DESIGN OF A LOW-LOSS BANDPASS FILTER USING DIELECTRIC ROD RESONATORS LOADED IN A HIGH-TC SUPERCONDUCTOR CYLINDER

A Chebyshev type bandpass filter using four TM01-delta-mode dielectric rod resonators oriented axially in a high-T(c) superconductor cylinder is designed with 3 dB bandwidth 36 MHz at 11.958 GHz. The single resonator which contains a Ba (MgTa)O3 ceramic rod of epsilon(r) = 24 and a YBa2Cu3Oy bulk cylinder is designed to realize temperature coefficient of f0, tau(f) = 0 ppm/K at 20 K. The unloaded Q, Q(u) measured at 20 K is 150,000 which is higher than Q(u) = 100,000 for a TM01-delta-mode resonator with a copper cylinder. When the constructed filter is cooled from room temperature to below 50 K, the center frequency shifted only 5 MHz which corresponds to tau(f) = 1.5 ppm/K and the insertion loss IL0 at the center frequency reduced from 3.0 dB to about 0 dB, the designed value of which is 0.04 dB, which is too small to be measured accurately.