Modelling of Antenna Responses

Mutonkole, Ngoy (2016-12)

Thesis (DPhil)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: This dissertation presents surrogate modelling techniques for the radiation patterns and scattering parameters of antennas. The models are developed in the context of calibration of re ector antennas as well as antenna design activities such as design space exploration, optimisation and sensitivity analysis. On the calibration front, a method is proposed to recover the radiation pattern, resulting from some physical deformation of an o set Gregorian re ector antenna, over a wide frequency bandwidth by taking a few directional measurements at a single frequency. The proposed technique combines characteristic basis function patterns (CBFPs) with the linear algebraic notion of subspace projection and is shown to achieve pattern recovery with better than -40 dB accuracy over a bandwidth of up to a decade. Concerning surrogate models for antenna design, models based on the parametrisation of CBFPs are presented at three levels: (i) CBFPs are parametrised on a xed grid of EM simulated samples to yield multivariate models of the full radiation pattern. The associated S-parameters are modelled through an indirect parametrisation of the poles and residues obtained by tting S-parameter data with rational functions. (ii) A univariate adaptive sampling algorithm is devised to model the frequency dependence of the full radiation pattern by judiciously selecting the frequency samples at which the antenna is simulated. The proposed algorithm is guaranteed to converge to an accurate model in a modest number of iterations, thereby improving the e ciency of frequency domain antenna simulations. (iii) A multivariate adaptive sampling algorithm is devised to model the full radiation pattern as well as S-parameters as a function of multiple design variables (including frequency). The proposed adaptive sampling techniques have the additional feature of approximation error control. The proposed surrogate modelling techniques can be used to improve the calibration e ciency of re ector antennas (since fewer measurements are required for wideband systems), as well as to improve the design work flow of antennas by reducing the computational cost of the associated design activities.

AFRIKAANSE OPSOMMING: Hierdie proefskrif stel surrogaat modelleringstegnieke voor vir die stralingspatrone en strooiparameters van antennas. Die modelle is ontwikkel binne die konteks van kalibrasie van weerkaatsantennas, sowel as antenna ontwerp aktiwiteite soos ontwerp-ruimte verkenning, optimering, en sensitiwiteitsanalise. Vir die kalibrasie is 'n metode voorgestel wat die stralingspatroon verkry, as gevolg van 'n siese vervorming van 'n afset Gregoriaanse weerkaatsantenna, oor 'n wye frekwensie bandwydte deur slegs 'n paar direksionele metings te neem by 'n enkele frekwensie. Die voorgestelde tegniek kombineer karakteristieke basisfunksiepatrone (KBFP's) met die idee van subspasie projeksie uit lineêre algebra, en toon patroon herwinning van beter as -40 dB akkuraatheid oor tot 'n dekade bandwydte. Met betrekking tot surrogaat modelle vir antenna ontwerp word daar modelle wat gebaseer is op die parameterisering van KBFP's voorgestel op drie vlakke: (i) KBFP's word geparameteriseer op 'n vaste rooster van EM-gesimuleerde monsters om multi-veranderlike modelle van die volledige stralingspatroon te kry. Die geassosieerde S-parameters word gemodelleer deur 'n indirekte parameterisering van die pole en residue wat deur die passing van rasionale funksies op S-parameters verkry is. (ii) 'n Enkel-veranderlike aanpasbare monsteringsalgoritme is voorgestel om die frekwensie-afhanklikheid van die volledige stralingspatroon te modelleer, deur oordeelkundig frekwensie-punte te kies waar die antenna gesimuleer moet word. Die voorgestelde algoritme is gewaarborg om te konvergeer na 'n akkurate model binne 'n beskeie aantal iterasies, wat die e ektiwiteit van frekwensie-gebied antenna simulasies verbeter. (iii) 'n Multi-veranderlike aanpasbare monsteringsalgoritme is voorgestel om die volledige stralingspatroon, sowel te modelleer as die S-parameters, as 'n funksie van veelvoudige ontwerpveranderlikes (insluitend frekwensie). Die voorgestelde aanpasbare monsteringstegnieke kan ook die benaderingsfout beheer. Die voorgestelde surrogaat modelleringstegnieke kan gebruik word om die kalibrasie e ektiwiteit van weerkaatsantennas te verbeter (aangesien minder metings nodig is vir wyeband stelsels), sowel as om die ontwerp werkswyse vir antennas te verbeter deur die rekenaar berekeningskoste van die geassosieerde ontwerp aktiwiteite te verminder.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/100048
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