Browsing by Author "Van Tonder, Geomarr"
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- ItemBeamforming techniques for a quad-mode antenna array(Stellenbosch : Stellenbosch University, 2017-03) Van Tonder, Geomarr; Meyer, Petrie; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: This thesis is based on a quad-mode antenna, designed by a group of researchers from the University of Stellenbosch. The antenna is designed using two co-located dipoles and a cylindrical monopole antenna folded back towards the ground plane. By exciting each dipole arm with a quadraxial feed line, four fundamental transverse electromagnetic propagating modes, also known as multi-modes, are observed. Using array theory and combining the multi-mode response, a unique radiation pattern is observed. Further research expands into effectively obtaining a combinational response which illustrates characteristics of an isotropic radiator. This is accomplished by using optimization techniques such as the genetic algorithm and the Nelder-Mead simplex algorithm. The four fundamental multi-modes can be fully characterized by their equivalent singleended mode excitations. A network terminated with single-ended excitations is obtained through a linear combination of the multi-mode excitations by implementing the generalized scattering matrix transformation technique. The focus of the thesis shifts towards the design of a feed network using this set of optimal excitations. Initially the feed network is designed in ADS Agilent. From there it is integrated into the quad-mode antenna design and simulated using CST Microwave Studio®. Research further extended into the field of beamforming by placing the quad-mode antenna in a 2 x 2 array configuration with an interelement spacing of a half-wavelength. Using the embedded element pattern, which includes the active reflection coefficient, the array's beam pattern is steered towards a desired observation point. This is achieved by solving the maximum-gain beamforming theorem and conjugate field matching condition. The maximum gain over a hemispheric field-of-view coverage is configured, and an overall gain variation of 2:7 dBi is obtained. Furthermore, by optimizing this set of multi-mode response patterns in an array configuration, a set of multi-mode excitations are obtained with a maximum gain variation over the hemisphere of 2:3 dBi, when simulated using the embedded element pattern.