High aspect ratio transmission lines and filters

There are a significant number of microwave applications, where improvement of such qualities as manufacturing costs, size, weight, power consumption, etc. have attracted much research interest. In order to meet these requirements, new technologies can be actively involved in fabrication of microwave components with improved characteristics. One such fabrication technology is called LIGA (a German acronym with an English translation of lithography, electroforming, and moulding) that allows fabrication of high aspect ratio (tall) structures, and only recently is receiving growing attention in microwave component fabrication. The characteristics of high aspect ratio microstrip and coplanar waveguide (CPW) transmission lines are investigated in this thesis. Very low impedance high aspect ratio CPW transmission lines can be realized. A high aspect ratio microstrip folded half wavelength open loop resonator is introduced. Effective configurations for external and bypass gap coupling with open loop resonators are given. Filters with transmission zeros in the stopband, consisting of high aspect ratio single mode open loop resonators are presented to demonstrate the advantages of high aspect ratio structures in realizing lower external quality factors or tight coupling. The transmission zeros are created by novel coupling routings. Some of the filters are fabricated and the filter responses are measured to validate high aspect ratio coupling structures. High aspect ratio diplexers with increased channel isolation are also designed by appropriately combining filters with transmission zeros. A wideband bandpass filter design method, based on the electromagnetic bandgap (EBG) concept is introduced in this thesis. The wideband filters are miniaturized as a result of using the EBG concept in design. An EBG based wideband filter consisting of unit cells that are realized by using high aspect ratio CPW stepped impedance resonators is also presented. The main advantage of this approach is that the high aspect ratio CPW structures make short unit cells practically realizable, resulting in compact filter structure

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

Theory and design of mixed lumped-distributed cross-coupled filters with applications to linear phase shifter and tunable filters

Using cross-coupled networks of a new concept, transmission zeros were efficiently located in the complex frequency-domain. With this approach, the group delay and attenuation slope of the circuit network can be controlled to get both sharp rejection characteristics and linear phase slopes. In order to achieve this performance, various types of combline filters are suggested. Various simulation tools (commercial linear circuit and E-M simulators), as well as the developed pole-zero locator program, were used to design a new class of cross-coupled networks. In particular, the polezero locator program can be used to extract an equivalent circuit of the topology that is established from ether EM-simulated data or measured data. A new cross-coupled quasi-elliptic combline bandpass filter is presented, borrowing the distributed implementation of the capacitance (a top surface metalized dielectric block added as an applique to the top of the circuit), which was conventionally used without metalization to enhance the directivity of the microstrip couplers. The required cross coupling value was achieved by changing the substrate thickness, dielectric constant and area of the top surface metallization of the dielectric block. Effectively, an inhomogeneous transmission line was used to achieve source-load direct crosscoupling with at least one additional transmission zero. The first application presented, is a new type of reflection-type analog phase shifter using tunable short-terminated combline filters (STCL). An asymptotically approached 360-degree total phase shift is obtained, with a large linear range and an insertion loss of less than -1.5 dB over the full phase shift range at 5 GHz. The second approach presented, which is a new concept, is a tunable finite-transmission-zero filter, taking advantage of the unavoidable frequency dependence of each coupling. In order to obtain such a performance, ferroelectric or ferromagnetic stacked substrates are suggested for tuning the extra transmission zeros as well as the center frequency

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

DESIGN OF A MICROSTRIP FILTER FOR MICROWAVE POINT-TO-POINT LINK

The goal of the project is to design a Microstrip Bandpass filter for a point-to-point exchange of information over the microwave-frequency signals. Thus, the main idea of this project is to design a bandpass Chebyshev-type 1 filter using a Microstrip as a transmission line. The biggest obstacle for the project is to have a high performance or in other words a high quality response using a Microstrip transmission line. The scope of the project embraces the understanding and application of techniques for designs of microwave filters, which takes us back to the two-port networks, transmission lines, bandpass filters and microwave communications with enabling us to make more research on the mentioned areas. The design was simulated on MATLAB and a 7th order Chebyshev type 1 filter response was generated. After the design calculations were done, it was simulated, tuned and optimized on AWR Microwave Office, simulation software for better approximations, where we could analyze the response of the filter. The AWR simulation software showed an almost equiripple response with 7 ripples, which concludes that the design was successful

The design and fabrication of miniature microwave bandpass filters using multilayer liquid crystal polymer technology

This thesis presents the design and fabrication techniques for miniature microwave bandpass filters using multilayer liquid crystal polymer (LCP) technology. As a multilayer technology for microwave devices, LCP is of low cost and light weight. It also has excellent electrical properties across a wide frequency range. These characteristics make it promising for the development of next generation microwave devices for applications across commercial, defence and civil sectors. However, very limited work has been found in the open literature to apply this technology to the design of miniature bandpass filters, especially at low microwave frequencies. In addition, the reported work shows lack of fabrication techniques, which limits the size reduction of multilayer LCP devices. To address these problems, this thesis develops advanced fabrication techniques for sophisticated LCP structures, such as multilayer capacitors, via connections and cavities. These techniques are then used to support the design of novel miniature bandpass filters for wideband and narrowband applications. For the design of miniature wideband bandpass filters, a cascaded approach, which combines highpass and lowpass filters, is presented first to provide a flexible design solution. This is followed by another novel ultra-wideband bandpass filter which produces extra transmission zeroes with minimum number of elements. It does not only have high performance but also a compact structure for high yield fabrication. For narrowband applications, two types of advanced coupled-resonator filters are developed. One type produces a very good selectivity at the upper passband edge, and its spurious-free stopband is extremely wide and of high interference attenuation. The other type, based on novel mixed-couplings approaches developed in this thesis, provides a solution to produce almost the same response as the coupling matrix prototype. This type is used to generate arbitrarily-located transmission zeroes. All designs presented in this thesis are simulated using CAD design tools and then validated by measurements of fabricated samples. Good agreements between simulations and measurements are shown in the thesis

The Design of an Anti-Aliasing Filter for the Next Generation Digitiser

MeerKAT, is a 64-element radio astronomy antenna array which has been recently constructed in the Northern Cape Province of South Africa. It serves as South Africa's contribution towards the international Square Kilometre Array (SKA) project. The MeerKAT array has been designed to observe radio signals produced by celestial sources at UHF-Band, L-Band, S-Band and X-Band frequencies. The first phase of the construction included the design, development and integration of the UHF-Band, L-Band and S-band Receivers, whilst the X-band design has been superseded by the incorporation of the next phase of the SKA international project. In preparation of the next the roll-out, research is required to determine optimal wideband filter topologies suitable for direct digitisation of signal frequencies over the frequency range of 3-6 GHz. In this thesis, exploration of suitable wideband planar filters is performed, noting those with an improved out-of-band rejection. The outcome of the investigation leads into the design and development of the suitable wideband planar filter based on key performance specifications. The performance of the manufactured wideband planar filter is then compared to the theoretical design, and validated against the key performance requirements

Systematic Design of Wideband Bandpass Filters Based on Short-Circuited Stubs and λ/2 Transmission Lines

!In this paper, a new technique to design wideband bandpass filters BPFs is proposed. It is based on the classical filter topology formed by shunt short-circuited stubs connected by transmission lines, where the λ/4 connecting lines are replaced by λ/2 lines. In this way, the connecting lines have a double functionality: to control the coupling between resonators and to add additional poles, increasing the filter order up to 2N -1, where N is the number of short-circuited stubs. In addition, their function as inverters is, theoretically, for all spectrum, avoiding the limitation of the λ/4 lines working as inverters or the coupled-line coupling mechanisms of classical configurations, which are of narrowband nature. Design equations are provided with up to N degrees of freedom, which allows for a proper selection of impedance values for the filter design. As a verification, a 5th-order BPF of fractional bandwidth 50and with a Chebyshev response is implemented, fullfiling the expections and validating, in this way, the proposed approach