Download or read book Performance Enhancement of Radiation and Scattering Properties of Circularly Polarized Antennas Using Frequency Selective Surface written by Mohammad Akbari Choubar and published by . This book was released on 2018 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt: At millimetre-wave (MMW) frequencies, losses associated with wireless link and system are critical issues that need to be overcome in designing high-performance wireless systems. To compensate the overall loss in a wireless communication system, a high-gain antenna is required. Circularly polarized (CP) antennas are among preferred choices to design because they offer many advantages due to their good resistance to polarization mismatch, mitigation of multipath effects, and some phasing issues and immunity to Faraday rotation. On the other hand, frequency selective surface (FSS) technology is recently employed to enhance the performance of radiation and scattering properties of antennas used in different sectors such as aerospace, medical, and microwave industry. Therefore, it is appropriate and attractive to propose the use of FSS technology to design practical and efficient CP antennas. CP Fabry-Perot cavity (FPC) antennas based on FSS are investigated in this thesis to fulfil the growing demand for broadband high-gain antennas with low radar cross section (RCS). The thesis investigates both characteristic improvement of CP antennas and RCS reduction issues employing FSS structures. Initially, a high gain CP dielectric resonator (DR) antenna is proposed. Using an FSS superstrate layer, a gain enhancement of 8.5 dB is achieved. A detailed theoretical analysis along with different models are presented and used to optimize the superstrate size and the air gap height between the antenna and superstrate layer. The second research theme focusses on developing an effective approach for mitigating the near-field coupling between four-port CP antennas in a Multiple-Input, Multiple-Output (MIMO) system. This is obtained by incorporating a two-layer transmission-type FSS superstrate based on planar crossed-dipole metal strips. Another technique for suppressing the spatially coupling between DR antennas using a new FSS polarization-rotator wall is studied as well. The coupling reduction is achieved by embedding an FSS wall between two DRAs, which are placed in the H-plane. Utilizing this FSS wall, the TE modes of the antennas become orthogonal, which reduces the spatially coupling between the two DRAs. The third research theme of this thesis is to enhance the purity and bandwidth of CP with the least amount of insertion loss by the use of an LP-to-CP-polarizer which is based on multilayer FSS slab. This polarizer is approximately robust under oblique illuminations. To have a high-gain CP antenna, an 8-element LP array antenna with Chebyshev tapered distribution is designed and integrated with the polarizer. Eventually, in order to enhance the scattering property, the fourth research theme investigates on RCS reduction by the use of two different approaches which are based on FSS. Initially, a wideband FSS metasurface for RCS reduction based on a polarization conversion is proposed. To distribute the scattered EM waves and suppress the maximum bistatic RCS of the metasurface over a broad band of incident angles at both polarizations, the elements are arranged using the binary coding matrix achieved by group search optimization (GSO) algorithm. The reflective two-layer metasurface is designed in such a way to generate reflection phase difference of 180° between two elements "0" and "1" on a broad frequency band. A theoretical analysis is performed on the ratio of the "0" and "1" elements using Least Square Error (LSE) method to find the best ratio value. As the second activity of this research theme, wideband CP antenna with low RCS and high gain properties is presented. The proposed antenna is based on a combination of the FPC and sequential feeding technique.

Download or read book Handbook of Metamaterial Derived Frequency Selective Surfaces written by Shiv Narayan and published by Springer Nature. This book was released on 2023-01-02 with total page 744 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume provides a consolidated reference for the applications of frequency selective surfaces (FSS) technology in different sectors such as wireless communications, smart buildings, microwave and medical industries. It covers all aspects of metamaterial FSS technology starting from theoretical simulation, fabrication and measurement all the way to actual hardware implementation. Also included are in-depth discussions on the design methodologies of metamaterial FSS structures and their practical implementation in devices and components. It will be of interest to researchers and engineers working on developing metamaterial-FSS technology.

Download or read book Applications of Frequency Selective Surfaces in Polarization Control of Antennas written by Farhad Khosravi and published by . This book was released on 2014 with total page 73 pages. Available in PDF, EPUB and Kindle. Book excerpt: The purpose of this dissertation is to address the problems associated with the current antennas deployed for wireless and navigation purposes. The focus in this work is on the circular polarization radiation of the antennas and the goal is to improve their radiation properties. The methods presented are based on Frequency Selective Surfaces (FSS); a group of periodic structures that behave as a spatial filter in principal but can be adjusted for other alterations to the incident electromagnetic wave. The FSS can be designed adequately so that the transmitted wave undergos a change in amplitude or phase. Moreover, adding the feature of selectivity over the incident polarization (TE or TM), can make the FSS shape the radiation pattern of the antenna in terms of amplitude or polarization; depending on whether the change is in the amplitude or phase of the wave transmitted through the FSS. The introduction chapter discusses the contemporary problems with these antennas and solution already proposed for these issues. Besides, it discusses drawbacks in current solutions and their limitations in those methods. The next chapter talks about bidirectional same sense circularly polarized antennas. The effort in this chapter is to present a method, besides those currently presented in literature, to achieve bidirectional antennas which radiate same sense of polarization on the two beams. A multilayer FSS is proposed to change the sense of the polarization by changing the phase of the wave passing through the structure. Then the FSS is combined with the antenna. Axial ratio of better than 3dB is achieved on both sides at the GPS L1 frequency band (f=1.575GHz). The next chapter is on improving one of the major issues in GPS antennas. Contemporary GPS antennas suffer from high axial ratio at angles close to 90o from the broadside direction. While there are some antennas available currently, they are either bulky or large in profile. It will be shown that, besides the presumed source of problem in previous works, another intrinsic factor in the radiation equations is also predominantly playing role in the corruption of axial ratio at those angles. Again, the approach presented for the aforementioned problem is based on FSS structures. The FSS will be appropriately designed for different angles to change the amplitude of the transmitted wave through the FSS and then is placed on the antenna. As will be shown, axial ratio is improved to the desired value with the low profile and low cost structure. As the results of this chapter shows, axial ratio of better than 2dB is achieved at angles up to 100o in all of the planes of the radiation pattern. Although the approach is to address one of the problems in the GPS antennas, the methodology seems pretty promising in many other applications where the radiation pattern of the antenna needs to be altered for different angles.

Download or read book Circularly Polarized Antenna Technology written by and published by Walter de Gruyter GmbH & Co KG. This book was released on 2020-11-23 with total page 494 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book presents basic and advanced concepts of circularly polarized antennas, including design procedure and recent applications. Cross dipole antennas, microstrip antennas, helical antennas, quadrifilar helix antennas, frequency independent antennas, horn antennas, omnidirectional circularly polarized antennas and radial line arry antennas are discussed. With abundant examples, the book is an essential reference for researchers and engineers.

Download or read book Near field Phase Transformation for Radiation Performance Enhancement and Beam Steering of Resonant Cavity Antennas written by Muhammad Usman Afzal and published by . This book was released on 2016 with total page 201 pages. Available in PDF, EPUB and Kindle. Book excerpt: Resonant-cavity antennas (RCAs) are promising candidates in advanced wireless applications because of their moderate-to-high gain, simple configuration, low and planar profile, and lack of feed networks. This dissertation presents novel mechanisms to enhance directivity and other radiation characteristics and to steer beam of RCAs. Solutions to both challenges are based on near-field phase transformation and have been demonstrated by designing metasurfaces for this transformation. A classical RCA comprising of a patch antenna and an unprinted all-dielectric superstructure is considered as the base antenna to assess the effectiveness of the proposed solutions. To enhance directive radiation characteristics, a near-field phase transformation methodology is developed to improve the uniformity of electric near-field phase distribution. This is realized by designing several phase-correcting structures/ surfaces (PCSs). This novel method employs electromagnetic (EM) simulators to accurately obtain a non-uniform phase distribution on the aperture of RCAs. Two different types of PCSs prototypes were developed. The first proof-of-concept prototype is an all-dielectric varying-height PCS with a stepped geometry, which corrects the phase at discrete points on the RCA aperture. Simulation and measurement results of the classical RCA with the PCS indicate that the PCS increases the peak directivity of the RCA by 9 dB (from 12.5 dBi to 21.2 dBi) and enhances its uniform aperture area by 178%. As an extension to this, a quasi-analytical approach is developed and is utilised to synthesise a continuous PCS for a circularly polarized ( CP) RCA. The performance of the continuous PCS is evaluated through numerical simulations, and predicted results indicate that the improvement in radiation performance is comparable to what was achieved with the former dielectric PCS. The second PCS prototype was a compact, lightweight design, which was implemented using printed phase-shifting elements. The planar PCS prototype is 57% lighter and is only 9% of the maximum height of the all-dielectric PCS prototype. The RCA with the planar PCS has the peak directivity of 20.5 dBi, which is 8 dB higher than that of without PCS. To address beam steering, a mechanism based on the rotation of a sawtooth time-delay (STD) metasurface pair is presented. The metasurface pair is physically located on the aperture of the RCA, in the near-field region for the purpose of phase transformation. Each metasurface was designed to create a STD in the propagating electric field so that the beam is tilted by an angle of 20°. The metasurface pair is rotated concurrently and independently, to move the beam to any direction in a conical region with a 92° vertex angle. As a technical demonstration, only a few angular positions were tested, however, the system is capable of scanning the whole angular space. The peak realized gain of 19.4 dBi was achieved in the broadside direction and the gain was 17.5 dBi when the beam was moved to the farthest elevation angle of 46°. The conspicuous attributes of the proposed beam-steering system are its extremely low-profile, which is 34.6 mm or 1.3;.\0, its passive nature, and its ability to maintain planar geometry during scanning. The proposed solution of near-field phase transformation successfully demonstrates radiation performance enhancements and beam steering of RCAs. Although the methodology was demonstrate for RCAs, this approach is applicable to other planar antennas and arrays.

Download or read book Analysis and Design of Reflectarray Antennas for Bandwidth Enhancement Feed Matching and Portability written by Muhammad Mustafa Tahseen and published by . This book was released on 2017 with total page 222 pages. Available in PDF, EPUB and Kindle. Book excerpt: Reflectarray (RA) antennas are introduced as an alternative to the conventional parabolic reflectors and antenna arrays. The RA provides the advantages of both reflectors and arrays. The narrow bandwidth is one of the distinct disadvantages of RA. The RA bandwidth is primarily limited by two factors, the element bandwidth, and the spatial phase delay. As the RA size is fixed with a proper focal distance, the second factor is hard to be used in the RA bandwidth optimization. It is impossible to design a broadband RA using narrowband elements, so wideband elements are developed in a unit cell of a periodic structure to further provide wider overall antenna bandwidth. In the literature review, 10-15 % RA bandwidth has been observed, which is mainly because of the used narrowband elements.Several RA antennas operating in the Ka-Band are designed and fabricated to learn an understanding of the RA with wideband characteristics. New wideband elements for linear polarization (LP) and circular polarization (CP) are utilized. A bandwidth of 22 % in LP-RA antennas is achieved using the proposed wideband elements. Over 50 % gain, and 50 % axial ratio bandwidth, and 57-62 % maximum aperture efficiency are experimentally measured for the CP. The effect of the edge diffraction on the phase correction is also investigated. The initial study showed little effect, but the considered RA size is small to highlight this effect. The matching of the feed is deteriorated when placed in front of the reflector. Therefore, few methods are implemented to improve the antenna reflection coefficients. The experimental results show possible improvements.The proposed work is categorized into three Parts. Part A provides a comprehensive study of the wideband element designs for both LP- and CP-RA. Part B utilizes the wideband elements developed in Part A, in the RA environment and introduces the performance of the antenna. In part C, textile-reflectarray (TRA) is proposed using conductive thread and shielded fabric, which is the first to be considered as a new trend in the field of RA. The element analysis and measurements show promising results. However, when implemented in the RA, the shielded fabric does not perform as expected. This problem is resolved by introducing a dual-sided embroidered reflectarray antenna where a flexible frequency selective surface (FSS) embroidered at the textile material using a conductive thread is used at the back side of the radiating elements replacing the ground plane. The measured results of the first ever built flexible, portable textile-RA show good antenna performance. An FSS based flexible portable and rollable circularly polarized TRA design is also presented using the wideband cross Bowtie elements. The radiating elements are embroidered using conductive thread.The initial results exhibit good performance of the proposed CP TRA antenna. For RA with small f/D, the spatial delay problem is the main reason for limiting the bandwidth even with wideband RA elements. This issue is solved by introducing a new split aperture into panels that reduce the difference in the path length between the center and those away towards the RA edge. This method shows a significant improvement in the RA bandwidth.

Download or read book Japanese Science and Technology 1983 1984 written by United States. National Aeronautics and Space Administration. Scientific and Technical Information Branch and published by . This book was released on 1985 with total page 1080 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Radiation and Polarization Diversities of Compact Archimedean Spiral Antennas written by Ali Momen Mehrabani and published by . This book was released on 2014 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this thesis, four-arm Archimedean spiral antennas are investigated, which are low profile and have compact structure. The operating frequency bands can be designed for any microwave and millimeter frequency ranges and the antenna may be utilized in any desired applications such as Global Positioning Systems, radars, navigation systems, modern satellite communications, adaptive nulling, beam shaping, and direction finding. The concept of cavity backed absorber-filled structure along with a small ground plane embedded inside, as an inexpensive and wideband balun, is employed to reduce the axial size of the antenna. The antenna can generate broadside and boresight-null radiation patterns at the dominant and higher order modes, respectively. The study demonstrates that the proposed compact structure successfully supports the excitation of higher order modes. Polarization diversity of spiral antennas is mathematically described for an N-arm spiral antenna along with the required feeding networks. Realization of circularly-polarized broadside radiation patterns, with both senses of polarization, is then elaborated for a center-fed low-profile four-arm Archimedean spiral antenna. The radiation active zones, for generating both right- and left-handed circular polarization waves, are determined and the antenna performance in a frequency band, shared by both senses of polarization, is investigated. The developed antennas can be utilized in frequency reuse applications to enhance the wireless channel capacity and as primary feeds in high gain reflector antennas. Their performance in small front-fed parabolic reflector antennas is numerically investigated. It is shown that excellent circular polarization performance, with a remarkable radiation pattern symmetry and axial ratios below 0.5dB, low cross polarization components, and reflector total efficiencies, as high as 77.8% can be attained. Moreover, backward radiation properties of center-fed four-arm Archimedean spiral antennas are also explored, and their possible applications in reflector antennas are presented. Finally, the proposed dual-polarized spiral antennas are further investigated by dielectric loading, for size reduction purposes and frequency tuning applications. Both full and partial dielectric loadings are considered and investigated for the spiral antenna performance. A grooved dielectric substrate is also utilized to enable generating low-contrast dielectric permittivities. The spiral antenna performance, etched on such a grooved substrate, is similarly investigated.

Download or read book Electrical Electronics Abstracts written by and published by . This book was released on 1997 with total page 1904 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Frequency Selective Surface and Grid Array written by T. K. Wu and published by Wiley-Interscience. This book was released on 1995-07-31 with total page 364 pages. Available in PDF, EPUB and Kindle. Book excerpt: This new addition to the prestigious Wiley Series in Microwave and Optical Engineering presents the first comprehensive coverage of Frequency Selective Surfaces (FSS) and active grid arrays, the two-dimensional periodically arranged array elements which may be etched on, or imbedded in, one or multiple layers of dielectric laminates. Because of its filtering frequency properties, this technology, which has attracted much interest over the past two decades, is being used to create filtering devices in microwave and higher frequency bands. With Frequency Selective Surface and Grid Array, it is no longer necessary to sift through a multitude of research papers and reports. Here, in one self-contained volume, is a thorough and up-to-date treatment of the concept, theory, applications, design, and fabrication techniques for periodic arrays. Furthermore, the book provides a complete reference for the technological advances in FSS, including the recent technology of active grid arrays. The first part of the book is devoted to the fundamentals and analytical techniques pertaining to FSS and grid arrays, including the advanced analyses of the conjugate gradient method and the generalized mode-matching technique with multiple dielectrics or nonsimilar grid arrays. In the second part, the book deals with implementation and application, describing the numerous applications of this technology, from the reflector antenna system used in satellite and spacecraft communications and bandpass radome to solar energy grids. The expert contributions to this volume make it useful both as a tutorial and as a reference for project and system/design engineers working with antennas, optics, millimeter waves, microwaves, radar, and low observable radomes. A comprehensive and self-contained reference for FSS and grid array technology Frequency Selective Surfaces (FSS), the two-dimensional periodic array elements with frequency filtering properties, have made important advances over the past two decades. They provide filtering devices in microwave and higher frequency bands with applications ranging from bandpass radome to solar energy grids—including satellite and spacecraft communications. Written by experts in the field and edited by Dr. T. K. Wu, an internationally recognized researcher in electromagnetics, Frequency Selective Surface and Grid Array provides the first comprehensive look at the theory, measurements, manufacturing, and applications of FSS and grid array technology. This publication brings together a wealth of information previously not available in book form, as well as material that has not been published anywhere, including: Passive and active grid design concepts and analysis, as well as FSS materials and fabrication techniques Practical design of frequency selective surface, high-performance bandpass radome, and active grid array Detailed equations for the reaction integrals Three computer codes to get readers started in the design of FSS and grid array (disk included) Case studies of FSS applications to multiband communication antenna systems Tables, figures, references, and numerous examples of practical FSS and grid array designs A tutorial analysis that includes the multilayer grid and dielectrics Frequency Selective Surface and Grid Array is an invaluable planning and design resource for research engineers and scientists dealing with FSS and grid array, as well as a handy reference for students and professionals entering the field.

Download or read book Improvement of Performance Characteristics of a Class of Broadband Circularly Polarized Antennas written by ANTENNA CORP OF AMERICA HARLEYSVILLE PA. and published by . This book was released on 1972 with total page 128 pages. Available in PDF, EPUB and Kindle. Book excerpt: The report covers a development program for the improvement of performance characteristics of a class of broadband circularly polarized antennas for use with tactical airborne jamming equipment. A historical record of the program, testing procedures, significant results, conclusions, and recommendations are covered. (Author).

Download or read book Application of Frequency Selective Surfaces in Circular Polarization Antenna Technologies written by Robert Mervyn Orr and published by . This book was released on 2014 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1992 with total page 332 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book International Aerospace Abstracts written by and published by . This book was released on 1996 with total page 944 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Characteristic Modes written by Yikai Chen and published by John Wiley & Sons. This book was released on 2015-06-15 with total page 291 pages. Available in PDF, EPUB and Kindle. Book excerpt: Describes how to systematically implement various characteristic mode (CM) theories into designs of practical antenna systems This book examines both theoretical developments of characteristic modes (CMs) and practical developments of CM-based methodologies for a variety of critical antenna designs. The book is divided into six chapters. Chapter 1 provides an introduction and discusses the recent advances of the CM theory and its applications in antenna engineering. Chapter 2 describes the formulation of the characteristic mode theory for perfectly electrically conducting (PEC) bodies and discusses its numerical implementations. Chapter 3 presents the CM theory for PEC structures embedded in multilayered medium and its applications. Chapter 4 covers recent advances in CM theory for dielectric bodies and also their applications. Chapter 5 discusses the CM theory for N-port networks and its applications to the design of antenna arrays. Finally, Chapter 6 discusses the design of platform-integrated antenna systems using characteristic modes. This book features the following: Introduces characteristic mode theories for various electromagnetic structures including PEC bodies, structures in multilayered medium, dielectric bodies, and N-port networks Examines CM applications in electrically small antennas, microstrip patch antennas, dielectric resonator antennas, multiport antennas, antenna arrays, and platform mounted antenna systems Discusses numerical algorithms for the implementation of the characteristic mode theories in computer code Characteristic Modes: Theory and Applications in Antenna Engineering will help antenna researchers, engineers, and students find new solutions for their antenna design challenges.

Download or read book The Engineering Index Annual written by and published by . This book was released on 1992 with total page 2264 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since its creation in 1884, Engineering Index has covered virtually every major engineering innovation from around the world. It serves as the historical record of virtually every major engineering innovation of the 20th century. Recent content is a vital resource for current awareness, new production information, technological forecasting and competitive intelligence. The world?s most comprehensive interdisciplinary engineering database, Engineering Index contains over 10.7 million records. Each year, over 500,000 new abstracts are added from over 5,000 scholarly journals, trade magazines, and conference proceedings. Coverage spans over 175 engineering disciplines from over 80 countries. Updated weekly.

Download or read book Frequency Selective Surfaces written by Ben A. Munk and published by John Wiley & Sons. This book was released on 2005-03-11 with total page 442 pages. Available in PDF, EPUB and Kindle. Book excerpt: "...Ben has been the world-wide guru of this technology, providing support to applications of all types. His genius lies in handling the extremely complex mathematics, while at the same time seeing the practical matters involved in applying the results. As this book clearly shows, Ben is able to relate to novices interested in using frequency selective surfaces and to explain technical details in an understandable way, liberally spiced with his special brand of humor... Ben Munk has written a book that represents the epitome of practical understanding of Frequency Selective Surfaces. He deserves all honors that might befall him for this achievement." -William F. Bahret. Mr. W. Bahret was with the United States Air Force but is now retired. From the early 50s he sponsored numerous projects concerning Radar Cross Section of airborne platforms in particular antennas and absorbers. Under his leadership grew many of the concepts used extensively today, as for example the metallic radome. In fact, he is by many considered to be the father of stealth technology. "This book compiles under one cover most of Munk's research over the past three decades. It is woven with the physical insight that he has gained and further developed as his career has grown. Ben uses mathematics to whatever extent is needed, and only as needed. This material is written so that it should be useful to engineers with a background in electromagnetics. I strongly recommend this book to any engineer with any interest in phased arrays and/or frequency selective surfaces. The physical insight that may be gained from this book will enhance their ability to treat additional array problems of their own." -Leon Peters, Jr. Professor Leon Peters, Jr., was a professor at the Ohio State University but is now retired. From the early sixties he worked on, among many other things, RCS problems involving antennas and absorbers. This book presents the complete derivation of the Periodic Method of Moments, which enables the reader to calculate quickly and efficiently the transmission and reflection properties of multi-layered Frequency Selective Surfaces comprised of either wire and/or slot elements of arbitrary shape and located in a stratified medium. However, it also gives the reader the tools to analyze multi-layered FSS's leading to specific designs of the very important Hybrid Radome, which is characterized by constant band width with angle of incidence and polarization. Further, it investigates in great detail bandstop filters with large as well as narrow bandwidth (dichroic surfaces). It also discusses for the first time, lossy elements used in producing Circuit Analog absorbers. Finally, the last chapter deals with power breakdown of FSS's when exposed to pulsed signals with high peak power. The approach followed by most other presentations simply consists of expanding the fields around the FSS, matching the boundary conditions and writing a computer program. While this enables the user to obtain calculated results, it gives very little physical insight and no help in how to design actual multi-layered FSS's. In contrast, the approach used in this title analyzes all curves of desired shapes. In particular, it discusses in great detail how to produce radomes made of FSS's located in a stratified medium (Hybrid Radomes), with constant band width for all angles of incidence and polarizations. Numerous examples are given of great practical interest. More specifically, Chapter 7 deals with the theory and design of bandpass radomes with constant bandwidth and flat tops. Examples are given for mono-, bi- and tri-planar designs. Chapter 8 deals with bandstop filters with broad as well as narrow bandwidth. Chapter 9 deals with multi-layered FSS of lossy elements, namely the so-called Circuit Analog Absorbers, designed to yield outstanding absorption with more than a decade of bandwidth. Features material previously labeled as classified by the United States Air Force.