RESONATOR FILTERS ON DIELECTRIC SUBSTRATES

摘要

A resonator filter has electrodes disposed in a confronting relationship to each other and has a dielectric base plate interposed therebetween. The filter has ground or common terminals on the electrode portions in different positions which do not include mutually confronting electrode portions. The electrodes have spiral configurations or configurations having at least one bent portion such that the electrodes have a lumped-constant inductance. Voltage signals induced in the electrodes due to mutual induction therebetween are opposite in phase with respect to each other and a parasitic distributed-constant capacitance is produced due to a potential difference between the electrodes and a dielectric constant of the dielectric base plate. As a consequence thereof, a two-terminal parallel resonance band pass filter circuit is formed on an equivalent basis which is composed of the lumped-constant inductance of one of the electrodes and the distributed-constant capacitance between the electrodes. The parallel resonance band pass filter has a resonance frequency which is lower than a frequency having its 1/4 wavelength equal to an equivalent electrical length of each electrode.