GENERAL-THEORY OF A CIRCULAR DUAL-MODE RESONATOR AND FILTER

A unified theory for the characteristics of dual modes in a circular r esonator is elucidated in simple analytical expressions. First, a circ ular resonator is considered as a ring transmission line which allows two oppositely traveling waves. The essential quantities that characte rize a transmission line, i.e., the propagation constant and character istic impedance are obtained theoretically and/or experimentally. Seco ndly, any circular resonator is described by a ring resonator model wh ich can be treated analytically, and the resonant frequencies are obta ined when perturbations are added along the periphery of a circular re sonator. A two stage BPF is created by adding I/O ports to the perturb ed circular resonator. Its center frequency and bandwidth is calculate d based on the ring resonator model. The circuit condition for obtaini ng two attenuation poles at both sides of the passband is given togeth er with the method for their control.