An investigation of the equivalence between combline and evanescent-mode waveguide filters & of aspects related to reduction of manufacturing costs for combline filters

Nassar, Shamim O. (2011-12)

Thesis (MScEng)--Stellenbosch University, 2011.

Thesis

ENGLISH ABSTRACT: An investigation of the functional similarities and di erences between a combline lter and an evanescent-mode waveguide lter is presented. The design theory of the two types of lters is outlined. Two lters are designed to operate at a centre frequency of 2 GHz with a 5% bandwidth using similar waveguide dimensions, but using the two di erent design theories. The bandpass characteristics of the two lters are then compared over the primary passband and over a broad range of frequencies to observe the stopband characteristics. It is shown that a combline lter with a large groundplane spacing behaves like an evanescent-mode waveguide lter but a di erence in bandwidth exists between the two. Di erent aspects related to the manufacture of coaxial cavity lters are addressed with speci c emphasis on cost reduction. The considerations to be made when choosing the right materials, manufacturing techniques and surface nishes for microwave coaxial cavity lters so that good performance is obtained while reducing the overall costs associated with manufacturing are discussed. The concept of Design for Manufacture (DFM) is discussed. Three combline lters are designed for reduced manufacturing cost, applying di erent changes in the physical structure to suit the speci c manufacturing technique used. Two of these have the same design speci cations, operating at a centre frequency of 1.3 GHz with a 10% bandwidth but are designed for manufacture using two di erent manufacturing techniques: milling and wire-cutting EDM. The third lter is designed for manufacture using a combination of the milling and wirecutting processes to have a bandwidth of 1.8% with the primary passband centred at 2.125 GHz. Problems encountered in manufacturing are explained, one of which results in the use of waterjet cutting for the manufacture of lters initially supposed to be manufactured using wirecutting EDM. Measurement results for the manufactured lters show a good agreement between the bandwidths of the 3D electomagnetic simulation results. The obtained results also show the e ects of poor surface nishing and of deformations on the resonant frequency and the unloaded Q of the lters.

AFRIKAANSE OPSOMMING: 'n Studie van die funksionele ooreenkomste en verskille tussen kamlyn lters en gol eier-onder-afknip lters word aangebied. Die ontwerpstegnieke van beide tipes lters word aangebied. Twee lters word ontwerp met 'n senterfrekwensie van 2GHz en 'n bandwydte van 5%, met soortgelyke gol eierafmetings maar deur gebruik te maak van die verskillende ontwerpstegnieke. Die gedrag van die twee lters word vergelyk in die deurlaatband sowel as oor 'n wye stopband. Dit word getoon dat 'n kamlyn lter met 'n groot grondvlakspasi ering soos 'n gol eier-onder-afknip lter optree, met 'n verskil in bandwydte. Verskillende aspekte wat verband hou met die vervaardiging van koaksiale lters, met spesi eke klem op koste vermindering, word aangebied. Die oorwegings wat die keuses van materiaal, vervaardigingstegnieke en oppervlakte afwerking be nvloed word bespreek. Die konsep van Ontwerp vir Vervaardiging (DFM in Engels) word bespreek. Drie kamlyn lters word ontwerp vir verminderde vervaardigingskoste deur die siese sruktuur aan te pas by die spesi eke vervaardigingstegniek. Twee van die lters het dieselfde spesi kasie, naamlik 'n senterfrekwensie van 1.3GHz en 'n 10% bandwydte, maar word ontwerp vir twee verskillende vervaardigingsprosesse, naamlik frees en draadsny. 'n Derde lter word ontwerp vir 'n kombinasie van hierdie twee prosesse, en met 'n senterfrekwensie van 2.125GHz en 'n bandwydte van 1.8%. Probleme met die vervaardiging word bespreek, onder andere die verandering van draadsny na water-sny tegnieke. Gemete resultate toon goeie ooreenstemming met die teoretiese analise wat die bandwydtes betref, maar swak oppervlak afwerking het 'n verswakking van die onbelaste Q van die resoneerders tot gevolg.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/18064
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