MIT/PCM-based RF Switches for Tunable Filter Application

Tunable filters are promising for reducing the size of communication systems by replacing switch filter bank, also they are gaining more attention for satellite applications which will need to change the frequency bands. One of the main requirements for tunable filters is to maintain low passband insertion loss and high stopband rejection over the tuning range. The key to achieving this goal is using high quality factor (high-Q) resonators such as three-dimensional (3D) structure resonators (dielectric resonators, coaxial resonators, waveguide resonators, etc.). For high-Q tunable filters, not only do the resonators need to have high unloaded Q, the tuning elements also need to have low loss. Over the past years, various tuning techniques have been employed to realize tunable filters, including solid-state tuning, mechanical tuning, piezoelectric tuning, magnetic tuning, and MEMS tuning. All of these techniques have both advantages and drawbacks in terms of insertion loss, DC power consumption, tuning speed, non-linearity, and reliability. The objective of the research presented in this thesis is to investigate the feasibility of using metal-insulating transition (MIT) material and phase-change material (PCM) to realize high-Q tunable/ reconfigurable filters for base station in communication and satellite applications. Fabrication methods of MIT material VO2 (Vanadium Dioxide) and PCM GeTe (Germanium Telluride) are first investigated to obtain optimal MIT/PCM materials with high resistivity ratio between different states. RF switches based on both VO2 and GeTe integrated with micro-heaters are then developed. VO2-based variable attenuators are realized at both X-band and Ka-band. A switch capacitor bank is also designed and fabricated, integrating GeTe RF switches and MIM (metal-insulator-metal) capacitors in a six-layer microfabrication process. A novel structure for wideband dielectric substrate-based filters is developed. The cavity of the filter is separated into two thin dielectric substrates (DSs), a metal frame for holding the dielectric substrates, and two metal covers. The filter is compact in size and ideal for integration with antennas because of its relatively thin profile. Since it uses separated DSs attached to the two sides of the metal frame, the input/output probe can be placed at the middle of the cavity, leading to a significant increase in the input/output coupling compared to conventional dielectric resonator filters. Additionally, the filter structure lends itself to realizing relatively large values of inter-resonator coupling. A five-pole Chebyshev filter with a fractional bandwidth of 9.6%, a four-pole filter having two transmission zeros with a fractional bandwidth of 9%, and a three-pole filter with a fractional bandwidth of 13% are designed, fabricated and tested. The filter structure promises to be useful in sub-6 GHz 5G base station applications that require the use of low-cost, miniature, high-Q wideband filters with a thin profile. Furthermore, a novel tuning structure with multiple strip lines is developed in this work. The tuning structure is designed to employ RF switches to tune 3D filters, eliminating the need to use variable capacitor loading, which is known to degrade the filter’s loaded Q over the tuning range. Two- and three-pole filters with combline configuration are designed, fabricated and measured with wire bonding, MEMS switches, and VO2 switches. With wire bonding, all of the tuning states demonstrate measured Q higher than 2000, whereas with the fabricated VO2 switches, the measured Q was lower. The test data confirm however the tunability and feasibility of using the proposed tuning scheme to realize a reasonable high-Q tunable filters that maintain Q values over the tuning range. A DS-loaded three-pole tunable filter is designed, fabricated, and measured. The results show the potential of realizing a tunable dielectric filter with a low loss VO2-based switch

High Q Tunable Filters

Microwave tunable filters are key components in radar, satellite, wireless, and various dynamic communication systems. Compared to a traditional filter, a tunable filter is able to dynamically pass the required signal and suppress the interference from adjacent channels. In reconfigurable systems, tunable filters are able to adapt to dynamic frequency selection and spectrum access. They can also adapt to bandwidth variations to maximize data transmission, and can minimize interferences from or to other users. Tunable filters can be also used to reduce size and cost in multi-band receivers replacing filter banks. However, the tunable filter often suffers limited application due to its relatively low Q, noticeable return loss degradation, and bandwidth changing during the filter tuning. The research objectives of this thesis are to investigate the feasibility of designing high Q tunable filters based on dielectric resonators (DR) and coaxial resonators. Various structures and tuning methods that yield relatively high unloaded Q tunable filters are explored and developed. Furthermore, the method of designing high Q tunable filters with a constant bandwidth and less degradation during the tuning process has been also investigated. A series of novel structures of dielectric resonators have been proposed to realize in a high Q miniature tunable filters. The first type of TME mode DR filter is designed to be tuned by piezoelectric bending actuators outside the cavity, and has achieved a tuning range from 4.97 to 5.22 GHz and unloaded Q better than 536 over the tuning range. The second type of TME mode tunable filters are integrated with various tuning elements: GaAs varactors, MEMS switches, and MEMS capacitor banks are employed. The designed filter with MEMS switches operates at 4.72 GHz, and has achieved a tuning ratio of 3.5% with Q better than 510 over the tuning range. The designed filter with GaAs varactors operates at 4.92 GHz, and has achieved a tuning ratio of 2% with Q better than 170 over the tuning range. Finally, the designed filter with MEMS capacitor bank operates at 5.11 GHz, delivering a tuning ratio of 3.5% with Q better than 530 over the tuning range. Cavity combline/coaxial resonators are also used in the design of high Q tunable filters. This thesis presents a novel approach to design a tunable cavity combline filter tuned by a MEMS switched capacitor bank. Instead of mechanically moving the tuning disk, the cavity combline filter is tuned with capacitances loading on the tuning disks, which are electrically adjusted by MEMS switched capacitor bank. The assembled 2-pole filter operates at 2.5 GHz with a bandwidth of 22 MHz, a tuning range of 110 MHz and a Q better than 374 over the tuning range. The assembled 6-pole filter operates at 2.6 GHz with a bandwidth of 30 MHz and has a tuning range of 44 MHz. Finally, the design of high Q tunable filter with constant bandwidth is explored. A 4-pole high Q cavity combline tunable filter with constant bandwidth is demonstrated. The tuning has been realized manually and by using a piezoelectric motor respectively. The designed filter operates at 2.45 GHz and has achieved a stable bandwidth of 30 ±1.1 MHz over a tuning range of 400 MHz and an unloaded Q better than 3000. This design method for a constant bandwidth filter is applicable to both cavity combline filters and dielectric resonator filters.1 yea

The Design and Implementation of Continuous Frequency and Bandwidth Tunable Combline Cavity Filters

Design methods for the implementation of continuous centre frequency and bandwidth tunability in bandpass filtering structures are presented in this thesis. Initially, the use of discrete electronic components as providers of tunability are explored for use in planar filters. PIN and varactor diodes are used to control capacitance at key nodes in the circuit through use of voltage or current biasing. The limitations of these devices are explored in terms of linearity. Intermodulation distortion is measured using two-tone characterisation tests. Configurations of three-dimensional combline filters are analysed using HFSS. Filter structures are treated as a combination of resonant frequencies, external couplings and inter-resonator couplings which control centre frequency, return loss ripple level and bandwidth and respectively. A variety of bespoke components are introduced and compared with each other through simulation for their effectiveness of tunability with actuation. Novel, and independent techniques for tuning both resonant frequency and coupling bandwidths are proposed and implemented in physical TEM combline filters simultaneously. The method introduced for resonance tuning allows for the mounting of motorised actuators to be internal to the filter cavity - thereby adding the complexity of tunability to the structure without needing to increase the volume. Two filters of differing complexity incorporating the developed tuning methods (for centre frequency, return loss and bandwidth) are designed and fabricated to the same tuning specifications as each other - centre frequency from 1.8 GHz to 2.0 GHz and bandwidth from 40 MHz to 60 MHz. The first filter is a second-order combline cavity filter capable of bandwidth tunability from 49 MHz to 67 MHz for all centre-frequencies in the range of 1.751 GHz to 1.998 GHz. Passband insertion loss is kept below 1.2 dB for all tuning states with return loss above 10 dB. The second filter is a five-pole design. This filter achieves frequency tunability from 1.764 GHz to 2.015 GHz and 15 dB bandwidth tunability from 41MHz to 85MHz. Midband insertion loss is kept below 1.4 dB in all tuned states

Planar groove gap waveguides

With the increasing demand for wireless services and applications, the integration and coexistence of multi-standard and multi-band operations into a single device has led to intensive research in the design of tunable and reconfigurable planar devices. A planar medium to achieve this integration is the Substrate Integrated Waveguide (SIW). However, due to a lack of DC isolated planes of the structure, bridging wires or concentric etched rings are often used to enable active device biasing. This research presents a novel planar structure referred to as the Planar Groove Gap Waveguide (PGGWG). The new structure has similar modal characteristics to air-filled machined Groove Gap Waveguide (GGWG), but in a low-cost fabrication technology that is readily integrated with surface mount components. The structure provides two DC isolated conducting planes, while still providing a low loss planar transmission medium. Simulation results demonstrate the existence of a TE10 propagating mode within the artificially created bandgap. There is good agreement between de-embedded simulated and measured results over the usable bandwidth of the waveguide (28 to 40 GHz). A passband is measured having an average insertion loss of 1.2 dB and 0.5 dB insertion loss variation implemented on a substrate of relative permittivity r of 3.5, and loss tangent of 0.004. The broadband characterization of the transmission line loss and phase constant for PGGWG at Ka-band shows that PGGWG has comparable attenuation over the band of interest to SIW. The transmission line Q-factor is found to vary from 135 to 140 over the band of interest, which is comparable to SIW in the same medium. PGGWG is also found to have a phase constant of nearly double that of comparable SIW, which is a significant results for system miniaturization. The unloaded Q-factor of a 33.5GHz PGGWG rectangular cavity resonator is measured to be 209. This is found to be comparable to an SIW resonator on the same substrate and frequency band. This work further explores the DC isolation property of the PGGWG by presenting electrically tunable PGGWG resonant cavities. It is found that a simple biasing network can be applied to the cavity using a varactor diode to vary the resonant frequency of the cavity. This is done without bridging wire and concentric etched rings as a direct result of the DC isolation of the PGGWG. A tuning range of 4.5% is achieved in measurement. From the experiments conducted, it is concluded that PGGWG can be used as an alternative planar waveguide media. The PGGWG platform can be used in the design and implementation of RF front-end components at millimeter waves. Its DC isolated conducting planes also provide a simple way of biasing active components in frequency agile applications

A study of tunable filters technology in RF/microwave engineering

Due to increasing demand for wireless communication systems, and because of the stringent requirements of the congested RF-frequency spectrum, reconfigurable/tunable filters have advanced significantly in recent years. Tunable filters can be tuned to different frequency bands constituted a qualitative shift in the field of civil and military communications because of their great potential to minimise the size, complexity, power consumption and cost of traditional filter banks. At the same time, high performance is becoming increasingly important to meet the modern communication systems’ specifications. Against this background, this dissertation provides a study of tunable filters technology in RF/microwave Engineering. In order to accomplish this study, several tunable filters using different tuning approaches have been presented in this dissertation. A mechanically tuned lowpass filter is presented achieving a good tuning range over the filter’s passband. The suspended substrate stripline (SSS) topology has been utilized to obtain a high-quality response while the generalized Chebyshev responses has been applied to obtain flexible transmission zeros in terms of controlling their locations. Tuning was achieved by using a fabricated mechanical structure to tune a set of five SSS resonators synchronously. A systematic numerical design of this type of filters has been offered with full equations’ derivations and consequentially manufactured samples are validated experimentally and presented in this work. A novel design of a narrow tunable bandwidth bandpass filter with two transmission zeros has been developed. In this project, two different structures were combined containing the microstrip structure to simplify the integration with other system parts and the SSS structure to obtain high quality response. Moreover, it introduces two transmission zeros at both sides of the filter’s passband without the need of using the conventional cross coupling method. Furthermore, two different tuning approaches have been used, one for tuning the bandwidth and the two transmission zeros while the second one was for fine tuning. An extensive design methodology and a numerical design example for both, the fixed and tunable filters have been presented and consequentially the proposed design has been proven experimentally. A new cascaded bandpass filter is presented offering an outstanding response with relatively small number of cascaded elements. This filter utilizes the characteristics of the Step Impedance resonators (SIR) in terms of their flexibility of controlling the spurious response and the insertion loss by changing the ratio of the filter’s high to low impedance. In addition, it offers high quality responses by using SSS structures. The filter’s design methodology is presented, extensively illustrated with a numerical example and proven experimentally. A tuning feasibility of the cascaded SSS filter has been introduced where the electrical tuning has been used to tune the lower side of the passband while the upper side is mechanically tuned. The proposed tuning approach has been simulated by using an EM full-wave simulation software and presented whereas the manufacturing was unfortunately postponed due to the end of the research time

Electronically reconfigurable wideband microwave filters

Many systems require multi function capability in the filter aspects of systems; the method currently used is filter banks which take up a lot of board space. It is thought that reconfigurable filters hold the key to replacing filter banks in order to save board space and thus potentially increasing functionality of the systems. The aim of this research is to develop electronically reconfigurable microwave filters for future communication systems. The project investigates some key design issues of reconfigurable filters. Circuits were modelled and full-wave electromagnetic simulations were performed for the investigation. Experimental work was carried out to demonstrate advanced reconfigurable microwave devices. The components used in each concept investigated were pin diodes due to their superior performance in wideband and high frequency applications. Firstly a single coupled line concept was looked at for bandwidth reconfigurability. This concept was then further developed for industrial applications by simply cascading these sections to obtain a high selective filter. A design method was developed for any number of cascades both with and without an impedance transformer; the use of LCP was used to increase flexibility due to its desirable characteristics. The most desirable outcome would be filter to simultaneously control bandwidth and frequency. In order to tackle this issue the coupled line concept was adapted to incorporate frequency tunability, along with a design method being presented. Furthermore, a cascaded highpass/ lowpass filter was also explored for this concept for added flexibility in the design of a filter capable of control of both bandwidth and center frequency

Advances in pedestal substrate integrated waveguide filters

Thesis (MEng)--Stellenbosch University, 2022.ENGLISH ABSTRACT: This dissertation presents a set of advances to the recently proposed Pedestal Substrate Integrated Waveguide (SIW) structure as a solution to various problem areas in the field of microwave filters. The structure consists of an evanescent-mode SIW cavity that is loaded with a square pedestal connected to the ground with a metal post. This structure is firstly investigated and compared to other common microwave resonators. It is then utilized in 3 different ways. The work includes the design of a coupled resonator filter with both positive and negative cross-coupling. Electric coupling is obtained with an I-shaped line between pedestal tops, while positive coupling is obtained in the traditional manner with inductive irises. Both types of couplings offer large ranges of coupling values and are easily implemented in this structure. The proposed structure can also introduce mixed coupling. A proof-of-concept sixth order cross-coupled bandpass filter, with a 5 % bandwidth at 5 GHz, and both real and imaginary axis transmission zeros, is designed and measured. Secondly, the dissertation presents a novel partially air filled pedestal resonator. The pedestal SIW topology is adapted to create partially air filled pedestal SIW resonators to reduce losses and increase Q factors while maintaining small sizes. A comparison of three different types of pedestal resonators is done between a totally filled pedestal SIW resonator, a partially air-filled pedestal resonator and an empty pedestal resonator, show ing the increase in Q factor for the same size. Then the use of micro-machining to create these novel resonators is illustrated and explained. A resonator and second order filter prototypes are manufactured, using the manufacturing process explained, and tested. It was shown that the Q factor can be increased from 186 for a fully filled dielectric resonator to 285 for a partially air filled resonator. This shows a 34.7 % increase. The last application of the pedestal resonator is in the use of tunable structures. The pedestal resonator is shown to be made easily tunable by the addition of PIN diodes to the pedestal post, seperated with an annular ring. Four separate stages of frequency are obtained in this manner. Two resonators and one third order filter are designed, manufac tured and tested. Good frequency tunability is obtained in simulation and measurement, but high losses were observed in the measured prototypes.AFRIKAANSE OPSOMMING: Hierdie verhandeling bied ’n aantal uitbreidings ann tot die onlangse voorgestelde voet stuk oppervlak geïntegreerde golfleier struktuur, as ’n oplossing vir verskeie probleemareas op die gebied van mikrogolffilters. Die struktuur bestaan uit ’n onder afsny holte wat ge vul is met ’n vierkantige voetstuk, gekonnekteer aan die grond met metaal. Eerstens is die struktuur ondersoek en vergelyk met ander algemene mikrogolfresoneerders. Daarna is dit op 3 verskillende maniere toegepas. Hierdie werk sluit die ontwerp van ’n gekoppelde resoneerder filter in met beide positiewe en negatiewe kruis-koppeling. Elektriese koppeling is bereik met ’n I-vormige lyn tussen die voetstuk toppe, terwyl positiewe koppeling op die tradisionele manier van induktiewe openinge bereik is. Beide tipe koppelings bied ’n wye reeks van koppelingwaardes en kan maklik geimplementeer word in hierdie struktuur. Die voorgestelde struktuur kan ook gemengde koppelings voorstel. Om die konsep te bewys is ’n sesde orde kruiskoppeling banddeurlaat filter met ’n 5% bandwydte teen 5 GHz is ontwerp en gemeet. Die verhandeling bied die nuwe gedeeltelike luggevulde voetstuk resoneerder aan. Die voetstuk oppervlak geïntegreerde golfleier topologie is aangepas om ’n gedeeltelike lugge vulde voetstuk oppervlak geïntegreerde golfleier resoneerder te maak om die verliese en toegevoegde Q faktore te verminder terwyl die kleiner vorm behou is. ’n Vergelyking van drie verskillende tipe pedestal resoneerders is gedoen. ’n Geheelgevulde pedestal SIW resoneerder, ’n gedeeltelik luggevulde voetstuk resoneerders en ’n leë voetstuk resoneerder is met mekaar vergelyk om die toenname in Q faktor aan te dui vir dieselfde grootte. Daarna word die gebruik van mikro-masjinerie geillustreer om hierdie nuwe resoneerder te vervaardig en te bespreek. Prototipes van ’n resoneerder en ’n tweede orde filter is vervaardig deur gebruik te maak van die bespreekte proses en daarna getoets. Dit het aangedui dat die Q faktor van 186 vir ’n ten volle di-elektriese resoneerder toe kan neem tot 285 vir ’n gedeeltelike luggevulde resoneerder. Hierdie is ’n toenname van 34,7%. Die laaste toepassing van die voetstuk resoneerder is met die gebruik van verstelbare strukture. Die voetstuk resoneerder blyk maklik verstelbaar te wees met die toevoeging van PIN diodes aan die voetstuk, wat met ’n annular ring geskei word. Vier verskillende frekwensie stadia word op hierdie manier bereik. ’n Resoneerder ’n derde orde filter is ontwerp, vervaardig en getoets. Goeie verstelbare frekwensie is bereik in simulasie en metings, maar groot verliese is gesien tydens metings.FRENCH RESUME: Cette thèse concerne l’étude de structures de type guide d’ondes intégrés aux substrats (Substrate Integrated Waveguide - SIW) et plus particulièrement les structures appelées Pedestal Substrate Integrated Waveguide. Celle-ci est constituée d’une cavité SIW fonc tionnant sur des modes évanescents, chargée par une capacité, laquelle est physiquement constituée d’une plaque métallique située sur un plan intermédiaire et reliée au plan mé tallique inférieur par un trou métallisé. Ce type de structures, récemment apparue dans la littérature scientifique, apparait comme l’une des solutions pertinentes aux problèmes rencontrés dans le domaine de la conception et l’intégration de filtres micro-ondes. Cette topologie Pedestal SIW est présentée et son fonctionnement est détaillé, puis elle est com parée à d’autres résonateurs micro-ondes classiquement utilisés. Trois axes de travail autour de cette structure sont ensuite présentés. Le premier concerne la conception de filtres s’appuyant sur ce type de résonateur et présentant des couplages croisés électriques et magnétiques. Le couplage électrique est obtenu grâce à l’introduc tion d’une ligne en forme de I située au niveau des plaques métalliques chargeant les cavités SIW, tandis que le couplage magnétique est obtenu de façon plus traditionnelle via des iris de couplages. Ces deux types de couplages offrent de larges plages de valeurs de couplage et la configuration proposée peut également produire un couplage mixte. Afin de démontrer la pertinence et la facilité de mise en œuvre, une preuve de concept a été réalisée grâce à un filtre passe-bande d’ordre six à couplage croisé générant des zéros de transmission situés sur les axes réels et imaginaires (zéros de transmission visibles sur la réponse en amplitude et en phase), a été conçu, réalisé et mesuré. Ce filtre présente une bande passante relative de 5 % à 5 GHz. Le deuxième axe investigué concerne l’utilisation de résonateurs de type Pedestal SIW au sein de structures accordables. Il est démontré que le résonateur est facilement rendu accordable par l’ajout de diodes PIN connectées sur la face supérieure du résonateur sur laquelle est gravée une bague annulaire. Deux résonateurs et un filtre d’ordre trois ac cordables sur quatre états ont été conçus, réalisés et testés. Finalement, le troisième axe porte sur le développement de résonateurs Pedestal SIW partiellement vides. L’objectif de l’utilisation d’une telle configuration technologique est de réduire les pertes et d’augmenter les facteurs Q tout en conservant une bonne compac ité. Après une étude théorique, les éléments de réalisation technologique sont présentés puis l’optimisation de différentes configurations est menée. Ensuite, La conception, la réalisation et la mesure d’un résonateur et d’un filtre de second ordre sont présentées. Les résultats démontrent une augmentation du facteur de de qualité de l’ordre de 35% par rapport à une structure entièrement emplie de diélectrique, permettant d’atteindre un facteur de qualité de 285.Master

Broadband mm‐wave propagation characterization of planar groove gap waveguide

We present, experimental broadband propagation characterization of a planar groove gap waveguide (PGGWG) from 29 to 40 GHz. The transmission line Q‐factor is found to vary from 110 to 130 over the band, which is shown by comparison of measurement data to be comparable to substrate integrated waveguide (SIW). PGGWG is found to have a phase constant of nearly double that of SIW using the same materials and manufacturing process. This is a significant result for system miniaturization.The National Research Foundation of South Africahttp://wileyonlinelibrary.com/journal/mop2021-05-01hj2020Electrical, Electronic and Computer Engineerin

Fully Integrated High-Performance MEMS Lumped Element Filters for Reconfigurable Radios.

In this research, we present RF MEMS filters which address the most challenging performance requirements of modern RF front-end systems, namely multi-band processing capability, low energy consumption, and small size. These filters not only provide a wide tuning range for multiple-band selection, but also offer low loss, high power handling capability, fast tuning speed, and temperature stability. Two different technologies are considered for tunable lumped element filter targeting UHF range. The first technology is a tunable RF MEMS platform based on surface micromachining, enabling fabrication of continuously tuned capacitors, capacitive and ohmic switches, as well as high-Q inductors, all on a single chip. The filter is in a third-order coupled resonator configuration. Continuous electrostatic tuning is achieved using three tunable capacitor banks each consisting of one continuously tunable capacitor and three switched capacitors with pull-in voltage of less than 40V. The center frequency of the filter is tuned from 1GHz to 600MHz while maintaining a 3dB-bandwidth of 13 to 14% and insertion loss of 2%. The filter occupies a small size (1.5 cm x 1.0 cm). This filter shows the best published performance yet in terms of insertion loss, out-of-band rejection, temperature stability, and tuning range. The second technology is based on a new tuning mechanism utilizing phase-change (PC) materials. PC technology has been investigated and adopted in memory industry due to its fast transition time in nano second range, small size, and high resistance change ratio. Although PC materials offer several benefits, they have not been considered for RF applications because of their limited power handling capability and relatively higher on-resistance in their current form. In this work, germanium tellurium (GeTe) is considered as it offers a low on-resistivity and pronounced resistance change ratio of up to 106. To characterize RF properties of GeTe, different types of RF switches have been fabricated and compared. Such PC switches can be monolithically integrated with other micromachined components to implement reconfigurable front-end modules, potentially offering high tuning speed, low loss, high linearity, and small size.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/98038/1/yhshim_1.pd