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

[摘要] ENGLISH ABSTRACT: An investigation of the functional similarities and di erences between a comblinelter and an evanescent-modewaveguidelter is presented. The design theory of the two types oflters is outlined. Twolters are designedto operate at a centre frequency of 2 GHz with a 5% bandwidth using similar waveguide dimensions, but usingthe two di erent design theories. The bandpass characteristics of the twolters are then compared over theprimary passband and over a broad range of frequencies to observe the stopband characteristics. It is shownthat a comblinelter with a large groundplane spacing behaves like an evanescent-mode waveguidelter but adi erence in bandwidth exists between the two.Di erent aspects related to the manufacture of coaxial cavitylters are addressed with speci c emphasis oncost reduction. The considerations to be made when choosing the right materials, manufacturing techniquesand surfacenishes for microwave coaxial cavitylters so that good performance is obtained while reducingthe overall costs associated with manufacturing are discussed. The concept of Design for Manufacture (DFM)is discussed.Three comblinelters are designed for reduced manufacturing cost, applying di erent changes in the physicalstructure 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 twodi erent manufacturing techniques: milling and wire-cutting EDM. The thirdlter is designed for manufactureusing a combination of the milling and wirecutting processes to have a bandwidth of 1.8% with the primarypassband centred at 2.125 GHz. Problems encountered in manufacturing are explained, one of which results inthe use of waterjet cutting for the manufacture oflters initially supposed to be manufactured using wirecuttingEDM. Measurement results for the manufacturedlters show a good agreement between the bandwidths of the3D electomagnetic simulation results. The obtained results also show the e ects of poor surfacenishing andof deformations on the resonant frequency and the unloaded Q of thelters.

[发布机构] Stellenbosch University