PURPOSE: To adjust the resonance frequency of a dielectric coaxial resonator by trimming an electrode connected to the inner conductor of the dielectric coaxial resonator to change the inductance component on the load side to the coaxial resonator.

CONSTITUTION: The front end of a coupling rod 6 electrically connected to the inner conductor (omitted in the figure) of a dielectric coaxial resonator 3 is electrically connected to a land 7 for connection. Coupling capacitors 2 and 4 are electrically connected to both ends of the land 7 for connection. Since the dielectric coaxial resonator 3 is relatively larger than coupling capacitors 2 and 4, the land 7 for connection is formed to have a relatively large area. According as the area of the land 7 for connection is larger, the inductance component based on this land 7 is reduced. Consequently, the resonance frequency is raised. The land 7 for connection is trimmed, and the length of the land 7 for connection is extended to adjust the resonance frequency to a lower value.