On the Design of Optimal Noise Matching Networks for a Class of Multi-Mode Antennas
Thesis (PhD)--Stellenbosch University, 2019.
ENGLISH ABSTRACT: In modern times, Multiple-Input-Multiple-Output (MIMO and Multiple-Input- Single-Output (MISO receivers have commonly been implemented using coupled antenna arrays. This holds many advantages, including but not limited to, increased channel capacity, decreased mechanical size and weight, ease of operation and maintenance and reduced cost. A large body of theory exists on the properties and effects of mutually coupled radiating structures and the differences exhibited compared to single radiating structures. This project investigates the use of impedance matching to achieve improvements in the output Signal-to-Noise Ratio of such coupled antenna arrays as they are scanned over angle. As an array is scanned over angle, the optimal source impedance for noise matching will vary. This project defines an approximation method for the varying optimal impedance, chooses fixed points either based on the varying impedance or coverage of the surface area of the Smith chart, and considers previously presented methods in literature for optimum impedance selection. The calculated performance is then numerically optimized. The methods are applied to a novel Quad Mode Antenna as well as a standard Four Monopole Array as control, so that conclusions on the SNR improvement ability of the Quad Mode Antenna can be drawn. In order to perform the approximation and numerical optimization, refinements to the theoretical models available in literature were made and a software based model constructed in MATLAB. A simulated model in ADS was also made to serve as confirmation of the values calculated by the refined model. The models are seen to agree with each other. The degree of similarity of receiver responses over implementation criteria for a given antenna array is quantitatively and qualitatively discussed at the hands of the Structural Similarity Index, an image processing technique. Secondary considerations for the selection of a matching criteria is discussed. Conclusions on the degree to which the Quad Mode Antenna lends itself to SNR improvement are drawn at the hand of the comparative improvements in the Four Monopole Array. Conclusions on the improvement of output SNR through the proposed methods are also drawn and discussed subject to the two cases for which the methods were implemented.
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