Analysis and Design of a Multifunctional Spiral Antenna

The Archimedean spiral antenna is well-known for its broadband characteristics with circular polarization and has been investigated for several decades. Since their development in the late 1950's, establishing an analytical expression for the characteristics of spiral antenna has remained somewhat elusive. This has been studied qualitatively and evaluated using numerical and experimental techniques with some success, but many of these methods are not convenient in the design process since they do not impart any physical insight into the effect each design parameter has on the overall operation of the spiral antenna. This work examines the operation of spiral antennas and obtains a closed-form analytical solution by conformal mapping and transmission line model with high precision in a wide frequency band. Based on the analysis of spiral antenna, we propose two novel design processes for the stripline-fed Archimedean spiral antenna. This includes a stripline feed network integrated into one of the spiral arms and a broadband tapered impedance transformer that is conformal to the spiral topology for impedance matching the nominally-high input impedance of the spiral. A Dyson-style balun located at the center facilitates the transition between guided stripline and radiating spiral modes. Measured and simulated results for a probe-fed design operating from 2 GHz to over 20 GHz are in excellent agreements to illustrate the synthesis and performance of a demonstration antenna. The research in this work also provides the possibility to achieve conformal integration and planar structural multi-functionality for an Unmanned Air Vehicle (UAV) with band coverage across HF, UHF, and VHF. The proposed conformal mapping analysis can also be applied on periodic coplanar waveguides for integrated circuit applications

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

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Analysis and synthesis of leaky-wave devices in planar technology

[ESP] ] El trabajo llevado a cabo durante la realización de esta tesis doctoral, se ha centrado en el análisis y síntesis de dispositivos de microondas en tecnología planar. En concreto, se han estudiado diferentes tipos de dispositivos basados en radiación por ondas de fuga "leaky waves", en los cuales las propiedades de radiación están determinadas por la constante de fase del modo "leaky" que es el que determina el ángulo de apuntamiento y por la tasa de radiación que es la que determina la intensidad de los campos radiados. De esta manera, controlando en amplitud y fase el modo "leaky" se puede obtener un control efectivo sobre el diagrama de radiación del dispositivo. Además, con el objetivo de poder obtener de una manera más eficiente las características de propagación de los modos de fuga "leaky" en función de los principales parámetros geométricos de la estructura, se han desarrollado diversas herramientas de análisis modal basadas en la técnica de resonancia transversa de la estructura. La capacidad para obtener un control simultáneo de la constante de propagación compleja del modo "leaky", ha sido demostrada mediante el diseño y fabricación de varios tipos de antena "leaky wave" (LWA) y de otros dispositivos como multiplexores y sistemas de enfoque en campo cercano. Para ello, se ha utilizado la tecnología planar de guía de onda integrada en sustrato (susbstrate integrated waveguide, SIW). Esta recientemente desarrollada tecnología, permite diseñar dispositivos de microondas basados en tecnología clásica de guía de ondas con sistemas de fabricación estándar usados en tecnología de circuitos impresos (printed circuit board, PCB). De esta forma, se pueden integrar en un mismo sustrato muchas de las diferentes partes que forman un sistema de comunicaciones, mejorando así su robustez y compactibilidad, además de reducir el coste y de contar con menores pérdidas que otras tecnologías planares como la microstrip. [ENG] The work developed along this doctoral thesis has been focused on the analysis and synthesis of microwave devices in planar technology. In particular, several types of devices based on the radiation mechanism of leaky waves have been studied. Typically, the radiation properties in leaky-wave devices are determined by the complex propagation constant of the leaky mode, wherein the phase constant is responsible for the pointing angle and the leakage rate for the intensity of the radiated fields. In this manner, by controlling both amplitude and phase of the leaky mode, an effective control over the device's radiation diagram can be obtained. Moreover, with the purpose of efficiently obtaining the leaky mode's radiation properties as function of the main geometrical parameters of the structure, several modal tools based on the transverse resonance analysis of the structure have been performed. In order to demonstrate this simultaneous control over the complex propagation constant in planar technology, several types of leaky-wave devices, including antennas (LWAs), multiplexors and near-field focusing systems, have been designed and manufactured in the technology of substrate integrated waveguide (SIW). This recently proposed technology, allows the design of devices based on classical waveguide technology with standard manufacturing techniques used for printed circuit board (PCB) designs. In this way, most of the parts that form a communication system can be integrated into a single substrate, thus reducing its cost and providing a more robust and compact device, which has less losses compared to other planar technologies such as the microstrip.Universidad Politécnica de Cartagen

Coordinate Transformation Based Electromagnetic Design and Applications.

PhDThe main objective of this thesis is to take one step forward to practical and realisable devices for antenna and microwave engineering, using the technique of discrete coordinate transformation (DCT), which is a practical implementation of the coordinate transformation method. During this thesis, the DCT technique was demonstrated and analysed from the theory, and was proved to provide an all-dielectric approach to design devices under certain conditions. Two schemes were proposed on how to use this technique in a practical design. The first one is to transform an existing device into a flattened profile, meanwhile maintaining its electromagnetic performance. As examples, a flat reflector and a flat lens were created from a parabolic reflector and a convex lens, respectively. The second scheme is to project the propagating paths of an electromagnetic wave, and then generate a distorted space according to the paths by engineering the electromagnetic properties of the media. In this scheme, two examples of application were presented: an undetectable antenna composed of a carpet cloak and a conducting cavity, and a broadband device which can extraordinarily enhance the transmission through a sub-wavelength aperture. Numerical simulations based on the Finite-Difference Time-Domain (FDTD) method were implemented to verify all the designs. Several specific configurations were employed in the modelling in order to simulate the DCT based devices more efficiently and precisely. Performance of these devices was validated and analysed, and the advantages and disadvantages of this technique were investigated. Realisation and fabrication methods i were also studied, and a prototype was designed, fabricated and measured. At the end, as an extension, a multiple discrete coordinate transformation method was proposed and presented. This multiple transformation was proved to effectively relax the limitation of the one-step transformation, and was used to design an all-dielectric thin absorber from a conventional pyramidal one for demonstration.China Scholarship Counci

Gain and Loss Factor for Conical Horns, and Impact of Ground Plane Edge Diffractions on Radiation Patterns of Uncoated and Coated Circular Aperture Antennas

abstract: Horn antennas have been used for over a hundred years. They have a wide variety of uses where they are a basic and popular microwave antenna for many practical applications, such as feed elements for communication reflector dishes on satellite or point-to-point relay antennas. They are also widely utilized as gain standards for calibration and gain measurement of other antennas. The gain and loss factor of conical horns are revisited in this dissertation based on spherical and quadratic aperture phase distributions. The gain is compared with published classical data in an attempt to confirm their validity and accuracy and to determine whether they were derived based on spherical or quadratic aperture phase distributions. In this work, it is demonstrated that the gain of a conical horn antenna obtained by using a spherical phase distribution is in close agreement with published classical data. Moreover, more accurate expressions for the loss factor, to account for amplitude and phase tapers over the horn aperture, are derived. New formulas for the design of optimum gain conical horns, based on the more accurate spherical aperture phase distribution, are derived. To better understand the impact of edge diffractions on aperture antenna performance, an extensive investigation of the edge diffractions impact is undertaken in this dissertation for commercial aperture antennas. The impact of finite uncoated and coated PEC ground plane edge diffractions on the amplitude patterns in the principal planes of circular apertures is intensively examined. Similarly, aperture edge diffractions of aperture antennas without ground planes are examined. Computational results obtained by the analytical model are compared with experimental and HFSS-simulated results for all cases studied. In addition, the impact of the ground plane size, coating thickness, and relative permittivity of the dielectric layer on the radiation amplitude in the back region has been examined. This investigation indicates that the edge diffractions do impact the main forward lobe pattern, especially in the E plane. Their most significant contribution appears in far side and back lobes. This work demonstrates that the finite edge contributors must be considered to obtain more accurate amplitude patterns of aperture antennas.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

Design and Analysis of Microstrip Filtennas

The Goal of this thesis is to design and analyses the filtenna, also called by name filtering antenna. Designed by integration of the filter and antenna. In modern day wireless devices multiple antennas are required to make sure that it can be used for multiple communication services, this not only make the system bulky but the power loss is also more. In filtenna using active components can replace them making a system with low profile, more light weight, and energy efficient characteristics. In this thesis includes the first part which is an introduction to computational electromagnetics and using this analysis of microstrip antenna and second is the proposed design of two microstrip filtennas. Under computation electromagnetics, the Maxwell equation and antenna parameter are analyzed using finite difference method. The design and simulation of this filtenna have been done in ANSYS-HFSS-15 simulation tool. The first filtenna designed structure is the integration of the band-rejection filter with monopole antenna for UWB and X-Band applications. Where after applying the open stub it only passes the X-Band i.e. 8-12 GHz. The second proposed filtenna is for overlay cognitive radio application. This is design using the bandpass filter which is integrated with the antenna. In bandpass filter, the frequency tuning is done by varactor diode. This filtenna resonates at frequency 2.6 to 3 GHz and gain of 2.7dB. The fabrication of second filtenna using bandpass characteristics is done and analyzed the results