PCB based Modulated Scatter with Enhanced Modulation Depth

The Modulated Scatterer Technique (MST) Has Shown Promise for Applications in Microwave Imaging, Electric Field Mapping, and Materials Characterization. Traditionally, MST Scatterers Are Dipoles Centrally Loaded with an Element Capable of Modulation (E.g., a PIN Diode). by Modulating the Load Element State, the Scattered Fields Are Also Modulated. However, Due to the Small Size of Such Scatterers, It Can Be Difficult to Reliably Detect the Response. Increasing the Modulation Depth (MD) of the Scattered Signal May Improve Detectability. This Paper Presents Simulations and Measurements of PCB-Based MST Elements that, through Reactive Loading, Are Designed to Be Electrically Invisible during the Reverse Bias State of the Modulated Element (A PIN Diode in This Case) While Producing Detectable Scattering during the Forward Bias State. the Results Show a Significant (\u3e 90%) Improvement in the MD of the Scattered Signal When Compared to a Traditional MST Scatterer

Maxwellian Circuits-Based Analysis of Loaded Wire Antennas and Scatterers

Based on the recently proposed Maxwellian circuit (MC) theory, a new method to analyze wire antennas and scatterers loaded with linear lumped elements is demonstrated in this letter. To effectively incorporate the load boundary condition into the numerical solution, the MC model is solved herein using finite element method (FEM)

Experimental performance evaluation and design of schemes for passive RFID network

Passive Radio Frequency Identification (RFID) is a short range technology for transferring information. The main advantage of passive RFID systems over active communication systems is the battery-less operation at the client sides. However, there are two major challenges that limit the widespread adaptation of passive RFID systems: short communication range and low read rate in dense deployments. This dissertation addresses these issues by studying the root causes and develops solutions for them. In this dissertation, understanding the backscattering behavior of antennas and also the mutual coupling interactions among them are found to be the root causes of the two above-mentioned challenges for RFID networks. Thus, by studying these two main root causes solutions for them are proposed, investigated and verified, by simulations and measurements. The contributions in this dissertation include: (1) Design of a new measurement technique to estimate the structural scattering coefficient of a linear antenna. (2) Showing that the well-known Green model cannot completely explain the variation of the radar cross section of a T-match bowtie antenna over its Г plane. (3) Introducing dual loading in designing RFID antenna tags to: (a) Increase the vector differential backscattering signal, (b) Produce higher order modulations. (4) Introducing a new state for RFID tags in that tags switch to a low scattering states to: (a) suppress their interference to a target antenna in the network. (b) Stabilize the RCS of the target antenna. (c) Increase read rate in RFID networks. (5) Numeric analysis of the mutual coupling impedance for two side by side scattering antennas. (6) Introducing a multi-port RFID which can switch to different load impedances to help a target antenna in its vicinity increase its signal over the level when the target is alone in the field --Abstract, page iv

Analysis and Reduction of the Scattering by Cloaked Metallic Cylinders Beyond the Quasi-static Limit

L'abstract è presente nell'allegato / the abstract is in the attachmen

Non-Invasive Near-Field Measurement Setup Based on Modulated Scatterer Technique Applied to Microwave Tomographhy

Résumé L’objectif principal de cette thèse est d’aborder la conception et le développement d’un montage d’imagerie en champ proche (CP) basé sur la technique de diffusion modulé (TDM). La TDM est une approche bien connue et utilisée pour des applications où des mesures précises et sans perturbations sont nécessaire. Parmi les applications possibles disponibles pour la fabrication d’une sonde TDM, que ce soit électrique, optique, mécanique, le diffuseur optique modulé DOM a été pris en considération afin de fournir des mesures quasi sans-perturbations en raison de l’invisibilité des fibres optiques face aux champs radiofréquence électromagnétiques. La sonde est composée d’une puce photodiode commerciale “off-the-shelf” (dispositif non-linéaire), d’une antenne dipôle courte agissant comme diffuseur et un réseau d’adaptation (cir¬cuit passif). Cet dernieér améliore les propriétés de diffusion et augmente également la sensibilité de la sonde DOM dans la bande de fréquence pour laquelle le réseau correspondant est optimisé. Les caractéristiques de rayonnement de la sonde, y compris sa réponse de polarisation croisée et sa sensibilité omnidirectionnelle, ont été théoriquement et expérimentalement étudiés. Enfin, la performance et la fia¬bilité de la sonde a été étudiée en comparant des mesures de distribution de champs proche avec une distribution de champs simulé. Une vitesse d’imagerie accrue a été obtenue utilisant un réseau de sondes DOM, ce qui réduit les mouvements mécaniques résultant ansi en une amélioration remarquable de la vitesse de mesure. Le couplage mutuel, le temps de commutation et l’effet d’obscurité, des effets qui peuvent affecter les performances du réseau ont été explorés. Ensuite, les résultats obtenus par le réseau ont été validé par une imagerie CP en mesurant la distribution des champs E d’une antenne sous test (AST) et la comparant à des résultats de simulation. Une calibration et un calcul de moyenne ont été appliqués à des données brutes pour com¬penser pour les incertitudes dans la fabrication et l’interaction entre réseau/AST et réseau/antenne de réception. La plage dynamique et la linéarité de la réponse de l’imagerie CP ont été améliorées en ajoutant un circuit suppresseur de porteuse en avant de l’antenne. Le suppresseur élimine la porteuse sur laquelle aucune information n’est transmise et laisse les bandes latérales intactes.----------Abstract The main focus of this thesis is to address the design and development of a near-field (NF) imaging setup based on the modulated scatterer technique (MST). MST is a well-known approach used in applications where accurate and perturbation-free mea¬surement results are necessary. Of the possible implementations available for making an MST probe, including electrical, optical and mechanical, the optically modulated scatterer OMS was considered in order to provide nearly perturbation-free measure¬ment due to the invisibility of optical fiber to the radio-frequency electromagnetic fields. The OMS probe consists of a commercial, off-the-shelf (COTS) photodiode chip (nonlinear device), a short-dipole antenna acting as a scatterer and a match¬ing network (passive circuit). The latter improves the scattering properties and also increases the sensitivity of the OMS probe within the frequency range in which the matching network is optimized. The radiation characteristics of the probe, includ-ing cross-polarization response and omnidirectional sensitivity, were both theoreti¬cally and experimentally investigated. Finally, the performance and reliability of the probe was studied by comparing measured near-field distributions on a known field distribution with simulations. Increased imaging speed was obtained using an array of OMS probes, which re¬duces mechanical movements. Mutual-coupling, switching time and shadowing effect, which all may affect the performance of the array, were investigated. Then, the re¬sults obtained by the array were validated in a NF imager by measuring the E-field distribution of an antenna under test (AUT) and comparing it with a simulation. Cal¬ibration and data averaging were applied to raw data to compensate the probes for uncertainties in fabrication and interaction between array/AUT and array/receiving antenna. Dynamic range and linearity of the developed NF imager was improved by adding a carrier canceller circuit to the front-end of the receiver. The canceller eliminates the carrier on which no information is transmitted and leaves the sidebands intact. This enables us to increase the amplification gain to achieve better signal-to-noise ratio (SNR) and more importantly to expand the imager’s dynamic range

Novel modulated antennas and probes for millimeter wave imaging applications

Microwave and millimeter wave (300 MHz - 300 GHz) imaging techniques have shown great potential for a wide range of industrial and medical applications. These techniques are fundamentally based on measuring relative and coherent electromagnetic fields distributions, e.g., electric fields, around the object to be imaged. Various imaging systems can be devised for measuring relative electric field distributions; each with it own advantages and limitations. This dissertation is focused on addressing critical challenges related to the practical implementation of various microwave and millimeter wave imaging systems. Specifically, this research is meant to achieve three main objectives related to designing efficient modulated imaging methods/array elements, reducing the sensitivity to standoff distance variations in near-field imaging, and designing a simple and accurate vector network analyzer (VNA) for in-situ imaging applications. The concept of modulating millimeter wave antenna and scatterer structures, directly to increase the overall system sensitivity and reduce the image acquisition time, is central to the development presented herein. To improve upon the conventional modulated scatterer technique (MST) based on dipole scatterers; a new multiple loaded scatterer (MLS) method and novel loaded elliptical slot are introduced and analyzed. A unique near-field differential probe based on dual-loaded modulated single waveguide aperture is developed to compensate for and reduce the effect of standoff distance variations in near-field imaging. Finally, a novel vector network analyzer (VNA) design is introduced to meet the rising need for in-situ vector measuring devices. To realize a robust handheld millimeter wave VNA, a custom-designed waveguide phase shifter based on sub-resonant loaded slots is introduced. The proposed MLS method, modulated elliptical slot, dual-loaded modulated aperture probe, and VNA are thoroughly investigated and their efficacy for microwave and millimeter wave imaging is demonstrated --Abstract, page iii

Terahertz integrated antenna arrays for imaging applications

Terahertz is the portion of the spectrum that covers a frequency range between 300 GHz - 3 THz. This frequency band has proven its potential for imaging applications thanks to the good compromise between spatial resolution and penetration; however, this push towards high frequencies contains many technological difficulties in all the subsystems involved in the signal generation, transmission and detection. The power budget restrictions and high losses that sources and receivers currently suffer at these frequencies require systems with a high level of integration among all the devices and components of the systems and subsystems. Therefore, the antennas needed for these systems require to be integrated within the same fabrication processes and technologies as the sensing and power converting devices that are used at their terminals. This doctoral thesis has focused on the development of integrated antenna arrays at Terahertz frequencies for imaging applications, for both near-field and focal-plane geometries, with a special emphasis on the technologies and the fabrication capabilities that can be potentially used and are currently available. The current imaging systems require large arrays of antennas in order to achieve the high-speed image acquisition that is required in most THz applications. This fact increases considerably the difficulty and complexity to achieve highly integrated and efficient antennas. This thesis has characterized and analyzed these difficulties and provided solutions to the development of antenna arrays at millimeter and submillimeter wave frequencies. The first part of this thesis has focused on the study of a planar antenna array, called retina, for a specific near-field imaging system based on the Modulated Scatterer Technique (MST) at millimeter and submillimeter-wave frequencies. This system has been selected for its capabilities to perform high-speed imaging and because it does not require a high frequency distribution line network. However, it is hindered by many technological difficulties: the selection of an antenna geometry that achieves high efficiency, the selection of the adequate active element and its integration with the antenna. In this thesis, these challenges have been addressed and studied in-depth, and a design methodology that integrates all the different aspects of the system has been developed. Because planar antennas at millimeter and submillimeter wave frequencies suffer from high losses due to the surface wave modes inside substrate, these losses have been analyzed and quantified for different antennas, and an antenna geometry that reduces significantly this problem has been developed. Different switching technologies currently or potentially available at these high frequencies have been considered in order to study and analyze their capabilities and their integration possibilities: PIN diodes, Schottky diodes and RF-MEMS. These technologies have been studied through the development of three retina prototypes, which have been fabricated using high precision fabrication processes such as laser micromachining and photolithographic. Different measurement set ups were fabricated and assembled to validate the different premises presented. The second part of the thesis is devoted to the study of integrated Focal Plane Arrays (FPA). The development of FPA at submillimeter wave frequencies is highly on demand due to the enormous progress in designing integrated heterodyne receivers. These receivers integrate arrays of submillimeter-wave diode-based mixers and multipliers with Monolithically Integrated Circuit (MIC) amplifiers on the same wafer stack. For this stackable multi-pixel terahertz camera technology to work, a leaky wave antenna with silicon micro-lenses has been developed, which allows wafer level integration compatible with silicon micro-fabrication techniques for bulk array manufacturing and has high directivity in order to illuminate a reflector efficiently. Detailed and thorough design guidelines for this antenna are presented. Two antenna prototypes were built in order to evaluate the two fabrication possibilities: advanced laser micro-fabrication and photolithographic fabrication. A study of the aberrations of the lens has been developed in order to evaluate the performance of the lens profile fabricated. Moreover, a set of radiation pattern measurements of the fabricated prototypes was performed in order to evaluate the performance of the antenna and its possibilities to be used as a FPA

Anomalies in Light Scattering

Scattering of electromagnetic waves lies at the heart of most experimental techniques over nearly the entire electromagnetic spectrum, ranging from radio waves to optics and X-rays. Hence, deep insight into the basics of scattering theory and understanding the peculiar features of electromagnetic scattering is necessary for the correct interpretation of experimental data and an understanding of the underlying physics. Recently, a broad spectrum of exceptional scattering phenomena attainable in suitably engineered structures has been predicted and demonstrated. Examples include bound states in the continuum, exceptional points in PT-symmetrical non-Hermitian systems, coherent perfect absorption, virtual perfect absorption, nontrivial lasing, non-radiating sources, and others. In this paper, we establish a unified description of such exotic scattering phenomena and show that the origin of all these effects can be traced back to the properties of poles and zeros of the underlying scattering matrix. We provide insights on how managing these special points in the complex frequency plane provides a powerful approach to tailor unusual scattering regimes

Modulated Microwave Retro-reflectors and Their Applications

This work seeks to investigate the viability of establishing communications links using modulated microwave reflectors, and explores potential application areas. A primary and underlying objective has been to combine modulation of radar cross section (RCS) with the wide-angle RCS response of a microwave retro-reflector so as to yield a transponder which imparts information content on the reflected spectrum. Since the RCS is electrically large, the communications link is directive and yet the transponder is not a transmitter of microwave energy and hence has modest power needs. The microwave retro-array was quickly identified as the most promising structure to achieve these aims, and hence the further objectives of the work have been to investigate this structure and fabricate working prototypes so as to: • achieve a manufacturable structure. • perform measurements to compare with theoretical models of behaviour. • explore the limits of performance, and seek to expand them. • identify applications and markets. • explore and pursue such related discoveries that may occur. All the above aims have been explored to some extent, and the findings have been reported in the body of the thesis. The background and historical context is discussed in chapter 1, while chapter 2 reports on the construction and characterisation of 16- element modulated retro-array prototypes operating at a 2.5 GHz carrier frequency. The applied nature of this work is extended in chapters 3 and 4 to printed integrated circuits for passive transponders, and the scaling of these methods to frequencies around 9.2 GHz. Theoretical models for the properties of much larger arrays are presented in chapter 5, and range finding applications and results presented in chapter 6. Two applications are then discussed for which the required array dimensions are estimated, before closing with conclusions and suggestions for future work