Development of turnable and miniature microwave filters for modern wireless communication

Due to the increasing demand for new wireless services and applications, the high level of integration and the coexistence of multi-standard (MS) or multi-band operations into a single device are becoming defining trends in designing microwave filters. This has driven considerable technological advances in reconfigurable/tunable and miniaturized filters. More specifically, reconfigurable/tunable filters that tune to different frequency bands instead of classical filter banks have great potential to significantly reduce the system size and complexity; while reducing the filter size becomes essential to achieve the highest degree of integration density in compact and portable wireless devices. In the light of this scenario, the objective of this dissertation is to develop the new design technologies, concepts and filtering configurations for tunable microstrip filters and compact passive microwave filters. To this aim, this dissertation is divided into two main parts. The first part (Part I) focuses on the designs of novel varactor-tuned microstrip filters with advanced performances. In this aspect, new topologies for realizing tunable lowpass and highpass filters are firstly developed. State-of-the-art performances, including wide tuning range, high selectivity with multiple transmission zeros, low insertion loss and compact size for all the tuning states are obtained in both of these filters. Secondly, two novel classes of tunable bandpass filters are presented. One of them is designed based on varactor-loaded parallel-coupled microstrip lines (PCML) and short-circuited stubs, which allows the lower passband edge together with two transmission zeros located around the lower passband skirt to be reconfigured separately. While the other tunable bandpass filter is iii constructed by the combination of tunable bandpass and lowpass filters, featuring both centre frequency and bandwidth tunabilities, as well as high selectivity with abundant transmission zeros. Furthermore, a new concept of tunable lossy filter is demonstrated, which attempts to achieve an equivalent high-Q tunable performance by using low-Q resonators. This concept makes the presented tunable combline filter interesting for some frequency-agile applications in which the low in-band loss variation and high selectivity are much desired while the absolute insertion loss can be a tradeoff. The second part (Part II) is devoted to the design of miniaturized passive microwave filters with improved characteristics. For this, the concept of artificial right-handed and left-handed transmission lines are applied to the signal interference filtering topology, which results in a compact circuit size and good out-of-band performance. In particular, for a further size reduction, such filter is implemented in the forms of multilayered structure by using liquid crystal polymer (LCP) technology. Additionally, another two types of miniaturized bandpass filters using stepped impedance resonators are demonstrated, which are implemented based on different fabrication processes (i.e. LCP bonded multilayer PCB technology and a standard planar PCB technology). Among their main features, the compact size, wide passband, broad stopband with multiple transmission zeros and circuit simplicity are highlighted. For all the proposed design techniques and filtering structures, exhaustive theoretical analyses are done, and design equations and guide rules are provided. Furthermore, all the proposed schemes and/or ideas have been experimentally validated through the design, implementation and measurement of different filters. The fabrication processes of multilayer technology utilized: liquid crystal polymer (LCP) technology and liquid crystal polymer (LCP) bonded multilayer printed circuit board (PCB) technology, are also demonstrated for reference. All of the results achieved in this dissertation make the proposed filters very attractive for their use in modern wireless communication systems.MultiWaves Project (PIRSES-GA-2010-247532) of the Seventh Framework Programme (FP7), European Commission

Development of tunable and miniature microwave filters for modern wireless communications

Due to the increasing demand for new wireless services and applications, the high level of integration and the coexistence of multi-standard (MS) or multi-band operations into a single device are becoming defining trends in designing microwave filters. This has driven considerable technological advances in reconfigurable/tunable and miniaturized filters. More specifically, reconfigurable/tunable filters that tune to different frequency bands instead of classical filter banks have great potential to significantly reduce the system size and complexity; while reducing the filter size becomes essential to achieve the highest degree of integration density in compact and portable wireless devices. In the light of this scenario, the objective of this dissertation is to develop the new design technologies, concepts and filtering configurations for tunable microstrip filters and compact passive microwave filters. To this aim, this dissertation is divided into two main parts. The first part (Part I) focuses on the designs of novel varactor-tuned microstrip filters with advanced performances. In this aspect, new topologies for realizing tunable lowpass and highpass filters are firstly developed. State-of-the-art performances, including wide tuning range, high selectivity with multiple transmission zeros, low insertion loss and compact size for all the tuning states are obtained in both of these filters. Secondly, two novel classes of tunable bandpass filters are presented. One of them is designed based on varactor-loaded parallel-coupled microstrip lines (PCML) and short-circuited stubs, which allows the lower passband edge together with two transmission zeros located around the lower passband skirt to be reconfigured separately. While the other tunable bandpass filter is constructed by the combination of tunable bandpass and lowpass filters, featuring both centre frequency and bandwidth tunabilities, as well as high selectivity with abundant transmission zeros. Furthermore, a new concept of tunable lossy filter is demonstrated, which attempts to achieve an equivalent high-Q tunable performance by using low-Q resonators. This concept makes the presented tunable combline filter interesting for some frequency-agile applications in which the low in-band loss variation and high selectivity are much desired while the absolute insertion loss can be a tradeoff. The second part (Part II) is devoted to the design of miniaturized passive microwave filters with improved characteristics. For this, the concept of artificial right-handed and left-handed transmission lines are applied to the signal interference filtering topology, which results in a compact circuit size and good out-of-band performance. In particular, for a further size reduction, such filter is implemented in the forms of multilayered structure by using liquid crystal polymer (LCP) technology. Additionally, another two types of miniaturized bandpass filters using stepped impedance resonators are demonstrated, which are implemented based on different fabrication processes (i.e. LCP bonded multilayer PCB technology and a standard planar PCB technology). Among their main features, the compact size, wide passband, broad stopband with multiple transmission zeros and circuit simplicity are highlighted. For all the proposed design techniques and filtering structures, exhaustive theoretical analyses are done, and design equations and guide rules are provided. Furthermore, all the proposed schemes and/or ideas have been experimentally validated through the design, implementation and measurement of different filters. The fabrication processes of multilayer technology utilized: liquid crystal polymer (LCP) technology and liquid crystal polymer (LCP) bonded multilayer printed circuit board (PCB) technology, are also demonstrated for reference. All of the results achieved in this dissertation make the proposed filters very attractive for their use in modern wireless communication systems

Advanced microwave miniature and lossy tunable filters for wireless communication applications

Microwave filters play very important roles in many RF/microwave applications, which are employed to separate or combine different frequencies. Emerging applications, such as wireless communications, challenge the design of microwave filters with more functionalities and higher performance, such as reconfigurable or tunable, compact size, light weight and lower cost. In order to meet the increasing challenge requirements, the objective of this dissertation is to develop new multilayer miniaturized filters, compact lossy microstrip filters, and reconfigurable lossy filters. To achieve this, this dissertation is divided into three main parts. The first part focuses on the design of novel miniature bandpass filter with improved performance. In this aspect, a novel microstrip bandpass filter using slow-wave open-loop resonators is presented, which concentrates on the stopband rejection performance to suppress the harmonic standing wave rather than the passband performance by using multilayer LCP technology. The multilayer open-loop slow-wave resonator has not only very compact size, but also exhibits an excellent wider upper stopband resulting from the dispersion property. Based on this type of resonator, a five-pole bandpass filter has been proposed, which has good stopband rejection and high selectivity as well as compact size and light weight. The second part is devoted to the design of compact lossy filters with improved performance characteristics. To achieve this, lossy synthesis and extracted-pole technology are combined together to design microstrip filters with flat passband and high selectivity. Two six-pole filters has been analysed from the theoretical circuit model to EM simulations, fabricated to demonstrate the response performance in narrowband and wideband respectively. The third part concentrates on the designs of novel varactor-tuned microstrip lossy bandpass filters. Firstly, state-of-the-art literature review is given to have a general view of reconfigurable bandpass filter with different tuning centre frequency and bandwidth characteristics. Then, three types of tunable microstrip bandpass filters with resistor loading under symmetric tuning method are presented to introduce additional loss into the passband to make it flat over the entire tuning range. The first filter is designed to control the bandwidth and selectivity. The second one is designed to control the bandwidth at fixed centre frequency, while the third filter is extended from the first one to combine resistor loading and cross coupling. Finally, microstrip tunable bandpass lossy filters with extracted-pole technology are proposed. Three six-pole filters of this type have been analysed and fabricated. Due to the asymmetric tuning method, the number of tuning components and dc bias schemes are increased, which is a kind of tradeoff with performance. For all the presented filters, theoretical analyses, implementations and measurements have been given. All of the results achieved in this thesis make the proposed filters attractive for their applications in modern wireless communication systems

Development of planar filters and diplexers for wireless transceiver front ends

The central theme of this work is the design of compact microstrip bandpass filters and diplexers and the investigation of applications of these circuits in integrated transceiver RF front-end. The core of this thesis therefore presents the following stages of the work: - Analysis of coupled pseudo-interdigital resonators and lines; formulation of approximate transmission zero conditions and the investigation of coupling between these two resonators and related structures. - Development of compact, low loss and high selectivity microstrip pseudointerdigital bandpass filters. The design procedure of the filter consists of three simple steps, starting from the design of a parallel-coupled bandpass filter using the image parameter method applied to coupled microstrip lines. The development of compact microstrip diplexers composed of these filters uses the optimized common-transformer diplexing technique. An experimental verification of the developed filters and diplexers is made. - Investigation of the use of stepped impedance resonators (SIR) for the design of pseudo-interdigital bandpass filters with advanced characteristics. The design of compact dual-band filter using SIR. The investigation of possible improvement of the stopband of bandpass filters using bandstop generating structures. The application of SIR, defected ground structures (DGS), spur-lines, and opencircuited stubs in the design of compact bandpass filters with improved stopband. - The application of the proposed filters and diplexers in the design of integrated antenna filters and antenna diplexers. Improvement of performance of patch antennas, such as suppression of spurious harmonics of single-band antenna and improvement of bandwidth and selectivity of dual-band antenna, as a result of integration with filters. Separation of antennas’ bands and reduction of component count in integrated antenna diplexer

Miniaturised bandpass filters for wireless communications

The wireless industry has seen exceptional development over the past few decades due to years of sustained military and commercial enterprise. While the electromagnetic spectrum is becoming increasingly congested, there is a growing tendency to strive for higher bandwidths, faster throughputs, greater versatility, compatibility and interoperability in current and emerging wireless technologies. Consequently, an increasingly stringent specification is imposed upon the frequency utilization of wireless devices. New challenges are constantly being discovered in the development and realization of RF and microwave filters, which have not only sustained but fuelled microwave filter research over the many years. These developments have encouraged new solutions and techniques for the realization of compact, low loss, highly selective RF and microwave bandpass filters. The theme of this dissertation is the realization of planar compact performance microwave and RF bandpass filters for wireless communication systems. The work may be broadly categorised into three sections as follows. The first section presents a novel compact planar dual-mode resonator with several interesting and attractive features. Generally, planar microwave dual-mode resonators are known to half the filter footprint. However, it is found that the proposed resonator is capable of achieving further size reductions. In addition the resonator inherently possesses a relatively wide stopband as the lowest spurious harmonic resonance is observed at thrice the fundamental frequency. Properties of this resonator, such as these and more are explored in depth to arrive at an accurate electrical equivalent circuit, which is used as the basis for high order filter design. The application of these resonators in the design of bandpass filters is the subject of the second section. A general filter design procedure based on the equivalent circuit is presented to assist the design of all-pole filters. Alternatively, it is shown that generalised Chebyshev filters with enhanced selectivity may be developed with cross coupled resonator topologies. The discussions are supplemented with detailed design examples which are accompanied by theoretical, simulated and experimental results in order to illustrate the filter development process and showcase practical filter performance. The third section explores the possibility of employing these resonators in the development of frequency tunable bandpass filters. Preference is given to varactor diodes as the tuning element due to the numerous qualities of this device in contrast to other schemes. In particular, interest is paid to center frequency tuned filters with constant bandwidth. Tunable filters constructed with the dual-mode resonator are shown to have a relatively wide tuning range as well as significantly higher linearity in comparison to similar published works. In line with the previous section, experimental verification is presented to support and supplement the discussions

Innovative Butler Matrix Concepts Based on Novel Components For 2-D Beamforming

Several innovative concepts and schemes to enrich the features of Butler matrices (BMs) to enhance their suitability over the conventional schemes are discussed, demonstrated, and analyzed. Mobile communication and radar systems require compact and versatile multibeam-forming networks (MBFNs). Therefore, the study is aimed to provide feasible and practical solutions with more flexible beam numbers of BMs, more concise configurations of the two-dimensional (2-D) beamforming, and broadband characteristics while maintaining the intrinsic merits of conventional BMs (such as theoretically lossless, spatially orthogonal beams, and relatively simple structure). In addition, the study implements some of the concepts to millimeter-wave (mm-wave) frequencies applications. Concretely, the effects of some components, such as T-junctions and crossovers, on the bandwidth of parallel-feeding networks and MBFNs, are investigated and analyzed. The corresponding solutions to broaden the bandwidth are suggested and verified by the measurements. Further, for the 2-D beamforming based on BMs, a generalized scheme to build 2-D MBFN with any 2M+N beams based on traditional 2M× 2M- and 2N× 2N BMs is elaborated and experimentally verified. Especially as the key component of 2-D BMs, an innovative eight-port coupler with a very compact structure is proposed. The applications of the coupler for 2-D monopulse arrays, dual-polarized monopulse arrays, and mm-wave 2-D beamforming are also demonstrated. Besides, two solutions to extend the numbers of beams of BMs from traditional 2N × 2N to almost arbitrary number, such as 2M×3N or M × 2N, are introduced by using a three-way coupler and electrically switchable coupler, respectively (M and N are arbitrary integers greater than 0). Though the majority of ideas and examples presented is exemplified by planar circuits and transverse-electro-magnetic (TEM) transmission lines, they can also be transferred to and applied on other circuit forms, such as ridge-gap waveguide (RGW), printed RGW (PRGW), substrate-integrated waveguide (SIW), and packaged microstrip line (PMSL) for mm-wave applications. Keywords: Butler matrices, two-dimensional Butler matrices, directional couplers, reconfigurable couplers, phase shifters, crossovers, eight-port couplers, packaged microstrip line

Practical realisation of multiband planar filters on multilayer substrates

This research presents the design of planar microwave filters implemented on microstrip multi-layer technology. These should be able to attain and realize specified essential requirements such as multi-band operation, compact size, and without significant deteriorated filter performance in comparison with single-band filters. The focus is placed on new synthesis and design procedures for multiband responses. In some cases, the possibility to include re-configurable characteristics of these filters is required. The focus of the research is entirely on examining the properties and implications of a previously proposed reactance transform method for multiband filter synthesis. The research commences with reviews of multi-band filter synthesis methods. The research specifically examines a full analytical synthesis approach based on reactance transforms method and the implications for practical design approaches Investigations on narrowband with coupled resonator filters representation and wide-band with quasi-lumped element filters representation of up to quad-bands based on reactance transform method are undertaken. With the emphasis on practical aspects such as losses and selectivity, which are related to the physical implementation on multi-layer substrate, the key differences between multiband and single-band filters based on a reactance transform are highlighted. It is illustrated that, in addition to the order of the basis filter, selectivity is influenced by the number of bands, the spacing of the bands and the relative bandwidths. It is also shown that loss has a significant effect on multiband filter responses, in a somewhat different way from that for single-band filters. Physical designs of narrow- band coupled resonators filters are implemented with the aim of examining the degrees of design freedom for multi-layer substrate design, considering the resonance properties and couplings between resonators and considering loss for resonators on different layers. Mercurywave 9350, a low-cost multi-layer substrate is chosen and deemed suitable for a number of reasons, including relatively constant permittivity over frequency. The designs consist of novel topologies: parallel connected multi-path referred to as transversal and also all-pole topologies. A transversal topology includes a dual-band dual-path design as well as a dual-band triple-path design while the all-pole topology is a quad-band design. The research explores re-configurable characteristics of narrow-band coupled resonators of a dual-band dual-path design. A process to obtain a re-configurable multi-band filter with electronically selected pass-bands, based on a reactance transform method for coupled resonator filters, is described. A dual-band multi-band filter realized on multi-layer substrate is designed for passive space applications and reconfigurability is demonstrated using a pre-selection method. For wide-band, quasi-lumped element filters are realized on multi-layer substrate, the inductors are implemented as rectangular spiral inductors and Capacitors as broadside coupling plates connected from two different layers through metallic vias. Parasitic that may influence the relative bandwidths

Impedance Transformers

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