Thesis (PhD)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Multi-mode coupled cavity filters have been the mainstay of commercial satellite
communications systems since their introduction in 1970. Multi-mode filters use more than
one resonant mode in a single cavity resonator, thereby reducing the size and weight of the
filter. This is especially advantageous for satellite applications where the size and weight of
the communications payload must be minimised. The use of more modes also increases the
complexity of the filter design.
Iris design plays an integral part in the design of multi-mode coupled cavity filters. Currently,
irises are mostly designed using either the small aperture theory derived by Bethe, or a
standard numerical technique. A recent study comparing these two techniques shows that
approximations made in standard correction factors applied to small aperture theory, can lead
to unacceptable errors. While numerical techniques are clearly required for the accurate
design of complex irises, the standard numerical technique is only suited to the design of
relatively simple iris structures.
This dissertation presents three new CAD procedures for the design of irises in multi-mode
coupled cavity devices. The new procedures are verified by numerical examples and
measurements.
Two new multi-mode coupled cavity devices were designed and tested using the CAD
procedures developed in this work. The first is a new diplexer structure that realises two
fourth order Chebyschev filter channels in three quadruple-mode cavities. Through correct
placement and accurate design of irises, channel isolation was increased beyond that of
existing multi-mode diplexer structures.
The second application is the development of a new coupling structure for the replacement of
coupling and tuning screws. A third order triple-mode cavity filter, including this new fixed
coupling element, was designed using the CAD procedures developed in this dissertation. / AFRIKAANSE OPSOMMING: Multi-modale gekoppelde resoneerder filters word reeds vanaf die eerste verskyning van
kommersiele sateliet-kommunikasiestelsels in 1970 gebruik. Vir hierdie toepassing is die
fisiese grootte en massa van die filters in die kommunikasiestelsels van groot belang. Multimodale
filters gebruik meer as een resonante modus in ‘n golfgeleier resoneerder om die
fisiese grootte en massa van die filter te verminder. Hoe meer resonante modusse in een
golfgeleier resoneerder, hoe kleiner en ligter die filter. Die gebruik van meer modusse
kompliseer egter die ontwerp van die filter.
‘n Baie belangrike aspek van multi-modale filterontwerp is die ontwerp van die irisse wat die
golfgeleier resoneerder skei. Die irisse word tans ontwerp, of deur middel van Bethe se klein
iris teorie, of met die gebruik van ‘n standaard numeriese metode. ‘n Onlangse studie toon
aan dat sekere standaard toevoegings tot Bethe se teorie, benaderings bevat wat tot foutiewe
iris ontwerp kan lei. Numeriese metodes is dus noodsaaklik vir akkurate iris ontwerp.
Hierdie studie wys egter dat die bestaande numeriese tegnieke beperk is tot die ontwerp van
relatief eenvoudige irisse.
Hierdie proefskrif bied drie nuwe rekenaargesteunde ontwerpsprosedures vir die doeltreffende
ontwerp van verskillende klasse irisse in multi-modale golfgeleier resoneerder filters. Die
nuwe metodes word getoets aan die hand van numeriese voorbeelde, en/of gemete resultate.
Twee nuwe komplekse multi-modale golfgeleier resoneerder filter toepassings is ontwerp
deur gebruik te maak van die nuwe ontwerpsprosedures. Die eerste is ‘n nuwe diplekser
struktuur met twee vierde-orde Chebyschev filterkanale in drie golfgeleier resoneerders wat
elk vier resonante modusse ondersteun. Deur korrekte en akkurate plasing van die irisse word
‘n groot verbetering in kanaalisolasie bo ‘n bestaande multi-modale diplekser verkry.
Die tweede toepassing is die ontwikkeling van ‘n nuwe koppelstruktuur vir die vervanging
van die gebruiklike koppel- en aanpassingskroewe. ‘n Derde-orde trippel-modus filter,
gebaseer op hierdie nuwe struktuur, is ook ontwerp deur van die nuwe ontwerpsalgoritmes
gebruik te maak.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52723 |
| Date | 04 1900 |
| Creators | Steyn, Werner |
| Contributors | Meyer, P., 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 | Unknown |
| Type | Thesis |
| Format | 146 p. : ill. |
| Rights | Stellenbosch University |
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