CAD-based iris design procedures for multi-mode coupled cavity devices

Steyn, Werner
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Stellenbosch : Stellenbosch University
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.
Thesis (PhD)--Stellenbosch University, 2002.
Electric filters, Wave-guide, Dissertations -- Electronic engineering, Diplexer