divergence sur un mois sont présentés.La direction relative du vent par rapport à la direction de visée du radar est mesurée à travers le ratio des amplitudes des pics de Bragg. Différents modèles empiriques sont employés pour obtenir la vitesse relative du vent par inversion radar. Les résultats présentés sont en accord avec les estimations prédites par le modèle. Différents modèles de distribution directionnelle sont utilisés pour mesurer le facteur de diffusion pour la mer d’Iroise.Cette thèse se concentre sur l’étude des paramètres de houle. Les résultats sont validés à l’aide de bouées et de données du modèle de vagues (Wavewatch III). L’estimation montre que la précision de la fréquence de houle est très bonne, la précision sur la hauteur significative de houle est très raisonnable et la précision sur la direction absolue de la houle est faible. La cohérence des mesures par chacune des stations radars est vérifiée par comparaison entre les deux. L’utilisation conjointe des échantillons est également prise en charge pour réaliser l’inversion. L’utilisation de deux radars n’améliore pas seulement la précision, mais résout aussi l’ambiguïté de direction relative de houle à partir d’une unique station et donne la direction absolue de vague avec une certaine précision
Nearshore marine environment contains many complex processes, but the lack of high-resolution data over a large area during a long time is often the primary obstacle to further research. High-frequency (HF) radar is a mean of remote sensing which obtains continuous near-real time sea surface information over a large area. Thus the study of inversion of marine parameters from HF radar data is very meaningful. Thisthesis makes use of a 13-month-long dataset collected by two phased array HF radar to investigate the characteristics of the sea echo signals, study the data processing and inversion methods, compute sea surface parameters and evaluate the accuracy of radarinversion of swell parameters.The thesis refers to the ground wave HF radar, whose radio waves interact with ocean by Bragg resonance scattering. The development history and applications of HF radar is introduced. The basic theory of electromagnetic wave is reviewed. The principles of inversion of sea surface current, wind direction and swell parameters are described. The feasibility of the swell parameter inversion is investigated. Based on theoretical analysis and statistical studies of a large number of samples, the thesis proposes a series of methods on raw signal processing and quality control, including the determination of the noise level, data averaging in space and time, the proper identification of spectral peaks, the peak width threshold, etc. Respecting the characteristics of different physical processes, inversions of current and wind use spectra collected every 20 min; inversion of swell parameters uses one-hour averaged spectra. The statistics of qualified spectra for swell parameter calculations are presented for both stations. A set of efficient, with a reduced computational cost, automatic computing programs are developed to do the processing and derive marine parameters. Radial current velocities are derived from single radar station. Current vector fields are obtained by combination of both stations. One-year mean flow field in the Iroise Sea is shown, together with the computation of vorticity and divergence. A one-month SeaSonde radar dataset off Qingdao is studied. One-month mean flow pattern together with vorticity and divergence are presented.Relative wind direction with respect to radar look direction is measured through ratio of Bragg peaks amplitudes. Different empirical models are employed to derive radar-inverted relative wind direction. Results show reasonable agreement with model estimations. Different directional distribution models are used to measure the spreading factor for the Iroise Sea. The thesis focuses on the study of swell parameters. Results are validated by buoy and wave model (WAVEWATCH III) data. The assessments show that the accuracy of swell frequency is very good, the accuracy of swell significant waveheight is reasonable, and the accuracy of relative swell direction is low.Consistency of measurements by both radar stations is verified by comparison between the two. This also supports the use of double samples to do the inversion. Use of two radars not only further improves the accuracy but also solves the ambiguity of relative swell direction from single station and gives the absolute wave direction to a certain precision. The thesis proposes a constant relative directionmethod to derive swell significant waveheight, based on the studies of radar integral equation and the inverted results of relative swell direction. This proposal is demonstrated to improve the agreement of radar inversion and buoy/model provided significant waveheight and increases significantly the number of samples. The thesis investigates the accuracy of swell parameters obtained by HF radar. Contributions of random errors in radar observations are quantified. Comparing the differences between radar and buoy/model estimations gives assessments of the contribution of radar intrinsic uncertainty and contribution of other factors

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37

Blom, Martin. "En oscillatorbank till en lågfrekvensradar : LORA/VHF". Thesis, Linköping University, Department of Electrical Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-2153.

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The goal of this thesis work is to enable an existing UHF radar to operate in the VHF band instead. In order to achieve this, new coherent local oscillators are required. Different options are suggested and one of them is implemented and analyzed.

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Gurel, Ilker. "Channel Estimation For Ofdm Systems". Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606940/index.pdf.

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In this thesis, various pilot symbol aided channel estimation and tracking methods are investigated and their performances are compared for an OFDM system with packet based communication on HF channel. For the HF channel, Watterson HF channel model is used. The compared methods are least squares (LS) channel estimation, linear minimum mean square error (LMMSE) channel estimation, least mean squares (LMS) channel tracking, recursive least squares (RLS) channel tracking, constant position model based Kalman filter channel tracking, and constant velocity model based Kalman filter channel tracking. For LMS and RLS methods some adaptive approaches are also investigated.

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Gasperini, David. "A multi-harmonic finite element method for the micro-Doppler effect, with an application to radar sensing". Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0026.

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Nous proposons une méthode de résolution par éléments finis et en domaine fréquentiel de problèmes de diffraction d'ondes au sein de domaines dont les frontières se déforment au cours du temps. Le problème original est exprimé sous forme faible, puis approché par une formulation simplifiée basée sur des développements asymptotiques valides lorsque l'amplitude des déformations est faible. Nous introduisons alors des développements en séries de Fourier de certaines grandeurs géométriques, ainsi que de la solution dans le cas de mouvements périodiques. Cela permet ainsi d'obtenir une formulation multi-harmonique couplée du problème de diffraction initial. Une méthode de résolution standard par éléments finis, couplée avec un solveur itératif, est alors appliquée afin de résoudre le système résultant. En vue d'accélérer la solution du système linéaire, définie sur des sous-espaces de Krylov, nous proposons un préconditionneur diagonal par bloc, indispensable à la convergence de la méthode pour les problèmes hautes fréquences. L'efficacité de la méthode présentée est enfin illustrée à travers une application à la détection radar pour l'industrie automobile
A finite element method in the frequency domain is proposed for solving wave scattering problems with moving or, more generally, deforming boundaries. First, the original problem is rewritten as an equivalent weak formulation set in a fixeddomain. Next, this formulation is approximated as a simpler weak form based on asymptotic expansions when the amplitude of the movements or the deformations is small. Fourier series expansions of some geometrical quantities under the assumption that the movement is periodic, and of the solution are next introduced to obtain a coupled multi-harmonic frequency domain formulation. Standard finite element methods can then be applied to solve the resulting problem and a block diagonal preconditioner is proposed to acceleratethe Krylov subspace solution of the linear system for high frequency problems.The efficiency of the resulting method is demonstrated on a radar sensing application for the automotive industry.A finite element method in the frequency domain is proposed for solving wave scattering problems with moving or, more generally, deforming boundaries. First, the original problem is rewritten as an equivalent weak formulation set in a fixeddomain. Next, this formulation is approximated as a simpler weak form based on asymptotic expansions when the amplitude of the movements or the deformations is small. Fourier series expansions of some geometrical quantities under the assumption that the movement is periodic, and of the solution are next introduced to obtain a coupled multi-harmonic frequency domain formulation. Standard finite element methods can then be applied to solve the resulting problem and a block diagonal preconditioner is proposed to acceleratethe Krylov subspace solution of the linear system for high frequency problems.The efficiency of the resulting method is demonstrated on a radar sensing application for the automotive industry

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40

Narayanan, V. Lakshmi. "Study of dynamical coupling of the mesosphere-lower thermosphere-ionosphere region at low latitudes". Thesis, Indian Institute of Geomagnetism, Mumbai, 2011. http://localhost:8080/xmlui/handle/123456789/223.

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41

Pecen, Vojtěch. "Výkonové zesilovače v pevné fázi pro pásmo L". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2017. http://www.nusl.cz/ntk/nusl-316425.

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The goal of this diploma's thesis is to create a design of a two stages amplifier working in a band reserved for the secondary surveillance radar at the frequency of 1090 MHz. Output power of the amplifier should be 20 W and efficiency should be as high as possible. Because of this the second stage is designed in class C. Contents of this diploma's thesis include a theoretical analysis, simulations of the amplifier parameters, comparison of the Ansys Designer and AWR Microwave Office simulation programs and design of both stages of the amplifier, followed by a comparison of the measured parameters with the simulations.

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Thiébaut, Maxime. "Énergie marine renouvelable : caractérisation des ressources hydrocinétiques en Manche et étude d'impact de la turbulence sur l'efficacité de systèmes de récupération d'énergie tidale". Thesis, Littoral, 2017. http://www.theses.fr/2017DUNK0457/document.

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Malgré l'intérêt suscité, l'exploitation de l'énergie hydrolienne accuse toujours un sérieux retard par rapport à d'autres ressoures renouvelables. Ce développement tardif s'explique d'une part par l'absence d'une méthodologie pertinente de quantification du potentiel hydrocinétique, d'autre part, par le milieu marin, jugé hostile, au sein duquel des phénomènes turbulents,appliquent des contraintes sur la structure des hydroliennes. Offrant une vision précise de l'écoulement et de son hétérogénéité spatiale et temporelle, la courantographie radar, présentée dans la première partie de cette thèse, constitue un outil puissant d'analyse de la dynamique de la marée. Inédite dans le domaine des énergies renouvelables, elle offre une alternative probante à la modélisation numérique, souvent privilégiée bien que générant des résultats contestables compte tenu de sa conceptualisation simpliste des phénomènes réels. L'étude d'impact d'un écoulement turbulent pleinement développé sur la performance énergétique de prototypes d'hydroliennes de type Darrieus constitue la seconde partie de cette thèse. L'analyse spectrale des signaux temporels de vitesse de courant a permis de révéler les propriétés scalaires de l'écoulement. La caractérisation multi-échelle a montré que l'écoulement est animé par un processus dynamique de brisures successives des structures fluides imbriquées de taille allant de l'échelle d'injection à l'échelle de diffusion moléculaire. Enfin, le partitionnement en échelles dynamiques de la turbulence des spectres de vitesse et de puissance générée par l'hydrolienne a mis en évidence une certaine similarité entre la taille des structures tourbillonnaires qui régissent l'écoulement et les dimensions de la turbine
Despite the growing interest , the use of tidal energy still lags far behind other renewable resource. This delayed development can be explained, on the one hand, by the absence of a relevant methodology for quantifying the hydrokinetic potential and, on the other hand, by the hostile marine environment, in which turbulent phenomena apply constraints on the structure of marine current turbines. The use of High Frequency Radar, presented in the first part of this thesis, provides a powerful tool for analyzing tidal dynamics and its spatial and temporal heterogeneity. Never used in the fields of renewable marine energy, it offers a convincing alternative to numerical modeling which is often chosen although generating questionable results because of simplistic conceptualization of real phenomena. The second part of this thesis is the study of the impact of a fully developed turbulent flow on the performance of a Darrieus-type turbine prototypes. The spectral analysis of the current velocity time series revealed the scalar properties of the flow. Multiscale characterization showed that the flow is driven by a dynamic process of successive breaks of fluid structures of size ranging from the injection scale to the molecular diffusion scale. Finally, the dynamical scaling of the turbulence of the velocity and power spectra generated by the marine current turbine has revealed a certain similarity between the size of the eddies structures that govern the flow and the dimensions of the turbine

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Sari, Murat Ozgur. "A New Approach For The Assessment Of Hf Channel Availability Under Ionospheric Disturbances". Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607686/index.pdf.

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High Frequency (3-30 MHz) (HF) Ionospheric Channel is used for military, civilian and amateur communications. By using Ionosphere, communication for distances beyond the line of sight is achieved. The main advantage of this type of communication is that it does not to require a satellite to communicate with a point beyond the line of sight. Actually the Ionosphere is used instead of a satellite. To use Ionosphere but not a satellite means independent communication for a country. The disadvantage of HF Ionospheric Communication is that the characteristics of the reflecting media (i.e. channel&rsquo
s transfer function) depends on many variables, e.g. sun spot number, hour of the day, season, solar cycles etc., so that mathematically modeling the channel is very difficult. Since military standards like STANAG 4538, STANAG 4285, STANAG 4415, MIL-STD-188-110A and MIL-STD-188-141A define the required performance of an HF modem in terms of Signal to Noise Ratio (SNR), Doppler Spread and Delay Spread according to desired conditions, a new approach to characterize the channel in terms of these three parameters is presented. In this thesis, HF Channel is considered as a system which involves various physical and chemical processes. A new method to characterize the HF channel to be used for modem performance evaluation is presented. In this study, it is aimed to relate modem/channel availability with the magnetic indices, which may be considered as the disturbances to the system. For this purpose the data taken from an HF communication experiment is used to model the channel to be used for modem availability calculations. The aim of the study is to asses the HF Channel Availability under Ionospheric Disturbances. This new technique will be a useful tool for HF Modem operators to select the optimum data rate or modulation method during HF Communication.

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Bennich, David, William Bredberg, Jimmy Olsson, Stenberg Louis Rulewski, Malin Smith e Johnny Söderqvist. "En jämförelse mellan fjärranalystekniker och vågbojar för mätning av oceanografiska parametrar i svenska vatten". Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-323069.

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För övervakning av svenska vatten krävs noggranna mätningar av oceanografiska parametrar såsom våghöjd, vågriktning, ytvattentemperatur och ytströmmar. Mätdata för parametrarna samlas in av Sveriges Meteorologiska och Hydrologiska Institut (SMHI) och används till prognoser, sjöfart samt forskning. I denna studie undersöktes möjligheten att ersätta eller komplettera vågbojarna av modellen Directional Waverider MkIII som SMHI använder idag, med ny kommersiellt tillgänglig fjärranalysteknik. Projektet begränsades till att studera två högfrekvens-radartekniker och en X-bandradar. Studien är platsspecifik och utreder kvalitetsmässiga, ekonomiska och miljömässiga för- och nackdelar med de utvalda radarteknikerna i relation till vågbojarna. En litteraturstudie och modellering av data över parametrar som påverkar radarteknikernas räckvidd och datatillgänglighet genomfördes. Ur modelleringen drogs slutsatsen att det är möjligt att erhålla likvärdig datatillgänglighet med vågradar som med vågboj. Vidare modellering ledde till slutsatsen att radarteknikerna begränsas till ungefär hälften av sin optimala räckvidd i Östersjön på grund av den låga salthalten, och därför är Sveriges västkust bättre lämpad för placering av radarteknik. Undersökning av isbildning i havsvatten, som kan begränsa radarteknikernas räckvidd, ledde till slutsatsen att Sveriges västkust också är att föredra utifrån detta perspektiv. Med anledning av radarteknikers möjlighet att utföra mätningar över större områden, finner studien att det finns goda grunder för att motivera en ersättning eller komplettering av vågbojarna med modern radarteknik. Vidare talar radarteknikernas goda anpassningsförmåga, lägre inverkan på miljön och enklare underhållskrav jämfört med vågbojarna till dess fördel. Att övergå till radarteknik medför däremot högre installations- och driftkostnader i jämförelse med vågbojar.

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Zelenke, Brian Christopher. "An empirical statistical model relating winds and ocean surface currents : implications for short-term current forecasts". Thesis, Connect to the title online, 2005. http://hdl.handle.net/1957/2166.

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46

Saleh, Oliver S. "Adaptive Processing in High Frequency Surface Wave Radar". Thesis, 2008. http://hdl.handle.net/1807/17219.

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High-Frequency Surface Wave Radar (HFSWR) is a radar technology that offers numerous advantages for surveillance of coastal waters beyond the exclusive economic zone. However, target detection and tracking is primarily limited by ionospheric interference. Ionospheric clutter is characterized by a high degree of nonhomogeneity and nonstationarity, which makes its suppression difficult using conventional processing techniques. Space-time adaptive processing techniques have enjoyed great success in airborne radar, but have not yet been investigated in the context of HFSWR. This thesis is primarily concerned with the evaluation of existing STAP techniques in the HFSWR scenario and the development of a new multistage adaptive processing approach, dubbed the Fast Fully Adaptive (FFA) scheme, which was developed with the particular constraints of the HFSWR interference environment in mind. Three different spatio-temporal partitioning schemes are introduced and a thorough investigation of the performance of the FFA is conducted.

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Wang, Jian Ph D. "High resolution methods for small target detection and estimation in high frequency radar". 2004. http://hdl.handle.net/1828/487.

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The detection and tracking of small slow moving targets by High Frequency Surface Wave radar are limited by the presence of a dominate sea clutter spectrum. The ocean surface behaves as a distributed source in contrast to targets that are point sources. It is shown that by mapping data to eigenspaces, the sea clutter level decreases due to its nondeterministic behaviour while point targets' levels remain unchanged. The high resolution (subspace-based or eigenspace) methods and frequency tracking method for slowly time varying frequencies are evaluated to suppress this sea clutter to enhance detection of weak signals. Experimental results verify the advantage of subspace-based methods over the traditional processing techniques. Conventional subspace methods can be utilized to enhance the detection, but they deteriorate dramatically in the presence of correlated sea clutter. In our thesis some adaptive sea clutter pre-filtering schemes are introduced which improve the threshold and accuracy of subsequent subspace methods. Both simulated and real ship targets are used to verify the effectiveness of our proposed method. Furthermore, we propose another novel subspace algorithm to estimate the directions of arrival of superimposed cisoidal radar echoes from far-field targets in the radar pulse domain. The improvement provided by this algorithm is based on the use of a state space model that more accurately represents the received Doppler radar array signal prior to spatial processing such as MUSIC. A 2-d (spatial and temporal) pre-filtering matrix is structured and applied to the received array signal, which is finally combined with the high-resolution (MUSIC) method for DOA estimation. Lower resolution threshold and estimation variance are achieved by this algorithm compared to conventional beam-space MUSIC and sensor-space MUSIC. A simplified theoretical resolution threshold is derived, and both the theory and simulations verify the effectiveness of our proposed algorithm. Results from an experiment using a simulated target superimposed on real HF radar sea clutter also confirm the algorithm.

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Huang, Yu-Wei, e 黃裕崴. "Frequency Swept THz Fiber-Based High-Speed Imaging Radar". Thesis, 2009. http://ndltd.ncl.edu.tw/handle/28533794757959303323.

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碩士
國立臺灣大學
光電工程學研究所
97
Since lots of methods for generating and detecting terahertz (THz) had been proposed, various THz scientific investigations were intensively performed. Also, within the last several years, THz imaging technology has been attracting more and more attentions. Amount all the setups of the THz imaging researches and applications nowadays, THz waves are usually conducted by planar or curved metal reflector in free space, which makes the THz system very rigid and vulnerable to environmental disturbance and unreliable. For more advanced THz application with flexible THz system, a reliable and compact guiding structure with low loss is highly desired. Moreover, for a conventional two dimensional THz image, it takes about several minutes to hours due to the slow mechanical movement of the translational stages. This is very unpractical for the daily application. Thus, in this thesis, we proposed the “frequency swept THz fiber-based high-speed imaging radar” which replaced the slow mechanical movement with fast sweeping frequency technique to acquire a two dimensional THz image in less than 7 seconds. To make the whole system be reliable and compact, THz waves were transmitted by the one-point-touched THz fiber-based directional coupler which was constructed by the low loss sub-wavelength PE fiber. As radar, in addition to acquire a fast image, measuring the distance or ranging the object is probably the most magnificent attribute, just like our THz imaging radar does. Although the speed of 7 seconds is still slower than the conventional radar system, the accomplished THz fiber-based imaging radar system has more compact size and an acceptable image acquisition time.

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Whitelonis, Nicholas John 1984. "Investigation of high-frequency propagation channels through pipes and ducts for building interior reconnaissance". Thesis, 2012. http://hdl.handle.net/2152/ETD-UT-2012-05-5651.

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Recently, there is strong interest in the through-wall sensing capabilities of radar for use in law enforcement, search and rescue, and urban military operations. Due to the high attenuation of walls, through-wall radar typically operates in the low GHz frequency region, where resolution is limited. It is worthwhile to explore other means of propagating radar waves into and back out of a building’s interior for sensing applications. One possibility is through duct-like structures that are commonly found in a building, such as metal pipes used for plumbing or air conditioning ducts. The objective of this dissertation is to investigate techniques to acquire radar images of targets through a pipe. First, using the pipe as an electromagnetic propagation channel is studied. A modal approach previously developed for computing the radar cross-section of a circular duct is modified to compute the transmission through a pipe. This modal approach for transmission is validated against measured data. It is also shown that a pipe is a high-pass propagation channel. The modal analysis is then extended to two-way, through-pipe propagation for backscattering analysis. The backscattering from a target is observed through a pipe in simulation and measurement. Next, methods to form two-dimensional radar images from backscattering data collected through a pipe are explored. Four different methods previously developed for free-space imaging are applied to the problem of imaging through a pipe: beamforming, matched filter processing, MUSIC, and compressed sensing. In all four methods it is necessary to take into account the propagation through the pipe in order to properly generate a focused radar image. Each method is demonstrated using simulation and validated against measurement data. The beamforming and matched filter methods are found to suffer from poor cross-range resolution. To improve resolution, the MUSIC algorithm is applied and shown to give superior resolution at the expense of more complicated data collection. The final method, compressed sensing, is shown to achieve good cross-range resolution with simpler data collection. A comparison of the tradeoffs between the four methods is summarized and discussed. Two additional extensions are studied. First, a method for computing the transmission through an arbitrary pipe network using the generalized scattering matrix approach is proposed and implemented. Second, a new method for computing joint time-frequency distributions based on compressed sensing is applied to analyze the backscattering phenomenology from a pipe.
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Green, David W. "Extraction of wind speed from high frequency ground wave radar oceanic backscatter /". 2005.

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