Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: This dissertation presents modal-based techniques for the effective systematic design of
quadruple-ridged flared horns (QRFHs) as reflector feeds for radio astronomy applications.
A new excitation technique is proposed, consisting of a quadraxial line that terminates in the
quad-ridges through the back lid of the QRFH, which allows for the integration with differential
low-noise amplifiers. An equivalent circuit of this quadraxial feed is presented that allows fast
synthesis of optimal feeding designs for QRFHs. In addition, the quadraxial feeding network
suppresses higher-order modes significantly. The effect of eliminating these unwanted modes
are investigated and the quadraxial feed is shown to outperform the coaxial feed in the known
detrimental aspects of the QRFH – beamwidth narrowing for increased frequency, beamwidth
variation over the upper bandwidth, high cross-polarisation levels, high co-polar sidelobes and
variable phase centre – for the specific QRFH designs.
Ridge-loaded modes are analysed and a large number of cut-off frequencies presented which
are unavailable in literature. The pure-mode excitation of the quadraxial feed allows more
effective control over the modal content in the QRFH. This is exploited in a proposed design
technique where the cut-off frequencies throughout the horn are used to synthesise the ridge
taper profile, in order to achieve the desired modal distribution in the aperture.
The proposed feeding solution is compact and therefore is also attractive for use with cryocoolers,
typically employed with front-end electronics in telescopes for radio astronomy. A
prototype was successfully manufactured and the mechanical implementation of the quadraxial
feed proved to be much more simple than that of the conventional feed – consisting of a coaxial
line realised within the thin ridges. / AFRIKAANSE OPSOMMING: Hierdie proefskrif stel modus gebasseerde tegnieke voor vir die effektiewe sistematiese ontwerp
van viervoud gerifte oopgesperde horings (VGOHs) as weerkaatser voere vir radio astronomie
toepassings.
’n Nuwe voertegniek word voorgestel, wat bestaan uit ’n kwadraksiale lyn wat termineer in
die vier riwwe deur die agterkant van die VGOH, wat die integrasie met differensiële laeruis
versterkers toelaat. ’n Ekwivalente stroombaan van hierdie kwadraksiale voer word aangebied
vir die vinnige sintese van optimale voer ontwerpe vir VGOHs. Boonop onderdruk die kwadraksiale
voer netwerk ook beduidend hoër orde modusse. Die effek van die uitskakeling van
hierdie ongewensde modusse word ondersoek en die kwadraksiale voer oortref die gedrag van
die koaksiale voer in die bekende nadelige aspekte van die VGOH – bundelwydte vernouing
met toenemende frekwensie, bundelwydte variasie oor die boonste bandwydte, hoë kruispolarisasie
vlakke, hoë kopolarisasie sybande en wisselvallige fase senter – vir die spesifieke VGOH
ontwerpe.
Rifgelaaide modusse word geanaliseer en ‘n groot aantal afsnyfrekwensies word aangebied
wat nie beskikbaar is in literatuur nie. Die suiwermodus opwekking van die kwadraksiale voer
bied meer effektiewe beheer oor die modusinhoud in die VGOH. Hierdie aspek word benut in ‘n
voorgestelde tegniek waar die afsnyfrekwensies deur die horing gebruik word om die rif tapsheid
profiel te sintetiseer, sodat die gewensde modale distribusie in die stralingsvlak behaal word.
Die voorgestelde voer oplossing is kompak en daarom ook aantreklik vir die gebruik met
krioverkoelers, wat tipies gebruik word met die voorkant elektronika in teleskope vir radio astronomie.
‘n Prototipe was suksesvol vervaardig en die meganiese implimentasie van die kwadraksiale
voer toon dat dit eenvoudiger is as met die gebruiklike koaksiale voer – wat bestaan uit
‘n koaksiale lyn bewerkstellig binne die dun riwwe.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/96948 |
| Date | 03 1900 |
| Creators | Beukman, Theunis Steyn |
| Contributors | Meyer, Petrie, Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 108 pages : illustrations |
| Rights | Stellenbosch University |
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