Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: This work in this study covers a powerful technique to derive propagation and scattering information in an expedient fashion. Expedient because time-domain (TD) data gathers a broad spectrum in a single transmitted pulse. TD has been criticised because of a lack of dynamic range, which has now been overcome by the direct sampling system, RATTY and RTA. This study focuses on the investigation of a TD metrology system, to assist with the characterisation of MeerKAT systems. The elementary components of the system include a fast-rising impulse generator that was coupled with an impulse radiating antenna (IRA). The system was calibrated and tested before practical measurements and preliminary testing in the Karoo were done. For TDmetrology a larger bandwidth accelerates measurements without the loss of accuracy. The pulse generator’s (PG’s) fundamental components are an avalanche transistor and a step recovery diode (SRD), to sharpen the leading edge of the pulse. Improving the rise-time of a pulse increases its bandwidth in the spectrum. The external circuitry around these components is pivotal and it determines the shape, amplitude and rise-time of the pulse. In the course of the investigation, the general circuitry around the PG was improved to obtain the best possible pulse for measurements inside a reverberation chamber (RC) and for measurements in the Karoo. In light of this, a second and third PG source were obtained. For measurements in the Karoo, a larger amplitude pulse was required to increase the spectral content and this is essential for propagation measurements over distance and the shielding effectiveness (SE) of structures. Stacking avalanche transistors allow larger amplitude pulses and it improves the dynamic range of the spectrum. A PG incorporating stacked avalanche transistors, was designed, built and measured to assist with RC and small-scale field measurements in the Karoo. The third PG was bought for the practical measurements in the Karoo. The PG produces kilovolt pulses with pico-second rise-times that extend the spectral range of the current PGs at our disposal. With these PGs, an antenna is required for the radiation of impulse-like transients. The IRA is a high-gain large-bandwidth antenna. The IRA consists of a parabolic reflector, conical-plate transmission lines that are terminated through resistors onto the dish, and a feeding balun. The IRA design was thoroughly discussed and a first model for metrology was designed, measured and optimised. The IRA was also simulated with computation software code, FEKO. Before deployment of theTDsystem, calibration and characterisation measurements are required. The measuring devices used within this study were sampling oscilloscopes and direct sampling systems. The limitations of each device were explored and are discussed. The final measurements that were conducted contribute to work related to the SKA. This incorporated antenna pattern calibration, propagation over distance and the SE of a berm built from Karoo soil. The system investigated the propagation attenuation over the Karoo soil and vegetation, with great promise. A broad spectrum was measured over a few kilometres and compared to free-space loss. The SE of the berm covered the same spectral bandwidth. In this measurement, scattering effects and knife-edge diffraction were observed. / AFRIKAANSE OPSOMMING: Die werk in hierdie studie dek ’n kragtige tegniek wat gebruik kan word om die voortplanting en die verstrooiingsinligting van elektromagnetiese golwe op ’n voordelige manier af te lei. Dit is voordelig, want tydgebieddata versamel ’n wye spektrum in ’n enkele oordraagbare puls. Tydgebied is in die verlede baie gekritiseer omdat dit ’n dinamiese reikwydte kortkom en dit is nou oorwin deur die direkte steekproefnemingstelsel, RATTY en RTA. Hierdie studie fokus op die ondersoek van ’n tydgebiedmetingssisteem en dit help met die karakterisering van MeerKAT sisteme. Die elementêre komponente van die sisteem bestaan uit ’n vinnig-stygende impulsgenerator wat gekoppel is aan ’n impulsuitstralende-antenna (IRA). Die sisteem is gekalibreer en getoets voordat praktiese metings en toetse in die Karoo uitgevoer kon word. Vir tydgebiedmetings versnel ’n groter bandwydte die metings sonder om die akkuraatheid daarvan te beïnvloed. Die pulsgenerator se fundamentele komponente is ’n stortvloedtransistor en ’n stap-herstel diode (SRD) wat die voorpunt van die puls verskerp. Die eskterne stroombaan rondom hierdie komponente is noodsaaklik en dit bepaal die vorm, amplitude en die stygtyd van die puls. Deur die loop van hierdie ondersoek is die algemene stroombaan rondom die puls verbeter, om die beste moontlike puls vir metings binne in die weerkaatsingskamer en vir metings in die Karoo, te verkry. Na aanleiding van dit is ’n tweede en derde pulsgenerator bron verkry. Vir die metings in die Karoo is ’n puls met ’n groter amplitude vereis om die spektrale inhoud te vermeerder. Dit is noodsaaklik vir elektromagnetiese golf voortplantingsmetings oor afstand asook die beskermings effektiwiteit (SE) van die strukture. Stapel-stortvloed transistors skep pulse met groter amplitudes en dit verbeter die dinamiese reikwydte van die spektrum. ’n Pulsgenerator wat gestapelde stortvloedtransistors insluit is ontwerp, gebou en gemeet om te help met metings in die weerkaatsingskamer en kleinskaal veldmetings in die Karoo. Die derde pulsgenerator is gekoop vir praktiese metings in die Karoo. Die pulsgenerator vervaardig kilovolt pulse met pikosekond stygtye, wat die reikwydte van die spektrum van ons huidige puls uitbrei. Hierdie pulsgenerators vereis ’n antenna vir die uistraling van impulsagtige seine. Die IRA is ’n hoë-wins, groot-bandwydte antenna. Die IRA bestaan uit ’n paraboliese weerkaatser, konieseplaat transmissielyne wat deur weerstande op die skottel getermineer word, asook ’n voedings "balun". Die IRA ontwerp is deeglik bespreek en ’n model is ontwerp, gemeet en verbeter. Die IRA is ook gesimuleer met behulp van ’n rekenaarsagtewareprogram, FEKO. Voordat die tydgebiedsisteem benut kan word, moet dit gekalibreer word en karakteriseringsmetings moet ook daarmee uitgevoer word. Die meetinstrumente wat in hierdie studie gebruik is, is steekproefneming-ossilloskope en direkte steekproefneming-sisteme. Die tekortkominge van elke instrument is ondersoek en bespreek. Die finale meting wat uitgevoer is, dra by tot die werk wat geassosieer word met die SKA. Dit behels antennapatroonkalibrasie, voortplanting van elektromagnetiese golwe oor afstand en die SE van ’n "berm"wat gebou is uit Karoo-grond. Hierdie sisteem is gebruik om die voortplantings-verswakking oor die Karoo-grond en plantegroei te ondersoek en dit lyk baie belowend. ’nWye spektrumis oor ’n paar kilometer gemeet en dit is met wrywinglose ruimte vergelyk. Die SE van die "berm"het dieselfde spektrale bandwydte gedek. In hierdie meting is verstrooiingseffekte en mespunt-diffraksie waargeneem.

This thesis describes research on Efficient Discrete Modelling of Axisymmetric Radiating Structures . Investigating the possibilities of surmounting the inherent limitation in the Cartesian rectangular Transmission Line Modelling (TLM) method due to staircase approximation by efficiently implementing the 3D cylindrical TLM mesh led to the development of a numerical model for simulating axisymmetric radiating structures such as cylindrical and conical monopole antennas. Following a brief introduction to the TLM method, potential applications of the method are presented. Cubic and cylindrical TLM models have been implemented in MATLAB and the code has been validated against microwave cavity benchmark problems. The results are compared to analytical results and the results obtained from the use of commercial cubic model (CST) in order to highlight the benefit of using a cylindrical model over its cubic counterpart. A cylindrical TLM mesh has not previously been used in the modelling of axisymmetric 3D radiating structures. In this thesis, it has been applied to the modelling of both cylindrical monopole and the conical monopole. The technique can also be applied to any radiating structure with axisymmetric cylindrical shape. The application of the method also led to the development of a novel conical antenna with periodic slot loading. Prototype antennas have been fabricated and measured to validate the simulated results for the antennas.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23206号 / 工博第4850号 / 新制||工||1757(附属図書館) / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 篠原 真毅, 教授 和田 修己, 教授 山本 衛 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Cette thèse s'inscrit dans le projet FUI-2011 BELOCOPA (Bouée Éjectable pour la LOcalisation et la COllecte des Paramètres de vol d'un Aéronef abîmé en mer). Il s'agissait de concevoir et de développer un équipement embarqué, extractible et autonome pour localiser rapidement et avec précision un aéronef abîmé en mer et récupérer par liaisons radio les principales données de vol à partir d'un patrouilleur maritime. Le but de cette thèse, au sein de l'Institut Fresnel, concernait l'étude et la réalisation de l'antenne principale de la balise. Cette antenne devait être très flexible et de petites dimensions pour être pliée et insérée dans un espace réduit de la balise et résistante lors son déploiement après son éjection de l'avion. La première partie du travail a eu pour objectif de caractériser en terme de permittivité les différents matériaux diélectriques entrant dans la constitution de la balise, à savoir les substrats sur lesquels sont fixées les antennes et le radôme. La deuxième partie de la thèse porte sur la conception d'antennes multi-bandes fonctionnant en modes dipolaires sur le plan de fréquences du cahier des charges du projet. Ces antennes ont la particularité d'être extrêmement souples. Cette souplesse a été obtenue en réalisant des motifs métalliques rayonnants sur une toile polyamide. Plusieurs motifs ont été étudiés et testés pour converger vers une antenne méandre fonctionnant à trois fréquences distinctes. A l'issue de cette étude, un prototype de l'antenne finale positionnée dans son radôme constitue le dernier maillon du prototype de la balise de détresse du projet BELOCOPA. / This thesis is part of the BELOCOPA project FUI-2011 (BELOCOPA means Ejected Buoy to LOcalize and COllect the data of a crashed plane in sea). It was about designing and developing an on-board, removable and autonomous, equipment to localize quickly and precisely an aircraft crashed in the sea, and to collect by telecommunication the main flight data from a patrol boat. The aim of this thesis, in the Fresnel Institute, was the study and the realization of the main antenna of the beacon. This antenna had to be very flexible with small dimensions to be folded and integrated in a reduced space of the beacon, and had to be strong during its deployment after the ejection of the plane. The aim of the first part of the work was to characterize in term of permittivity the different dielectric materials included in the composition of the beacon, namely the substrates of the antennas and the radome. The second part of the thesis was on the design of multi-band antennas working in dipolar modes on the frequency plan of the specification of the project. The characteristic of these antennas is to be very flexible. This flexibility was obtained realizing metal radiating pattern on a polyamide material. Several patterns have been studied and tested to get the final antenna with meander working at three different resonance frequencies. Following this study, a prototype of the final antenna integrated in the radome is the last link of the prototype of the distress beacon BELOCOPA.

There exists substantial applications motivating the study of nonlinear longitudinal wave propagation in layered (or laminated) elastic waveguides, in particular within areas related to non-destructive testing, where there is a demand to understand, reinforce, and improve deformation properties of such structures. It has been shown [76] that long longitudinal waves in such structures can be accurately modelled by coupled regularised Boussinesq (cRB) equations, provided the bonding between layers is sufficiently soft. The work in this thesis firstly examines the initial-value problem (IVP) for the system of cRB equations in [76] on the infinite line, for localised or sufficiently rapidly decaying initial conditions. Using asymptotic multiple-scales expansions, a nonsecular weakly nonlinear solution of the IVP is constructed, up to the accuracy of the problem formulation. The asymptotic theory is supported with numerical simulations of the cRB equations. The weakly nonlinear solution for the equivalent IVP for a single regularised Boussinesq equation is then constructed; constituting an extension of the classical d'Alembert's formula for the leading order wave equation. The initial conditions are also extended to allow one to separately specify an O(1) and O(ε) part. Large classes of solutions are derived and several particular examples are explicitly analysed with numerical simulations. The weakly nonlinear solution is then improved by considering the IVP for a single regularised Boussinesq-type equation, in order to further develop the higher order terms in the solution. More specifically, it enables one to now correctly specify the higher order term's time dependence. Numerical simulations of the IVP are compared with several examples to justify the improvement of the solution. Finally an asymptotic procedure is developed to describe the class of radiating solitary wave solutions which exist as solutions to cRB equations under particular regimes of the parameters. The validity of the analytical solution is examined with numerical simulations of the cRB equations. Numerical simulations throughout this work are derived and implemented via developments of several finite difference schemes and pseudo-spectral methods, explained in detail in the appendices.

The performance of commercial Radio Frequency Identification (RFID) tags is primarily limited by present techniques used for tag antenna design. Currently, industry techniques rely on identifying the RFID tag application (books, clothing, etc.) and then building antenna prototypes of different configurations in order to satisfy minimum read range requirements. However, these techniques inherently lack an electromagnetic basis and are unable to provide a low cost solution to the tag antenna design process. RFID tag performance characteristics (read-range, chip-antenna impedance matching, surrounding environment) can be very complex, and a thorough understanding of the RFID tag antenna design may be gained through an electromagnetic approach in order to reduce the tag antenna size and the overall cost of the RFID system. The research presented in this thesis addresses RFID tag antenna design process for passive RFID tags. With the growing number of applications (inventory, supply-chain, pharmaceuticals, etc), the proposed RFID antenna design process demonstrates procedures to design tag antennas for such applications. Electrical/geometrical properties of the antennas designed were investigated with the help of computer electromagnetic simulations in order to achieve optimal tag performance criteria such as read range, chip-impedance matching, antenna efficiency, etc. Experimental results were performed on the proposed antenna designs to compliment computer simulations and analytical modelling.

Ce travail de thèse porte sur l'extension et l'analyse d'un solveur volumes finis eulérien, co-localisé avec capture d'interfaces pour la simulation des écoulements multi-matériaux non miscibles. Les extensions proposées s'inscrivent dans la volonté d'élaborer un outil de simulation multi-physiques. Dans le cadre de ce mémoire, le caractère multi-physiques recouvre les champs que nous allons détailler. Nous traitons le cas des écoulements radiatifs modélisés par un système à deux températures qui couple les phénomènes purement hydrodynamiques aux phénomènes radiatifs. Nous proposons un solveur permettant la prise en compte des effets de tension superficielle à l'interface entre deux fluides. Nous développons un solveur implicite permettant la simulation précise d'écoulements faisant intervenir de faibles nombres de Mach par le biais d'une méthode de renormalisation de la diffusion numérique. Enfin, les effets tri-dimensionnels sont considérés ainsi que la possibilité d'étendre le schéma de base aux écoulements à un nombre quelconque de matériaux. A chaque étape, les solveurs développés sont validés sur des cas-tests. / This work is devoted to the extension of a eulerian cell-centered finite volume scheme with interfaces capturing for the simulation of multimaterial fluid flows. Our purpose is to develop a simulation tool which could be able to handle multi-physics problems in the following sense. We address the case of radiating flows, modeled by a two temperature system of equations where the hydrodynamics are coupled to radiation transport. We address a numerical scheme for taking surface tension forces into account. An implicit scheme is proposed to handle low Mach number fluid flows by means of a renormalization of the numerical diffusion. Eventually, the scheme is extended to three-dimensional flows and to multimaterial flows, that is with an arbitrary number of materials. At each step, numerical simulations validate our schemes.

The performance of commercial Radio Frequency Identification (RFID) tags is primarily limited by present techniques used for tag antenna design. Currently, industry techniques rely on identifying the RFID tag application (books, clothing, etc.) and then building antenna prototypes of different configurations in order to satisfy minimum read range requirements. However, these techniques inherently lack an electromagnetic basis and are unable to provide a low cost solution to the tag antenna design process. RFID tag performance characteristics (read-range, chip-antenna impedance matching, surrounding environment) can be very complex, and a thorough understanding of the RFID tag antenna design may be gained through an electromagnetic approach in order to reduce the tag antenna size and the overall cost of the RFID system. The research presented in this thesis addresses RFID tag antenna design process for passive RFID tags. With the growing number of applications (inventory, supply-chain, pharmaceuticals, etc), the proposed RFID antenna design process demonstrates procedures to design tag antennas for such applications. Electrical/geometrical properties of the antennas designed were investigated with the help of computer electromagnetic simulations in order to achieve optimal tag performance criteria such as read range, chip-impedance matching, antenna efficiency, etc. Experimental results were performed on the proposed antenna designs to compliment computer simulations and analytical modelling.

Society’s dependence on electronic and electrical systems has increased rapidly over the past few decades, and people are relying more and more on these gadgets in their daily life because of the efficiency in operation which these systems can offer. This has revolutionized many areas of electrical and electronics engineering including power sector, telecommunication sector, transportation and many other allied areas. With progress in time, the sophistication in the systems also increased. Also as the systems size reduced from micro level to nano level, the compactness of the systems increased. This paved the way for development in the digital electronics leading to new and efficient IC 0s that came into existence. Power sector also faced a resurge in its technology. Most of the analog meters are now replaced by digital meters. The increased sophistication and compactness in the digital system technology made it susceptible to electromagnetic interference especially from High Power Electromagnetic Sources. Communication, data processing, sensors, and similar electronic devices are vital parts of the modern technological environment. Damage or failures in these devices could lead to technical or financial disasters as well as injuries or the loss of life. Electromagnetic Interference (EMI) can be explained as any malicious generation of electromagnetic energy introducing noise or signals into electric and electronic systems, thus disrupting, confusing or damaging these systems. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit. These effects can range from a simple degradation of data to a total loss of data. The source may be any object, artificial or natural, that carries rapidly changing electrical currents, such as an electrical circuit. The sources of electromagnetic interference can be either unintentional or intentional. The sources producing electromagnetic interference can be of different power levels, different frequency of operation and of different field strength. One such classification of these sources are the High Power Electromagnetic Sources (HPEM) High Power Electromagnetic environment refers to sources producing very high peak electromagnetic fields at very high power levels. These power levels coupled with the extremely high magnitude of the fields are sufficient to cause disastrous effects on the electrical and electronic systems. There has been a lot of developments in the field of the source technology of HPEM sources so that they are now one of the strongest sources of electromagnetic interference. High Power Electromagnetic environment refers to the sources producing very high peak electromagnetic fields at very high power levels. These power levels coupled with the extremely high magnitude of the fields are sufficient to cause disastrous effects on the electrical and electronic systems. HPEM environments are categorized based on the source characteristics such as the peak electric field, often called threat level, frequency coverage or bandwidth, average power density and energy content. The sources of electromagnetic interference can be either unintentional or intentional. Some examples of unintentional sources are the increased use of electromagnetic spectrum which generates disturbance to various systems operating in that frequency band, poor design of systems without taking care of other systems present nearby as well as lightning. Intentional sources are High altitude Electromagnetic Pulse (HEMP) or Nuclear Electromagnetic Pulse (NEMP) due to nuclear detonations, Ultra Wide Band (UWB) field from Impulse Radiating Antennas (IRA), Nar-row band fields like those coming from High Power Microwaves (HPM), High Intensity Radio Frequency (HIRF) sources. Of these the lightning is natural and all other sources are man-made. The significant progress in the Intentional High-Power Electromagnetic (HPEM) sources and antenna technologies and the easy access to simple HPEM systems for anyone entail the need to determine the susceptibility of electronic equipment as well as coupling of these fields with systems such as cables (buried as well as aerial), airborne vehicle etc. to these types of threats. Buried cables are widely used in the communication and power sectors due to their efficient functioning in urban cities and towns. These cables are more prone to electromagnetic interferences from HPEM sources. The buried communication cables or even the buried data cables are connected to sensitive equipments and hence even a slight rise in the voltage or the current at the terminals of the equipments can become a serious problem for the smooth operation of the system. In the first part of the thesis the effect of the electromagnetic field due to these sources on the cables laid underground has been studied. The second part of this thesis deals with the study of the interaction of the EM field from the above mentioned HPEM sources with an airborne vehicle. Airborne vehicle and its payload are extremely expensive so that any destruction to these as a result of the voltages and currents induced on the vehicle on account of the incoming HPEM fields can be quite undesirable. The incoming electromagnetic fields will illuminate the vehicle along its axis which results in the induction of currents and voltages. These currents and voltages will get coupled to the internal control circuits that are extremely sensitive. If the induced voltage/ current magnitude happen to be above the damage threshold level of these circuits then it will result in either a malfunction of the circuit or a permanent damage of it, with both of them being detrimental to the success of the mission. This will even result in the abortion of the mission or possible degradation of the vehicle performance. Hence it is worthwhile to see what will be the influence of an incoming HPEM electromagnetic field on the airborne vehicle with and without the presence of an exhaust plume. In this work, the HPEM sources considered are NEMP, IRA and HPM. The electromagnetic fields produced by the EMP can induce large voltage and current transients in electrical and electronic circuits which can lead to a possible malfunction or permanent damage of the systems. The electric field at the earth 0s surface can be modelled as a double exponential pulse as per the IEC standard 61000-2-9. The NEMP field incident on the earth’s surface is considered as that coming from a source at a distance far away from the earth’s surface; hence a plane wave approximation has been used. Impulse radiating antennas are the ones that are used as the major source of ultra wide band radiation. These are highly powerful antennas that use a pulsed power source as the input and this power source is conditioned to get an extremely sharp rise time pulse. These antennas are very high power antennas that are capable of producing a significant electromagnetic field. Impulse radiating antenna is a paraboloidal reflector and hence is an aperture antenna. Initially the radiated field due to this aperture needs to be found out at any observation point from the antenna. In this thesis, the aperture distribution method is used to accurately determine the field due to the aperture. In this method the field reflected from the surface of the reflector is first found on an imaginary plane through the focal point of the reflector that is normal to the axis of the reflector, by using the principles of geometrical optics, which then is extended to the observation point. The IRA considered for the present work is the one of the most powerful IRA as per the published literature available in the open domain. This has an input voltage of 1.025 MV. The far field electric field measured at the boresight (at r =85 m) being equal to 62 kV/m, and the uncorrected pulse rise time (10%-90%) is 180 ps for this IRA. HPM sources are usually electromagnetic radiators having a reflector with a horn antenna kept at their focal point for excitation. HPM sources generally operate in single mode or at tens or hundreds of Hz repetition rates. Many HPM radiators are developed in the world each with their own peculiar geometry and power levels. In the present thesis, a single waveguide (WR-975) fed HPM antenna assembly has been studied. The chosen waveguide has a cut-o_ frequency of 1 GHz and a power level of 10 GW. The wavelength associated with the waveguide is 0.3 m. The field pattern shows a definite peak in its response when the frequency is 1 GHz, the cut-off frequency of the waveguide. The electric field coming out of the HPEM sources travel through the medium that is either air alone or a combination of air and soil respectively depending upon whether the circuit on which the coupling is analysed is an airborne vehicle or an underground cable. The media plays a major role in the coupling, as the field magnitude is influenced by the characteristic properties of the media. As height increases the magnitude of the electric field decreases for all types of sources and also the time before which the field waveform starts is increased. The electric field in the soil is decided by the soil properties such as its conductivity and permittivity. The soil is modelled in frequency domain and the high frequency behaviour of soils is considered with its conductivity and permittivity taken as functions of frequency, as the incident field has high frequency components. A soil medium can be electromagnetically viewed as a four component dielectric mixture consisting of soil particles, air voids, bound water, and free water. When electric field is incident on the soil, it gets polarized. This is as a result of a wide variety of processes, including polarization of electrons in the orbits around atoms, distortion of molecules, reorientation of water molecules, accumulation of charge at interfaces, and electrochemical reactions. Whatever is the HPEM source, an increase in the soil conductivity results in an increased attenuation of the field. Also there is a significant loss of high frequency components in the GHz range in the field due to the selective absorption by the soil. This effect causes the percentage attenuation to be maximum for HPM and minimum for NEMP and IRA lying in between these two extremities. Increase in permittivity of the soil causes attenuation of the electric field for all HPEM sources. This is due to the relaxation mechanisms in the soil due to atomic- or molecular-scale resonances. The coupling of the electromagnetic fields due to HPEM sources is considered in the first phase. Two cables are considered (i) buried shielded and (ii) buried shielded twisted pair cables. The results are arrived at using the Enhanced Transmission Line model. The induced current is more for a shielded cable than a twisted pair cable of the same configuration. The induced current magnitude depends upon the type of the HPEM source, the depth of burial of the cable and the point on the cable where the current/ voltage is computed. Current is maximum at the centre of the cable for a matched termination and the voltage is the minimum at this point. The ratio of the induced current in the inner conductor with respect to the shield current of a shielded cable is the least for an HPM, and maximum for NEMP. This is due to the fact that higher frequencies are absorbed more by the shield of the cable. This affects HPM induced current the maximum and NEMP the least because of the presence of the lower frequency components in NEMP. Induced current in the twisted pair cable depends upon the number of pairs of the cable and the pitching of the cable. The electromagnetic field from the HPEM sources propagates with less attenuation in air due to the lower resistance this medium offers for electromagnetic wave propagation. Hence any system in air, be it electrical or electronic, will be under the strong illumination by these electromagnetic fields. As the second part of this thesis, the influence of the electromagnetic fields from all the three HPEM sources on an airborne vehicle in flight is analysed. For this part of study, the Electromagnetic (EM) fields radiated by all the three sources at different heights from the earth 0s surface have been computed. The coupling study has been done for the case of a vehicle with plume as well as without plume. For the second case, the electromagnetic modelling of the plume has been done taking into consideration its conductivity, which in turn depends on the different ionic species present in the plume. The species of the exhaust plume depends upon the chemical reactions taking place in the combustion chamber of the nozzle of the vehicle. The presence of the alkali metals as impurity in the airborne vehicle propellant will generate considerable ion particles such as Na+, Cl in addition to e- in the plume mixture during combustion which makes the plume electrically conducting. But it does not influence the pressure, temperature and velocity of the plume. After the nozzle throat, the exhaust plume regains the supersonic speed, so the flow of the exhaust plume is assumed as compressible flow in the second region. The electrons have high collision frequency, high number density, high plasma frequency and lower molecular mass and hence the highly mobile electrons dominate the heavy ion particle in the computation of the electrical conductivity of the plume. The plume conductivity decreases marginally from the axis till a distance equal to the nozzle radius but the peak value increases sharply towards the exit plane edge of the nozzle radius. The induced current is computed using Method of Moments. The induced current depends upon the type of interference source, its characteristics, whether the plume is present or not and the type of the plume. The HPM induces maximum current in the vehicle because of the fact that the plume has a tendency to become more conductive at these frequencies. The induced currents due to the EM fields from IRA and NEMP comes after the HPM. The presence of the plume enhances the magnitude of the induced current. If the plume is homogeneous then the current induced in it is more.

The performance of commercial Radio Frequency Identification (RFID) tags is primarily limited by present techniques used for tag antenna design. Currently, industry techniques rely on identifying the RFID tag application (books, clothing, etc.) and then building antenna prototypes of different configurations in order to satisfy minimum read range requirements. However, these techniques inherently lack an electromagnetic basis and are unable to provide a low cost solution to the tag antenna design process. RFID tag performance characteristics (read-range, chip-antenna impedance matching, surrounding environment) can be very complex, and a thorough understanding of the RFID tag antenna design may be gained through an electromagnetic approach in order to reduce the tag antenna size and the overall cost of the RFID system. The research presented in this thesis addresses RFID tag antenna design process for passive RFID tags. With the growing number of applications (inventory, supply-chain, pharmaceuticals, etc), the proposed RFID antenna design process demonstrates procedures to design tag antennas for such applications. Electrical/geometrical properties of the antennas designed were investigated with the help of computer electromagnetic simulations in order to achieve optimal tag performance criteria such as read range, chip-impedance matching, antenna efficiency, etc. Experimental results were performed on the proposed antenna designs to compliment computer simulations and analytical modelling.