Um die anderen Arten von Veröffentlichungen zu diesem Thema anzuzeigen, folgen Sie diesem Link: Radio waves.
Dissertationen zum Thema „Radio waves“
Geben Sie eine Quelle nach APA, MLA, Chicago, Harvard und anderen Zitierweisen an
Machen Sie sich mit Top-50 Dissertationen für die Forschung zum Thema "Radio waves" bekannt.
Neben jedem Werk im Literaturverzeichnis ist die Option "Zur Bibliographie hinzufügen" verfügbar. Nutzen Sie sie, wird Ihre bibliographische Angabe des gewählten Werkes nach der nötigen Zitierweise (APA, MLA, Harvard, Chicago, Vancouver usw.) automatisch gestaltet.
Sie können auch den vollen Text der wissenschaftlichen Publikation im PDF-Format herunterladen und eine Online-Annotation der Arbeit lesen, wenn die relevanten Parameter in den Metadaten verfügbar sind.
Sehen Sie die Dissertationen für verschiedene Spezialgebieten durch und erstellen Sie Ihre Bibliographie auf korrekte Weise.
1
Starck, Patrik. „Energy harvesting of ambient radio waves“. Thesis, Uppsala universitet, Avdelningen för datorteknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-355020.
Der volle Inhalt der QuelleAnnotation:
The aim for this thesis was to investigate if harvesting of ambient radio waves could be a viable source of energy and where and when it can be used. A survey of the signal strengths at different locations in Uppsala, Sweden was performed which showed that the cellular frequency bands were the ones that carried the most energy. One circuit was manufactured and two more were simulated, together with the circuitry required to measure and display how much energy that was being harvested. The design was tested at the same locations as the survey of the signal strength was conducted at. The maximum harvested energy was 35µW which was at a location inside in a window facing a cellular transmittor with an approximate distance of 100m. At 200m away from a cellular transmitter, the output was 1µW. In a typical city environment, the output from the harvester was 0µW. The harvesting technique was also compared to energy from solar- and thermal energy. The comparison showed that it is almost always more beneficial to use an alternative source of energy, such as solar cells, even indoors.
2
Hawbaker, Dwayne Allen. „Indoor wide band radio wave propagation measurements and models at 1.3 ghz and 4.0 ghz /“. This resource online, 1989. http://scholar.lib.vt.edu/theses/available/etd-08182009-040436/.
Der volle Inhalt der Quelle
3
Pala, Fatih. „Frequency and polarization diversity simulations for Urban UAV communication and data links“. Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Sep%5FPala.pdf.
Der volle Inhalt der Quelle
4
Rasam, Setty Harish Raghav. „Assessment of Volumetric Water Content Using Radio Waves“. Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
Den vollen Inhalt der Quelle findenAnnotation:
Volumetric water content evaluation in structures, substructures, soils, and subsurface in general is a crucial issue in a wide range of applications. The main weakness of subsurface moisture sensing techniques is usually related both to the lack of cost-effectiveness of measurements, and to unsuitable support scales with respect to the extension of the surface to be investigated. In this regard, Wireless Underground Sensor Network are increasingly used non-destructive tool specifically suited for characterization and measurement. It is undeniable that wireless communication technology has become a very important component of modern society. One aspect of modern society in which application of wireless communication technologies has tremendous potential is in agricultural production. This is especially true in sensing and transmission of relevant farming information such as weather, crop development, water quantity and quality, among others, which would allow farmers to make more accurate and timely farming decisions. Although many systems are commercially available for soil moisture monitoring, there are still many important factors, such as cost, limiting widespread adoption of this technology among growers. Our objective in this study was, therefore, to develop and test an affordable wireless communication system for monitoring soil moisture. WUSN is a specialized kind of WSN that mainly focuses on the use of sensors at the subsurface region of the soil, that is, the top few meters of the soil. This thesis emphasizes on comparison of experimental measurements conducted with wireless devices based on LoRa using point to point communication to the advanced channel models (precisely on single-path channel model) that were developed to characterize the underground wireless channel considering the characteristics of the propagation of EM waves in soil and their relationship with the frequency of these waves, the soil composition, and the soil moisture.
5
Ciavarella, Michele. „Volumetric soil moisture evaluation via radio waves propagation“. Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
Den vollen Inhalt der Quelle findenAnnotation:
Nowadays technology plays an important role in different sectors of farm management, in particular technologies based on soil moisture assessment have proven to be efficient in helping farmers who need timely techniques to determine crop water requirements.
The main weakness of subsurface moisture sensing techniques is usually related both to the lack of cost-effectiveness of measurements and to unsuitable support scales with respect to the extension of the surface to be investigated. In this regard, Wireless Underground Sensor Network are increasingly used non-destructive tool specifically suitable for characterization and measurement.
Wireless communication within a dense substance such as soil is, however, significantly more challenging than through air. This factor, combined with the necessity to conserve energy due to the difficulty of unearthing and recharging WUSN devices, requires that communication protocols be redesigned to be as efficient as possible.
This work focuses on problem of implementing a Wireless Underground Sensor Network using LoRa technology, one of the most prominent Low Power Wide Area Network technologies, for communication. A system for monitoring soil moisture is implemented using low cost solutions and results are presented.
6
Lange, Martin, und Christoph Jacobi. „Analysis of gravity waves from radio occultation measurements“. Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-217072.
Der volle Inhalt der QuelleAnnotation:
In the height range 10–30 km atmospheric gravity waves lead to periodic perturbations of the background temperature field in the order of 2-3 K, that are resolved in temperature profiles derived from radio occultation measurements. Due to the spherical symmetry assumption in the retrieval algorithm and the low horizontal resolution of the measurement damping in the amplitude and phase shift of the waves occurs leading to remarkable errors in the retrieved temperatures. The influence of the geometric wave parameters and the measurement geometry on plane gravity waves in the range 100-1000 km horizontal and 1-10 km vertical wavelength is investigated with a 2D model ranging ±1000 km around the tangent point and 10-50 km in height. The investigation shows, that with radio occultation measurements more than 90 % of the simulated waves can be resolved and more than 50% with amplitudes above 90%. But the geometrical parameters cannot be identified, since one signal can be attributed to different combinations of wave parameters and view angle. Even short waves with horizontal wavelengths below 200 km can be derived correctly in amplitude and phase if the vertical tilt is small or the view angle of the receiver satellite is in direction of the wave crestsAtmosphärische Schwerewellen führen im Höhenbereich 10-30 km zu periodischen Störungendes Hintergrundtemperaturfeldes in der Größenordnung von 2-3 K, die in Temperaturprofilen aus Radiookkultationsmessungen aufgelöst werden. Aufgrund der sphärischen Symmetrieannahme im Retrievalverfahren und durch die niedrige horizontale Auflösung des Messverfahrens werden Phasenverschiebungen und Dämpfung der Amplitude verursacht, die zu beachtlichen Fehlern bei den abgeleiteten Temperaturen führen. Der Einfluss der geometrischen Wellenparameter und der Messgeometrie auf ebene Schwerewellen im Bereich 100-1000 km horizontale und 1-10 km vertikale Wellenlänge wird untersucht mit einem 2D-Modell, dass sich auf ein Gebiet von ±1000 km um den Tangentenpunkt und von 10-50 km in der Höhe erstreckt. Die Untersuchung zeigt, dass mit Radiookkultationsmessungen mehr als 90% der simulierten Wellen aufgelöst werden und mehr als 50% mit Amplituden oberhalb von 90% der ursprünglichen. Die geometrischen Parameter können jedoch nicht aus Einzelmessungen abgeleitet werden, da ein Signal zu verschiedenen Kombinationen von Wellenparametern und Sichtwinkel zugeordnet werden kann. Auch relativ kurze Wellen mit horizontalen Wellenlängen unterhalb von 200 km können korrekt in der Amplitude und Phase aufgelöst werden, falls die Neigung des Wellenvektors gegen die vertikale gering ist oder der Sichtwinkel des Empfängersatelliten in Richtung der Wellenberge ist
7
Lange, Martin, und Christoph Jacobi. „Analysis of gravity waves from radio occultation measurements“. Wissenschaftliche Mitteilungen des Leipziger Instituts für Meteorologie ; 26 = Meteorologische Arbeiten aus Leipzig ; 7 (2002), S. 101-108, 2002. https://ul.qucosa.de/id/qucosa%3A15225.
Der volle Inhalt der QuelleAnnotation:
In the height range 10–30 km atmospheric gravity waves lead to periodic perturbations of the background temperature field in the order of 2-3 K, that are resolved in temperature profiles derived from radio occultation measurements. Due to the spherical symmetry assumption in
the retrieval algorithm and the low horizontal resolution of the measurement damping in the amplitude and phase shift of the waves occurs leading to remarkable errors in the retrieved temperatures. The influence of the geometric wave parameters and the measurement geometry on plane gravity waves in the range 100-1000 km horizontal and 1-10 km vertical wavelength is investigated with a 2D model ranging ±1000 km around the tangent point and 10-50 km in height. The investigation shows, that with radio occultation measurements more than 90 % of the simulated waves can be resolved and more than 50% with amplitudes above 90%. But the geometrical parameters cannot be identified, since one signal can be attributed to different combinations of wave parameters and view angle. Even short waves with horizontal wavelengths below 200 km can be derived correctly in amplitude and phase if the vertical tilt is small or the view angle of the receiver satellite is in direction of the wave crests.Atmosphärische Schwerewellen führen im Höhenbereich 10-30 km zu periodischen Störungendes Hintergrundtemperaturfeldes in der Größenordnung von 2-3 K, die in Temperaturprofilen aus Radiookkultationsmessungen aufgelöst werden. Aufgrund der sphärischen Symmetrieannahme im Retrievalverfahren und durch die niedrige horizontale Auflösung des Messverfahrens werden Phasenverschiebungen und Dämpfung der Amplitude verursacht, die zu beachtlichen Fehlern bei den abgeleiteten Temperaturen führen. Der Einfluss der geometrischen Wellenparameter und der Messgeometrie auf ebene Schwerewellen im Bereich 100-1000 km horizontale und 1-10 km vertikale Wellenlänge wird untersucht mit einem 2D-Modell, dass sich auf ein Gebiet von ±1000 km um den Tangentenpunkt und von 10-50 km in der Höhe erstreckt. Die Untersuchung zeigt, dass mit Radiookkultationsmessungen mehr als 90% der simulierten Wellen aufgelöst werden und mehr als 50% mit Amplituden oberhalb von 90% der ursprünglichen. Die geometrischen Parameter können jedoch nicht aus Einzelmessungen abgeleitet werden, da ein Signal zu verschiedenen Kombinationen von Wellenparametern und Sichtwinkel zugeordnet werden kann. Auch relativ kurze Wellen mit horizontalen Wellenlängen unterhalb von 200 km können korrekt in der Amplitude und Phase aufgelöst werden, falls die Neigung des Wellenvektors gegen die vertikale gering ist oder der Sichtwinkel des Empfängersatelliten in Richtung der Wellenberge ist.
8
Thomas, Edwin Christopher. „Phase and amplitude variations in the wave fields of ionospherically reflected radio waves“. Thesis, University of Leicester, 1986. http://hdl.handle.net/2381/35807.
Der volle Inhalt der QuelleAnnotation:
The wavefronts of high frequency (HF) radio waves received after reflection from the ionosphere exhibit both spatial non-linearities and temporal variations which limit the performance of large aperture receiving arrays. The objective of this investigation was to measure the phase and amplitude of ionospherically propagated signals in order to relate these parameters to the reflection process. This thesis describes the design and construction of a large aperture multi-element array and its implementation for wavefrot investigations. The hardware and software developed to control the equipment and to record the measurements are described. The procedures required to verify the performance of the experimental system are discussed and results are presented which demonstrate the accuracy of the measurements. The array was utilised for studies of signals received from several transmitters situated throughout Western Europe. The results obtained demonstrate the widely different behaviour of signals received over the various propagation paths and these have been related to the modal content of the received signals. Limited periods existed during which a single ionospheric mode was received and data corresponding to this condition have been compared with those which would be expected if the signal consisted of both a specular component and a cone of diffracted rays. This model is unable to explain the experimental results. Numerical models of the received signal were therefore developed. Results of these and comparisons with experimental results suggest that the measured parameters can be explained by the existence of a specular component with a varying direction of arrival (DOA), plus some contribution from random components. The experimental results indicate that the random or diffracted components normally contribute less than 10% of the received power in a single moded signal.
9
Russell, Thomas A. „Predicting microwave diffraction in the shadows of buildings“. Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-10222009-125156/.
Der volle Inhalt der Quelle
10
Carozzi, Tobia. „Radio waves in the ionosphere : Propagation, generation and detection“. Doctoral thesis, Uppsala universitet, Institutionen för astronomi och rymdfysik, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-1184.
Der volle Inhalt der QuelleAnnotation:
We discuss various topics concerning the propagation, generation, and detec-tionof high-frequency (HF) radio waves in the Earth's ionosphere. With re-gardsto propagation, we derive a full wave Hamiltonian and a polarization evo-lutionequation for electromagnetic waves in a cold, stratified magnetoplasma.With regards to generation, we will be concerned with three experiments con-ducted at the ionosphere- radio wave interaction research facilities at Sura, Rus-siaand Tromsø, Norway. These facilities operate high power HF transmittersthat can inject large amplitude electromagnetic waves into the ionosphere andexcite numerous nonlinear processes. In an experiment conducted at the Surafacility, we were able to measure the full state of polarization of stimulatedelectromagnetic emissions for the first time. It is expected that by using thetechnique developed in this experiment it will be possible to study nonlinearpolarization effects on powerful HF pump waves in magnetoplasmas in the fu-ture.In another experiment conducted at the Sura facility, the pump frequencywas swept automatically allowing rapid, high-resolution measurements of SEEdependence on pump frequency with minimal variations in ionospheric condi-tions.At the Tromsø facility we discovered by chance a highly variable, pumpinduced, HF emission that most probably emanated from pump excited spo-radicE. Regarding detection, we have proposed a set of Stokes parametersgeneralized to three dimension space; and we have used these parameters in aninvention to detect the incoming direction of electromagnetic waves of multiplefrequencies from a single point measurement.
11
Bond, Giles Edward. „The interaction of radio waves with the auroral ionosphere“. Thesis, University of Leicester, 1997. http://hdl.handle.net/2381/30629.
Der volle Inhalt der QuelleAnnotation:
A high power radio wave propagating through the ionosphere perturbs the natural plasma in a number of ways. These include bulk changes in the electron temperature and density, and the excitation of plasma waves and instabilities. The ionosphere can be regarded as a natural plasma laboratory, with far greater scale sizes then anything achievable in a conventional laboratory, thus giving unique access to a range of plasma waves and instabilities. In this thesis results from two campaigns involving the EISCAT (European Incoherent SCATter) ionospheric modification facility (heater) at Tromso, Northern Norway are presented. The first campaign, in February 1995, was principally concerned with modification of the auroral electrojet region during both disturbed and quiet conditions. During this campaign the EISCAT UHF incoherent scatter radar was utilised to achieve the first experimental demonstration of artificial inospheric cooling by a high power radio wave. For the second campaign, in April 1996, the most important diagnostic was CUTLASS (Co-operative UK Twin Located Auroral Sounding System), which can measure power backscattered from field aligned irregularities produced during heating. It has been found that irregularities are excited over a horizontal spatial extent of around 175 km, which far exceeds the normal width of the heater beam. The temporal decay of artificial irregularities remain in the ionosphere for up to four minutes after heater-off. In addition to these experimental studies, a computer model has been developed to investigate the electron temperature and density changes which are induced in the ionospheric D- and E-regions during periods of electrojet activity. The model reproduces the experimental observations, and predicts reduced artificial heating efficiency under distributed natural conditions.
12
Carozzi, Tobia D. „Radio waves in the ionosphere : propagation, generation, and detection /“. Uppsala : Institutionen för astronomi och rymdfysik, Univ. [distributör], 2000. http://publications.uu.se/theses/99-3364278-2/.
Der volle Inhalt der Quelle
13
Ellis, Russell Brian. „Linearity of fibre network supported transmission of radio waves“. Thesis, Bangor University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389521.
Der volle Inhalt der Quelle
14
Gåvermark, Erik. „Modeling of Current Drive with Radio Waves on DEMO“. Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-239380.
Der volle Inhalt der QuelleAnnotation:
In fusion reactors, one has to make sure that the plasma does not come in contact with the reactor wall. This is done by accelerating electrons within the plasma creating a current. One method to do this is to transmit radio waves into the plasma from antennas which are located in the reactor wall. In this paper, the current current has been studied in a new design of DEMO. In this new design the placement of the antennas is meant to enable a more effective generation of current.A program called FEMIC has been used to create a model of DEMO consisting of plots and data that describes how the radio waves propagate through the plasma and how ions and electrons absorb energy from the radio waves. A function for the current drive efficiency has been implemented in FEMIC. FEMIC has then been used to calculate the wave field and generated current. The study showed that there is one particular frequency of the radio wave that enables optimal generation of current which agrees qualitatively with results from other experiments. The study also showed that the placement of the antennas is not optimal considering the current drive as the radio wave does not reach the center of the plasma where the current was found to be most effective generated.
15
Hahlin, Axel. „Coupled waves as a model to describe chaotic turbulence pumped by radio waves in the ionosphere“. Thesis, Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-356265.
Der volle Inhalt der QuelleAnnotation:
Experimental results concerning plasma turbulence pumped in theionosphere by powerful radio waves suggest that the turbulence is due todeterministic chaos. To investigate the possibility of deterministic chaosin the ionosphere coupled wave systems have been studied to see chaoticdynamics. If coupled waves can exhibit chaos it is a possible way tomodel ionospheric chaos. The result showed that chaos was present inboth wave systems studied which means that they could possibly explainthe chaos, to verify this more studies needs to be done on theparameters relevant to the coupled wave systems in the ionosphere andfind if they are in a regime where chaos developsStudier av plasmaturbulens i jonosfären som pumpas av kraftfulla radiovågor antyder att turbulensen är kopplat till deterministiskt kaos. För att undersöka möjligheten för deterministiskt kaos i jonosfären studeras kopplade vågsystem om de kan innehålla kaotiska regimer. Om dessa system visar kaotiskt beteende skulle de kunna användas för att beskriva kaos i jonosfären. Resultatet visade att kaos var närvarande i de kopplade vågsystem som studerats, för att verifiera om de kan användas för att beskriva kaos i jonosfären måste närmare studier av de parametrar som modellen använder sig av göras för att se om de faller inom ett intervall där kaos uppstår.
16
Adaszynski, Wojciech. „Interactive visualization of radio waves propagation in 5G massive MIMO“. Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-254958.
Der volle Inhalt der QuelleAnnotation:
The complexity of advanced antenna techniques used in the new generation of wireless networks (5G) makes communication between experts and non-technical staff more difficult than ever. As cooperation between network vendors and network operators affects the adoption of the new standard, a need for a new tool has emerged to make technical presentations more engaging and compelling. This thesis presents an exploratory study that aims to examine various design options for an interactive visualization of radiowave propagation to be used by advanced antenna systems experts. Through a Research-oriented Design, functional and non-functional requirements were identified with the help of domain expert. Later, an interactive prototype was designed and developed using a participatory design approach. Qualitative and quantitative data was gathered through usability testing, System Usability Scale (SUS) questionnaires and semi-structured interviews conducted with 12 researchers and engineers at Ericsson AB a multinational telecommunication company. User evaluation proved that such a tool could facilitate communication between technical experts and non-technical staff. The developed prototype was considered intuitive and useful by the majority of study participants as measured by interviews and the SUS survey. Future research is encouraged to include the target audience representatives in order to measure their engagement while using the tool.Komplexiteten hos avancerade antenntekniker som anvnds i den nya generationen av mobilntverk (5G), gr kommunikationen mellan experter och icke-teknisk personal svrare n ngonsin. Eftersom samarbetet mellan telekommunikationsfretag och ntoperatrer pverkar anpassningen av den nya standarden, har behovet av ett nytt verktyg uppsttt fr att gra tekniska presentationer mer engagerande och vertygande. Avhandlingen presenterar en underskande studie som syftar till att underska olika designalternativ fr en interaktiv visualisering av radiovgsfrkning som anvnds av avancerade antennsystems experter. Genom en forskningsinriktad design identifierades funktionella och icke-funktionella krav med hjlp av en domnexpert. Senare konstruerades och utvecklades en interaktiv prototyp med hjlp av en co-operativ designmetod. Kvalitativa och kvantitativa data samlades in genom anvndbarhetstester, System Usability Scale (SUS) frgeformulr och halvstrukturerade intervjuer med 12 forskare och ingenjrer p Ericsson AB ett multinationellt telekommunikationsfretag. Anvndarutvrdering visade att ett sdant verktyg skulle underltta kommunikationen mellan tekniska experter och icke-teknisk personal. Den utvecklade prototypen ansgs intuitiv och anvndbar av majoriteten av studiedeltagarna, mtt genom intervjuer och SUS-underskningen. Framtida forskning uppmuntrar till att inkludera mlgruppsrepresentanterna fr att mta deras engagemang medan de anvnder verktyget.
17
Tshisaphungo, Mpho. „Validation of high frequency propagation prediction models over Africa“. Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1015239.
Der volle Inhalt der QuelleAnnotation:
The ionosphere is an important factor in high frequency (HF) radio propagation providing an opportunity to study ionospheric variability as well as the space weather conditions under which HF communication can take place. This thesis presents the validation of HF propagation conditions for the Ionospheric Communication Enhanced Profile Analysis and Circuit (ICEPAC) and Advanced Stand Alone Prediction System (ASAPS) models over Africa by comparing predictions with the measured data obtained from the International Beacon Project (IBP). Since these models were not developed using information on the African region, a more accurate HF propagation prediction tool is required. Two IBP transmitter stations are considered, Ruaraka, Kenya (1.24°S, 36.88°E) and Pretoria, South Africa (25.45°S, 28.10°E) with one beacon receiver station located in Hermanus, South Africa (34.27°S, 19.l2°E). The potential of these models in terms of HF propagation conditions is illustrated. An attempt to draw conclusions for future improvement of the models is also presented. Results show a low prediction accuracy for both ICEPAC and ASAPS models, although ICEPAC provided more accurate predictions for daily HF propagation conditions. This thesis suggests that the development of a new HF propagation prediction tool for the African region or the modification of one of the existing models to accommodate the African region, taking into account the importance of the African ionospheric region, should be considered as an option to ensure more accurate HF Propagation predictions over this region.
18
Smit, Jacobus Petrus. „Theoretical development and implementation of algorithms for the inversion of frequency domain airborne electromagnetic data into a layered earth“. Pretoria : [s.n.], 2005. http://upetd.up.ac.za/thesis/available/etd-02222007-142602.
Der volle Inhalt der Quelle
19
Ding, Ming Sheng. „Modelling and measurement of the scatter of microwaves by buildings“. Thesis, University of South Wales, 1994. https://pure.southwales.ac.uk/en/studentthesis/modelling-and-measurement-of-the-scatter-of-microwaves-by-buildings(ab8b0911-5e4f-48ed-882c-d646b5df266f).html.
Der volle Inhalt der QuelleAnnotation:
The growing usage and demand for microwave communications has led to the increase in system density, particularly in urban areas, and consequently to the increase in the probability of mutual interference between systems sharing the same frequency band. Satellite and point to point microwave communication systems might have to rely on site shielding to reduce the level of this co-channel interference. In urban areas, there is a great possibility of a building obstructing the interference path, thus providing protection. However, there could be more than one interference path. Scattered interference from other buildings in the vicinity of the site is one which can be found to be almost as harmful as the direct interference. Although site shielding has long been identified as an interference reduction technique, most studies have been devoted to the protection obtained from the obstruction of interference paths, namely diffraction. There is little information available regarding the effects of building scatter in site shielding. The work reported in this thesis was set to carry out theoretical and experimental investigations and characterisation of building scatter. The studies are aimed at the effects of building scatter on site shielding at microwave frequencies. Building scatter prediction models are developed based on Fresnel-Kirchhoff diffraction theory and verified against results obtained from measurement campaigns conducted at a frequency of 11.2 GHz using firstly a perfectly conducting reflector and later a number of buildings in urban environments as the scattering obstacles. Scattering prediction models are developed as extending to that originally applicable to the far field for use in the near and very near field regions of the scattering surface. The very near field model is found to be particularly useful in site shielding applications in urban environments. Furthermore, it has been possible to establish the scattering characteristics in terms of angular and distance dependence of the scattering coefficient using the expansions of the Fresnel integral with appropriate approximations. The effects of building features and surface variations, e.g. protruding and recessed features, windows and surface deviations, are analysed and characterised. These effects are particularly significant in the interpretation of measurement results obtained from buildings in typical urban environments. The thesis provides a prediction procedure which radio system planners and design engineers can use for determining the effects of building scatter on the site shielding factor for specified radio path geometries. The procedure is expected, through UK study group 3, to add considerably to a revised ITU-R (CCIR) procedure and recommendations for building scatter effects in radiowave propagation. The work has also contributed regularly to the technical output of European COST project 235.
20
Kincaid, Cheryl-Annette Mikler Armin. „Analyzing microwave spectra collected by the solar radio burst locator“. [Denton, Tex.] : University of North Texas, 2007. http://digital.library.unt.edu/permalink/meta-dc-3655.
Der volle Inhalt der Quelle
21
Stocker, Alan John. „Modification of the ionosphere by means of high power radio waves“. Thesis, University of Leicester, 1990. http://hdl.handle.net/2381/35799.
Der volle Inhalt der QuelleAnnotation:
Experiments have been performed at Troms?, Norway and Arecibo, Puerto Rico to investigate the effects produced by high power radio waves (heating) on the high and low latitude ionospheres, respectively. The modifications induced in the F-region have been observed with both incoherent scatter radars and tow power HF diagnostic radio waves. These observations provide information on both heater-induced large scale changes, and small scale density structures. The spatial and temporal development of the perturbation in electron temperature caused by heating, measured at Troms? for the first time, compares well with theory. Observations of thermal striations, which may be the result of the thermal self-focussing of the heater wave, are also presented. The large-scale heater-induced changes in the electron density measured by EISCAT have been compared with those derived from measurements of the phase of reflected HF diagnostic signals. Both methods yield consistent results with regard to whether the electron density is enhanced or depleted but there are, however, differences in the magnitudes of the measured changes. The sign of the perturbation can reveal aeronomical information on the chemical and diffusion characteristics of the unheated ionosphere. The first observations of tow latitude heating by means of low power HF diagnostic waves are presented. The anomalous absorption measured at tow latitudes is less than that at high latitudes, in agreement with theory. The scale length and amplitude of the associated small-scale density structures are comparable at both high and low latitudes. A detailed comparison has been undertaken of the effect of heating at high and low latitudes and the results compared with current theoretical models. The two independent diagnostic techniques (incoherent scatter and low power HF waves) provide a consistent picture of the ionospheric perturbation induced by both heating facilities.
22
Sim, Chow Yen Desmond. „The propagation of VHF and UHF radio waves over sea paths“. Thesis, University of Leicester, 2002. http://hdl.handle.net/2381/7444.
Der volle Inhalt der QuelleAnnotation:
This thesis is concerned with the statistical studies of VHF/UHF radio wave propagation over the sea path at the limits of line-of-sight range. The objective is to provide a set of data that leads to the understanding of the characteristic of VHF/UHF radio wave over the sea path. A series of experiments were conducted using two paths of around 33 and 48 km across the English Channel. These two paths are between fixed land-based locations that provide an unobstructed condition. This allows a prolonged period of data collection under several sea states and atmospheric conditions without the heavy expenses of ship borne trial. The statistic studies showed that the high signal strength variation observed at both receiving sites are the results due to ducting and super-refraction. It occurred around 43 to 76% and 31 to 48% of the total time (percentage of days) during summer 2001 and 2002 respectively. In comparison, the total time was below 10% during winter period. Across the Jersey-Alderney path (48 km), high fading phenomenon was observed which is a result due to interference fading between the diffracted and troposcattered signal. The statistics showed that it occurred at around 35 to 55% of the total times during summer with an average fading range of around 10 and 7 dB during autumn and summer respectively, with an average fading period of around 7 seconds. The results from simulation showed that when the VHF/UHF signal reaches the radio horizon, the dominant propagating mechanism is smooth earth diffraction. Beyond the radio horizon, the attenuation rate increases dramatically and at a certain distance (depending on the frequency, antenna height and seasonal condition), the diffracted signals will be weaken and the troposcatter effect will become the dominant propagating mechanism.
23
Vidojevic, Sonja. „Statistics of Langmuir Waves Associated with Type III Solar Radio Bursts“. Observatoire de Paris, 2012. https://hal.science/tel-02095131.
Der volle Inhalt der QuelleAnnotation:
Nous avons examiné les 16 premières années des données ondes et particules par la sonde WIND dans le vent solaire afin de rechercher les évènements de type III in-situ. L'application de critères rigoureux a fourni un ensemble de 36 évènements de grande qualité. Avec un tel ensemble, statistiquement représentatif du phénomène étudié, il est désormais possible de mieux contraindre les modèles de génération de type III. Nous avons étudié les formes précises des distributions de puissance des ondes Langmuir, observées dans le domaine spectral et modélisé ces distributions avec un système de distribution de type Pearson. Nous avons montré que les distributions du logarithme de la densité de puissance spectrale des ondes de Langmuir appartiennent à trois types "principaux" de distributions de Pearson : type I, IV, et VI. En outre, nous avons simulé les effets dus à la fonction de transfert instrumentale des récepteurs radio de WIND sur les distributions de puissance des ondes de Langmuir observées. En combinant nos observations avec nos simulations, nous avons montré qu'il n'était pas possible de conclure de façon définitive que la distribution de l'énergie des ondes Langmuir dans le domaine temporel réel est log-normale, comme prévu par certaines théories de type "croissance stochastique". Nous avons montré comment notre base d'évènements de type III in-situ peut être utilisée pour d'autres études permettant d'encore mieux contraindre les modèles théoriques. Par exemple, la corrélation entre la puissance des ondes de Langmuir et l'énergie des électrons impulsifs ou bien encore la puissance des émissions radio elles-mêmesWe examine the first 16 years of radio, waves and particles data recorded by the WIND spacecraft in the Solar Wind and look for in-situ Type IIIs. Applying rigorous and careful criteria, this examination has yielded to a data set of 36 high-quality events. With such a data set, which is statistically representative of the studied phenomenon, it is now possible to constrain observationally and with a better confidence the Type III generation models. We have studied, for each of the events, the precise shapes of the Langmuir wave power distributions, observed in the spectral domain. The observed distributions are fitted by a Pearson's system of probability distributions and have shown that the probability distributions of the logarithm of the Langmuir waves power spectral density belong to three "main" types of Pearson's probability distributions : type I, type IV and type VI. In addition we have modeled the effects of the instrumental integration time of the WIND radio receivers on the observed Langmuir wave power distributions. By combining our observations with models we have shown that it was not possible to conclude definitively, that the distribution of the Langmuir waves energy in the real temporal domain is lognormal, as it is predicted in some theories as the Stochastic Growth Theory. In the last part of the thesis, we have shown how our high-quality data set of 36 in-situ Type III events can be used for further studies that could allow to constrain the theoretical models even better. For instance we have investigated the correlation between the Langmuir waves power and the energy of impulsive electron or with the power of the radio emissions themselves
24
Kurniawan, Teddy. „Analytical methods for near field radio frequency dosimetry for tissue layers and celluar structures“. Swinburne Research Bank, 2009. http://hdl.handle.net/1959.3/48743.
Der volle Inhalt der QuelleAnnotation:
Thesis (PhD) - Faculty of Life and Social Sciences, Swinburne University of Technology, 2009.A thesis submitted in total fulfillment of the requirements for the degree of Doctor of Philosophy, Faculty of Life and Social Science, Swinburne University of Technology - 2009. Typescript. Includes bibliographical references.
25
Barroso, MoÌ‚nica Mazzer. „Waves in the forest : radio communication and forest livelihoods in Brazilian Amazonia“. Thesis, London School of Economics and Political Science (University of London), 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.436117.
Der volle Inhalt der Quelle
26
Kennett, M. I. „An analysis of the scattering of radio waves within a temperature glacier“. Thesis, University of Bristol, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376616.
Der volle Inhalt der Quelle
27
Kasaba, Yasumasa. „Study of Radio Waves in Geospace via Spacecraft Observations and Numerical Simulations“. Kyoto University, 1997. http://hdl.handle.net/2433/154674.
Der volle Inhalt der QuelleAnnotation:
本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものであるKyoto University (京都大学)
0048
新制・課程博士
博士(工学)
甲第6871号
工博第1622号
新制||工||1069(附属図書館)
UT51-97-H255
京都大学大学院工学研究科電子工学専攻
(主査)教授 松本 紘, 教授 橋本 弘藏, 教授 津田 敏隆
学位規則第4条第1項該当
28
Munns, David P. D. „"Wizards of the micro-waves" a history of the radio astronomy community /“. Available to US Hopkins community, 2002. http://wwwlib.umi.com/dissertations/dlnow/308073.
Der volle Inhalt der Quelle
29
Nordblad, Erik. „Opening New Radio Windows and Bending Twisted Beams“. Doctoral thesis, Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-158797.
Der volle Inhalt der QuelleAnnotation:
In ground based high frequency (HF) radio pumping experiments, absorption of ordinary (O) mode pump waves energises the ionospheric plasma, producing optical emissions and other effects. Pump-induced or natural kilometre-scale field-aligned density depletions are believed to play a role in self-focussing phenomena such as the magnetic zenith (MZ) effect, i.e., the increased plasma response observed in the direction of Earth's magnetic field. Using ray tracing, we study the propagation of ordinary (O) mode HF radio waves in an ionosphere modified by density depletions, with special attention to transmission through the radio window (RW), where O mode waves convert into the extraordinary (X, or Z) mode. The depletions are shown to shift the position of the RW, or to introduce RWs at new locations. In a simplified model neglecting absorption, we estimate the wave electric field strength perpendicular to the magnetic field at altitudes normally inaccessible. This field could excite upper hybrid waves on small scale density perturbations. We also show how transmission and focussing combine to give stronger fields in some directions, notably at angles close to the MZ, with possible implications for the MZ effect. In a separate study, we consider electromagnetic (e-m) beams with helical wavefronts (i.e., twisted beams), which are associated with orbital angular momentum (OAM). By applying geometrical optics to each plane wave component of a twisted nonparaxial e-m Bessel beam, we calculate analytically the shift of the beam's centre of gravity during propagation perpendicularly and obliquely to a weak refractive index gradient in an isotropic medium. In addition to the so-called Hall shifts expected from paraxial theory, the nonparaxial treatment reveals new shifts in both the transverse and lateral directions. In some situations, the new shifts should be significant also for nearly paraxial beams.
30
VARGAS, CARLOS EDUARDO ORIHUELA. „ANTENNA PROJECT AND IMPLEMENTATION FOR CHARACTERIZATION OF MOBILE RADIO CHANNEL IN MILLIMETER WAVES“. PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2015. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=25606@1.
Der volle Inhalt der QuelleAnnotation:
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
FUNDAÇÃO DE APOIO À PESQUISA DO ESTADO DO RIO DE JANEIRO
PROGRAMA DE EXCELENCIA ACADEMICA
O termo de ondas milimétricas refere-se à porção do espectro eletromagnético com frequências entre 30 e 300 GHz, correspondente a comprimentos de onda de 10 até 1 mm, respectivamente. As características das ondas milimétricas diferem das micro-ondas e das infravermelhas, e são estas diferenças que fazem com que um sistema de ondas milimétricas seja o candidato ideal para algumas aplicações. Nos anos passados, a falta e o alto custo de fontes, dispositivos, componentes e instrumentação adequada, para esta faixa de frequências, levaram a um progresso muito devagar nesta área, no entanto, as limitações dos sistemas infravermelhos e ópticos e a superlotação da região do micro-ondas do espectro ocasionaram um maior interesse em frequências milimétricas nos últimos anos. A quinta geração dos sistemas móveis deve estar pronta nos próximos anos, e muitas pesquisas estão se desenvolvendo nas faixas de 28 GHz, 38 GHz e 60 GHz. A faixa de 60 GHz, na qual as ondas têm uma maior atenuação comparada com as outras duas, oferece um maior espectro eletromagnético. Nesta faixa de frequência, as ondas se refletem muito e pode se aproveitar estas reflexões para uma melhor recepção sendo, por tanto, uma ótima opção para comunicação móvel de curta distância com altas taxas de transferência de dados. Para poder aproveitar a maior quantidade de multipercursos, a antena receptora deve ter uma largura de feixe grande. Assim, neste trabalho, duas antenas foram projetadas, construídas e, de alguma forma, testadas para uma frequência de 60 GHz, onde as larguras de feixe simuladas obtidas foram de 112 graus e 115 graus.
The millimeter wave term refers to that portion of the electromagnetic spectrum with frequencies between 30 and 300 GHz corresponding to wavelengths of 1 to 10 mm. The characteristics of the millimeter wave differ from microwave and infrared, and these differences make a millimeter wave system, an ideal candidate for some applications. In the past the lack and the high cost of supplies, devices, components and instrumentation suitable for this frequency band caused very rambling progress in this area. However, the limitations of infrared optical systems and overcrowding of the microwave spectrum region led to a greater interest in the millimeter frequency in recent years and it is expected an increase in this interest. The fifth generation of mobile systems should be ready in the coming years, and many studies are developing in the 28 GHz, 38GHz and 60GHz bands. In the 60 GHz band, waves has a higher attenuation compared to the other two, but also offers greater electromagnetic spectrum, in this band, waves has a lot of reflection, then, scattering can be taken for better reception. So, this band is a great choice for short distance mobile communication with high data rates. To get the greatest amount of multipath, the receiving antenna must have a wide beam width. In this work, two antennas were designed, built and somewhat tested for a frequency of 60 GHz for mobile environment, where the beam widths obtained are 112 degrees and 115 degrees.
31
Gunashekar, Salil David. „An investigation of the propagation of 2 GHz radio waves over sea paths“. Thesis, University of Leicester, 2006. http://hdl.handle.net/2381/30235.
Der volle Inhalt der QuelleAnnotation:
Three long-range 2 GHz radio paths have been established in the British Channel Islands in order to investigate the characteristics of long-range propagation of UHF radio waves over the sea as part of a project supported by Ofcom, UK. The relationship between specific over-sea propagation mechanisms (such as evaporation ducting and super-refraction) in the lower troposphere and signal strength distribution patterns has been examined, modelled and correlated with meteorological parameters. A number of radio meteorological statistics specifically related to evaporation duct propagation in a temperate region such as the English Channel has been presented to confirm the capability of this key propagation mechanism to guide radio waves to distances well beyond the normal radio horizon. Evaporation ducting and diffraction appear to be the dominant propagation mechanisms at most times. Signal strength enhancements have been observed on all three radio paths, primarily in the late afternoon and evening periods, in the spring and summer months. During periods of enhanced propagation, which occur approximately 8% of the time of a 50 km path, the presence of additional higher-level ducting/super-refractive structures has been verified and their influence has been modelled with reasonable success. Additionally, the statistical variation of bulk meteorological parameters in the context of enhanced signal propagation has also been examined. The relatively long-term observations made during this study confirm the fact that the constantly changing weather patterns in the troposphere (e.g. the occurrence of anticyclonic weather) are directly responsible for the occurrence of enhanced signals at certain periods of time. The various issues under investigation are of direct relevance in the planning of radio communication systems operating in the UHF band (e.g. GSM and UMTS) in marine and coastal regions.
32
Lindeberg, Axel. „Hacking Into Someone’s Home using Radio Waves : Ethical Hacking of Securitas’ Alarm System“. Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-302999.
Der volle Inhalt der QuelleAnnotation:
The number of IoT systems in our homes has exploded in recent years. By 2025 it is expected that the number of IoT devices will reach 38 billion. Home alarm systems are an IoT product that has increased dramatically in number and complexity in recent years. Besides triggering an alarm when an intruder tries to break in, a modern system can now control your light bulbs, lock and unlock your front door remotely, and interact with your smart speaker. They are undeniably effective in deterring physical intrusion. However, given the recent rise in complexity how well do they hold up against cyber attacks? In this thesis, a smart home alarm system from SecuritasHome is examined. A comprehensive security analysis was performed using penetration testing techniques and threat modeling. The work focused mainly on radio frequency (RF) hacking against the systems RF communication. Among other things, a critical vulnerability was found in the proprietary RF protocol, allowing an attacker to disarm an armed system and thus completely bypass the system’s functionality. The security of the system was deemed to be lacking.Antalet IoT system i våra hem har exploderat de senaste åren. Vid år 2025 förväntas antalet IoT enheter nå 38 miljarder. Hemlarmsystem är en typ av IoT-produkt som ökat dramatiskt i komplexitet på senare tid. Förutom att framkalla ett larm vid ett intrång kan ett modernt hemlamsystem numera kontrollera dina glödlampor, låsa och låsa upp din ytterdörr, samt kontrollera dina övervakningskameror. De är utan tvekan effektiva på att förhindra fysiska intrång, men hur väl står de emot cyberattacker? I denna uppsats undersöks ett hemlarmsystem från SecuritasHome. En utförlig säkerhetsanalys gjordes av systemet med penetrationstestnings-metodiker och hotmodellering. Arbetet fokuserade mestadels på radiovågshackning (RF) mot systemets RF-kommunikation. Bland annat hittades en kritiskt sårbarhet i systemets RF-protokoll som gör det möjligt för en angripare att avlarma ett larmat system, och därmed kringå hela systemets funktionalitet. Säkerheten av systemet bedömdes vara bristfällig.
33
Ehn, Jonas. „Propagation of Radio Waves in a Realistic Environment using a Parabolic Equation Approach“. Thesis, Linköpings universitet, Teoretisk Fysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-157610.
Der volle Inhalt der QuelleAnnotation:
Radars are used for range estimation of distant objects. They operate on the principle of sending electromagnetic pulses that are reflected off a target. This leads to the propagation of electromagnetic waves over large distances. As the waves propagate, they are affected by several aspects that decrease the performance of the radar system. In this master thesis, we derive a mathematical model that describes electromagnetic propagation in the troposphere. The model developed is based on a parabolic equation and uses the split-step Fourier method for its numerical solution. Using the model, we estimate the influence of a varying, complex, refractive index of the atmosphere, different lossy materials in the ground, terrain, and oceans. The terrain is described using a piecewise linear shift map method. The modelling of the ocean is done using a novel model which is a combination of terrain for large swells and Miller surface roughness for smaller waves, both based on a Pierson-Moskowitz sea spectrum. The model is validated and found to agree very well, with results found in the literature.
34
Monaghan, William D. „Experimental studies of electromagnetic signals to enhance radio imaging method (RIM)“. Morgantown, W. Va. : [West Virginia University Libraries], 2007. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=5422.
Der volle Inhalt der QuelleAnnotation:
Thesis (M.S)--West Virginia University, 2007.Title from document title page. Document formatted into pages; contains xi, 104 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 69-70).
35
Mason, Sammuel P. „Atmospheric effects on radio frequency (RF) wave propagation in a humid, near-surface environment“. Monterey, California : Naval Postgraduate School, 2010. http://edocs.nps.edu/npspubs/scholarly/theses/2010/Mar/10Mar%5FMason.pdf.
Der volle Inhalt der QuelleAnnotation:
Thesis (M.S. in Meteorology)--Naval Postgraduate School, March 2010.Thesis Advisor(s): Guest, Peter S. ; Goroch, Andreas K. "March 2010." Author(s) subject terms: Electromagnetic propagation, electromagnetic scattering, groundwave propagation, mathematical techniques, variance reduction. Includes bibliographical references (p. 67-68). Also available in print.
36
Brown, Martin. „High voltage soliton production in nonlinear transmission lines and other pulsed power applications“. Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364003.
Der volle Inhalt der Quelle
37
Babcock, Bruce Kevin. „Electronic communications systems and the frequency domain an illustrated primer for C3 student /“. Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA236936.
Der volle Inhalt der QuelleAnnotation:
Thesis (M.S. in Systems Technology)--Naval Postgraduate School, June 1990.Thesis Advisor(s): Weir, Maurice D. Second Reader: Schwendtner, Thomas A. "June 1990." Description based on title screen as viewed on October 16, 2009. DTIC Descriptor(s): Frequency, integrated systems, high rate, students, electronic equipment, transmittance, spectra, pulses, graphics, attenuation, communication and radio systems, width, noise, data rate, vocabulary, bandwidth, modulation, multiplexing, radio transmission, radio waves, transmitting, fourier DTIC Indicator(s): Command control and communications, radio waves, theses. Author(s) subject terms: Command and control, C2, C3 systems, communications, frequency spectrum, bandwidth, Fourier analysis, multiplexing, modulation, radio wave propagation, transmission impairments Includes bibliographical references (p. 111-114). Also available in print.
38
Martínez-Sansigre, Alejo. „Distant obscured quasars“. Thesis, University of Oxford, 2006. http://ora.ox.ac.uk/objects/uuid:a764a410-4464-4b92-831d-34e8a383d78f.
Der volle Inhalt der QuelleAnnotation:
This thesis presents a study of high-redshift obscured (type-2) quasars, selected at mid-infrared and radio wavelengths. This population had remained elusive, even to hard X-ray surveys, and in Chapter 2 I compare the selection of type-2 quasars in X-ray and mid-infrared surveys, as well as explaining the criteria I will use to search for these objects at z ~ 2, around the peak in the unobscured (type-1) quasar activity. Chapter 3, presents a sample of radio-intermediate type-2 quasars selected from the criteria de- scribed in Chapter 2. Optical spectroscopy shows indeed that at least half of the objects have the characteristic narrow emission lines, and lie around the expected redshift of z = 2. The other half of the objects are consistent with also being type-2 quasars at similar redshifts, although no emission lines are visible. In Chapter 4,1 discuss the possibility of two types of obscured quasars, some obscured by a dusty torus and some by a dusty host galaxy, to explain the lack of emission lines in half of the sample. I model the number of type-1 quasars expected to follow similar selection criteria and at the same redshifts as our type-2 quasars, and find that the obscured quasars outnumber the unobscured by a ~2-3:1 ratio. I conclude that most supermassive black hole growth is obscured by dust. When comparing this to predictions from unified schemes, I find that this result is only consistent with the schemes provided host-obscuration is indeed happening. The lower ratio of type-2 to type-1 quasars inferred from X-ray surveys (~1:1) suggests that some of the type-2 quasars in this sample might be Compton thick. Radio data taken at three frequencies, are presented in Chapter 5, to study the spectral properties and intrinsic luminosities of our sample. I show that some type-2 quasars have flat radio spectra, which is inconsistent with obscuration by the torus, but consistent with host-obscuration. Some gigahertz-peaked spectra, characteristic of young radio jets, are present, but the majority of the sources have very steep spectra. These steep spectral indices can be explained by active developed jets in which continuous injection of electrons is accompanied by inverse-Compton losses against the cosmic microwave background. In Chapter 6, I select a similar sample of type-2 quasars in a different field, where X-ray data are available. The selection criteria are kept identical, except for the radio flux density cut, which is lowered. This is expected to introduce significant numbers of starburst contaminants. To filter these out, and due to a lack of spectroscopy, I use a bayesian method to fit the spectral energy distributions, obtain photometric redshifts, and select between a quasar and a starburst model. I measure the X-ray properties for the resultant sample of type-2 quasars. The entire sample is found to be Compton-thick, and repeating the modelling of Chapter 4, I find that the population of Compton-thick quasars is at least comparable to the population of unobscured quasars, and probably larger.
39
Fan, Shu-Hao. „Convergence of millimeter-wave and photonic interconnect systems for very-high-throughput digital communication applications“. Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42888.
Der volle Inhalt der QuelleAnnotation:
In the past, radio-frequency signals were commonly used for low-speed wireless electronic systems, and optical signals were used for multi-gigabit wired communication systems. However, as the emergence of new millimeter-wave technology introduces multi-gigabit transmission over a wireless radio-frequency channel, the borderline between radio-frequency and optical systems becomes blurred. As a result, there come ample opportunities to design and develop next-generation broadband systems to combine the advantages of these two technologies to overcome inherent limitations of various broadband end-to-end interconnect systems in signal generation, recovery, synchronization, and so on. For the transmission distances of a few centimeters to thousands of kilometers, the convergence of radio-frequency electronics and optics to build radio-over-fiber systems ushers in a new era of research for the upcoming very-high-throughput broadband services.
Radio-over-fiber systems are believed to be the most promising solution to the backhaul transmission of the millimeter-wave wireless access networks, especially for the license-free, very-high-throughput 60-GHz band. Adopting radio-over-fiber systems in access or in-building networks can greatly extend the 60-GHz signal reach by using ultra-low loss optical fibers. However, such high frequency is difficult to generate in a straightforward way. In this dissertation, the novel techniques of homodyne and heterodyne optical-carrier suppressions for radio-over-fiber systems are investigated and various system architectures are designed to overcome these limitations of 60-GHz wireless access networks, bringing the popularization of multi-gigabit wireless networks to become closer to the reality.
In addition to the advantages for the access networks, extremely high spectral efficiency, which is the most important parameter for long-haul networks, can be achieved by radio-over-fiber signal generation. As a result, the transmission performance of spectrally efficient radio-over-fiber signaling, including orthogonal frequency division multiplexing and orthogonal wavelength division multiplexing, is broadly and deeply investigated. On the other hand, radio-over-fiber is also used for the frequency synchronization that can resolve the performance limitation of wireless interconnect systems. A novel wireless interconnects assisted by radio-over-fiber subsystems is proposed in this dissertation.
In conclusion, multiple advantageous facets of radio-over-fiber systems can be found in various levels of end-to-end interconnect systems. The rapid development of radio-over-fiber systems will quickly change the conventional appearance of modern communications.
40
Ahmad, Saad. „Modeling the Discharge Loading of Radio Frequency Excited CO2 Slab lasers“. Digital WPI, 2011. https://digitalcommons.wpi.edu/etd-theses/1081.
Der volle Inhalt der QuelleAnnotation:
"RF excited CO2 lasers are widely used in industry. They provide relatively high power discharge levels while maintaining compactness, simplicity, and durability with respect to other competing laser technologies. To attain high power levels in the range of 5-10 KW, lasers with large electrode areas have to be designed. Unfortunately, due to the large electrode length requirements, transmission line effects make the discharge loading nonlinear, adversely affecting the efficiency of the CO2 laser. A standard approach to linearize the discharge loading is to introduce shunt inductors across the length of the electrodes in an effort to counter the capacitive nature of the discharge behavior. This thesis investigates and improves the theoretical models found in the literature in an effort to predict the discharge non-uniformity and allow for multiple shunt inductors installation. Specifically, we discuss the coupling of a CO2 laser discharge model with an electrical circuit solving scheme and how it can be characterized as one dimensional (1-D) and two dimensional (2-D) systems. The 1-D system is modeled using transmission line (TL) theory, where as the 2-D system is modeled using a finite difference time domain (FDTD) scheme. All our models were implemented in standard MATLAB code and the results are compared with those found in the literature with the goal to analyze and ascertain model limitations."
41
Bignall, Hayley Emma. „Radio variability and interstellar scintillation of blazars“. [Adelaide : H.E. Bignall, 2003. http://web4.library.adelaide.edu.au/theses/09PH/09phb5931.pdf.
Der volle Inhalt der QuelleAnnotation:
Bibliography: leaves 191-202. 1. Introduction -- 2. Instrumentation and calibration -- 3. A radio monitoring program for southern blazars -- 4. Analysis of long-term blazar radio variability -- 5. Probing microarcsecond-scale structure using interstellar scintillation -- 6. The rapid scintillator, PKS 1257-326 -- 7. Conclusions and scope for further work.
42
Channamallu, Aditya. „Software Defined Radio Based Modulated Scatterer Antenna Measurement“. PDXScholar, 2018. https://pdxscholar.library.pdx.edu/open_access_etds/4447.
Der volle Inhalt der QuelleAnnotation:
The modulated scattering technique is used in conjunction with a Software Defined Radio (SDR) dongle to obtain a software-based modulated signal output. SDR# is the software package used to get spectrum analysis of the modulated signal. A transmitter yagi antenna sends a 2.304GHz signal on to an antenna connected to a reflector coefficient modulator (700Hz) and the modulated waves are received by another yagi. The receiver yagi antenna is then connected to a frequency converter to convert a 2.304GHz signal to a 144MHz dongle input signal which finally puts the scattered output on computer software with a SDR dongle. The output has a center frequency with modulated spectral lines on either side of the measured frequency. Finally, antenna patterns are measured with different types of antennas by rotating the antennas and observing the baseband modulation sidebands.
43
Löfås, Henrik. „Ionospheric modification by powerful HF-waves : Underdense F-region heating by X-Mode“. Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-121898.
Der volle Inhalt der QuelleAnnotation:
Observations of modifications of the electron temperature in the F-region produced by powerful high-frequency waves transmitted in X-mode are presented. The experiments were performed during quiet nighttime conditions with low ionospheric densities so no reflections occurred. Nevertheless temperature enhancements of the order of 300-400K were obtained. The modifications found can be well described by the theory of Ohmic heating by the pump wave and both temporal and spatial changes are reproduced. A brief overview of several different experimental campaigns at EISCAT facilities in the period from October 2006 to February 2008 are also given pointing out some interesting features from the different experiments. The main focus is then on the campaign during October 2006 and modifications of the electron temperature in the F-region.
44
Hawbaker, Dwayne Allen. „Indoor wide band radio wave propagation measurements and models at 1.3 ghz and 4.0 ghz“. Thesis, Virginia Tech, 1991. http://hdl.handle.net/10919/44287.
Der volle Inhalt der QuelleAnnotation:
An extensive radio wave propagation measurement campaign was conducted at 1.3 GHz and 4.0 GHz inside four buildings, including a sports arena, a modern closed-plan office building, and two dissimilar, open-plan factories. Measurements were recorded at 57 locations using base station antenna heights of 1.7 meters and 4.0 meters. Results were obtained for mean and maximum excess delay, rms delay spread, time delay jitter, differential delay jitter, and path loss through analyses of impulse response estimates, which were obtained via repetitive 5 ns probing pulses. The effects of frequency, antenna height, topography (line-of-sight or obstructed direct path), and building environment on delay spread and path loss are quantified. Results indicate that, on average, the frequencies and antenna heights used in this study have minimal impact on rms delay spread and path loss. However, topography and building environment significantly affect these parameters. RMS delay spread values as high as 230 ns were observed in open plan factories. Computed path loss power law exponents are 1.84 and 2.35 for line-of-sight and obstructed topographies, respectively. A second campaign was conducted to determine the effects of antenna directivity and polarization on propagation parameters. On average, line-of-sight indoor channels offer 8 dB of cross-polarization discrimination, whereas obstructed environments offer less than 3 dB. Directional antennas provide a significant reduction in rms delay spread over omni-directional antennas. In line-of-sight environments, circular polarization provides an additional delay spread reduction.Master of Science
45
Pecoraro, Michael A. „Characterization of the effects of the human head on communication with implanted antennas /“. Online version of thesis, 2010. http://hdl.handle.net/1850/11698.
Der volle Inhalt der Quelle
46
Kincaid, Cheryl-Annette. „Analyzing Microwave Spectra Collected by the Solar Radio Burst Locator“. Thesis, University of North Texas, 2007. https://digital.library.unt.edu/ark:/67531/metadc3655/.
Der volle Inhalt der QuelleAnnotation:
Modern communication systems rely heavily upon microwave, radio, and other electromagnetic frequency bands as a means of providing wireless communication links. Although convenient, wireless communication is susceptible to electromagnetic interference. Solar activity causes both direct interference through electromagnetic radiation as well as indirect interference caused by charged particles interacting with Earth's magnetic field. The Solar Radio Burst Locator (SRBL) is a United States Air Force radio telescope designed to detect and locate solar microwave bursts as they occur on the Sun. By analyzing these events, the Air Force hopes to gain a better understanding of the root causes of solar interference and improve interference forecasts. This thesis presents methods of searching and analyzing events found in the previously unstudied SRBL data archive. A new web-based application aids in the searching and visualization of the data. Comparative analysis is performed amongst data collected by SRBL and several other instruments. This thesis also analyzes events across the time, intensity, and frequency domains. These analysis methods can be used to aid in the detection and understanding of solar events so as to provide improved forecasts of solar-induced electromagnetic interference.
47
Цопа, А. И., В. К. Иванов, В. И. Леонидов, Ю. И. Малешенко, В. В. Павликов, Н. В. Руженцев und А. А. Зарудный. „The research Program of millimetric Radio waves attenuation characteristics on perspective communication lines of Ukraine“. Thesis, Proc. of XIII International Conf. Modern problems of Radio Engineering, Telecommunications and Computer Science /TCSET’2016/. – Lviv-Slavsko, 2016. – P. 638-642, 2016. http://openarchive.nure.ua/handle/document/3555.
Der volle Inhalt der Quelle
48
Krupař, Vratislav. „Stereoscopic Observations of Solar Radio Emissions by the S/Waves Instrument onboard the STEREO Spacecraft“. Observatoire de Paris, 2012. https://hal.science/tel-02095132.
Der volle Inhalt der QuelleAnnotation:
Cette thèse est principalement consacrée à une étude des sursauts radio type III observés par l'instrument S/Waves à bord du satellite Solar TErrestrial RElations Observatory (STEREO). Ces émissions sont produites lors de période d'activité solaire accrue par des faisceaux d'électrons suprathermiques s'échappant de la couronne solaire le long de lignes de champ magnétique ouvertes. Lorsque des électrons rapides se propagent dans le milieu interplanétaire (IP), des ondes de Langmuir sont générées à la fréquence plasma locale des électrons fpe par une instabilité dite "bump-on-tail". Ces instabilités peuvent ensuite être converties par un processus non-linéaire en des émissions radio à fpe et/ou à 2fpe : les sursauts radio de type III. Nous avons développé une méthode d'inversion goniopolarimétrique (GP, aussi appelée "direction-finding") en utilisant la technique de décomposition en valeurs singulières (SVD) appliquée aux mesures des trois antennes électriques non-orthogonales. Elle nous permet de retrouver la direction du vecteur d'onde des ondes radio de Type III ainsi que leurs propriétés de polarisation. Nous avons également étudié l'influence des sources étendues (qui sont caractéristiques des sursauts radio de type III) sur les matrices spectrales mesurées. Nous avons trouvé une relation empirique entre la taille des sources apparentes et les matrices spectrales décomposées par SVD. Les techniques précitées ont été largement testées sur des données obtenues par le receveur haute fréquence (HFR, une composante de l'instrument S/Waves). Nous avons comparé des densités de flux et des produits GP de plusieurs sursauts radio intenses observés simultanément par les satellites STEREO et Wind (en utilisant la méthode de démodulation de spin pour inversion GP), lorsque ceux-ci étaient proches, avec des résultats satisfaisants. Nous avons réalisé une analyse statistique d'un grand nombre de sursauts radio de type III observées par STEREO entre mai 2007 et septembre 2011. Seuls les cas intenses, simples, et isolés ont été inclus dans notre ensemble de données. Nous avons constaté que la densité de flux maximale se produit autour de 1 MHz. La taille apparente de la source est très étendue (∼40°) pour les fréquences inférieures à 500 kHz tout en restant à peu près constante (∼25°) entre 500 kHz et 2 MHz. Les positions calculées des sources radio suggèrents que la diffusion de la configuration primaire du faisceau joue un rôle important dans la propagation de sursauts radio de type III dans l'environnement IPThis PhD thesis is primarily dedicated to a study of type III radio bursts observed by the S/Waves instrument onboard Solar TErrestrial RElations Observatory (STEREO). These emissions are produced by beams of suprathermal electrons escaping the corona along open magnetic field lines during increased solar activity. As fast electrons propagate in the interplanetary (IP) medium, Langmuir waves are generated at the local electron plasma frequency fpe by bump-on-tail instability and can be afterwards converted by a non linear process into radio emissions at fpe and/or 2 fpe : type III radio bursts. We have developed a goniopolarimetric (GP, also referred to as direction-finding) inversion using the Singular Value Decomposition (SVD) technique for electric measurements on three non-orthogonal antennas. It allows us to retrieve both wave vector directions and polarization properties of incident waves. We also investigated the influence of extended sources (as a typical feature of type III radio bursts) on measured spectral matrices. We have found an empirical relation between apparent source sizes and spectral matrices decomposed by SVD. Abovementioned techniques have been extensively tested on data obtained by the High Frequency Receiver (HFR, a part of S/Waves). We have compared flux densities and GP products of several intense radio bursts observed simultaneously by the two STEREO spacecraft and the Wind spacecraft (using the spin demodulation method for the GP inversion) during small separation distances with satisfary results. We have performed statistical analysis of a large number of type III radio bursts observed by STEREO between May 2007 and September 2011. Only intense, simple, and isolated cases have been included in our data set. We have found that the maximum flux density occurs around 1 MHz. The apparent source size is very extended (∼40°) for frequencies above 500 kHz while remaining almost constant (∼25°) between 500 kHz and 2 MHz. Calculated positions of radio sources suggest that scattering of the primary beam pattern plays an important role in the propagation of type III radio bursts in the IP medium
49
Harding, James. „3D Simulation of the Quasilinear Electron-Langmuir Wave Interaction in Type III Solar Radio Bursts“. Thesis, University of Sydney, 2020. https://hdl.handle.net/2123/23289.
Der volle Inhalt der QuelleAnnotation:
This thesis presents a three-dimensional relativistically correct model of the electron beam-Langmuir wave interaction in the solar corona, as well as a model of the radial electron density profile of the ambient solar plasma through which an electron beam passes. 1D models of the beam/plasma interaction have long been used, as have empirical fits for the electron density profile. In support of the overall goal of this thesis, to develop a more realistic understanding of the plasma physics processes underlying Type III solar radio bursts, we first present strong evidence for a new and physically significant analytic model for the radial density profile in the corona. The thesis then demonstrates the need to develop a 3D picture of the resonance between streaming electrons and Langmuir waves, and the coupled evolution of this system. A new picture of quasilinear relaxation of electron beams is described qualitatively and quantitatively. This 3D picture changes the way electron distributions are considered in terms of their stability or instability to the growth of Langmuir waves. The thesis also develops a numerical method utilising the analytical development of the 3D model, with initial tests and examples described in detail.
50
Knotts, Michael E. „Experimental studies of multiple scattering by rough surfaces“. Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/30269.
Der volle Inhalt der Quelle