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

Novel Topologies Based Rf Filtering Components And Methodologies For Wireless Communication System

Driven by the rapid progress of wireless communication technology in the past several decades, multiple generations of cellular technologies have been developed, deployed, and adopted to provide more convenient communication services to users. Nowadays, the personal hand-held devices, supporting multiple wireless standards, have been a multimedia terminal encompassing elements and functions such as video callers, Internet connectivity, home appliances remote controller, GPS, TV reception, and beyond. In order to accommodate a variety of wireless standards in a single device without imposing a substantial increase in cost and size, current and future RF transceiver front-ends should be designed with more attention. The main objective of this dissertation is to study new design topologies and implement a series of high performance RF filtering components which play critical roles in miniaturized RF transceivers supporting multiple wireless standards. A compact dual-band filter with high selectivity and wide rejection band, a filtering Wilkinson power divider, and balanced filters with fixed/reconfigurable center frequencies are proposed and successfully developed. In addition, an equation-based methodology is also first proposed and fully investigated to r

Compact Quad-Band Bandpass Filter Based on Stub-Loaded Resonators

This paper presents a planar quad-band bandpass filter with high out-of-band rejection. The filter is based on intercoupled stub-loaded resonators, where pairs of resonators are electromagnetically coupled to each other and the feedlines. This results in excitation of passbands, where the first and the third passbands are generated by /4 resonators. The second and the fourth passbands are excited by /2 resonators. The proposed technique provides sufficient degree of freedom to control the center frequency and bandwidth of the four passbands. In addition, the five transmission zeros created around the passbands results in a quad-band filter with high selectivity, sharp 3 dB cut-off frequency, high isolation, and low passband insertion-loss. The proposed technique was verified practically. Design methodology and experimental results of the prototype filter are provided

When Compactness Meets Flexibility: Basic Coaxial SIW Filter Topology for Device Miniaturization, Design Flexibility, Advanced Filtering Responses, and Implementation of Tunable Filters

[EN] Substrate integrated waveguide (SIW) technology [1], [2] is a well established and successful approach for implementing planar microwave filters with very stringent requirements in terms of quality (Q) factor and also with the ability to integrate into a system. Optimized SIW filters can reach a Q factor of 200-800 using low-loss substrates and standard fabrication procedures [3]. Furthermore, packaging and electromagnetic (EM) shielding, power-handling capabilities, and low-cost batch manufacturing are other broadly recognized strengths of this approach. However, SIW filters are still larger than most of their planar counterparts; in addition, advanced topologies are not always easy to accommodate, and filter reconfigurability usually leads to very complex implementation [4]-[6]Martínez Pérez, JD.; Sirci, S.; Boria Esbert, VE.; Sánchez-Soriano, MÁ. (2020). When Compactness Meets Flexibility: Basic Coaxial SIW Filter Topology for Device Miniaturization, Design Flexibility, Advanced Filtering Responses, and Implementation of Tunable Filters. IEEE Microwave Magazine. 21(6):58-78. https://doi.org/10.1109/MMM.2020.2979155S587821

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

Microstrip Triplexer using a common triple-mode resonator

An all-resonator based triplexer is presented using a double-stub-loaded resonator (DSLR) that acts as a common resonator at the junction of the three channels. The open stub DSLR has been analysed using even and odd-mode method to reveal the relationship between the three resonant modes. The design offers flexibility of frequency selection. The DSLR resonator is coupled with three sets of hairpin resonators to form the triplexer at 1.8, 2.1, and 2.6 GHz for mobile communication applications. The measurement results are in very good agreement with the simulations

Tunability and performance enhancement for planar microwave filters

Radio-frequency (RF) spectrum is exploited as a valuable resource for wireless applications such as mobile and satellite communications. As a result, communication systems including satellite communication and emerging 5G are trending to have frequency-agility to adapt to highly complex RF environments. However, due to the nature of materials and components, electrically-tunable planar filters, which play essential roles in frequency agile RF systems, have their disadvantages of low-order, high-loss, and poor selectivity. This has limited the overall performances of the frequency agile RF systems. In the light of this scenario, the objective of this thesis is to develop efficient performance-enhancement techniques, including the lossy technique, and the active technique, into the high-selective tunable planar filters to boost the performances of tunable RF systems. First of all, an electrically reconfigurable microstrip dual-mode filter is demonstrated with nonuniform-quality-factor lossy technique. The 4-pole bandpass filter exhibits a continuously bandwidth tuning and centre frequency tuning capability. By making use of the doubly tuned resonant property of the dual-mode microstrip open-loop resonator, passband flatness can be improved by simply loading resistors on the even-odd mode symmetrical plane of resonators. Moreover, two intrinsic transmission zeros are in upper and lower stopbands enhancing the filter selectivity. The coupling matrix synthesis is introduced to describe the nonuniform-quality-factor distribution in a filter network. The experiment of this type of four-pole tunable lossy filter has presented a good agreement with the simulation. Then, the thesis reports a novel 5-pole lossy bandpass filter with the bandwidth tunability. In order to improve the filter selectivity, we choose a hybrid filter structure consist of hairpin resonators and dual behaviour resonators to produce two adjustable transmission zeros for high selective responses. A novel lossy technique named centre-loaded resistive cross-coupling is developed to efficiently reduce the insertion-loss variation of the tuned passband. The fabricated filter demonstrates an insertion loss variation of less than 1 dB for all bandwidth states. To compensate the loss within the varactor-tuned narrowband filter, a tunable 2-pole active filter is presented with a constant absolute bandwidth. The negative resistance generated from active circuits successfully cancels the loss within the varactor-loaded resonators resulting in high quality-factor resonator filter responses. With the transistor small-signal model, the value of the negative resistance of the active circuit can be predicted by network analysis. Experiments were carried out to validate the design

A Class of Compact Substrate Integrated Waveguide Filters

This thesis work explores the design of compact and high performance microwave filters using substrate integrated waveguide technology. A substrate integrated waveguide is aplanar version of a conventional waveguide, which is having features like planar circuit integrability, ease of fabrication, low-cost and high power handling. A class of Substrate Integrated Waveguide (SIW) and Half mode Substrate Integrated waveguide (HMSIW) bandpass filters are proposed in this context. Applications like satellite communication uses devices which can withstand high power. Therefore, SIW filters can be used for satellite applications in the microwave bands like Ku, X, C, S, and L etc.The main objective of this thesis is to design SIW bandpass filters using simple planar technology and low-cost substrates. To fulfill this, a class of compact and easily fabricable SIW bandpass filters are proposed for Ku-band (12 − 18GHz) and S-band (2 − 4GHz) applications. These filters are designed using simple electromagnetic band gap (EBG) structures and latest feeding techniques like tapered-via feeding. Filters are designed using low-cost and easily available substrate FR4 with the help of High frequency structural simulator (HFSS) V.14. The dimensions of the filters are optimized and simulation results are analyzed. The proposed Ku-band filter has proven to be compact since its footprint is 160mm2. The S-band filter has been fabricated using low-cost and easily available FR4 substrate. The measurement results are found to be good in agreement with the simulation results. Though the obtained results are similar to the other reported filters, there is a huge demand of compactness in this miniaturization era. Therefore, another well-established concept of Half-mode SIW (HMSIW) technology is used to further reduce the size of the designed filters. So a compact HMSIW bandpass filter is designed for the Ku-band applications which is almost half in size as compared to conventional SIW designs. The return loss is achieved as 45dB and insertion loss is 1.5dB in the passband of the filter, which is promising corresponding to the size. Another similar design is made for X-band (8 − 12GHz) applications using HMSIW technology. The overall footprint of the filter which shows its compactness; is 102mm 2 i.e. almost half the size of its equivalent SIW filter

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