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

Ceramic waveguide bandpass filters with spurious modes suppression

An investigation of various ceramic bandpass filters with an improved spurious performance for use in cellular base station filtering applications is presented in this thesis. Monolithic integrated ceramic bandpass filters offer more than 50% size reduction compared to air-filled coaxial resonator filters with the same unloaded Q-factor. However, the stopband performance of these filters is deteriorated by spurious frequencies of the fundamental mode and higher order modes. The probable solution to reducing the effects of these undesired modes is to add a low-pass filter or band-stop filter at the expense of higher in-band losses and bulky volumes. In this work, multiple geometrical design techniques are explored to achieve the optimum out of band performance without any need for a low-pass filter. The improvement in spurious performance of Chebyshev ceramic bandpass waveguide filters is explored. In particular, its design solution aimed to improve the stopband attenuation for these filters. The design of the Chebyshev monolithic ceramic bandpass filter is reviewed, and some realizations are proposed and compared with the filter. The sixth order Chebyshev ceramic bandpass filters with posts were designed with improved spurious performance. The input/output couplings are realized through the use of a coaxial cable placed at the center of the external resonator. The inter-resonator couplings are achieved by placing various metal plated through-holes in the broad dimension of a waveguide. The broad dimension of integrated ceramic waveguide resonators can be utilized as an extra degree of freedom that can be integrated into filter design procedure and a better spurious performance is achieved by mixing resonators of non-uniform widths. Chebyshev ceramic bandpass filters are designed with two and three non-uniform width resonators and significant improvement has been achieved in the stopband performance of the filters. Other solutions involve the mixing of resonators with posts and non-uniform width resonator. The six order ceramic waveguide bandpass filters are simulated and fabricated in an air filled waveguide with tuning screws. Metal tuning screws are included to overcome mechanical discrepancies and imperfections. The stepped impedance resonators were previously applied to both planar, coaxial and air-filled rectangular waveguide filters. Here, for the first time, their use has been extended to monolithic integrated ceramic waveguide filters, accomplishing an exceptional spurious free stopband bandwidth for the filters. Finally, sixth order ceramic loaded waveguide filters were designed and fabricated with ridge and non-uniform width ceramic blocks. Their top and bottom surfaces are metalized through the silver paint with the conductivity of 4 x 10⁷ s/m. Inductive irises are used for inter-resonator coupling where the coaxial probe excites the external resonators of the filter and the excellent stopband attenuation of up to 2.45 *f_o is achieved

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

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

CAS - CERN Accelerator School: RF for Accelerators

These proceedings present the lectures given at the twenty-fourth specialized course organized by the CERN Accelerator School (CAS). The course was held in Ebeltoft, Denmark, from 8-17 June, 2010 in collaboration with Aarhus University, with the topic 'RF for Accelerators' While this topic has been covered by CAS previously, early in the 1990s and again in 2000, it was recognized that recent advances in the field warranted an updated course. Following introductory courses covering the background physics, the course attempted to cover all aspects of RF for accelerators; from RF power generation and transport, through cavity and coupler design, electronics and low level control, to beam diagnostics and RF gymnastics. The lectures were supplemented with several sessions of exercises, which were completed by discussion sessions on the solutions.These proceedings present the lectures given at the twenty-fourth specialized course organized by the CERN Accelerator School (CAS). The course was held in Ebeltoft, Denmark, from 8-17 June, 2010 in collaboration with Aarhus University, with the topic 'RF for Accelerators'. While this topic has been covered by CAS previously, early in the 1990s and again in 2000, it was recognized that recent advances in the field warranted an updated course. Following introductory courses covering the background physics, the course attempted to cover all aspects of RF for accelerators/ from RF power generation and transport, through cavity and coupler design, electronics and low level control, to beam diagnostics and RF gymnastics. The lectures were supplemented with several sessions of exercises, which were completed by discussion sessions on the solutions

Abstracts on Radio Direction Finding (1899 - 1995)

The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion

Bibliography of Lewis Research Center technical publications announced in 1992

This compilation of abstracts describes and indexes the technical reporting that resulted from the scientific and engineering work performed and managed by the Lewis Research Center in 1992. All the publications were announced in the 1992 issues of STAR (Scientific and Technical Aerospace Reports) and/or IAA (International Aerospace Abstracts). Included are research reports, journal articles, conference presentations, patents and patent applications, and theses

Bibliography of Lewis Research Center technical publications announced in 1984

This compilation of abstracts describes and indexes the technical reporting that resulted from the scientific and engineering work performed and managed by the Lewis Research Center in 1984. All the publications were announced in the 1984 issues of STAR (Scientific and Technical Aerospace Reports) and/or IAA (International Aerospace Abstracts). Included are research reports, journal articles, conference presentations, patents and patent applications, and theses