Impedance Transformers

Non

Integrated Filtering Antennas for Wireless Communications

In traditional radio frequency (RF) front-end subsystems, the passive components, such as antennas, filters, power dividers and duplexers, are separately designed and cascaded via the 50 ? interfaces. This traditional approach results in a bulky and heavy RF front-end subsystem, and suffers from compromised efficiency due to the losses in the interconnections and the mismatching problems between different components. The frequency responses of the antennas such as the frequency selectivity and bandwidth are usually degraded, especially for microstrip antennas. To improve the frequency responses and reduce the size of RF front ends, it is important to investigate novel highly integrated antennas which exhibit multiple functions such as radiation, filtering, power dividing and combining or duplexing, simultaneously. In this thesis, several innovative designs of compact, multi-functional integrated an-tennas/arrays are proposed for wireless communication applications. First, new methods of designing integrated filtering antenna elements with broadband or dual-band performance are investigated. These antennas also feature high frequency selectivity and wideband harmonic suppression. Based on these studies, several integrated filtering array antennas with improved gains and frequency responses are developed for the first time. Compared with traditional array antennas, these proposed antennas exhibit improved bandwidths, out-of-band rejection and wideband harmonic suppression. The application of the filtering antennas in millimeter-wave (mm-Wave) frequency band is also investigated as it can potentially reduce the cost of the mm-Wave front-end subsystems significantly while providing the improved impedance bandwidth. The integrated design techniques are further developed to design novel dual-port highly integrated antennas with filtering and duplexing functions integrated. Such a new concept and the prototypes could find poten-tial applications in wireless communication systems and intelligent transportation system (ITS). In this thesis, comprehensive design methodologies and synthesis methods are provid-ed to guide the design of the integrated filtering antennas. The performance is evaluated with the help of full-wave electromagnetics (EM) simulations. All of the prototypes are fabricated and tested for validating the design concepts. Good agreement between the simulation and measurement results is achieved, demonstrating the integrated antennas have the advantages of compact size, flat gain performance, low losses and excellent harmonic suppression performance. These researches are important for modern wireless communication systems

Recent Advances in Antenna Design for 5G Heterogeneous Networks

The aim of this book is to highlight up to date exploited technologies and approaches in terms of antenna designs and requirements. In this regard, this book targets a broad range of subjects, including the microstrip antenna and the dipole and printed monopole antenna. The varieties of antenna designs, along with several different approaches to improve their overall performance, have given this book a great value, in which makes this book is deemed as a good reference for practicing engineers and under/postgraduate students working in this field. The key technology trends in antenna design as part of the mobile communication evolution have mainly focused on multiband, wideband, and MIMO antennas, and all have been clearly presented, studied and implemented within this book. The forthcoming 5G systems consider a truly mobile multimedia platform that constitutes a converged networking arena that not only includes legacy heterogeneous mobile networks but advanced radio interfaces and the possibility to operate at mm wave frequencies to capitalize on the large swathes of available bandwidth. This provides the impetus for a new breed of antenna design that, in principle, should be multimode in nature, energy efficient, and, above all, able to operate at the mm wave band, placing new design drivers on the antenna design. Thus, this book proposes to investigate advanced 5G antennas for heterogeneous applications that can operate in the range of 5G spectrums and to meet the essential requirements of 5G systems such as low latency, large bandwidth, and high gains and efficiencies

Design and analysis of wideband passive microwave devices using planar structures

A selected volume of work consisting of 84 published journal papers is presented to demonstrate the contributions made by the author in the last seven years of his work at the University of Queensland in the area of Microwave Engineering. The over-arching theme in the author’s works included in this volume is the engineering of novel passive microwave devices that are key components in the building of any microwave system. The author’s contribution covers innovative designs, design methods and analyses for the following key devices and associated systems: Wideband antennas and associated systems Band-notched and multiband antennas Directional couplers and associated systems Power dividers and associated systems Microwave filters Phase shifters Much of the motivation for the work arose from the desire to contribute to the engineering o

Ultrawideband and Multi-state Reconfigurable Antennas with Sum and Difference Radiation Patterns

Pattern diversity is a term used to describe the operation of several antenna elements working together to produce multiple different radiation patterns with the aim of improving the quality and reliability of a communications system. One useful implementation of pattern diversity considers sum and difference radiation patterns which can be exploited to extend high-gain space coverage and tackle multipath fading. The conventional forms of such pattern diversity antennas are generally working at a single or multiple narrowband frequencies and are designed for specific applications. Hence, generating sum and difference pattern diversity in wide range of frequencies requires the development of new pattern diversity antenna designs. Ultrawideband and frequency reconfigurable designs of pattern diversity antennas are desirable to help reduce the cost and increase the flexibility in applications of pattern diversity antennas. These two types of performances constitute the principal parts of this thesis. The first part of this thesis deals with the challenges of designing ultrawideband Vivaldi antennas with sum and difference radiation patterns. When two Vivaldi antennas are placed next to each other, two mutually exclusive phenomena of grating lobe generation at the highest end of frequency and mutual coupling at the lowest end of frequency will define the bandwidth. Hence, to enhance the bandwidth, the separation between the antenna elements is reduced, which delays the grating lobes generation, and the coupling at lower frequencies is mitigated by introducing an asymmetry in the design of each Vivaldi antenna element. It is shown that this method can be extended to multi-element Vivaldi antennas for higher gain. Next, the bandwidth is further enhanced by adding two vertical metal slabs between the antenna elements improving the isolation at lower frequencies. The proposed antennas use commercially available couplers as feeding networks. As a potential replacement for couplers, an out-of-phase power divider with unequal power division is also proposed. In the second part of this thesis, the pattern diversity function is combined with multistate frequency-reconfigurable filtering functions in a series of novel designs. In the first proposed design, two quasi-Yagi-Uda antennas are used for pattern diversity, while two switchable and reconfigurable bandpass-to-bandstop filters are used to excite the antenna elements. The whole system is excited by an external commercially available rat-race coupler. In a next step, this design is modified to attain wideband, tunable bandpass, and tunable bandstop operations while obviating the need for an external coupler by using three antenna elements excited by a switchable power divider. In another implementation, the filtering functions is extended to dual-band independently tunable bandpass and bandstop to excite wideband antennas. While all the former designs featured E-plane pattern diversity, in another design aiming at increasing space coverage, a switchable patch antennas with sum and difference radiation patterns in both E- and H-plane of the antenna is designed.Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 202

HIGH-PERFORMANCE PERIODIC ANTENNAS WITH HIGH ASPECT RATIO VERTICAL FEATURES AND LARGE INTERCELL CAPACITANCES FOR MICROWAVE APPLICATIONS

Modern communications systems are evolving rapidly to address the demand for data exchange, a fact which imposes stringent requirements on the design process of their RF and antenna front-ends. The most crucial pressure on the antenna front-end is the need for miniaturized design solutions while maintaining the desired radiation performance. To satisfy this need, this thesis presents innovative types of periodic antennas, including electromagnetic bandgap (EBG) antennas, which are distinguished in two respects. First, the periodic cells contain thick metal traces, contrary to the conventional thin-trace cells. Second, such thick traces contain very narrow gaps with very tall sidewalls, referred to as high aspect ratio (HAR) gaps. When such cells are used in the structure of the proposed periodic antennas, the high capacitance of HAR gaps decreases the resonance frequency, mitigates conduction loss, and thus, yields considerably small high efficiency antennas. For instance, one of the sample antenna designs with only two EBG cells offers a very small XYZ volume of 0.25λ×0.28λ×0.037λ with efficiency of 83%. Also, a circularly polarized HAR EBG antenna is presented which has a footprint as small as 0.26λ×0.29λ and efficiency as high as 94%. The main analysis method developed in this thesis is a combination of numerical and mathematical analyses and is referred to as HFSS/Bloch method. The numerical part of this method is conducted using a High Frequency Structure Simulator (HFSS), and the mathematical part is based on the classic Bloch theory. The HFSS/Bloch method acts as the mainstay of the thesis and all designs are built upon the insight provided by this method. A circuit model using transmission line (TL) theory is also developed for some of the unit cells and antennas. The HFSS/Bloch perspective results in a HAR EBG TL with radiation properties, a fragment of which (2 to 6 cells) is introduced as a novel antenna, the self-excited EBG resonator antenna (SE-EBG-RA). Open (OC) and short circuited (SC) versions of this antenna are studied and the inherently smaller size of the SC version is demonstrated. Moreover, the possibility of employing the SE-EBG-RA as the element of a series-fed array structure is investigated and some sample high-efficiency, flat array antennas are rendered. A microstrip antenna is also developed, the structure of which is composed of 3×3 unit cells and shows fast-wave behaviors. Most antenna designs are resonant in nature; however, in one case, a low-profile efficient leaky-wave antenna with scanning radiation pattern is proposed. Several antenna prototypes are fabricated and tested to validate the analyses and designs. As the structures are based on tall metal traces, two relevant fabrication methods are considered, including CNC machining and deep X-ray lithography (DXRL). Hands-on experiments provide an outlook of possible future DXRL fabricated SE-EBG-RAs

Radar Technology

In this book “Radar Technology”, the chapters are divided into four main topic areas: Topic area 1: “Radar Systems” consists of chapters which treat whole radar systems, environment and target functional chain. Topic area 2: “Radar Applications” shows various applications of radar systems, including meteorological radars, ground penetrating radars and glaciology. Topic area 3: “Radar Functional Chain and Signal Processing” describes several aspects of the radar signal processing. From parameter extraction, target detection over tracking and classification technologies. Topic area 4: “Radar Subsystems and Components” consists of design technology of radar subsystem components like antenna design or waveform design

30 GHz Broadband Bow-tie Printed Ridge Gap Waveguide Antennas

The development of wireless and satellite communication systems has led to high demand for microwave and millimeter wave application components, which play an essential role in the upcoming 5G communication. The coverage area of such systems is control by transmitted power as well as the antenna gain of the system. Hence, it is essential to design a high gain antenna that can mitigate the losses and extend the system coverage area. Higher frequencies lead to smaller sizes of RF components including antennas. However, the implementation of passive components and guiding structure becomes difficult based on traditional guiding structures such as microstrip lines, and waveguides at millimeter wave bands. Microstrip line suffers from cavity modes, which leads to surface waves and has more losses at higher frequencies. The rectangular waveguide has high power handling capability, low losses, and high Q-factors which makes it very attractive for high-frequency applications. On the other hand, at high frequencies, the wavelengths become challenging to construct with current machining techniques as ensuring good electrical contact become very challenging. In this thesis, planar high gain antennas are designed based on Printed Ridge Gap Waveguide (PRGW). The primary objective of this work is to develop high gain, wideband antennas that can support the future demand for high data transmission. Therefore, a detailed analysis for PRGW has been introduced as well as featured designs of the high gain antenna. This antenna array can perform for future 5G communication purpose, and it fulfills all the requirements of mm-wave bands. In this work, a groove-based wideband bow-tie slot antenna array is designed at 30 GHz based on printed ridge gap waveguide technology (PRGW). A two-section T-shaped ridge is designed to feed a bow tie slot placed on the upper ground of PRGW. The gain of the proposed slot antenna is enhanced by using a horn-like groove. Then, the proposed high gain element is deployed to build up a 1 x 4 bow-tie slot antenna array loaded with three-layer groove antenna. The proposed antenna array is fabricated and measured, where the measured results show a -10 dB impedance bandwidth from 29.5 to 37 GHz (22%). The fabricated prototype achieves a high gain of 15.5 dBi and a radiation efficiency higher than 80% over the operating frequency bandwidth. Besides, to reduce the edge diffraction in the E-plane, an artificial corrugation ring is deployed with a certain depth so that it can improve the overall antenna performance

Antennas and Propagation

This Special Issue gathers topics of utmost interest in the field of antennas and propagation, such as: new directions and challenges in antenna design and propagation; innovative antenna technologies for space applications; metamaterial, metasurface and other periodic structures; antennas for 5G; electromagnetic field measurements and remote sensing applications