General response dual-mode, dielectric resonator loaded cavity filter

Abstract

A ceramic resonator element having high Q, high dielectric constant, and a low temperature coefficient of resonant frequency is enclosed within a cavity to form a composite microwave resonator having reduced dimensions and weight as compared to a simple cavity resonator. In an exemplary embodiment, a pair of tuning screws extend into the cavity along orthogonal axes to tune the structure to resonance along these axes at frequencies near the fundamental resonance of the ceramic element. Several such cavities can be formed in a short length of waveguide by the use of transverse partitions at spaced intervals and coupling between cavities can be accomplished by using simple slot, cross or circular irises. In each cavity, a mode-perturbing screw is positioned along an axis 45° from each of the orthogonal tuning screws, such that resonance along either of the orthogonal axes is coupled to excite resonance also along the other. The input and output coupling devices are disposed at locations that are angularly separated from the corresponding tuning devices by a selectable angle that varies between 0 degrees and ±180 degrees. This Variability in location of the input and output coupling devices provides for a filter having adjustable input/output coupling. The realization of complex filter functions requiring cross couplings is feasible by means of coupling separately to only one of the two orthogonal resonant-modes in the cavities.