Triple-Mode Cavity Bandpass Filter on Doublet with Controllable Transmission Zeros

© 2013 IEEE. On the basis of doublet and its properties, a class of multiple-mode narrow band bandpasss filter is designed and fabricated by simultaneously exploiting the three resonant modes in a single rectangular cavity: TE101, TE011, and TM110 modes. The input/output ports of the proposed filter are fed by coupling a microstrip line to a slot on the side wall of a rectangular cavity. Different modes are excited by changing the position and shape of the two slots at input and output of the rectangular cavity without any intra-cavity coupling. Besides three poles within the passband, a pair of transmission zeros (TZs) is achieved, which can be controlled independently by setting the positions of the two TZs at the lower and/or upper stopband. High stopband attenuation and high filtering selectivity are achieved by considerably allocating three transmission poles and two zeros. In order to verify the proposed theory, two filter prototypes are fabricated and measured

Miniaturized Dual-Band Dual-Mode TM-Mode Dielectric Filter in Planar Configuration

This paper reports a new class of compact inline dual-band bandpass filters using TM-mode dielectric resonators in planar configuration. Thanks to the employment of the dielectric-loaded TM-mode waveguide configuration and the dual-mode TM120 and TM210 resonances, substantial size miniaturization and volume saving (>70%) can be obtained in comparison with conventional waveguide technology. Additionally, the planar topology of the presented concept offers highly desirable advantages for industry and mass production including the ease of manufacturing, assembly, and tuning. Furthermore, the resonating doublets and the nonresonating TM110 mode are effectively utilized to introduce and control both inter-band and outer-band transmission zeros, advantageously increasing the isolation between the two passbands and enhancing the outer-band rejection regions. The general design procedure of the proposed filter is discussed in detail. A three-pole C-band dual-band dual-mode TM-mode dielectric filter is designed, implemented, and measured to validate the proposed configuration

Miniaturized High-Q Tunable RF Filters

This dissertation focuses on the investigation and development of novel efficient tuning techniques and the design of miniaturized high-Q tunable RF filters for high-performance reconfigurable systems and applications. First, a detailed survey of the available tuning concepts and state-of-art tunable filters is provided. Then, a novel so-called inset resonator configuration is presented for the applications of fixed and tunable coaxial filters. The design procedure of frequency tunable filters with constant absolute bandwidth (CABW) is described, and various tunable inset filters are implemented, offering many desirable merits, including the wide tuning range and stable high-Q with minimum variation. For wide octave frequency tuning ranges with CABW, a second novel concept is presented using so-called re-entrant caps tuners. Beside simplicity and compactness, this technique also features enhanced spurious performance and wider tuning capabilities than the conventional means. Also, in this dissertation, various miniaturized reconfigurable dual-band/dual-mode bandpass filters and diplexers are presented using compact dual-mode high-Q TM-mode dielectric resonators. Furthermore, a novel microfluidic-based ultra-wide frequency tuning technique for TM010-mode dielectric resonators and filters is introduced in this dissertation. In addition to the very wide tuning window, this mechanism has key advantages of low-cost, simplicity, and intrinsic switch-off. Lastly, the dissertation includes a novel bandwidth reconfiguration concept with multi-octave tuning using a single element for coaxial bandpass filters. This mechanism brings many features including the fast tuning, constant high-Q, intrinsic switch-off, and wide BW-reconfiguration

Advanced Filtering Solutions in Coaxial SIW Technology Based on Singlets, Cascaded Singlets, and Doublets

(c) 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.[EN] The use of singlets, cascaded singlets and doublets in coaxial substrate integrated waveguide (SIW) technology is proposed in this paper, with the aim of implementing low-loss filters with very compact size and highly-selective symmetric, asymmetric as well as dual-band responses. Singlets based on coaxial SIW resonator structures with source-load coupling are presented and studied. Then, different filter examples based on N cascaded singlets are designed, fabricated and measured at 7.5 GHz, with up to N transmission zeros (TZs) that can be easily located below and above the passband. Moreover, the application of doublets based on a dual-mode coaxial SIW resonator with source-load coupling for achieving extremely compact dual-band filters is presented, and two examples with different bandwidth configuration for each channel are designed, demonstrating the flexibility of the proposed coaxial SIW structure. The obtained experimental results of the different implemented filters show a good agreement with simulations, thus confirming the interesting potential application of these structures for the design of very compact devices with advanced filtering responses.This work was supported by the Ministerio de Economia, Industria y Competitividad, Spanish Government, under Project TEC2016-75934-C4-3-R.Sirci, S.; Sánchez-Soriano, MÁ.; Martínez Pérez, JD.; Boria Esbert, VE. (2019). Advanced Filtering Solutions in Coaxial SIW Technology Based on Singlets, Cascaded Singlets, and Doublets. IEEE Access. 7:29901-29915. https://doi.org/10.1109/ACCESS.2019.2902956S2990129915

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

Planar microwave filters with electronically tunability and other novel configurations

In order to meet the increasing demands of advance wireless communications and radar systems, several novel types of bandpass filters and bandstop filters have been developed in this thesis. A new type of varactor-tuned dual-mode bandpass filters have been presented to achieve a nearly constant absolute bandwidth over a wide tuning range by using a single DC bias circuit. Since the two operating modes (i.e., the odd and even modes) in a dualmode microstrip open-loop resonator do not couple to each other, tuning the passband frequency is accomplished by merely changing the two modal frequencies proportionally. Design equations and procedures are derived, and two two-pole tunable bandpass filters and a four-pole tunable bandpass filter of this type are demonstrated experimentally. Miniature microstrip doublet dual-mode filters that exhibit quasi-elliptic function response without using any cross coupling have been developed. It shows that a single two-pole filter or the doublet can produce two transmission zeros resulting from a double behaviour of the dual-mode resonator of this type. Electromagnetic (EM) simulation and experiment results of the proposed filters are described. Parallel feed configuration of a microstrip quasi-elliptic function bandpass filter has been built with a pair of open-loop dual-mode resonators. By employing this new coupling scheme, a novel filter topology with three-pole quasi-elliptic function frequency response can be obtained, leading to good passband performance, such as low insertion loss and good matching at the mid-band of passband. A designed three-pole bandpass filter of this type is demonstrated experimentally. A new class of dual-band filters based on non-degenerate dual-mode microstrip slow-wave open-loop resonators, which support two non-degenerate modes that do not couple, have been introduced. Different feed schemes that affect the filtering characteristics are investigated. Examples of dual-band filters of this type are described with simulation and experiment results. iii In order to achieve a wide spurious-free upper passband, a novel design of bandstop filter with cancellation of first spurious mode by using coupled three-section step impedance resonators (SIRs) has been developed. This cancellation occurs when two transmission poles coincide with the first spurious mode (transmission zero) by properly choosing the step impedance ratio and the gap between the SIR and the main transmission line. A stripline bandstop filter and a microstrip bandstop filter of this type are designed, fabricated and tested. As a preliminary investigation, the microstrip filter is tuned electronically using ferroelectric thin film varactors

Development of tunable and miniature microwave filters for modern wireless communications

Due to the increasing demand for new wireless services and applications, the high level of integration and the coexistence of multi-standard (MS) or multi-band operations into a single device are becoming defining trends in designing microwave filters. This has driven considerable technological advances in reconfigurable/tunable and miniaturized filters. More specifically, reconfigurable/tunable filters that tune to different frequency bands instead of classical filter banks have great potential to significantly reduce the system size and complexity; while reducing the filter size becomes essential to achieve the highest degree of integration density in compact and portable wireless devices. In the light of this scenario, the objective of this dissertation is to develop the new design technologies, concepts and filtering configurations for tunable microstrip filters and compact passive microwave filters. To this aim, this dissertation is divided into two main parts. The first part (Part I) focuses on the designs of novel varactor-tuned microstrip filters with advanced performances. In this aspect, new topologies for realizing tunable lowpass and highpass filters are firstly developed. State-of-the-art performances, including wide tuning range, high selectivity with multiple transmission zeros, low insertion loss and compact size for all the tuning states are obtained in both of these filters. Secondly, two novel classes of tunable bandpass filters are presented. One of them is designed based on varactor-loaded parallel-coupled microstrip lines (PCML) and short-circuited stubs, which allows the lower passband edge together with two transmission zeros located around the lower passband skirt to be reconfigured separately. While the other tunable bandpass filter is constructed by the combination of tunable bandpass and lowpass filters, featuring both centre frequency and bandwidth tunabilities, as well as high selectivity with abundant transmission zeros. Furthermore, a new concept of tunable lossy filter is demonstrated, which attempts to achieve an equivalent high-Q tunable performance by using low-Q resonators. This concept makes the presented tunable combline filter interesting for some frequency-agile applications in which the low in-band loss variation and high selectivity are much desired while the absolute insertion loss can be a tradeoff. The second part (Part II) is devoted to the design of miniaturized passive microwave filters with improved characteristics. For this, the concept of artificial right-handed and left-handed transmission lines are applied to the signal interference filtering topology, which results in a compact circuit size and good out-of-band performance. In particular, for a further size reduction, such filter is implemented in the forms of multilayered structure by using liquid crystal polymer (LCP) technology. Additionally, another two types of miniaturized bandpass filters using stepped impedance resonators are demonstrated, which are implemented based on different fabrication processes (i.e. LCP bonded multilayer PCB technology and a standard planar PCB technology). Among their main features, the compact size, wide passband, broad stopband with multiple transmission zeros and circuit simplicity are highlighted. For all the proposed design techniques and filtering structures, exhaustive theoretical analyses are done, and design equations and guide rules are provided. Furthermore, all the proposed schemes and/or ideas have been experimentally validated through the design, implementation and measurement of different filters. The fabrication processes of multilayer technology utilized: liquid crystal polymer (LCP) technology and liquid crystal polymer (LCP) bonded multilayer printed circuit board (PCB) technology, are also demonstrated for reference. All of the results achieved in this dissertation make the proposed filters very attractive for their use in modern wireless communication systems

Development of turnable and miniature microwave filters for modern wireless communication

Due to the increasing demand for new wireless services and applications, the high level of integration and the coexistence of multi-standard (MS) or multi-band operations into a single device are becoming defining trends in designing microwave filters. This has driven considerable technological advances in reconfigurable/tunable and miniaturized filters. More specifically, reconfigurable/tunable filters that tune to different frequency bands instead of classical filter banks have great potential to significantly reduce the system size and complexity; while reducing the filter size becomes essential to achieve the highest degree of integration density in compact and portable wireless devices. In the light of this scenario, the objective of this dissertation is to develop the new design technologies, concepts and filtering configurations for tunable microstrip filters and compact passive microwave filters. To this aim, this dissertation is divided into two main parts. The first part (Part I) focuses on the designs of novel varactor-tuned microstrip filters with advanced performances. In this aspect, new topologies for realizing tunable lowpass and highpass filters are firstly developed. State-of-the-art performances, including wide tuning range, high selectivity with multiple transmission zeros, low insertion loss and compact size for all the tuning states are obtained in both of these filters. Secondly, two novel classes of tunable bandpass filters are presented. One of them is designed based on varactor-loaded parallel-coupled microstrip lines (PCML) and short-circuited stubs, which allows the lower passband edge together with two transmission zeros located around the lower passband skirt to be reconfigured separately. While the other tunable bandpass filter is iii constructed by the combination of tunable bandpass and lowpass filters, featuring both centre frequency and bandwidth tunabilities, as well as high selectivity with abundant transmission zeros. Furthermore, a new concept of tunable lossy filter is demonstrated, which attempts to achieve an equivalent high-Q tunable performance by using low-Q resonators. This concept makes the presented tunable combline filter interesting for some frequency-agile applications in which the low in-band loss variation and high selectivity are much desired while the absolute insertion loss can be a tradeoff. The second part (Part II) is devoted to the design of miniaturized passive microwave filters with improved characteristics. For this, the concept of artificial right-handed and left-handed transmission lines are applied to the signal interference filtering topology, which results in a compact circuit size and good out-of-band performance. In particular, for a further size reduction, such filter is implemented in the forms of multilayered structure by using liquid crystal polymer (LCP) technology. Additionally, another two types of miniaturized bandpass filters using stepped impedance resonators are demonstrated, which are implemented based on different fabrication processes (i.e. LCP bonded multilayer PCB technology and a standard planar PCB technology). Among their main features, the compact size, wide passband, broad stopband with multiple transmission zeros and circuit simplicity are highlighted. For all the proposed design techniques and filtering structures, exhaustive theoretical analyses are done, and design equations and guide rules are provided. Furthermore, all the proposed schemes and/or ideas have been experimentally validated through the design, implementation and measurement of different filters. The fabrication processes of multilayer technology utilized: liquid crystal polymer (LCP) technology and liquid crystal polymer (LCP) bonded multilayer printed circuit board (PCB) technology, are also demonstrated for reference. All of the results achieved in this dissertation make the proposed filters very attractive for their use in modern wireless communication systems.MultiWaves Project (PIRSES-GA-2010-247532) of the Seventh Framework Programme (FP7), European Commission

Design and analysis of miniaturized substrate integrated waveguide reconfigurable filters for mm-wave applications.

Doctoral Degree. University of KwaZulu-Natal, Durban.Microwave filters are an integral part of communication systems. With the advent of new technologies, microwave devices, such as filters, need to have superior performance in terms of power handling, selectivity, size, insertion loss etc. During the past decade, many applications have been added to the communication networks, resulting in communication systems having to operate at high frequencies in the region of THz to achieve the stringent bandwidth requirements. To achieve the requirements of the modern communication system, tunability and reconfigurability have become fundamental requirements to reduce the footprint of communication devices. However, the communication systems that are more prevalent such as planar circuits have either a large footprint or are not able to handle large amounts of power due to radiation leakage. In this thesis, Substrate Integrated Waveguide (SIW) technology has been employed. The SIW has the same properties as the conventional rectangular waveguide; hence it benefits from the high quality (Q) factor and can handle large powers with small radiation loss. The Half-mode (HMSIW), Quarter-mode (QMSIW), and Eighth-mode (EMSIW) cavity resonators have been designed and used for the miniaturization of the microwave filters. The coupling matrix method was used to implement a filter that uses cross-coupled EMSIW and HMSIW cavity resonators to improve the selectivity of the filter. Balanced circuit techniques have been used to design the circuits that preserve communication systems integrity whereby the Common Mode (CM) signal was suppressed using Deformed Ground Structure (DGS) and a center conductor patch with meandered line. For the designed dual-band filter, the common mode signal was suppressed to -90 dB and - 40 dB for the first and second passband, respectively. The insertion loss observed is 2.8 dB and 1.6 dB for the first and second passband, respectively. For tunability of the filter, a dual-band filter utilizing triangular HMSIW resonators has been designed and reconfigurability is achieved by perturbing the substrate permittivity by dielectric rods. The dielectric rods’ permittivity was changed to achieve tunability in the first instance, and then the rods’ diameter changed in the second instance. For the lowerband, frequency is tunable from 8.1 GHz to 9.15 GHz, while the upper band is tuned from 14.61 GHz to 16.10 GHz. A second order SIW filter with a two layer substrate was then designed to operate in the THz region. For reconfigurability, Graphene was sandwiched between the Silicon Di-Oxide substrate and the top gold plate of the filter, and the chemical potential of Graphene was then varied by applying a dc bias voltage. With a change in dc voltage the chemical potential of Graphene changes accordingly. From the results, a chemical potential change of 0.1 eV to 0.6 eV brings about a frequency change from 1.289 THz to 1.297 THz

Novel miniature microwave quasi-elliptical function bandpass filters with wideband harmonic suppression

Filters are integral components in all wireless communication systems, and their function is to permit predefined band of frequencies into the system and reject all other signals. The ever-growing demand in the use of the radio frequency (RF) spectrum for new applications has resulted in the need for high performance microwave filters with strict requirements on both inband and out-of-band characteristics. High selectivity, high rejection, low loss and extremely wide spurious-free performance are required for both transmitter and receiver channels. In addition, these devices need to be highly compact, easy to integrate within transceivers and should be amenable to low cost manufacturing. High selectivity is essential to enable the guard band between adjacent channels to be reduced thus improving the efficiency of the RF spectrum and hence increasing the capacity of the system. A low insertion-loss, high return-loss and small group-delay in the passband are necessary to minimize signal degradation. A wide stopband is necessary to suppress spurious passbands outside the filter’s bandwidth that may allow spurious emissions from modulation process (harmonic, parasitic, intermodulation and frequency conversion products) and interfere with other systems. The EMC Directive 89/336/EEC mandates that all electronic equipment must comply with the applicable EN specification for EMI. This thesis presents the research work that has resulted in the development of innovative and compact microstrip bandpass filters that fulfil the above stringent requirements for wireless communication systems. In fact, the proposed highly compact planar microstrip filters provide an alternative solution for existing and next generation of wireless communications systems. In particular, the proposed filters exhibit a low-loss and quasi-elliptic function response that is normally only possible with filter designs using waveguides and high temperature superconductors. The selectivity of the filters has been improved by inserting a pair of transmission zeros between the passband edges, and implementing notched rejection bands in the filter’s frequency response to widen its stopband performance. The filter structures have been analysed theoretically and modelled by using Keysight Technologies’ Advanced Design System (ADS™) and Momentum® software. The dissertation is essentially composed of four main sections. In the first section, several compact and quasi-elliptic function bandpass filter structures are proposed and theoretically analysed. Selectivity and stopband performance of these filters is enhanced by loading the input and output feed-lines with inductive stubs that introduce transmission zeros at specified frequencies in the filter’s frequency response. This technique is shown to provide a sharp 3-dB roll-off and steep selectivity skirt with high out-of-band rejection over a wide frequency span. In addition, the 3-dB fractional bandwidth of the filters is shown to be controllable by manipulating the filter’s geometric parameters. Traditional microwave bandpass filters are designed using quarter-wavelength distributed transmission-line resonators that are either end-coupled or side-coupled. The sharpness of the filter response is determined by the number of resonators employed which degrades the filter’s passband loss performance. This results in a filter with a significantly larger footprint which precludes miniaturization. To circumvent these drawbacks the second section describes the development of a novel and compact wideband bandpass filter with the desired characteristics. The quasi-elliptic function filter comprises open-loop resonators that are coupled to each other using a stub loaded resonator. The proposed filter is shown to achieve a wideband 3-dB fractional bandwidth of 23% with much better loss performance, sharp skirt selectivity and very wide rejection bandwidth. The third section describes the investigation of novel ultra-wideband (UWB) microstrip bandpass filter designs. Parametric study enabled the optimization of the filter’s performance which was verified through practical measurements. The proposed filters meet the stringent characteristics required by modern communications systems, i.e. the filters are highly compact and miniature even when fabricated on a low dielectric constant substrate, possess a sharp quasi-elliptic function bandpass response with low passband insertion-loss, and ultra-wide stopband performance. With the rapid development of multi-band operation in modern and next generation wireless communication systems, there is a great demand for single frequency discriminating devices that can operate over multiple frequency bands to facilitate miniaturization. These multi-band bandpass filters need to be physically small, have low insertion-loss, high return-loss, and excellent selectivity. In the fourth section two miniature microstrip dual-band and triple-band bandpass filter designs are explored. A detailed parametric study was conducted to fully understand how the geometric parameters of the filters affected their performance. The optimized filters were fabricated and measured to validate their performance