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

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the design, development and integration of the UHF-Band, L-Band and S-band Receivers, whilst the X-band design has been superseded by the incorporation of the next phase of the SKA international project.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

Design methods for microwave filters and multiplexers

This thesis is concerned with developing synthesis and design procedures for microwave filters and multiplexers. The core of this thesis presents the following topics. 1) New classes of lumped lowpass prototype filters satisfying generalized Chebyshev characteristics have been investigated. Exact synthesis procedures are given using a relatively new technique termed the alternating pole synthesis technique to solve the accuracy problem. The properties of these filters and their practical advantages have been discussed. Tables of element values for commonly used specifications are included. 2) A new design procedure has been developed for bandpass channel multiplexers connected at a common junction. This procedure is for multiplexers having any number of Chebyshev channel filters, with arbitrary degrees, bandwidths and inter-channel spacings. The procedure has been modified to allow the design of multi-octave bandwidth combline channel filter multiplexers. It is shown that this procedure gives very good results for a wide variety of specifications, as demonstrated by the computer analysis of several multiplexers examples and by the experimental results. 3) A compact exact synthesis method is presented for a lumped bandpass prototype filter up to degree 30 and satisfies a generalized Chebyshev response. This prototype has been particularly utilized in designing microwave broadband combline filters. 4) Different forms of realization have been discussed and used in design and construction of different devices. This includes a new technique to realize TEM networks in coaxial structure form having equal diameter coupled circular cylindrical rods between parallel ground planes. Other forms of realization have been discussed ranging from equal diameter posts, direct coupled cavity waveguide filters to microwave integrated circuits using suspended substrate stripline structure. The experimental results are also given. In addition, the fundamentals of lumped circuits and distributed circuits have been briefly reviewed. The approximation problem was also discussed

Lowpass lter design for space applications in waveguide technology using alternative topologies

The main goal of this project is to study the possibility of utilizing topologies based on curved surfaces (metallic posts) to realize low pass lters in waveguide technologies, as an alternative to the traditional implementation based on rectangular irises, in order to obtain devices that present a higher multipaction threshold. In the rst chapters, the theoretical synthesis techniques utilized are explained. Understanding the synthesis of the di erent types of lter polynomials and prototype networks is necessary in order to precisely design lters with a predictable frequency response. The commercial package HFSS will be used for the design and veri cation of the lters, controlling its operation with scripts in order to automate the design process.Escuela Técnica Superior de Ingeniería de TelecomunicaciónUniversidad Politécnica de Cartagen

System implications of large radiometric array antennas

Current radiometric earth and atmospheric sensing systems in the centimeter wavelength range generally employ a directive antenna connected through a single terminal pair to a Dicke receiver. It is shown that this approach does not lend itself to systems with greatly increased spatial resolution. Signal to noise considerations relating to antenna efficiency force the introduction of active elements at the subarray level; thus, if Dicke switching is to be used, it must be distributed throughout the system. Some possible approaches are suggested. The introduction of active elements at the subarray level is found to ease the design constraints on time delay elements, necessary for bandwidth, and on multiple beam generation, required in order to achieve sufficient integration time with high resolution