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

Microwave Filters in Planar and Hybrid Technologies with Advanced Responses

[ES] La presente tesis doctoral tiene como principal objetivo el estudio, diseño, desarrollo y fabricación de nuevos dispositivos pasivos de microondas, tales como filtros y multiplexores con respuestas avanzadas para aplicaciones de alto valor añadido (i.e. comerciales, militares, espacio); orientados a distintos servicios, actuales y futuros, en sistemas inalámbricos de comunicación. Además, esta investigación se centrará en el desarrollo de filtros encapsulados de montaje superficial y con un elevado grado de miniaturización. Para ello, se propone investigar distintas técnicas que consigan respuestas muy selectivas o con unas características exigentes en rechazo (mediante la flexible introducción de ceros de transmisión), así como una excelente planaridad en banda (aplicando técnicas tales como la mejora del Q o el diseño de filtros con pérdidas, lossy filters), obteniendo de este modo respuestas mejoradas, con respecto a soluciones conocidas, en los componentes de microondas desarrollados. De forma general, la metodología seguida se iniciará con una búsqueda y conocimiento del estado del arte sobre cada uno de los temas que se acometerán en esta tesis. Tras ello, se establecerá un procedimiento de síntesis que permitirá acometer de forma teórica los objetivos y especificaciones a conseguir en cada caso. Con ello, se establecerán las bases para iniciar el proceso de diseño, incluyendo co-simulación circuital/electromagnética y optimización que permitirán, en última instancia, implementar la solución planteada en cada caso de aplicación concreto. Finalmente, la demostración y validez de todas las investigaciones realizadas se llevará a cabo mediante la fabricación y caracterización experimental de distintos prototipos.[CA] La present tesi doctoral té com a principal objectiu l'estudi, disseny, desenvolupament I fabricació de nous dispositius passius de microones, com ara filtres i multiplexors amb respostes avançades per a aplicacions d'alt valor afegit, (comercials, militars, espai); orientats a oferir diferents serveis, actuals i futurs, en els diferents sistemes sense fils de comunicació. A més, aquesta investigació es centrarà en el desenvolupament de filtres encapsulats de muntatge superficial i amb un elevat grau de miniaturització. Per a això, es proposa investigar diferents tècniques que aconsegueixin respostes molt selectives o amb unes característiques exigents en rebuig (mitjançant la flexible introducció de zeros de transmissió), així com una excel·lent planaritat en banda (aplicant tècniques com ara la millora de l'Q o el disseny de filtres amb perdues, lossy filters), obtenint d'aquesta manera respostes millorades, respecte solucions conegudes, en els components de micrones desenvolupats. De forma general, la metodologia seguida s'iniciarà amb una recerca i coneixement de l'estat de l'art sobre cadascun dels temes que s'escometran en aquesta tesi. Després d'això, s'establirà un procediment de síntesi que permetrà escometre de forma teòrica els objectiusi especificacions a aconseguir en cada cas. Amb això, s'establiran les bases per iniciar el procés de disseny, amb co-simulació circuital / electromagnètica i optimització que permetran, en última instància, implementar la solució plantejada en cada cas d'aplicació concret. Finalment, la demostració i validesa de totes les investigacions realitzades es durà a terme mitjançant la fabricació i caracterització experimental de diferents prototips.[EN] The main objective of this doctoral thesis is the study, design, development and manufacture of new passive microwave components, such as filters and multiplexers with advanced responses for commercials, military and space applications; oriented to other different services, in current and future wireless communication systems. In addition, this research will focus on the development of surface-mounted encapsulated filters with a high degree of miniaturization. With this purpose, it is proposed to investigate different techniques that achieve highly selective responses or with demanding characteristics in rejection (through the flexible introduction of transmission zeros), as well as an excellent in-band planarity (applying techniques such as the Q enhancement or lossy filters), thus obtaining improved responses, with respect to known solutions, in the developed microwave components. In general, the followed methodology will begin with a search and knowledge of the state of the art on each of the topics addressed in this thesis. After that, a synthesis procedure will be established, which will allow the achievement of the objectives and specifications in a theoretical way, for each case. With this, the bases will be established to start the design process, with circuital and electromagnetic co-simulations and optimizations that will allow, ultimately, to implement the proposed solution, in every application case, specifically. Finally, the demonstration and validity of all the investigations will be carried out through the manufacture and experimental characterization of different prototypes.Marín Martínez, S. (2022). Microwave Filters in Planar and Hybrid Technologies with Advanced Responses [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/18894

A Lowpass Filter with Sharp Roll - off and High Relative Stopband Bandwidth Using Asymmetric High - Low Impedance Patches

In this letter, a microstrip lowpass filter with -3 dB cut-off frequency at 1.286 GHz is proposed. By using two main resonators which are placed symmetrically around Y axis a sharp roll-off rate (250 dB/GHz) is obtained. The proposed resonators are consisted of two asymmetric high-low impedance patches. To achieve a high relative stopband bandwidth (1.82) four high - low impedance resonators and four radial stubs as suppressing cells are employed. Furthermore, a flat insertion loss in the passband and a low return loss in the stopband can prove desired in-band and out-band frequency response. The proposed LPF has a high FOM about 63483

A novel low-cost microstrip bandpass filter for ultra-wideband RF applications

A novel wideband bandpass filter (WBPF) using planar technology with compact size and sharp cutoff frequency is proposed. The presented microstrip filter consists of a three parallel coupled lines (TPCL) with a radial open stub. To validate the designed filter in term of compactness, insertion loss, return loss, and transmission zeros, a high meshing density is applied in two electromagnetic solvers Advanced Design System (ADS) and CST-Microwave Studio. The proposed filter is fabricated on an FR4 substrate with a relative dielectric constant of 4.4 and 1.58mm of substrate thickness and fed by a two 50Ω microstrip lines. Further, the filter is measured which exhibits a return and insertion losses of 20dB and 0.49dB, respectively, with a center frequency around 3.5 GHz and an operating bandwidth (2.1 GHz to 5.22 GHz) of about 85 %. Good agreement between the simulated and measured results demonstrates the proposed filter design. The overall circuit size of the filter was taken to be 23.24 X 40 mm2

Multiple Order Dual-Band Active Ring Filters with Composite Right/Left Handed Cells

In this paper, a novel dual-band active filter topology is presented. The non-linear phase response of a composite right/left-handed cell is used to achieve the desired dual-band performance. Additionally, the proposed structure based on coupled ring resonators yields a very compact solution in which high-order implementations can be easily obtained by cascading multiple rings. The theoretical principles of this type of filters are analyzed in detail. Finally, three prototypes based on first-, second- and third-order structures validate the feasibility of this type of filters. Good agreement between simulations and measurements has been achieved

Emerging Trends in Techniques and Technology as Applied to Filter Design

In the last decade, the filter community has innovated both design techniques and the technology used for practical implementation. In design, the philosophy has become "if you can't avoid it, use it", a very practical engineering approach. Modes previously deemed spurious are intentionally used to create in-line networks incorporating real or imaginary transmission zeros and also reduce the number of components and thus further miniaturize; spurious responses are re-routed to increase the passband width or stopband width, frequency variation in couplings is used to create complex transfer functions, with all of these developments using what was previously avoided. Clever implementations of baluns into passive and active networks is resulting in a new generation of noise-immune filters for 5G and beyond. Finally, the use of a diakoptic approach to synthesis has appeared an evolving approach in which small blocks ("singlets", "doublets", etc.) are cascaded to implement larger networks, (reducing the need for very complex synthesis), with this new approach promising a large impact on the implementation of practical structures. Filter technology has migrated towards "observe it and then adapt it", pragmatically repurposing tools not specifically originally intended for the applications. Combinations of surface wave and bulk wave resonators with L-C networks are improving the loss characteristics of filters in the region below 2 GHz. Lightweight alloys and other materials designed for spacecraft are being used in filters intended for space, to provide temperature stability without the use of heavy alloys such as Invar. Fully-enclosed waveguide is being replaced in some cases by planar and quasiplanar structures propagating quasi-waveguide modes. This is generically referred to as SIW (Substrate Integrated Waveguide). Active filters trade noise figure for insertion loss but perhaps will offer advantage in terms of size and chip-level implementation. Finally, the era of reconfiguration might be approaching, as the basic networks are evolving, perhaps lacking only the appearance of lower-loss, higher-IP solid-state tuning elements

Tunable Superconducting Microwave Filters

Adaptive microwave systems can benefit from the use of low loss tunable microwave filters. Realizing these tunable filters that show low loss characteristics can be very challenging. The proper materials, tuning elements, and filter designs need to be considered when creating a low loss tunable filter. The integration of low loss microelectromechanical systems (MEMS) and superconducting circuits is one method of achieving these types of tunable filters. The thesis introduces new multi-layer low temperature superconducting (LTS) filters and diplexers and novel topologies for tunable filters and switched multiplexers. An efficient method of designing such filters is proposed. A fabrication process to monolithically integrate MEMS devices with high temperature superconducting (HTS) circuits is also investigated in this thesis. The reflected group delay method, usually used for filter tuning, is further developed for use in designing microwave filters. It is advantageous in the design of filters to have electromagnetic simulation results that will correlate well to the fabricated microwave filters. A correction factor is presented for use with the reflected group delay method so the group delay needs to be matched to the appropriate value at the center frequency of the filter and be symmetric about the center frequency of the filter. As demonstrated with an ideal lumped element filter, the group delay method can be implemented when a closed form expression for the circuit is not known. An 8-pole HTS filter design and an 8-pole multi-layer LTS filter design demonstrate the use of the reflected group delay method. Low temperature superconducting filters, couplers and diplexers are designed and fabricated using a multilayer niobium fabrication process traditionally used for superconducting digital microelectronics. The feasibility of realizing highly miniaturized microwave niobium devices allows for the integration of superconducting digital microelectronics circuits and analog microwave devices on a single chip. Microwave devices such as bandpass filters, lowpass filters, bandstop filters, quadrature hybrids, and resistive loads are all demonstrated experimentally. New tunable filter designs are presented that can make use of MEMS switches. A manifold-coupled switched multiplexer that allows for 2^N possible states is presented. The tunable multiplexer has N filters connected to two manifolds and has embedded switches, which detune certain resonators within the filters to switch between ON and OFF states for each channel. The new concept is demonstrated with a diplexer design and two 3-pole coplanar filters. The concept is further developed through test results of a fabricated HTS triplexer and electromagnetic simulations to demonstrate a superconducting manifold-coupled switched triplexer. Another filter design is presented that makes use of switches placed only on the resonators of the filters. This filter design has N possible states and the absolute bandwidth can be kept constant for all N states. Finally, the integration of HTS circuits and MEMS devices is investigated to realize low loss tunable microwave filters. The hybrid integration is first performed through the integration of an HTS microstrip filter and commercially available RF MEMS switches. A fabrication process to monolithically integrate MEMS devices and high temperature superconducting circuits is then investigated. The fabrication process includes a titanium tungsten layer, which acts as both a resistive layer and an adhesion for the dielectric layer, an amorphous silicon dielectric layer, a photoresist sacrificial layer, and the top gold layer. The fabrication process is built up on a wafer with a thin film of a high temperature superconducting material covered with a thin film of gold. Several processes are tested to ensure that the superconducting properties of the thin film are not affected during the MEMS fabrication process

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