Dissertations / Theses on the topic 'Passive bistatic radar techniques'

With the rapid development and deployment of 802.11 wireless network signals over recent years, wireless network transmission has become widely available in many public places. This has given rise to interest from many researchers in application of these systems to detection and tracking. However, the majority of this research is focussed on co-operative detection using base station signal triangulation methods. There has been little research on non-cooperative indoor detection using wireless communication signals. This dissertation offers a comprehensive study of non-cooperative passive bistatic wireless detection methods. This includes a review of the literature, and a detailed theoretical and experimental study to evaluate the performance of the performance of bistatic passive radar (PBR) using wireless signals as an illuminator of opportunity. The characteristics of 802.11 wireless LAN signal were investigated, including the modulation scheme, the effective bandwidth, and the shifting transmission rate, which all influence and contribute to passive radar performance. The bistatic range resolution is 27 m when there is a lower transmission rate (1 Mbps and 2 Mbps) using DSSS PHY (with 11 MHz bandwidth); and the bistatic range resolution is 15 m when there is a higher transmission rate (above 5 Mbps) using OFDM PHY (with 20 MHz bandwidth). The ambiguity functions of typical waveforms of the 802.11 wireless LAN signals were simulated and analyzed from the radar perspective after the investigation of the communication signal characteristics. The echo power performance was then investigated as the initial experiment using the 802.11 beacon signal in an anechoic chamber and real wireless data transmissions in an office environment. The measurements seemed to agree quite closely with the theoretical values in an ideal environment. A comprehensive range of experiments in both indoor and outdoor environments were then conducted to examine the range and Doppler detection performance. These experiments demonstrated the first reported results for non-cooperative detection of human and other targets using wireless transmissions. Performance bounds were determined from these experiments and direct and multipath signal suppression identified as key areas to improve performance. Direct signal interference cancellation methods based on an adaptive filter were therefore developed and verified with effective cancellation results. The adaptive filter method developed in this study improved target SIR by about 30 – 40 dB. This study was finally extended to consider longer range outdoor detection using 802.16 (WiMax) transmissions. Simulations were carried out for real maritime surveillance scenarios and compared with existing active radars. This preliminary study showed that wireless based passive radar has the potential to replace active systems in some scenarios and is the subject of ongoing studies.

We present the design, development, and test of three novel, distinct automatic target recognition (ATR) systems for the recognition of airplanes and, more specifically, non-cooperative airplanes, i.e. airplanes that do not provide information when interrogated, in the framework of passive bistatic radar systems. Passive bistatic radar systems use one or more illuminators of opportunity (already present in the field), with frequencies up to 1 GHz for the transmitter part of the systems considered here, and one or more receivers, deployed by the persons managing the system, and not co-located with the transmitters. The sole source of information are the signal scattered on the airplane and the direct-path signal that are collected by the receiver, some basic knowledge about the transmitter, and the geometrical bistatic radar configuration. The three distinct ATR systems that we built respectively use the radar images, the bistatic complex radar cross-section (BS-RCS), and the bistatic radar cross-section (BS-RCS) of the targets. We use data acquired either on scale models of airplanes placed in an anechoic, electromagnetic chamber or on real-size airplanes using a bistatic testbed consisting of a VOR transmitter and a software-defined radio (SDR) receiver, located near Orly airport, France. We describe the radar phenomenology pertinent for the problem at hand, as well as the mathematical underpinnings of the derivation of the bistatic RCS values and of the construction of the radar images.For the classification of the observed targets into pre-defined classes, we use either extremely randomized trees or subspace methods. A key feature of our approach is that we break the recognition problem into a set of sub-problems by decomposing the parameter space, which consists of the frequency, the polarization, the aspect angle, and the bistatic angle, into regions. We build one recognizer for each region. We first validate the extra-trees method on the radar images of the MSTAR dataset, featuring ground vehicles. We then test the method on the images of the airplanes constructed from data acquired in the anechoic chamber, achieving a probability of correct recognition up to 0.99.We test the subspace methods on the BS-CRCS and on the BS-RCS of the airplanes extracted from the data acquired in the anechoic chamber, achieving a probability of correct recognition up to 0.98, with variations according to the frequency band, the polarization, the sector of aspect angle, the sector of bistatic angle, and the number of (Tx,Rx) pairs used. The ATR system deployed in the field gives a probability of correct recognition of $0.82$, with variations according to the sector of aspect angle and the sector of bistatic angle.

Passive radar detects and ranges targets by receiving signals which are reflected off targets. Communication transmissions are generally used, however, theoretically any signal with a suitable ambiguity function may be used. The exploitation of an existing transmitter and the removal of emissions allow passive radars to act as a complementary sensor which is useful in environments where conventional active radar is not well suited. Such environments are in covert operations and in situations where a low cost or spectrally efficient solution is required. Most developed passive radars employ intensive signal processing and use application specific equipment to achieve detection. The high-end processors and receiver equipment, however, detract from some of the inherent advantages in the passive radar architecture. These include the lower cost and power requirements achieved by removing transmitter hardware. This study investigates the challenges faced when removing application-specific and high end components from the system and replacing them with low-cost alternatives. Solutions to these challenges are presented and validated by designing and evaluating a radar using these principles. It was found that the major limitation in passive radar is the dynamic range of the receiver. While processing the signals was, and is, a significant challenge, be implemented on a low-cost, low-power embedded processor. This was achieved by asserting a few limitations to the configuration, exploiting the subsequently generated redundancy, and taking advantage of the parallelism by using general purpose graphics processing.. Even on this processor, the system was able to run in real time and able to detect targets up to 91 km (bistatic range of 195 km) from the radar.
Dissertation (MEng)--University of Pretoria, 2016.
Electrical, Electronic and Computer Engineering
MEng
Unrestricted

Passive Coherent Location (PCL) radar has proved to be feasible in a number of experimental systems, but the lack of comprehensive, published flight trials detracts somewhat from serious consideration of these PCL systems for operational applications, such as Air Traffic Control (ATC). The carrying out of flight trials is, in any case, difficult and very expensive. This dissertation presents a method for accurately predicting the performance of a bistatic passive coherent location radar with the effects of the environment taken into account. The effect of the environement on a propagating electromagnetic wave is obtained from the Advanced Refractive Effects Prediction System (AREPS) model. The resulting performance predictions, in the form of spatial signal-to-noise ratio (SNR), signal-to-interference ratio (SIR) and signal-to-noise-plus-interference ratio (SNIR) maps, provide a powerful planning tool for the application of systems such as ATC. Furthermore, the spatial coverage maps, based on the bistatic radar equation, can be related to a particular probability of detection and false alarm as well as to a required dynamic range of the receiver ADC. Overall, the method provides a visual, as well as a quantitative measure of radar coverage with region-specific atmospheric and terrain effects taken into account. The method proposed in this dissertation offers a marked improvement over traditional performance prediction methods based on the bistatic radar equation within a free space or flat terrain environment. It is understood that the direct path signal of the illuminating transmitter is the cause of some severe limitations within a PCL system. In the interest of suppressing the strong direct signal before the ADC and to complement the development of the prediction method, an antenna pattern was synthesised and applied to an array of folded dipoles in order to place a null in the direction of the strong transmitter. The synthesised antenna pattern and its improvement on the performance of the PCL system was then evaluated using the proposed prediction method presented in this dissertation.

A common way to measure height in aerial vehicles is to use a radar height altimeter (RHM). Since the RHM transmits radar pulses that can be detected, a passive alternative would be desirable in military applications. The idea to use reflected signals from the Global Positioning System (GPS) as a bistatic radar, has been established over the last years. The GPS signals are already present and would not reveal aeroplanes in covert operations.

In this thesis, the use of reflected GPS signals as a bistatic, passive altimeter is examined. A simulation model has been developed and implemented, and simulations using the model have been done. Different types of ground cover have been investigated, both water and land types, with varying reflectivity and scattering behaviour. For larger terrain variations, e.g. mountains and valleys, a ground elevation database has been used. Furthermore, several parameters, like the antenna coverage and the satellite elevation angle, have been varied and the result of this examined.

The results of these simulations show that measuring height is possible for bothsea and land surfaces. The accuracy depends on several error factors, like a bias originating from surface roughness and measurement errors due to noise in the receiver. The simulations also show that the most important design parameter is the antenna, which must be designed to give a sufficiently large SNR, capture the specular reflection and avoid unwanted reflections.

This thesis reports on research into the field of multiband Passive Bistatic Radar (PBR). The work is based on the premise that it is possible to improve on the PBR range resolution by exploiting the full broadcasted bandwidth from transmitters of opportunity. This work comprises both Frequency Modulated (FM) radio and Digital Video Broadcast - Terrestrial (DVB-T) waveforms. The work shows how the exploitation of the available frequency scattered bandwidth broadcasted from single broadcast towers can be achieved by coherently by combining each of the individual channels/bands, and that the range resolution is improved accordingly. The major contributions of this thesis may be divided into the following parts: Hardware (HW) design and development, algorithm development, simulations, real target data analysis, and finally non-cooperative target recognition and High Range Resolution (HRR) considerations. The work comprises simple PBR performance predictions for various strong transmitters of opportunity in the southeastern parts of Norway. Hardware for data recording was designed, produced and made working. The mathematics for coherently combining non-adjacent single channels/bands in the range correlation was developed. The range resolution performance of the algorithm was supported by theoretical simulations using pseudo random generated signals, as well as simulations using real recorded FM radio and DVB-T signals from nearby strong transmitters. For FM radio and DVB-T airliners and for DVB-T also a propeller aircraft were analyzed. The theoretical claims were supported by the real life target analysis, as the range resolution was improved as predicted for all targets. For the DVB-T waveform, an analysis of the HRR profiles showed that two targets of different type was manually classified as targets of different type. This work has fully closed the circle from idea, HW design, development and testing, theoretical algorithm development and simulations, and finally real world performance analysis as well as target analysis.

A passive radar systems opportunistic ability to exploit ambient radio signal reflections makes it ideal for covert target tracking. This strategy, referred to as passive covert radar (PCR) or passive coherent location (PCL), typically exploits FM radio or television signals from powerful local transmitters. In addition to covertness, the absence of a dedicated transmitter helps reduce costs and overall system complexity. While a variety of measurements can be used to estimate a targets position and velocity, such as time difference of arrival (TDOA) and direction of arrival (DOA), this thesis focuses on using only Doppler shift measurements to estimate a targets state. The work presented in this thesis examines the use of Doppler shift measurements from multiple receivers to solve the target tracking and association problem. A nonlinear least squares error (NLSE) estimation technique, called the Levenberg-Marquardt (L-M) algorithm, is used to determine a targets state (position, velocity) from these Doppler shift measurements. More than one target state can potentially produce identical Doppler shift profiles. In a single-receiver, single-target scenario, it is shown that three additional ghost targets caused by symmetry produce the same Doppler shift response. These ghosts may make state estimation impossible if receive antennas are not physically positioned to block out ghost targets. While the NLSE technique tends to give an accurate solution in one quadrant, three other solutions will symmetrically exist in each of the remaining three quadrants. The addition of either another receiver or another measurement (such as DOA) is needed to break this quadrant ambiguity. This thesis considers adding multiple receivers to accurately associate and track multiple targets. Two target association methods (sequential and simultaneous) are developed, and their computational requirements and accuracy are compared. A grid-aided L-M search technique is investigated in an attempt to provide a better initial target state guess to these association and tracking algorithms. The analysis and simulation results suggest it is feasible to perform multi-target association and tracking using Doppler shift as the sole measurement. Both of the proposed methods gave optimal target association and converged to reasonably accurate state estimates in most of the Monte Carlo runs.

Passive coherent location (PCL) radars employ illuminators of opportunity to detect and track targets. This silent operating mode provides many advantages such as low cost and interception immunity. Many radiation sources have been exploited as illumination sources such as broadcasting and telecommunication transmitters. The classical architecture of the bistatic PCL radars involves two receiving channels: a reference channel and a surveillance channel. The reference channel captures the direct-path signal from the transmitter, and the surveillancesignal collects the possible target echoes. The two major challenges for the PCL radars are the reference signal noise and the surveillance signal static clutter. A noisy reference signal degrades the detection probability by increasing the noise-floor level of the detection filter output. And the static clutter presence in the surveillance signal reduces the detector dynamic range and buries low magnitude echoes.In this thesis, we consider a PCL radar based on the digital video broadcasting-terrestrial (DVB-T) signals, and we propose a set of improved methods to deal with the reference signal noise and the static clutter in the surveillance signal. The DVB-T signals constitute an excellentcandidate as an illumination source for PCL radars; they are characterized by a wide bandwidth and a high radiated power. In addition, they provide the possibility of reconstructing the reference signal to enhance its quality, and they allow a straightforward static clutter suppressionin the frequency domain. This thesis proposes an optimum method for the reference signal reconstruction and an improved method for the static clutter suppression.The optimum reference signal reconstruction minimizes the mean square error between the reconstructed signal and the exact one. And the improved static clutter suppression method exploits the possibility of estimating the propagation channel. These two methods extend thefeasibility of a single receiver PCL radar, where the reference signal is extracted from the direct-path signal present in the surveillance signal.
Doctorat en Sciences de l'ingénieur et technologie
info:eu-repo/semantics/nonPublished

Le concept de radar passif aéroporté repose sur l’utilisation de plusieurs antennes réseau, disposées sur une plateforme en vue de couvrir un angle solide large de détection, en s’appuyant sur l’utilisation de signaux d’opportunité provenant d’émetteurs au sol. La détection aéroportée à partir de signaux d’opportunité est intéressante, notamment pour assurer l’autoprotection d’un avion ou d’un hélicoptère ; en revanche elle constitue un défi technique notamment en raison du niveau des signaux interférents, en provenance de l’émetteur et des trajets multiples indirects (le fouillis), bien supérieur au niveau de signal utile diffusé par la cible à détecter. D’autres effets, tels que la structure arbitraire des signaux (forme d’onde non-radar) et sa conséquence sur les lobes secondaires en distance, contribuent à la complexité du traitement à mettre en œuvre.Le point de départ des recherches se situe à l’intersection des techniques de radar passif (utilisant la corrélation entre un signal de référence non connu a priori et les signaux diffus renvoyés par l’environnement) et les techniques de type STAP (Space Time Adaptive Processing) utilisées pour la détection des cibles mobiles par les radars aéroportés conventionnels. Dans ce contexte, les travaux de thèse permettent d’étendre d’une part la caractérisation et la qualification des signaux « radar passif » à une configuration aéroportée, d’autre part les techniques STAP à une configuration bistatique et à des signaux de forme arbitraire et non structurés comme des signaux radar. Les recherches mettent en évidence l’importance primordiale du trajet direct et des premiers échos de fouillis qui parasitent la caractérisation spatio-temporelle des échos reçus dans la case distance de la cible sous test. La caractéristique du fouillis, habituellement tracée dans le plan Doppler-angle, se trouve affectée par ces interférences qu’il faut éliminer au préalable. Pour cela, un premier filtre à réponse finie est mis en œuvre sur chaque capteur, puis le traitement STAP est appliqué à l’ensemble du réseau d’antennes.Les traitements proposés sont simulés et les performances en détection sont analysées. Une expérimentation est conduite, à l’aide d’un réseau de 4 antennes mobiles au sol. Les conditions sont réunies pour collecter des signaux de fouillis étalés en Doppler et analyser l’effet d’une forme d’onde non-radar. Les traitements d’élimination des interférences sont mis en œuvre et ainsi qualifiés expérimentalement
The novel concept for the airborne passive radar is to have multiple passive receiving arrays covering a 4 steradian angle around the platform which makes use of the ground-based stationary transmitter as the illuminator of opportunity. This challenging passive radar configuration would well find application for localized covert surveillance on an airborne platform such as an unmanned aerial vehicle, helicopter, etc. For the airborne passive radar, during moving target detections, it encounters the effects of strong interfering signal returns against the weak target returns where this severe interfering environment is usually characterized by the high levels of direct path and clutter against the thermal noise background. Due to the continuous wave, random and aperiodic nature of the passive signal and given the strong direct path and clutter signals, their random range sidelobes couplings into further range cells will seriously exacerbate the background interference, making target detections a big challenge. Moreover, owing to the platform motion, the clutter received by the airborne passive radar is not only extended in both range and angle, it is also spread over a region in Doppler frequency which further complicates the problem.This research work is focused on identifying and analyzing the critical issues faced by the airborne passive radar on moving target detections and to develop effective signal processing schemes for improved performance. As a first step, it is important to accurately derive the model for the received passive signals and consequently, efficient signal processing schemes can be studied to mitigate and to improve detections performance. The signal processing schemes for the airborne passive radar can be segregated into a two-step interference cancellation process where the direct path and strong clutter coupling components (and their corresponding random range sidelobes) present in the received signal at each antenna element can first be effectively suppressed by the adaptive interference cancellation algorithm prior to matched filter processing. Further cancellation on the residual random range sidelobes couplings and on the spatial-Doppler dependent clutter can be achieved using reduced-dimension STAP. Trials based on the ground-based moving passive radar experiments are conducted as the final part of this research work to validate and evaluate the signal processing schemes which is a major progress towards implementing an operational airborne passive radar

Passive source localization is the estimation of the positions of the sources or emitters given the sensor data. In this thesis, some of the well known methods for passive source localization are investigated and compared in a stationary emitter sensor framework. These algorithms are discussed in detail in two and three dimensions for both single and multiple target cases. Passive source localization methods can be divided into two groups as two-step algorithms and single-step algorithms. Angle-of-Arrival (AOA) based Maximum Likelihood (ML) and Least Squares (LS) source localization algorithms, Time- Difference-of-Arrival (TDOA) based ML and LS methods, AOA-TDOA based hybrid ML methods are presented as conventional two step techniques. Direct Position Determination (DPD) method is a well known technique within the single step approaches. In thesis, a number of variants of DPD technique with better computational complexity (the proposed methods do not need eigen-decomposition in the grid search) are presented. These are the Direct Localization (DL) with Multiple Signal Classification (MUSIC), DL with Deterministic ML (DML) and DL with Stochastic ML (SML) methods. The evaluation of these algorithms is done by considering the Cramer Rao Lower Bound (CRLB). Some of the CRLB expressions given in two dimensions in the literature are presented for threedimensions. Extensive simulations are done and the effects of different parameters on the performances of the methods are investigated. It is shown that the performance of the single step algorithms is good even at low SNR. DL with MUSIC algorithm performs as good as the DPD while it has significant savings in computational complexity. AOA, TDOA and hybrid algorithms are compared in different scenarios. It is shown that the improvement achieved by single-step techniques may be acceptable when the system cost and complexity are ignored. The localization algorithms are compared for the multiple target case as well. The effect of sensor deployments on the location performance is investigated.

L’étude traite de la détection de cibles mobiles dans un contexte de radar passif bistatique utilisant les émetteursde télévision numérique TNT (DVB-T) comme émetteurs d’opportunité. Outre leur présence généralisée sur leterritoire, l’intérêt de ces émissions réside dans leur relative largeur de bande permettant une bonne précisiond’estimation. Le principal inconvénient de ce type d’approche réside dans l’éblouissement par le signal en trajetdirect, des échos de très faible intensité des cibles d’intérêt. Après un rappel du principe du radar bistatique etde la norme OFDM utilisée par les signaux TNT, une première étude donne une construction originale du signalde référence dans le cas multi-capteurs : le signal de référence est construit par un traitement d’antenne de typeCAPON où le balayage des paramètres optimaux est remplacé par la connaissance de signaux pilotes inséré dansles symboles OFDM. Ensuite le rapport se focalise sur l’estimation d’un filtre de canal multitrajet à partir dela connaissance de la modulation OFDM utilisée. Ce filtre, d’abord étudié comme réjecteur de fouillis originalavant détection par la fonction d’ambiguïté, donne des résultats semblables aux méthodes classiques de réjectionde fouillis standard. Étendu à toutes les fréquences Doppler, son module au carré est utilisé comme un nouveaudétecteur présentant un très faible niveau de clutter, surpassant ainsi la fonction d’ambiguïté. Une interprétationen terme de traitement d’antennes du nouveau détecteur ouvre la voie à des variantes haute-résolution de celui-ci.La validité du nouveau détecteur est illustrée par des résultats sur données réelles
The study focuses on moving target detection from passive bistatic radar with DVB-T transmitters used asopportunity transmitters. In addition to their widespread geographical coverage, they allow a good estimationaccuracy due to their quite large bandpass. Nevertheless the continuous powerful direct path masks the verylow intensity echoes of targets of interest. The passive bistatic radar principle and the CP-OFDM standardused by DVB-T are briefly reminded, then, a new first study of reference signal retrieving in multiple sensorsconfiguration is given : the reference signal is built using a Capon receptor where the parameters scan is replacedby the knowledge of pilot signals inserted in the OFDM symbols. Next, the report addresses the multipath channelestimate by using the OFDM signal structure. This channel is firstly studied for clutter rejection before detectionfrom the cross ambiguity function (CAF). We obtain similar results than those of the classical rejection methods.This channel is extended to the whole Doppler shift, and its squared modulus acts as a new low clutter detectorthat outperforms classical CAF. A virtual beamforming interpretation of the channel estimation opens a new pathtowards high resolution array processing. Results given on real data illustrate the validity of this new channeldetector (CHAD)

Les systèmes d’imagerie microonde suscitent un grand intérêt actuellement dans le domaine de la recherche, notamment pour des applications de sécurité (scanners corporels, vision à travers les murs, etc). Plusieurs techniques d’acquisition déjà existantes permettent d’optimiser l’ouverture rayonnante afin de garantir une bonne résolution sur l’image finale. Cependant, le verrou actuel des systèmes d’imagerie est de pouvoir atteindre un temps de rafraîchissement temps réel et d’adresser un grand nombre d’antennes. La majorité des systèmes actuels peinent à concilier la rapidité et la résolution, tout en garantissant une bonne sensibilité. Les travaux réalisés dans ce manuscrit visent à proposer une alternative aux systèmes existants en se basant sur des techniques de codage analogique des signaux d’antennes. Globalement, l’objectif est de minimiser le nombre de récepteurs sans affecter les performances. Les architectures proposées sont essentiellement basées sur le concept du Radar MIMO (pour les systèmes actifs) et du radiomètre à synthèse d’ouverture interférométrique ou SAIR (pour les systèmes passifs). Ces deux systèmes permettent de réduire considérablement le nombre d’antennes sans affecter la résolution de l’image, ce qui permet une première levée de contraintes. En sus, des composants compressifs entièrement passifs sont utilisés pour réduire le nombre de récepteurs des systèmes Radar MIMO et SAIR. Ces composants à diversité spatiale et fréquentielle présentent des fonctions de transfert orthogonales. Utilisés en émission, ils permettent un adressage simultané et indépendant des antennes du réseau. En réception, ils permettent de coder les signaux reçus par les antennes vers un nombre de voies RF considérablement réduit. En appliquant des techniques de décodage appropriées, les signaux reçus par chacune des antennes peuvent être estimées afin d’appliquer les algorithmes dédiés à la reconstruction de l’image. Ces composants offrent l’avantage de réduire fortement le nombre de voies RF tout en conservant la même ouverture rayonnante et en autorisant une acquisition simultanée des signaux. Des démonstrateurs laboratoires ont été réalisés en bande S afin de montrer une preuve de faisabilité des alternatives proposées. Enfin, les résultats obtenus ont fait l'objet d'une demande de brevet et un prototype d'imageur radiométrique à ondes millimétriques est en cours de prototypage dans le cadre du projet ANR-PIXEL
Microwave imaging systems are currently attracting great attention in the field of research, especially for security applications (body scanners, vision through walls, etc.). Several acquisition techniques already exist to optimize the antenna aperture in order to guarantee a good resolution on the final image. However, the current lock of imaging systems is to be able to achieve a real-time acquisition and address numerous antennas. Most of the current systems struggle to reconcile fast imaging and resolution while ensuring good sensitivity. The work carried out in this manuscript aims at proposing an alternative to the existing systems based on analog coding techniques of the antenna signals. Overall, the goal is to minimize the number of receivers without affecting performances. The proposed architectures are based essentially on the concept of the MIMO radar (for active systems) and the Synthetic Aperture Interferometric Radiometer or SAIR (for passive systems). These two systems allow a significant reduction of the number of antennas without affecting the resolution of the image, thus enabling a first lifting of constraints. In addition, passive compressive components are used to reduce the number of receivers in the MIMO Radar and the SAIR systems. These components with spatial and frequency diversity exhibit orthogonal transfer functions. Used in transmission, they allow simultaneous and independent addressing of each element of the antenna array. In reception, they allow the signals received by the antennas to be coded into a considerably reduced number of aggregate waveforms. By applying suitable decoding techniques, the signals received by each antenna can be estimated in order to apply imaging algorithms. These components offer the advantage of greatly reducing the number of RF channels while keeping the same number of antennas and allowing simultaneous acquisition of the signals. Laboratory demonstrators were carried out in S-band to demonstrate the feasibility of the proposed alternatives. Finally, the results obtained were the subject of a patent application and a prototype of a millimeter-wave radiometric imager is being developed in the framework of the ANR-PIXEL project

Les travaux présentés dans cette thèse sont une contribution à l’étude des systèmes d’imagerie active en bande millimétrique et plus spécifiquement sur les parties antennaires et le traitement de signal. Ces travaux ont été menés dans le cadre d’une collaboration entre Canon Research Center France et l’ETR. Une première étude a porté sur les antennes focalisantes et plus spécifiquement sur la lentille de Fresnel avec un procédé de fabrication de matériau à gradient d’indice qui a permis d’améliorer l’efficacité (59%) et la largeur bande de fréquence (75-110 GHz). Cette antenne a été utilisée sur un système rotatif pour imager une scène réelle extérieure. L’étude s’est ensuite focalisée sur la conception d’une configuration Multiple-Input Multiple-Output ou MIMO (entrées multiples, sorties multiples) grâce notamment à l’utilisation d’un dispositif compressif passif 4×1 permettant de réduire, par compression, le nombre de chaînes RF. Ces chaînes sont décompressées par post-traitement. Le dispositif, placé à l’émission, a été associé avec un scanner qui permet de synthétiser un réseau d’antennes à la réception. Cette configuration a permis de générer virtuellement un réseau de plus grande taille, permettant d’améliorer la résolution azimutale du système tout en limitant le nombre de chaînes RF. Cette configuration est utilisée pour imager une scène en chambre anéchoique afin de valider le concept. Pour améliorer encore plus la résolution du système avec un nombre limité de chaînes RF, l’étude d’algorithmes de haute-résolution, ou méthodes d’estimation spectrales, sont utilisés dans des configurations à large bande de fréquences pour imager des cibles en champs proche. L’association de la configuration MIMO, du dispositif compressif passif et des méthodes d’estimation spectrales permet d’améliorer la résolution du système tout en limitant le nombre de chaînes RF nécessaire
The broad topic of the presented Ph.D. thesis consists in the contribution to the study of Radar imaging systems at millimeter-wave and more specifically to the antennas and signal processing. These works have been carried out during a partnership between Canon Research Center France and IETR. A first study on focusing antennas, particularly on Fresnel lens antennas, thanks to a technological process to manufacture inhomogeneous materials, has allowed to improve the efficiency and the frequency bandwidth. The antenna has been mounted on a rotary system to image a real outdoor scene. Then, the study has been focused on the realization of a Multiple-Input Multiple-Output (MIMO) configuration notably using a 4 × 1 passive compressive device allowing to reduce, by compression, the number of radiofrequency (RF) chains. The chains are decompressed by post-processing. The device, used at the transmitting part, is associated with a scanner that synthetizes a receiving array of antennas. This configuration allows to generate a large virtual array, to improve the azimutal resolution of the system while maintaining acceptable the number of RF chains. This configuration has been used to image a scene in an anechoid chamber to validate the concept. To further improve the spatial resolution of the system for a given number of RF chains, the study of high resolution algorithms, or spectral estimation methods, are used to image scenes in near field and wide-band configurations. The combination of MIMO configurations, the passive compressive device and the spectral estimation methods have allowed to drastically improve the spatial resolution of the radar imaging system while limiting the number of RF chains

The multi-target tracking problem essentially involves the recursive joint estimation of the state of unknown and time-varying number of targets present in a tracking scene, given a series of observations. This problem becomes more challenging because the sequence of observations is noisy and can become corrupted due to miss-detections and false alarms/clutter. Additionally, the detected observations are indistinguishable from clutter. Furthermore, whether the target(s) of interest are point or extended (in terms of spatial extent) poses even more technical challenges. An approach known as random finite sets provides an elegant and rigorous framework for the handling of the multi-target tracking problem. With a random finite sets formulation, both the multi-target states and multi-target observations are modelled as finite set valued random variables, that is, random variables which are random in both the number of elements and the values of the elements themselves. Furthermore, compared to other approaches, the random finite sets approach possesses a desirable characteristic of being free of explicit data association prior to tracking. In addition, a framework is available for dealing with random finite sets and is known as finite sets statistics. In this thesis, advanced signal processing techniques are employed to provide enhancements to and develop new random finite sets based multi-target tracking algorithms for the tracking of both point and extended targets with the aim to improve tracking performance in cluttered environments. To this end, firstly, a new and efficient Kalman-gain aided sequential Monte Carlo probability hypothesis density (KG-SMC-PHD) filter and a cardinalised particle probability hypothesis density (KG-SMC-CPHD) filter are proposed. These filters employ the Kalman- gain approach during weight update to correct predicted particle states by minimising the mean square error between the estimated measurement and the actual measurement received at a given time in order to arrive at a more accurate posterior. This technique identifies and selects those particles belonging to a particular target from a given PHD for state correction during weight computation. The proposed SMC-CPHD filter provides a better estimate of the number of targets. Besides the improved tracking accuracy, fewer particles are required in the proposed approach. Simulation results confirm the improved tracking performance when evaluated with different measures. Secondly, the KG-SMC-(C)PHD filters are particle filter (PF) based and as with PFs, they require a process known as resampling to avoid the problem of degeneracy. This thesis proposes a new resampling scheme to address a problem with the systematic resampling method which causes a high tendency of resampling very low weight particles especially when a large number of resampled particles are required; which in turn affect state estimation. Thirdly, the KG-SMC-(C)PHD filters proposed in this thesis perform filtering and not tracking , that is, they provide only point estimates of target states but do not provide connected estimates of target trajectories from one time step to the next. A new post processing step using game theory as a solution to this filtering - tracking problem is proposed. This approach was named the GTDA method. This method was employed in the KG-SMC-(C)PHD filter as a post processing technique and was evaluated using both simulated and real data obtained using the NI-USRP software defined radio platform in a passive bi-static radar system. Lastly, a new technique for the joint tracking and labelling of multiple extended targets is proposed. To achieve multiple extended target tracking using this technique, models for the target measurement rate, kinematic component and target extension are defined and jointly propagated in time under the generalised labelled multi-Bernoulli (GLMB) filter framework. The GLMB filter is a random finite sets-based filter. In particular, a Poisson mixture variational Bayesian (PMVB) model is developed to simultaneously estimate the measurement rate of multiple extended targets and extended target extension was modelled using B-splines. The proposed method was evaluated with various performance metrics in order to demonstrate its effectiveness in tracking multiple extended targets.

Develop new strategies to design and operate the multilateration systems, used for air traffic control operations, in a more efficient way. The design strategies are based on the utilization of metaheuristic optimization techniques and they are intended to found the optimal spatial distribution of the system ground stations, taking into account the most relevant system operation parameters. The strategies to operate the systems are based on the development of new positioning methods which allow solving the problems of uncertainty position and poor accuracy that the current systems can present. The new strategies can be applied to design, deploy and operate the multilateration systems for airport surface surveillance as well as takeoff-landing, approach and enroute control. An important advance in the current knowledge of air traffic control is expected from the development of these strategies, because they solve several deficiencies that have been made clear, by the international scientific community, in the last years.
Mantilla Gaviria, IA. (2013). New Strategies to Improve Multilateration Systems in the Air Traffic Control [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/29688
Alfresco

The aim of this research is to use observations of Very High Frequency (VHF) radio wave propagation to estimate the refractive index of air over a propagation path and subsequently the pressure, temperature, and water vapour. This can be accomplished by transmitting a known signal from one spatial location to another, and accurately timing the signal. The research develops methods for accomplishing the required measurements by means of a passive bistatic radar setup with a cooperative target. Such an approach overcomes the timing problems that are normally associated with propagation measurements. A network of these measurements can then be assimilated into a numerical weather prediction model, such as that used by the Australia Bureau of Meteorology, to increase weather forecast capability. Importantly, this research develops novel techniques to relate the propagation of radio waves from weather data. These techniques are important in their own right to identify true propagation paths.
Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 2018

碩士
元智大學
通訊工程學系
98
A bistatic passive radar, which chooses the orthogonal frequency division multiplexing (OFDM) transmit signal of the digital video broadcasting-terrestrial (DVB-T) system, is studied in the thesis. The research items include ambiguity function analysis of an OFDM radar waveform and simulations of the radar detection performance. Through the observations of the ambiguity diagram, which is function of time delay and Doppler frequency, the parameters of range resolution and velocity resolution can be attained to evaluate the radar characteristics. The detection performance of the OFDM bistatic passive radar using fixed threshold and constant false alarm rate (CFAR) processing is simulated. The false alarm rate of a fixed threshold detection method will change with the variation of the radar operation environments. Therefore, the CFAR detection processing is used in radar practice to remain false alarm constant in changing clutter statistics Simulation results shows that the bistatic passive radar using CFAR detection processing can satisfy the requirement of the DVB-T signal detection.

碩士
元智大學
通訊工程學系
99
The aim of this thesis is the study of target detection and positioning for passive bistatic netted radar system (PBNRS) based on digital video broadcasting-terrestrial (DVB-T) signal source. First, the detection performance of energy detector, matched filter detector and cyclo-stationary detector on the DTV-B reflected signal is analyzed and simulated. The multi-receivers use the diversity methods to further improve the detection performance. Then the passive location system including one transmitting signal and four receivers is investigated. Firstly, the cross correlation method is used to estimate the time difference of arrival (TDOA) between a pair of receivers. Secondly, three pair of TDOA values is used to locate the target position. Thirdly, the measured TDOAs and coordination of the four receivers are employed to estimate the locus of flight target and evaluate the circular error probability using Gauss-Newton interpolation algorithm.

碩士
國立臺灣科技大學
電機工程系
99
Unlike an active radar system, a passive radar system only requires a dedicate receiver end to detect airborne targets. To locate the unknown targets, we jointly combine Angle-of-Arrival and Time-Different-of-Arrival information. In this work, we use Multiple Signal Classification algorithm to estimate angle of arrival information of targets, and use ambiguity function to detect targets ranges and Doppler shifts in a bistatic passive radar system. Combining these parameters, we can locate positions of targets. This thesis contains hardware implementation and software simulations. In hardware implementation, we use LYRTECH’s Software Defined Radio platform to implement Multiple Signal Classification algorithm, and use the least square method to compensate the phase and gain caused by RF front-end. In simulations, we first simulate an ambiguity function for digital video broadcasting terrestrial signal, which results in unwanted deterministic peaks due to the guard interval and the pilots in the digital video broadcasting terrestrial passive radar. In order to improve the accuracy of ambiguity function, we remove these unwanted peaks; in the meantime, we also apply a window function to further reduce the ambiguity function sidelobes. Second, we propose a method using beamforming technique and least square method to mapping angles, ranges, and Doppler shifts for multiple airborne targets. Simulation results shows that the proposed mapping scheme can effectively determine positions of multiple targets.