Beamforming techniques for a quad-mode antenna array

Van Tonder, Geomarr (2017-03)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

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.

AFRIKAANSE OPSOMMING: Hierdie tesis is gebaseer op 'n multimodus antenna ontwerp, deur 'n groep navorsers van die Universiteit van Stellenbosch. Die antenna is ontwerp met twee mede-geleë dipole en 'n silindriese monopool antenna, wat terug na die grond vlak gevou is. Deur elke dipool arm aan te dryf met 'n kwadraksiale voerlyn word vier fundamentele ortogonale elektromagnetiese modus, ook bekend as multimodus waargeneem. 'n Unieke stralingspatroon word waargeneem deur die verskeie multimodus reaksies te kombineer. Navorsing is verder uitgebrei om 'n stralingspatroon met isotropiese kenmerke te verkry. Dit word gedoen deur die gebruik van optimeringstegnieke soos die genetiese algoritme en die Nelder-Mead simpleks algoritme. Die vier fundamentele multimodusse kan ten volle gekenmerk word deur hul ekwivalente enkel geeindigde opwekking. 'n Netwerk, met enkele terminasies word verkry deur die line^ere kombinasie van die multimodusse opwekkings deur gebruik te maak van die algemene verstrooiing matriks transformasie tegniek. Die fokus van die proefskrif skuif na die ontwerp van 'n voernetwerk wat gebruik maak van 'n stel optimale opwekkings as die uitset metode. Die voernetwerk is ontwerp en geïntegreer in die multimodus antenna in ADS Agilent en gesimuleer met behulp van CST Microwave Studio®. Verdere ondersoek word in werking gestel om die antenna in 'n 2 x 2 samestelling te plaas met 'n spasiëring van 'n half-gol engte. Die skikking se bundel patroon word gestuur na 'n gewenste waarnemingspunt met behulp van die ingeboude elementpatroon, wat die aktiewe weerkaatskoësiënt insluit. Dit word bereik deur die oplossing van beide die maksimum-aanwins bundelvorming stelling en die toegevoegde veldaanpassing voorwaarde. Die maksimum aanwins oor 'n hemisferiese dekking is ingestel in 'n skikking, en 'n wins variasie van 2:7 dBi word uitgebeeld. Verder, deur die optimering van hierdie stel multimodus patrone in 'n skikking word 'n stel multimodus opwekkings verkry met 'n maksimum aanwins variasie oor die halfrond van 2:3 dBi, gesimuleer met behulp van die ingeboude elementpatroon.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101152
This item appears in the following collections: