Sidewall-Coupled Dielectric-Loaded Dual Mode Cavity Filter with Coupling from Non-adjacent modes into Adjacent cavities

Abstract

A cylindrical cavity is partially loaded with a high dielectric constant disk that is provided with an appropriate longitudinal slot. The resonance of the dielectric disk is thus split into a pair of dual modes with an approximately HE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11delta</sub> dependency. The cavity configuration is similar to a TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">111</sub> mode dual-mode resonator but with the addition of the dielectric disk, thus forming a "composite" resonator. The self-resonant frequency of the disk may be above or below the cutoff frequency of an infinite length of empty waveguide with the same cross-section as the cavity. Two such composite dual mode resonators are coupled together through the common wall using coupling wires, forming a coupled pair of dual mode resonators. The wire configuration enables partially independent control of coupling between pairs of modes (mode 1 and 2 are supported in cavity 1 while modes 3 and 4 are supported by cavity 2. Sequential coupling between modes provides the normal coupling in a "Chebychev" (ladder) structure while coupling between modes 1 and 4 allows for finite or imaginary frequency transmission zeros in the filter transfer function. Stray and unavoidable coupling between wires is minimized by choice of wire orientation. The filter is smaller than a conventional TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">111</sub> structure due to the partial dielectric loading, and is quite temperature stable as well, also due to the dielectric employed