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

Design and synthesis of lossy microwave filters

The design of microwave filters starts from the derivation of a defined lowpass prototype network. A general lossy synthesis method is given which can 1) derive the reflection function from the transfer function when the unitary condition is not satisfied; 2) find the expressions for the complex admittance parameters and 3) synthesize the lossy coupling matrix (CM) with prescribed loss distributions. Two special cases are discussed for solving the refection function from a prescribed transfer function. An alternative approach to cope with loss is studied. In a transversal array, some resonators can be replaced by their low-Q alternatives to reduce the manufacture cost as well as the cavity size. The exact values for the dissipations of resonators or couplings can be determined analytically or by methods of gradient based optimizations. A method of CM synthesis with non-ideal load is given which can be used in designing diplexers or multiplexers. Filter networks matching to complex load impedances can be found by renormalizing reference impedances. An iteration method is introduced which can deal with frequency variant load and can deliver the required reflection zeros. A method for the synthesis of directional filters is presented which can be used for designing combiners. While each section of directional filters provides a 1st order response, more complex filter characteristics can be realized by cascading those single sections. By proper transformations, directional filter networks can be realized using normal resonators and couplings. An example utilizing coaxial resonator is given. A method for the analysis of 2-D lumped element networks is presented. The method is based on the general telegrapher’s equations of multi-wire transmission lines. A 2-D lumped element network is equivalent to a combination of sub-networks which support single mode propagations. The method can be applied to the analysis of metamaterials and can be used for the design of waffle-iron filters

MICROWAVE FILTERS FOR NEXT GENERATION RADIO FREQUENCY TRANSCEIVERS

Increased data rates in wireless communications enforce unprecedented performance metrics on the front-end filters to operate in crowded spectral bands. These requirements include strong selectivity, low insertion loss, and good out-of-band (OOB) rejection in addition to the applicability in complementary metal oxide semiconductor (CMOS) integrated circuit layouts. The acoustic wave (AW) resonator based filter design technology has gained a very important role in the on-chip filter design techniques due to chip-scale physical resonator sizes and the ability of achieving high quality factor values at microwave frequencies. However, conventional synthesis methods used in the design of AW resonator based microwave filters suffer from limited achievable fractional bandwidth (FBW) and weak OOB rejection. The origin of these issues is the limitations on increasing the electromechanical coupling coefficient (kt2) of the resonators, which is an intrinsic property of the piezoelectric material in its design. This dissertation proposes a new class of hybrid acoustic-electromagnetic (Hybrid-ACEM) filters to overcome both of the aforementioned limitations of AW resonator-based filters. In other words, the main goal of this new topology is to maximize the ratio between the achievable FBW and the required kt2. This is achieved by employing one or two electromagnetic (EM) resonators that are placed at purposefully selected stages within the design. In addition, cross-coupling mechanisms are systematically used to reduce the required electromechanical coupling coefficient in certain filter orders. Altogether, the proposed method can achieve much larger FBW values and stronger OOB rejection compared to the conventionally synthesized ladder acoustic wave filters. The effect of finite quality factor of the EM resonators is analyzed. A new algorithm to convert extracted-pole sections to Butterworth-Van-Dyke (BVD) model for large FBW values is also presented. It has been shown in the simulations that FBW-to-kt2 ratios of four or above is achievable with this method. As a proof-of-concept, a sixth-order hybrid canonical prototype with a center frequency of 2.67 GHz and 11.2% FBW is designed and fabricated. The acoustic wave resonators used in the fabrication have kt2 values of 3.5%. The fabricated prototype proves the validity of the proposed method for achieving FBW values of 30% with required kt2 values of 7.5%, which is available with the common aluminum nitride (AlN) based bulk acoustic wave resonator technologies of today. The developed technique opens a new pathway to reduce the limitations of integrating microwave filters for future fully on-chip microwave transceivers

Analysis and Design of Low-Cost Waveguide Filters for Wireless Communications

The area of research of this thesis is built around advanced waveguide filter structures. Waveguide filters and the waveguide technology in general are renowned for high power capacity, low losses and excellent electromagnetic shielding. Waveguide filters are important components in fixed wireless communications as well as in satellite and radar systems. Furthermore, their advantages and utilization become even greater with increase in frequency, which is a trend in modern communication systems because upper frequency bands offer larger channel capacities. However, waveguide filters are relatively bulky and expensive. To comply with more and more demanding miniaturization and cost-cutting requirements, compactness and economical design represent some of the main contemporary focuses of interest. Approaches that are used to achieve this include use of planar inserts to build waveguide discontinuities, additive manufacturing and substrate integration. At the same time, waveguide filters still need to satisfy opposed stringent requirements like small insertion loss, high selectivity and multiband operation. Another difficulty that metal waveguide components face is integration with other circuitry, especially important when solid-state active devices are included. Thus, improvements of interconnections between waveguide and other transmission interfaces are addressed too. The thesis elaborates the following aspects of work: Further analysis and improved explanations regarding advanced waveguide filters with E-plane inserts developed by the Wireless Communications Research Group, using both cross coupled resonators and extracted pole sections (Experiments with higher filter orders, use of tuning screws, degrees of freedom in design, etc. Thorough performance comparison with competing filter technologies) - Proposing novel E-plane filter sections with I-shaped insets - Extension of the E-plane filtering structures with metal fins to new compact dual band filters with high frequency selectivity and miniaturized diplexers. - Introduction of easy-to-build waveguide filters with polymer insert frames and high-performance low-profile cavity filters, taking advantage of enhanced fabrication capabilities when using additive manufacturing - Developing new substrate integrated filters, as well as circuits used to transfer signals between different interfaces Namely, these are substrate integrated waveguide to metal waveguide planar transitions that do not require any modifications of the metal waveguides. Such novel transitions have been designed both for single and orthogonal signal polarizations

Passivity and Maximum Quality Factor Assessment in Lossy 2-port Transfer Functions

International audienceLossy transfer functions are appealing in the design of filters and electric networks, as they can be exactly implemented by physical passive components. However, lossy techniques relax most of the constraints governing the design and thus offer many degrees of freedom but with unclear effects on realizability. This work describes first an analytical method to check whether a given 2-port matrix transfer function is passive. Moreover, for comparison purposes, a technique to assess the maximum allowed predistortion is proposed, related to the highest required quality factor

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