Reconfigurable Antennas for UWB Cognitive Radio Communication Applications

In this chapter, reconfigurable antennas are reviewed for ultra-wideband (UWB) cognitive radio communication applications. The defected microstrip structure (DMS) has been reviewed and integrated into the UWB antennas to form the desired filtering antennas which can filter out unexpected narrowband signal interferences. Then, switches are incorporated into the filtering UWB antennas to construct the cognitive radio UWB (CR-UWB) antenna to make the antenna switch between the UWB antenna and band-notched UWB antenna. In these CR-UWB antennas, the DMSs are to give the desired notches while the switches are used for realizing the switchable characteristics. Several reconfigurable antennas and CR-UWB antennas are created and investigated. The results show that the designed CR-UWB antenna can switch between different modes, making it amazing for UWB, band-notched UWB, and multiband communication system applications

A novel compact fractal UWB antenna with triple reconfigurable notch reject bands applications

A compact, circular UWB fractal antenna with triple reconfigurable notch rejection bands is proposed. It rejects the crowded frequency bands WiMAX, WLAN and X band interferences produced in UWB communication systems. The proposed fractal structure consists of a basic circular patch with circular fractal iterations. By employing this new structure of fractals, the overall size of antenna is reduced 53% to 21 × 25 mm, in comparison with traditional circular monopole antenna. The implemented antenna operates at 3.1–10 GHz. Re-configurability is realized by designing slots and split ring resonators in desired frequencies with the attached PIN diodes. WLAN band rejection was realized by creating a pair of optimized L-shaped slots in the ground plane. By etching a split ring resonator and a U-shaped slot, X and WiMAX bands were also rejected. Furthermore, by attaching diodes to aforementioned slots and designating the diodes on/off, different bands can be included or rejected. In time domain, the antenna properties are evaluated by a figure of merit called fidelity factor. Finally, the antenna properties are measured in anechoic chamber and the results agrees with simulation findings

A Reconfigurable Triple-Notch-Band Antenna Integrated with Defected Microstrip Structure Band-Stop Filter for Ultra-Wideband Cognitive Radio Applications

A printed reconfigurable ultra-wideband (UWB) monopole antenna with triple narrow band-notched characteristics is proposed for cognitive radio applications in this paper. The triple narrow band-notched frequencies are obtained using a defected microstrip structure (DMS) band stop filter (BSF) embedded in the microstrip feed line and an inverted π-shaped slot etched in the rectangular radiation patch, respectively. Reconfigurable characteristics of the proposed cognitive radio antenna (CRA) are achieved by means of four ideal switches integrated on the DMS-BSF and the inverted π-shaped slot. The proposed UWB CRA can work at eight modes by controlling switches ON and OFF. Moreover, impedance bandwidth, design procedures, and radiation patterns are presented for analysis and explanation of this antenna. The designed antenna operates over the frequency band between 3.1 GHz and 14 GHz (bandwidth of 127.5%), with three notched bands from 4.2 GHz to 6.2 GHz (38.5%), 6.6 GHz to 7.0 GHz (6%), and 12.2 GHz to 14 GHz (13.7%). The antenna is successfully simulated, fabricated, and measured. The results show that it has wide impedance bandwidth, multimodes characteristics, stable gain, and omnidirectional radiation patterns

UWB Technology

Ultra Wide Band (UWB) technology has attracted increasing interest and there is a growing demand for UWB for several applications and scenarios. The unlicensed use of the UWB spectrum has been regulated by the Federal Communications Commission (FCC) since the early 2000s. The main concern in designing UWB circuits is to consider the assigned bandwidth and the low power permitted for transmission. This makes UWB circuit design a challenging mission in today's community. Various circuit designs and system implementations are published in this book to give the reader a glimpse of the state-of-the-art examples in this field. The book starts at the circuit level design of major UWB elements such as filters, antennas, and amplifiers; and ends with the complete system implementation using such modules

Antenna Design for 5G and Beyond

With the rapid evolution of the wireless communications, fifth-generation (5G) communication has received much attention from both academia and industry, with many reported efforts and research outputs and significant improvements in different aspects, such as data rate speed and resolution, mobility, latency, etc. In some countries, the commercialization of 5G communication has already started as well as initial research of beyond technologies such as 6G.MIMO technology with multiple antennas is a promising technology to obtain the requirements of 5G/6G communications. It can significantly enhance the system capacity and resist multipath fading, and has become a hot spot in the field of wireless communications. This technology is a key component and probably the most established to truly reach the promised transfer data rates of future communication systems. In MIMO systems, multiple antennas are deployed at both the transmitter and receiver sides. The greater number of antennas can make the system more resistant to intentional jamming and interference. Massive MIMO with an especially high number of antennas can reduce energy consumption by targeting signals to individual users utilizing beamforming.Apart from sub-6 GHz frequency bands, 5G/6G devices are also expected to cover millimeter-wave (mmWave) and terahertz (THz) spectra. However, moving to higher bands will bring new challenges and will certainly require careful consideration of the antenna design for smart devices. Compact antennas arranged as conformal, planar, and linear arrays can be employed at different portions of base stations and user equipment to form phased arrays with high gain and directional radiation beams. The objective of this Special Issue is to cover all aspects of antenna designs used in existing or future wireless communication systems. The aim is to highlight recent advances, current trends, and possible future developments of 5G/6G antennas

Micro-Switch Design and Its Optimization Using Pattern Search Algorithm for Application in Reconfigurable Antenna

This chapter reports the design and optimization algorithm of metal-contact RF microswitch. Various important evolutionary optimization techniques that can be used to optimize non-linear and even non-differentiable types of radio frequency (RF) circuit’s problems are also reviewed. The transient response of the proposed switch shows displacement time (i.e., squeezed-film damping effect) of 5.0 μs and pull-in voltage varying from 9.0 to 9.25 V. Primarily, the switch exhibits insertion loss of 0.15 to 0.51 dB in on-position and isolation of 75.96 to 35.83 dB in off-position at 0.1–10 GHz. Also, the proposed RF switch equivalent circuit and layout are validated in ADS software which was earlier simulated in HFSS. A pattern search (PS) algorithm is used to optimize RF characteristics of the proposed switch after a brief review of the different optimization techniques. After optimization, the switch shows decrement in insertion loss and increment in isolation at 0.1–10 GHz. Further, two such optimized switches are introduced on the defected ground structure (DGS) antenna to make it reconfigurable in terms of frequency. Reconfigurable antenna (RA) is simulated using HFSS software and simulation results are verified by showing the mark of agreement with the fabrication results. The novelty in the proposed design is due to dual-band behavior and better resonance performance than antennas available in the literature. Attractions of proposed RA are its miniaturization and its utility in IEEE US S-(2.0–4.0 GHz) and C-(4.0–8.0 GHz) band

Reconfigurable Microstrip Bandpass Filters, Phase Shifters Using Piezoelectric Transducers, and Beam-scanning Leaky-wave Antennas

In modern wireless communication and radar systems, filters play an important role in getting a high-quality signal while rejecting spurious and neighboring unwanted signals. The filters with reconfigurable features, such as tunable bandwidths or switchable dual bands, also play a key part both in realizing the compact size of the system and in supporting multi-communication services. The Chapters II-IV of this dissertation show the studies of the filters for microwave communication. Bandpass filters realized in ring resonators with stepped impedance stubs are introduced. The effective locations of resonant frequencies and transmission zeros are analyzed, and harmonic suppression by interdigital-coupled feed lines is discussed. To vary mid-upper and mid-lower passband bandwidths separately, the characteristic impedances of the open-circuited stubs are changed. Simultaneous change of each width of the open-circuited stub results in variable passband bandwidths. Asymmetric stepped-impedance resonators are also used to develop independently controllable dual-band (2.4 and 5.2 GHz) bandpass filters. By extending feed lines, a transmission zero is created, which results in the suppression of the second resonance of 2.4-GHz resonators. To determine the precise transmission zeros, an external quality factor at feeders is fixed while extracting coupling coefficients between the resonators. Two kinds of feed lines, such as hook-type and spiral-type, are developed, and PIN diodes are controlled to achieve four states of switchable dual-band filters. Beam-scanning features of the antennas are very important in the radar systems. Phase shifters using piezoelectric transducers and dielectric leaky-wave antennas using metal strips are studied in the Chapters V-VII of this dissertation. Meandered microstrip lines are used to reduce the size of the phase shifters working up to 10 GHz, and reflection-type phase shifters using piezoelectric transducers are developed. A dielectric film with metal strips fed by an image line with a high dielectric constant is developed to obtain wide and symmetrical beam-steering angle. In short, many techniques are presented for realizing reconfigurable filters and large beam-scan features in this dissertation. The result of this work should have many applications in various wireless communication and radar systems

Antenna Design for 5G and Beyond

This book is a reprint of the Special Issue Antenna Design for 5G and Beyond that was published in Sensors

Harmonic Suppressed Reconfigurable Dual-band, Multi-mode Ultra-wideband, and Compact High Selective Microstrip Bandpass Filters

As an indispensable component, microwave bandpass filters play a very important role in many modern wireless systems. They are used to carry out the selection of only the wanted frequencies from RF signals with various spurious frequencies. The reconfigurable filter with multi-band has attracted much attention for both research and industry because of the increasing importance in making RF components that have multi-function with compact size. Wide or Ultra-wideband (UWB) bandpass filters are becoming more and more in demand in many wireless applications due to the high data transmission rate. This dissertation focuses on the study of microwave filters with many applications in various wireless systems. Firstly, bandpass filters using stepped impedance stubs are presented. The resonant frequencies and transmission zeros are analyzed, and harmonic suppression by novel S-shaped coupled feed lines is presented. A resonator with a dual-band characteristic is introduced, and it is analytically shown that each passband can be independently controlled by the parameters of the resonator. PIN diodes are used to introduce an electrically controlled dual-band bandpass filter. Secondly, symmetric stepped impedance resonators with asymmetric stepped impedance stubs are also presented to develop Ultra-wide band (UWB) bandpass filters with and without a notched band. The resonant frequencies and transmission zeros of the resonator are effectively located to achieve a very wide passband and a high attenuation rate in rejection bands. The interdigital coupled feed lines with rectangular slots are designed for a better passband characteristic. A notched characteristic is introduced by using modified feed lines to avoid the interferences with other existing signals. UWB bandpass filter performances in time-domain and frequency-domain are analyzed and discussed. Thirdly, UWB bandpass filters with a different configuration are developed. Similarly, the analyzed resonant frequencies are used to achieve a passband for UWB applications. A different technique is used to introduce a very narrow notched band within the passband. Time-domain analysis is made to verify the frequency-domain performance. Lastly, a very high selective wideband bandpass filter is presented using an inverted T-shaped resonator. The characteristic of the resonator is analyzed to design a bandpass filter with specified bandwidth. The short stubs are introduced to achieve a very high attenuation rate at both sides of the passband and a wide stopband characteristic. In summary, various microwave filters to meet the requirements of specific applications are studied and designed. Analysis and design methodology of the proposed microwave filters in this dissertation can be applied in many applications in wireless systems

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