Waveguide bandpass filter having a non-contacting printed circuit filter

Abstract

A waveguide bandpass filter employs a waveguide section and a printed cirt filter assembly having a dielectric substrate positioned in the waveguide between the narrow walls thereof and a row or array of half-wavelength conductive metal plate elements lying in a surface plane of the dielectric substrate that is oriented substantially parallel to narrow walls and orthogonal to broad walls of the waveguide. The half-wavelength conductive metal plate elements, defining a parallel resonant array, are spaced in non-conductive relation from one another and from the broad and narrow walls of the waveguide so as to divide and transform a dominant waveguide propagation mode into a transformed propagation mode that approximates upper and lower microstrip sections interconnected by a metallic conductor. The filter also includes a pair of elongated foam dielectric bodies disposed in the waveguide and mounting therebetween the dielectric substrate and half-wavelength conductive plate elements thereon, and a pair of quarter-wavelength conductive metal plate elements on the dielectric substrate which are conductively connected to outermost ones of the half-wavelength conductive plate elements for defining impedance matching transformers adjacent input and output ends of the waveguide.