Antenna elements for sparse-regular aperture arrays

Klopper, Brandt (2019-04)

Thesis (PhD)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: The central theme of this dissertation regards the design and analysis of antenna elements in sparse-regular aperture arrays (AAs) for radio astronomy applications. Throughout this work, a set of modelling techniques are presented to efficiently analyse the impedance and radiation responses of sparse-regular AA elements, which are required to obtain key AA radiometric figures-of-merit. These modelling techniques are applied to a range of narrowband and broadband AA elements, including a novel sparse-regular candidate AA element for the Square Kilometre Array's Mid-Frequency Aperture Array (SKA MFAA). A thorough study of response models for sparse-regular AA elements is presented, considering several options for the radiometric and full-wave electromagnetic modelling of the antenna elements, as well as global surrogate models for multivariate AA element responses. A design study is presented in which global surrogate modelling techniques are applied for the first time to the design of broadband AA elements, with results that improve upon the per-element receiving sensitivity performance of prior work across a 4.5:1 bandwidth and multiple scan angles. To improve upon the limited scan and frequency coverage occurring in contemporary AA element design, a global modelling framework is proposed to efficiently estimate sparse-regular AA element impedance responses over a continuous and broad range of frequencies and scan angles. Special attention is paid to the incursion of grating lobes into visible space, which causes rapid response variation and can significantly degrade the elements' active impedance matching. A pre-sampling method is proposed to support the construction of adaptively sampled impedance response models, based on standard array theory and requiring no a priori information of the full-wave electromagnetic behaviour of the AA element under analysis. Global models built with the proposed method are shown to obtain significantly more accurate estimates of the global worst-case active reflection coeficient than models built with standard space-filling sampling and pure adaptive sampling techniques. The global impedance response modelling framework is extended to include the simultaneous modelling of the AA unit cell far-fields, thereby adding radiation responses to the modelling framework and allowing the subsequent determination of figures-of-merit such as receiving sensitivity and intrinsic cross-polarisation ratio. For efficient far-field modelling, two contemporary or-thogonal basis function decomposition techniques are considered, namely the Spherical Wave Expansion (SWE) and Characteristic Basis Function Pattern (CBFP) method. The two methods are tested for a variety of isolated antenna elements as well as elements in regular AAs, in the rst formal comparison of SWE versus CBFP for parametric modelling of antenna far-fields. Following consistent and clear evidence of higher modelling accuracy and computational efficiency, the CBFP method is chosen over SWE to be incorporated into the global modelling framework. A sparse-regular candidate AA element is proposed for use in SKA MFAA, in the form of a pyramidal sinuous AA element. The element geometry exhibits stable impedance behaviour over frequency and scan angle relative to other possible candidate elements, and is presented in dual-polarised form for MFAA. The element design is well-parametrised to allow further optimisation towards meeting all MFAA requirements. Finally, as part of realising an optimisation framework for antenna elements in sparse-regular AAs, an expedited performance modelling technique is proposed to rapidly estimate the sensitivity performance of sparse-regular AA elements. Instead of focusing on accurate global response model accuracy, this technique efficiently quantifies the multivariate response performance in a single scalar figure-of-merit incorporating response features such as the sensitivity minimum and overall response smoothness over its operating parameters. Narrowband and broadband examples yield accurate model results with few high-fidelity response samples, with reasonably accurate values provided for the MFAA pyramidal sinuous element within 350 samples.

AFRIKAANSE OPSOMMING: Die sentrale tema van hierdie proefskrif behels die ontwerp en analise van antenna elemente in yl, reëlmatige samestellings vir radio sterrekunde toepassings. 'n Stel modelleringstegnieke vir die effektiewe analise van impedansie en stralingspatrone van yl reëlmatige samestellings, wat benodig word vir die berekening van belangrike radio sterrekunde werkverrigtingsmaatstawwe, word deurgaans in die proefskrif aangebied. Hierdie modelleringstegnieke word toegepas op 'n reeks nou- en wyeband antenna elemente, wat onder andere 'n kandidaat element insluit vir 'n yl, reëlmatige implementering van die SKA se middelfrekwensie samestelling (SKA MFAA). 'n Sorgvuldige studie van modelle van die weergawes vir yl reëlmatige samestelling elemente word aangebied, waar verskeie opsies vir die radiometriese en vol-golf elektromagnetiese modellering, sowel as globale surrogaat modellering, oorweeg word. 'n Ontwerpstudie word aangebied waarin globale surrogaat modelleringstegnieke vir die eerste keer toegepas word op die ontwerp van wyeband samestelling elemente, met resultate wat verbeter op die per-element ontvangs sensitiwiteit van vorige werk oor 'n 4.5:1 bandwydte en verskeie stuurhoeke. Om te verbeter op die beperkte diskrete frekwensie- en stuurhoekdekking wat voorkom in moderne samestelling element ontwerp, word 'n globale surrogaat modellerings raamwerk voorgestel om op 'n effektiewe wyse die impedansie weergawes van yl reëlmatige samestelling elemente oor 'n kontinue en breë gebied van frekwensie en stuurhoeke af te skat. Spesiale aandag word gegee aan die inval van roosterlobbe in die sigbare gebied, wat vinnige verandering in die weergawe tot gevolg het, en wat die aktiewe impedansieaanpassing van die element beduidend kan beïnvloed. 'n Vooraf monstering metode word voorgestel om die konstruksie van aanpassingsvaardig gemonsterde impedansieweergawe modelle te ondersteun. Die metode is gebaseer op standaard antenna samestelling teorie, en benodig geen vooraf kennis van die vol-golf elektromagnetiese gedrag van die spesifieke element nie. Globale modelle wat met die voorgestelde metode gebou was lewer beduidend meer akkurate afskattings van die globale slegste geval aktiewe weerkaatskoëffisiënt as modelle wat met standaard ruimte-vul en suiwer aanpassingsvaardige monsteringstegnieke gebou was. Die globale impedansieweergawe modelleringsraamwerk word uitgebrei om die gelyktydige modellering van samestelling eenheidselement vervelde te inko-rporeer. Dit voeg stralingspatroon modellering by die raamwerk, wat die bepaling van werkverrigtingsmaatstawwe soos ontvangs sensitiwiteit en intrinsieke kruispolarisasie verhouding insluit. Vir effektiewe verveld modellering word twee moderne ortogonale basisfunksie tegnieke ondersoek, naamlik sferiese golf uitbreidings (SWE) en die karakteristieke basisfunksie patroon metode (CBFP). Die twee metodes word getoets vir 'n verskeidenheid antenna elemente in isolasie, sowel as in samestellings, in die eerste formele vergelyking van die SWE en CBFP vir parametriese modellering van antenna stralingspatrone. Na konsekwente en duidelike bewyse van beter akkuraatheid, sowel as berekeningseffektiwiteit, word die CBFP bo die SWE gekies om verder in die modelleringsraamwerk geïnkorporeer te word. 'n Yl reëlmatige samestelling antenna element word voorgestel vir gebruik in die SKA MFAA, in die vorm van 'n piramidiese sinus-kronkelende antenna. Die element geometrie toon stabiele impedansie gedrag oor frekwensie en stuurhoek relatief tot ander moontlike kandidaat elemente, en word in die dubbel gepolariseerde vorm vir die MFAA aangebied. Die element ontwerp is goed geparametriseer om verdere optimering toe te laat ten einde al die MFAA behoeftes te bevredig. Ten slotte, as deel van die realisering van 'n optimeringsraamwerk vir antenna elemente in yl reëlmatige samestellings, word 'n versnelde werkverrigtings modelleringstegniek voorgestel om vinnig die sensitiwiteit van die elemente af te skat. In stede daarvan om te fokus op 'n akkurate globale model, kwantifiseer hierdie tegniek die meervuldige veranderlike skalaar werkverrigting weergawes, soos die minimum van die sensitiwiteit en die algehele gladheid van die weergawe, op 'n effektiewe manier. Nou- en wyeband voorbeelde lewer akkurate model resultate met min simulasie model monsters, met redelik akkurate waardes gelewer vir die MFAA piramidiese sinus-kronkelende element met minder as 350 monsters oor frekwensie en stuurhoek.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105722
This item appears in the following collections: