Compact, die-cast precision bandstop filter structure

Abstract

A precision, waveguide-configured, bandstop filter comprises a substrate formed of a conductive material capable of being die cast. To facilitate manufacture and assembly, the substrate is preferably formed as a pair of symmetrically shaped substrate halves which, when mated together, define an interior filter structure that performs the required bandstop filter function. Each substrate half is configured to have a generally longitudinal slot that extends from a planar mating surface and effectively forms one half of an interior longitudinal waveguide section through the filter. Transverse to and located at spaced apart locations along the longitudinal slot are a plurality of channels, which define parallel conductive surface webs that extend from opposite sidewalls of the longitudinal slot. The channels serve as distributed, diametrically opposed pairs of lumped parameter tuning elements of the bandstop filter. A first end of each web forms a portion of a conductive sidewall of the longitudinal slot. Adjacent ones of the first ends of the webs are spaced apart from one another by land portions therebetween, the land portions forming part of the conductive sidewalls of the longitudinal slot. Each land portion has an opening which forms an iris that couples electromagnetic energy from the longitudinal waveguide slot into a respective channel. Each channel terminates at a conductive end thereof that is spaced apart from a respective land portion in which an iris is formed by a distance on the order of one-half the wavelength of the frequency to be excised.