Miniaturized High-Q Tunable RF Filters

This dissertation focuses on the investigation and development of novel efficient tuning techniques and the design of miniaturized high-Q tunable RF filters for high-performance reconfigurable systems and applications. First, a detailed survey of the available tuning concepts and state-of-art tunable filters is provided. Then, a novel so-called inset resonator configuration is presented for the applications of fixed and tunable coaxial filters. The design procedure of frequency tunable filters with constant absolute bandwidth (CABW) is described, and various tunable inset filters are implemented, offering many desirable merits, including the wide tuning range and stable high-Q with minimum variation. For wide octave frequency tuning ranges with CABW, a second novel concept is presented using so-called re-entrant caps tuners. Beside simplicity and compactness, this technique also features enhanced spurious performance and wider tuning capabilities than the conventional means. Also, in this dissertation, various miniaturized reconfigurable dual-band/dual-mode bandpass filters and diplexers are presented using compact dual-mode high-Q TM-mode dielectric resonators. Furthermore, a novel microfluidic-based ultra-wide frequency tuning technique for TM010-mode dielectric resonators and filters is introduced in this dissertation. In addition to the very wide tuning window, this mechanism has key advantages of low-cost, simplicity, and intrinsic switch-off. Lastly, the dissertation includes a novel bandwidth reconfiguration concept with multi-octave tuning using a single element for coaxial bandpass filters. This mechanism brings many features including the fast tuning, constant high-Q, intrinsic switch-off, and wide BW-reconfiguration

Widely Tunable TM-Mode Dielectric Filters With Constant Absolute Bandwidth Using Re-Entrant Caps

This paper reports octave tunable dielectric combline bandpass filters with constant absolute bandwidth (CABW) using a novel re-entrant cap tuning technique. The resonant frequency is tuned by the hollow re-entrant cap penetrating into the filter cavity as an envelope around the dielectric resonator. This mechanism of tuning provides wider tuning capabilities and better spurious performance than the conventional screw-based tuning. Also, the cap tuners can be employed effectively to tune the input-output and inter-resonator couplings simultaneously with the frequency reconfiguration, enabling a CABW over a wide frequency tuning window. For proof of concept purposes, a single widely tunable resonator is presented with octave tuning ratio of 2.64:1, high quality factor from 1705 to 5480, and spurious-free band up to 3.44⋅ f0 . Afterwards, two octave tunable re-entrant cap filters are designed, fabricated, and tested. The first filter is a 78% widely tunable two-pole filter with a CABW of 43.5 ± 12% MHz, low insertion loss equals to 0.28 ± 0.03 dB, and a compact volume of 39 cm 3 . The second design is a four-pole octave tunable bandpass filter from 2.96 GHz to 1.36 GHz with a constant 69 ± 13% MHz bandwidth, low insertion loss better than 0.6 dB, return loss higher than 16 dB, and a compact 62 cm 3 structure. According to our own knowledge, thanks to the proposed tuning mechanism, the presented designs are the first CABW octave tunable high Q waveguide-based filters, having the widest tuning ranges over all similar state-of-the-art-designs

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

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

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

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

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

Tunable Filter

Tunable filters enable dynamic spectrum access for the wireless systems, and the tunable bandpass filters with constant bandwidth (BW) are most favorable for practical applications. This chapter investigates the synthesis and realization techniques for the tunable filters using the coupling matrix with variable entries synthesizes the tunable filter and guides the filter design. The synthesis method and the matrix extraction procedures for the constant-bandwidth bandpass filter are included, and the typical numerical examples are given. This chapter also discusses the relationship between the theoretical matrix and the physical circuits, and then a planar tunable filter design is presented to verify this relationship. Furthermore, the general approach to designing the constant-bandwidth filters using the element variable coupling matrix is concluded. The planar circuit, as well as the 3D structure realizations, are offered to practically demonstrate the synthesis design approach

Frequency-Agile Microwave Filters For Radars With Simultaneous Transmission and Reception

Multi-band/multi-mode wireless communication systems have been receiving increased attention recently due to their potential for spectrum management in a dynamic spectral environment. Similarly radar systems, which can operate in a variety of frequency bands, could provide significant flexibility in the operation for the future applications. However, multi-band/multi-mode operation adds to the complexity of the microwave systems. Reconfigurable RF/microwave components in general, and tunable filters in particular, have been shown to be promising in significantly reducing the system complexity. On the other hand, current trend of development in wireless communication and radar systems, forces more stringent requirements for electromagnetic spectrum sharing. Therefore, in many microwave applications a very high level of isolation between the channels are required. This is including simultaneous transmit-receive systems or co-site interference scenarios where the leakage from high power transmitter into receiver degrades the system performance. In these applications, conventional tunable bandpass/bandstop filters cannot provide enough isolation between transmitter and receiver. A promising solution which provides a tunable null, independent of the tunable transmission passband, is a dynamic-tunable bandpass-bandstop filter cascade. In this research, a frequency-agile bandpass-bandstop filter cascade for radar systems with simultaneous transmission and reception is designed to create advanced filtering functionality to isolate the desired signals from interfering signals in a spectrally-crowded environment. For a radar with simultaneous transmit and receive, two filter cascade will be required. Each filter will be used on a separate frequency agile transceiver but they will be synchronized to provide simultaneously a deep isolation region at one frequency for receive and a high power tolerant passband at an adjacent frequency for transmit