Design of an elliptic function bandpass filter using a high dielectric ring resonator

A bandpass filter constructed by placing a TM_01δ dielectric ring around a resonator post of a conventional combline resonator in a TE₀₁ cut-off rectangular waveguide is presented. On the basis of a rigorous analysis by TLM technique, the coupling coefficients are determined accurately from the calculation of two resonant frequencies f_e and f_m when the structurally symmetric plane is short- and open-circuited. A fourth order elliptic function filter is fabricated. The measured frequency responses of the filter agree with the theory.