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

Microwave and RF Applications for Micro-resonator based Frequency Combs

Photonic integrated circuits that exploit nonlinear optics in order to generate and process signals all-optically have achieved performance far superior to that possible electronically - particularly with respect to speed. We review the recent achievements based in new CMOS-compatible platforms that are better suited than SOI for nonlinear optics, focusing on radio frequency (RF) and microwave based applications that exploit micro-resonator based frequency combs. We highlight their potential as well as the challenges to achieving practical solutions for many key applications. These material systems have opened up many new capabilities such as on-chip optical frequency comb generation and ultrafast optical pulse generation and measurement. We review recent work on a photonic RF Hilbert transformer for broadband microwave in-phase and quadrature-phase generation based on an integrated frequency optical comb. The comb is generated using a nonlinear microring resonator based on a CMOS compatible, high-index contrast, doped-silica glass platform. The high quality and large frequency spacing of the comb enables filters with up to 20 taps, allowing us to demonstrate a quadrature filter with more than a 5-octave (3 dB) bandwidth and an almost uniform phase response.Comment: 10 pages, 6 figures, 68 references. arXiv admin note: substantial text overlap with arXiv:1512.0174

Synthesis, design, and fabrication techniques for reconfigurable microwave and millimeter-wave filters

As wireless communication becomes increasingly ubiquitous, the need for radio receivers which can dynamically adjust to their operating environment grows more urgent. In order to realize reconfigurable receivers, tunable RF front-end components are needed. This dissertation focuses on the theory, design, and implementation of reconfigurable microwave and millimeter-wave filters for use in such receivers. First, a theoretical framework is developed for absorptive bandstop filters, a new class of bandstop filters which overcomes some of the limitations of traditional tunable bandstop filters caused by the use of lossy tunable resonators. This theory is used in conjunction with silicon-micromachining fabrication technology to realize the first ever tunable bandstop filter at W-Band frequencies, as well as a state-of-the-art Ka-band tunable bandstop filter. The problem of bandwidth variation in tunable filters is then addressed. Widely-tunable filters often suffer from variations in bandwidth, excluding them from many applications which require constant bandwidth. A new method for reducing the bandwidth variation of filters using low-loss evanescent-mode cavity resonators is presented, and this technique is used to realize up to 90% reduction of bandwidth variation in octave-tunable bandstop filters. Lastly, a new differential coupling structure for evanescent-mode cavity resonators is developed, enabling the design of fully-balanced and balanced-to-unbalanced (balun) filters. An octave-tunable 3-pole bandpass balun filter using this coupling structure is presented. The balun filter has excellent amplitude and phase balance, resulting in common-mode rejection of greater than 40 dB across its octave tuning range

Synthesis, design, and fabrication techniques for reconfigurable microwave and millimeter-wave filters

As wireless communication becomes increasingly ubiquitous, the need for radio receivers which can dynamically adjust to their operating environment grows more urgent. In order to realize reconfigurable receivers, tunable RF front-end components are needed. This dissertation focuses on the theory, design, and implementation of reconfigurable microwave and millimeter-wave filters for use in such receivers. First, a theoretical framework is developed for absorptive bandstop filters, a new class of bandstop filters which overcomes some of the limitations of traditional tunable bandstop filters caused by the use of lossy tunable resonators. This theory is used in conjunction with silicon-micromachining fabrication technology to realize the first ever tunable bandstop filter at W-Band frequencies, as well as a state-of-the-art Ka-band tunable bandstop filter. The problem of bandwidth variation in tunable filters is then addressed. Widely-tunable filters often suffer from variations in bandwidth, excluding them from many applications which require constant bandwidth. A new method for reducing the bandwidth variation of filters using low-loss evanescent-mode cavity resonators is presented, and this technique is used to realize up to 90% reduction of bandwidth variation in octave-tunable bandstop filters. Lastly, a new differential coupling structure for evanescent-mode cavity resonators is developed, enabling the design of fully-balanced and balanced-to-unbalanced (balun) filters. An octave-tunable 3-pole bandpass balun filter using this coupling structure is presented. The balun filter has excellent amplitude and phase balance, resulting in common-mode rejection of greater than 40 dB across its octave tuning range

Co-design of Reconfigurable and Multifunction Passive RF/Microwave Components

In order to meet the market demands, multi-band communication systems that are able to accommodate different wireless technologies to be compatible with different wireless standards should be investigated and realized. Multifunction and multi-band RF front-end components are promising solutions for reducing the size and enhancing the performance of multi-band communication systems. This dissertation focuses on the design and implementation of different multifunction and tunable microwave components for use in multi-standard, flexible transceiver. For frequency-domain duplexing (FDD) communication systems, in which the uplink and downlink channels are carried on different RF frequencies, a diplexer is an essential component to separate the transmitting and receiving signals from the antenna. Electrically tunable diplexers simplify the architecture of reconfigurable RF-front end. Moreover, in modern communication systems, the crowding of the spectrum and the scaling of electronics can result in higher common-mode interference and even-order non-linearity issues. In this dissertation, three tunable compact SIW-based dual-mode diplexers, with various SE (single-ended) and BAL (balanced) capabilities, are introduced for the first time. The dual-mode operation results in a dependent tuning between the two ports. The presented designs are for SE-SE, SE-BAL, and BAL-BAL. However, based on the presented design concepts, any combination of the diplexer ports can be achieved in terms of supporting the balanced and single-ended system interface. The fabricated diplexers show low insertion loss, high isolation, good tuning range and high common mode rejection. Tunable bandstop filter (BSF) is one of the essential components in the design of RF front-ends that require wide-band operations. A wide-open front-end leaves the receiver vulnerable to jamming by high-power signals. As a result, this type of front-ends requires dynamic isolation of any interfering signal. Realization of such filters in a balanced configuration, as a second function, is an important step in the realization of full-balanced RF front-ends. Balanced (differential) circuits have many important advantages over unbalanced (single-ended) circuits such as immunity to system noise, reduction of transient noise generation and inherent suppression of even-order nonlinearities. All reported balanced filters are bandpass filters that target wide pass-bands and high common-mode rejection. These filters are necessary for wide-band RF front-ends but, as mentioned above, leave the system open to interferers and jammers. In this dissertation, a new differential coupling structure for evanescent-mode cavity resonators is developed, enabling the design of fully-balanced tunable BSF. The proposed filter is tunable from 1.57-3.18 GHz with 102% tuning range. In addition, over the full range, the measured 10-dB fractional bandwidth ranges from 1-2.4%, and the attenuation level is better than 47 dB. Lastly, Substrate Integrated Waveguide (SIW) evanescent-mode cavity resonators (EVA) are employed in the design of RF couplers, quadrature hybrid and rat-race couplers. These couplers are used in the design of numerous RF front-end components such as power amplifiers, balanced mixers, and antenna array feeding networks. Utilizing such resonators (EVA) in the design allows the couplers to have wide spurious-free range, low power consumption, high power handling capability and both tunability and filtering capabilities. The proposed quadrature hybrid coupler can be tuned starting from 1.32–2.22 GHz with a measured insertion loss range from 1.29 to 0.7 dB. The measured reflection and isolation are better than 12 dB and 17 dB, respectively. Moreover, the coupler has a measured spurious free range of 5.1–3fo (lowest–highest frequency). Regarding rat-race coupler, two designs are introduced. The first design is based on a full-mode cavity while the second one is more compact and based on a half-mode cavity. Both designs show more than 70% tuning range, and the isolation is better than 30 dB

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

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

Miniaturised and reconfigurable planar filters for ultra-wideband applications

An increasing demand for electromagnetic spectrum has resulted from the emergence of feature-rich and faster throughputs wireless applications. This necessitates the developments of dynamic reconfigurable or multifunctional systems to better exploit the existing spectrum. Future wireless devices will be expected to communicate over several bands with various other devices in order to fine tune the services they provide to the user. Each band may require a separate RF transceiver and such modern wireless multi-band multi-mode communication systems call for high performance, highly integrated compact modules. Since the Federal Communications Commission (FCC) released the unlicensed frequency band 3.1-10.6 GHz for ultra-wideband (UWB) commercial communications, the development race for commercialising UWB technology has seen a dramatic increase around the world. The aim of this research is to develop reconfigurable planar microwave filters for ultrawideband applications. The project investigates some key design issues of reconfigurable filters, which are being observed constantly in the latest development and realisation of microwave filters. Both analytical and numerical methods are performed to construct a realistic and functional design. Two different types of frequency reconfigurability are investigated in this thesis: discrete (e.g. PIN diode, Optical switch) and continuous (e.g. varactor diode). Using the equivalent circuits and considering the direct coupled filter structure in most cases, several topologies with attractive features are developed for future communication systems. The proposed works may be broadly categorised into three sections as follows. The first section explores a square ring shape close loop resonator along with an opencircuited stub in the symmetry plane. To realise a reconfigurable frequency states within the same spectrum, an innovative approach is developed for this case. An optical or photoconductive switch, comprised of a silicon die activated using near infrared light is investigated as a substitute of PIN diode and performances are evaluated to compare the feasibilities. In addition, a in-band interference rejection technique via externally coupled Tshape resonator is shown. However, it is observed that both structures achieve significant size reductions by utilising the inner part of the resonators. To improve the filter selectivity, a convenient design approach generating a pair of transmission zeros between both passband edges and a single zero in the stop band for harmonic suppression is discussed in the second section. Moreover, the development of notched rejection bands are studied and several novel methods to create a single and multiple notched bands employing the square ring shape structure are proposed. On inspection, it is found that the notch structure can be implemented without deteriorating the filter performances. 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 reveals a novel highly compact planar dual-mode resonator with sharp rejections characteristics for UWB applications. A bandwidth reconfiguring technique is demonstrated by splitting its even-mode resonance. Filter structure with the dual-mode resonator is shown to have a relatively wide tuning range, significantly low insertion loss and a constant selectivity along with frequency variations in comparison to similar published works. Finally, the earlier dual-mode structure are modified to realise a dual wideband behaviour. A detail analysis with comprehensive design procedures is outlined and a solution for controlling the frequency bandwidths independently according to the application interest is provided. In line with the previous section, experimental verification is presented to support and supplement the discussions

Planar microwave filters with electronically tunability and other novel configurations

In order to meet the increasing demands of advance wireless communications and radar systems, several novel types of bandpass filters and bandstop filters have been developed in this thesis. A new type of varactor-tuned dual-mode bandpass filters have been presented to achieve a nearly constant absolute bandwidth over a wide tuning range by using a single DC bias circuit. Since the two operating modes (i.e., the odd and even modes) in a dualmode microstrip open-loop resonator do not couple to each other, tuning the passband frequency is accomplished by merely changing the two modal frequencies proportionally. Design equations and procedures are derived, and two two-pole tunable bandpass filters and a four-pole tunable bandpass filter of this type are demonstrated experimentally. Miniature microstrip doublet dual-mode filters that exhibit quasi-elliptic function response without using any cross coupling have been developed. It shows that a single two-pole filter or the doublet can produce two transmission zeros resulting from a double behaviour of the dual-mode resonator of this type. Electromagnetic (EM) simulation and experiment results of the proposed filters are described. Parallel feed configuration of a microstrip quasi-elliptic function bandpass filter has been built with a pair of open-loop dual-mode resonators. By employing this new coupling scheme, a novel filter topology with three-pole quasi-elliptic function frequency response can be obtained, leading to good passband performance, such as low insertion loss and good matching at the mid-band of passband. A designed three-pole bandpass filter of this type is demonstrated experimentally. A new class of dual-band filters based on non-degenerate dual-mode microstrip slow-wave open-loop resonators, which support two non-degenerate modes that do not couple, have been introduced. Different feed schemes that affect the filtering characteristics are investigated. Examples of dual-band filters of this type are described with simulation and experiment results. iii In order to achieve a wide spurious-free upper passband, a novel design of bandstop filter with cancellation of first spurious mode by using coupled three-section step impedance resonators (SIRs) has been developed. This cancellation occurs when two transmission poles coincide with the first spurious mode (transmission zero) by properly choosing the step impedance ratio and the gap between the SIR and the main transmission line. A stripline bandstop filter and a microstrip bandstop filter of this type are designed, fabricated and tested. As a preliminary investigation, the microstrip filter is tuned electronically using ferroelectric thin film varactors