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

Extended Path Filter Configurations

International audienceIn this work we introduce a method for increasing the maximum number of transmission zeros in the response of path filters. This recently introduced inline filter configuration allows for up to four transmission zeros on the imaginary axis. The solution proposed in this work, while maintaining the inline configuration, increases the number of transmission zeros up to N-1 (with N order of the filter). The novel concept allowing the additional zeros introduction is verified by means of the design of a waveguide filter of order 8 with 6 transmission zeros

Exhaustive synthesis of microwave circuits with frequency dependent couplings

International audienceThe synthesis of bandpass microwave filters is based on the use of equivalent circuit models made of coupled resonators. These couplings are usually supposed to be independent of the frequency. We present in this paper a circuit model including possibly frequency varying couplings. After presenting some of its properties we consider the associated synthesis problem and show how techniques such as Groebner basis computation and Schur analysis based extraction techniques can be used to solve the latter exhaustively

A True Inline Coaxial-Cavity Filter with Two Symmetric Zeros

This article has been presented at IEEE MTT-S International Microwave Symposium (IMS 2020), Atlanta, GA, USA, June 6–11, 2021.International audienceThis work deals with the design of true inline filters with two symmetric transmission zeros. A new filters category named "path filters" is introduced (including the considered filters), his general features are discussed and analyzed and a general method for the synthesis of the low-pass prototype network is proposed. To validate the proposed design approach, a coaxial-cavity filter with a true inline topology exhibiting two symmetrical transmission zeros has been designed and fabricated. The realized prototype shows a response in good agreement with the theory

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

Path Filters: A Class Of True In-Line Topologies With Transmission Zeros

International audienceIn this paper we present a comprehensive discussion of a new class of inline microwave filters with transmission zeros in the response, namely the path filters. The main features of this filters class are highlighted, and an original (synthesis-based) design approach is presented, relying on the derivation of suitable characteristic polynomials. In addition to the classical Generalized Chebyshev characteristic, two new characteristics are introduced (namely the Bounded Chebyshev and the Reduced Chebyshev), that allow improving the flexibility in the requirements assignment of path filters. A new method for the synthesis of the lowpass prototype is also introduced, that overcome the limitation in the classical synthesis based on the manipulation of the transversal prototype (whose synthesis may fail in case of path filters). Finally, the proposed approach for designing the class of considered filters has been validated by several examples that include the evaluation of the characteristic polynomials, the prototype synthesis and the dimensioning of the physical structures in waveguide technology

General Synthesis Method for Dispersively Coupled Resonator Filters With Cascaded Topologies

International audienceThis article presents a new synthesis technique for circuits that may include dispersively coupled resonators and admitting an overall cascaded topology. A decomposition technique of the Darlington type is first introduced to split the original response S of the filter, taken as its scattering matrix, into m subresponses S¹,...,S $^{m}$ corresponding to each subblock of the cascaded circuital structure. Each individual subresponse S $^{k}$ is then synthesized separately. In this article, the state space equations governing the model of dispersively coupled resonators are detailed. An extension to the case of dispersive coupling of the shortest path rule, which determines the maximum number of finite TZs realizable by a given topology, is then introduced. Congruent transformations that extend the concept of rotations or similarity transformations while preserving the filter response are exploited to reduce the individual synthesis problems to the determination of a basis of vectors verifying certain orthogonality relations. A direct synthesis technique for dispersive building blocks, such as duplets, triplets, and quadruplets, is then given in the form of an orthogonalization procedure used for the computation of the desired basis. This approach is then combined with the aforementioned decomposition technique to produce a versatile algorithm able to synthesize hybrid circuits made of cascaded subblocks of different orders and types that implement each a subset of the overall TZs by means of coupling topologies containing a mixture of dispersive and nondispersive couplings. The first synthesis example is detailed where two dispersive duplets are combined with a classical quadruplet to realize a symmetric 6-4 response. A hardware implementation of the synthesized circuit is presented in combline technology. The second example proposes a slightly more involved coupling topology able to realize 10-8 asymmetric responses by means of four cascaded basic dispersive blocks

Synthesis Technique of Thickness-Customizable Multilayered Frequency Selective Surface for Plasma-Based Electromagnetic Structures

This dissertation provides a synthesis technique for the design of thickness-customizable high-order (N ≥ 2) bandpass frequency selective surface (FSS) and its application in realizing versatile multi-layered FSS and absorbers. Admittance inverters layers are used to synthesize the transfer response of the filter given desired characteristics such as filter type, center frequency, and bandwidth. These inverter layers are essentially electromagnetic coupling interlayers that can be adjusted to customize the thickness of multilayered FSS without degrading the desired filter performance. A generalized equivalent circuit model is used to provide physical insights of the proposed design. This synthesis technique is adopted to deliver a versatile implementation capability of high-order FSS filters using various dielectric spacers with arbitrary thicknesses. Such technique enables the realization of spatial filters with variable size, while maintaining the desired filter response. To highlight the significance of the proposed synthesis technique, its concept is applied to two practical problems including the design of compact switchable FSS and adaptive/tunable microwave absorbers as it may allow simpler integration of active components that require specific physical dimensions. In the first practical problem, the feasibility of deploying plasma switchable compact spatial filter in harsh electromagnetic radiation environments is investigated. The proposed FSS integrates contained plasma (plasma-shells) as active tuning elements. These ceramic, gas-encapsulating shells are ideal for high-power microwave and electromagnetic pulse protection because they are rugged, hermetic, operable at extreme temperatures, and insensitive to ionizing radiation. A 2D periodic second-order switchable spatial filter is implemented. It is composed of electrically small Jerusalem cross structures embedded with discrete plasma shells strategically located to effectively switch the transfer function of the filter. This technique is used to realize compact low profile second order band pass spatial filter operating at S-band. It also has the ability to switch its transfer function within 20 to 100 ns while enabling in-band shielding protection for aerospace or terrestrial electromagnetic systems subjected to high power microwave energy (HPME) and high electromagnetic pulse (HEMP) in harsh space environment. Experimental results are shown to be in good agreement with simulation results. The second practical problem is addressed by deploying a large-scale adaptable compressed Jaumann absorber for harsh and dynamic electromagnetic environments. The multilayered conductor-backed absorbers are realized by integrating ceramic gas-encapsulating shells and a closely coupled resonant layer that also serves as a biasing electrode to sustain the plasma. These active frequency selective absorbers are analyzed using a transmission line approach to provide the working principle and its frequency tuning capability. By varying the voltage of the sustainer, the plasma can be modeled as a lossy, variable, frequency-power-dependent inductor, providing a dynamic tuning response of the absorption spectral band. To study the power handling capability of the tunable absorber, dielectric and air breakdowns within the device are numerically emulated using electromagnetic simulation by quantifying the maximum field enhancement factor (MFEF). Furthermore, a comprehensive thermal analysis using a simulation method that couples electromagnetics and heat transfer is performed for the absorber under high power continuous microwave excitations. The maximum power level handling capability of the microwave absorber has been numerically predicted and validated experimentally

Analysis and Design of a Substrate Integrated Waveguide Multi-Coupled Resonator Diplexer

A microwave diplexer achieved by coupling a section of a dual-band bandpass filter onto a section of two single-bands (i.e. transmit and receive) bandpass filters is presented. This design eliminates the need for employing external non-resonant junctions in diplexer design, as opposed to the conventional design approach which requires separate non-resonant junctions for energy distribution. The use of separate non-resonant junctions in diplexer design increases the design complexity, as well as gives rise to bulky diplexer devices. The proposed design also removes the too much reliance on the evaluation of suitable characteristic polynomials to achieve a diplexer. Though the evaluation of complex polynomials to achieve a diplexer is seen as a viable option, the technique is hugely dependent on optimisations which come with loads of uncertainties. This thesis relies on well-established design formulations to increase design reliability, as well as simplicity. A 10-pole (10ᵗʰ order) microwave diplexer circuit has been successfully designed, simulated, manufactured and measured. The measured results have been used to validate the circuit model and the electromagnetic (EM) simulated results. The diplexer is composed of 2 poles from a dual-band bandpass filter, 4 poles from a transmit bandpass filter and the remaining 4 poles from a receive bandpass filter. The design was initially implemented using asynchronously tuned microstrip square open-loop resonators. The EM simulation and the measurement results of the microstrip diplexer were presented and show good agreement with the proposed design theory. The design was also implemented using the substrate integrated waveguide (SIW) technique and results presented and discussed. In comparison to the results achieved with the microstrip diplexer, the EM simulation and the measurement results realised with the SIW diplexer, show that a slightly better insertion loss was attained across both the transmit and the receive channels, respectively

Development of resonant cavity-based microwave filters for axion detection

[SPA] Esta tesis doctoral aborda varias investigaciones para la detección de axiones y para la mejora de comunicaciones satelitales mediante el uso de cavidades resonantes en tecnología guía de onda. El axión es una partícula hipotética teorizada para resolver el problema CP fuerte (Charge conjugation Parity symmetry) en la cromodinámica cuántica (QCD) y que, de existir, podría ser componente de la materia oscura. En esta línea, el desarrollo de detectores axiónicos de materia oscura, comúnmente denominados haloscopios, se ha encontrado en auge en los últimos 20 años. En este trabajo se han desarrollado diversos métodos para la mejora de estos haloscopios empleando estructuras basadas en subcavidades conectadas por irises. Por otro lado, es bien sabido que el espectro electromagnético en las comunicaciones por satélite se encuentra saturado debido a la alta demanda de radiocomunicaciones hoy en día. Además, el coste de puesta en órbita de un satélite crece exponencialmente con el peso abordo de éste, cuya reducción será clave en cualquier programa espacial. Así, en esta tesis se abordan diversos diseños de filtros paso banda en guía de onda para la optimización del peso, volumen y huella abordo de los futuros satélites de comunicaciones. El espectro frecuencial barrido por la comunidad axiónica en busca de la ansiada partícula (el axión) es cada día mayor y hace que exista una alta competencia para participar en esta búsqueda con detectores de altas prestaciones. Además, las condiciones extremas a las que debe ser sometido un detector de axiones de materia oscura para que se cumplan las condiciones de detección (temperaturas criogénicas, campo magnetoestático alto, etc.) complican aún más esta tarea. Algunos de los parámetros que rigen el rendimiento de un haloscopio basado en cavidades resonantes son su volumen, factor de calidad y factor de forma. Durante la elaboración de este trabajo se han diseñado, fabricado y caracterizado diversas topologías novedosas para la creación de estos detectores, optimizando los tres parámetros mencionados, consiguiendo resultados satisfactorios. Esta tesis doctoral ha sido realizada en el marco de trabajo del grupo axiónico RADES (Relic Axion Detector Exploratory System). Se han llevado a cabo tareas de investigación para la mejora del factor de calidad en estructuras fabricadas en las primeras etapas por este grupo experimental mediante la aplicación de diversos tratamientos, como la aplicación de soldaduras. Además de la optimización de los parámetros en haloscopios, estos necesitarán escanear un espectro de frecuencias, como se ha mencionado anteriormente, para lo cual se deberá implementar sistemas de sintonía que permita el cambio de frecuencia de resonancia y otros sistemas para el ajuste del acoplamiento de entrada / salida del sistema (otro de los parámetros críticos del detector). Existen dos tipos de sintonía frecuencial, mecánica y electrónica. Para los sistemas de sintonía mecánicos, se han realizado estudios del comportamiento de los prototipos fabricados cuando estos se abren mediante un corte vertical, lo cual cambiará su frecuencia de búsqueda del axión. Por otro lado, para los sistemas de sintonía electrónicos se han desarrollado diversos diseños para la introducción de materiales ferromagnéticos y ferroeléctricos, que cambiarán la frecuencia de operación mediante el cambio de permeabilidad y permitividad del medio, respectivamente, aplicando un cambio de voltaje o temperatura. Se ha hecho un estudio mucho más extenso para estos últimos. Los sistemas electrónicos permiten evitar ciertos problemas que ocurren en los de tipo mecánico, como pueden ser fallos de movimiento a temperaturas criogénicas o la falta de escalabilidad. Para los elementos ferroeléctricos, se ha llegado a un diseño novedoso que ha aportado gran valor a la comunidad científica para la aplicación de este tipo de materiales en cualquier haloscopio. Además, se han desarrollado sistemas de acoplamiento entre subcavidades con láminas ferroeléctricas, evitando la fabricación de irises, los cuales pueden dar problemas en ciertos sistemas. Para los sistemas de ajuste de acoplamiento de entrada / salida, se ha desarrollado un prototipo preliminar que ha aportado buenos resultados experimentales. Asimismo, se han llevado a cabo otras tareas de investigación para el desarrollo de otras técnicas de mejora de haloscopios. Una de ellas es la del rechazo de resonancias no deseados cerca del modo axiónico por medio de la combinación de varios puertos coaxiales con el método phase-matching, para el cual se han realizado diversas simulaciones y fabricaciones, extrayendo resultados positivos que hacen viable dicho método. Otros estudios secundarios han sido los de la implementación de QuBits para reducir la temperatura del sistema (parámetro clave para el rendimiento), el uso de elementos HTS (High Temperature Superconductor) para aumentar el factor de calidad, el diseño de haloscopios a frecuencias en las bandas UHF y W, y el análisis electromagnético del acoplamiento axion-photon en haloscopios mediante el método BI-RME (Boundary Integral-Resonant Mode Expasion) 3D. Finalmente, como spin-off del desarrollo de haloscopios, se han realizado diversos estudios para el diseño, fabricación, caracterización y mejora de filtros paso banda para comunicaciones satelitales empleando la misma tecnología (cavidades resonantes acopladas por irises en guía de onda). Se ha han desarrollado varios filtros evanescentes basados en impresión 3D o fabricación aditiva de bajo coste, y mecanizado CNC (Computer Numerical Control). A estos filtros se les ha aplicado un sistema de sintonía de tornillos que ha permitido la mejora de la respuesta eléctrica de filtrado. Por otro lado, se ha llevado a cabo el diseño de un filtro asimétrico doblado horizontalmente para la implementación de ceros de transmisión, consiguiente un alto rechazo fuera de la banda de paso. Estos filtros son gran valor para la comunidad científica ya que permiten avanzar en el estado del arte de filtros con altas prestaciones (bajo peso, volumen y huella) para comunicaciones satelitales. [ENG] This PhD thesis addresses several investigations for the detection of axions and for the improvement of satellite communications using resonant cavities in waveguide technology. The axion is a hypothetical particle theorized that could explain the strong CP problem (Charge conjugation Parity symmetry) in quantum chromodynamics (QCD) and which, if it exists, could be a component of dark matter. In this line, the development of axion dark matter detectors, commonly called haloscopes, has been booming in the last 20 years. In this work, several methods have been developed for the improvement of these haloscopes using structures based on subcavities coupled by irises. On the other hand, it is well known that the electromagnetic spectrum in satellite communications is saturated due to the high demand for radio communication systems. In addition, the cost of putting a satellite into orbit grows exponentially with the weight on board, the reduction of which will be key in any space program. Thus, this PhD thesis deals with different waveguide bandpass filter designs for optimizing the weight, volume, and on-board footprint of future communication satellites. The frequency spectrum swept by the axion community in search of the coveted particle is increasing day by day, which means that there is a high level of competition to develop high-performance detectors. In addition, the extreme conditions to which a dark matter axion detector must be subjected in order to meet the detection conditions (cryogenic temperatures, high magnetostatic field, etc.) further complicate this task. Some of the parameters that govern the performance of a haloscope based on resonant cavities are its volume, quality factor and form factor. During the development of this work, several novel topologies have been designed, manufactured, and characterized for the creation of these detectors, optimizing the three above-mentioned parameters, achieving satisfactory results. This PhD thesis has been carried out within the framework of the RADES (Relic Axion Detector Exploratory System) axion group. Research work has been carried out to improve the quality factor in structures manufactured in the first stages of this experimental group through the application of various treatments, such as soldering. In addition, as the axion mass is unknown, it is important to scan in frequency to search for the axion over a range as large as possible, as mentioned above, for which tuning systems must be implemented to allow resonant frequency shift and other arrangements for adjusting the input / output coupling of the system (another key haloscope parameter). There are two types of frequency tuning, mechanical and electronic. For mechanical tuning systems, studies have been carried out on the behaviour of the fabricated prototypes when they are opened by a vertical cut, which will change their axion search frequency. On the other hand, for electronic tuning systems, various designs have been developed for the introduction of ferromagnetic and ferroelectric materials, which will change the operating frequency by changing the permeability and permittivity of the medium, respectively, by applying a change of voltage or temperature. A much more extensive study has been made for the use of ferroelectric tuning systems. Electronic systems avoid certain problems that occur in mechanical systems, such as motion failure at cryogenic temperatures or lack of scalability. For ferroelectric elements, a novel design as been achieved which has brought great value to the scientific community for the application of this type of material in any haloscope. Also, coupling systems have been developed between subcavities with ferroelectric films, avoiding the need to manufacture irises, which can cause problems in certain systems. For the input / output coupling adjustment systems, a preliminary prototype has been developed which has provided good experimental results. Other research works have also been carried out on the development of other haloscope enhancement techniques. One of them is the rejection of unwanted resonances near the axion mode by means of the combination of several coaxial ports with the phase-matching method, for which several simulations and fabrications have been carried out, obtaining positive results that make this method feasible. Other secondary studies have been the implementation of QuBit devices to reduce the system temperature (another key parameter for haloscope performance), the use of HTS (High Temperature Superconductor) elements to increase the quality factor, the haloscope design at frequencies in the UHF and W bands, and the electromagnetic analysis of axion-photon coupling in haloscopes using the BI-RME (Boundary Integral-Resonant Mode Expansion) 3D method. Finally, as a spin-off from the development of haloscopes, several studies have been carried out for the design, manufacture, characterization, and improvement of bandpass filters for satellite communications using the same technology (resonant cavities coupled by irises in waveguide). Several evanescent filters based on 3D printing or low-cost additive manufacturing and CNC (Computer Numerical Control) machining have been developed. A screw tuning system has been applied to these filters to improve the electrical filtering response. On the other hand, the design of a horizontally folded asymmetric filter for the implementation of transmission zeros, to increase the rejection capabilities of the filter, has been carried out. These filters could be of great value to the scientific community as they allow to advance in the state of the art of high-performance filters (low weight, volume, and footprint) for satellite communications.Escuela Internacional de Doctorado de la Universidad Politécnica de CartagenaUniversidad Politécnica de CartagenaPrograma Doctorado en Tecnologías de la Información y las Comunicacione