Ladder-type piezo-electric filter

Abstract

In radio communication equipment, a ladder-type piezo-electric filter is provided which operates in a high-frequency region of approximately 1.7 MHz-2 MHz. The filter is smaller than conventional ladder-type electric filters, less costly, and more easily handled and produced. In accordance with the present invention, rectangular piezo-resonators that longitudinally generate harmonic oscillation are used in the series and parallel branches of a ladder-type circuit. In each resonator, piezo-electric regions are formed by dividing surface electrodes with isolating slits. The slits are formed at the positions corresponding to the node points of the harmonic oscillation waveforms. For the piezo-resonators placed in the series branches of the ladder-type circuit, the piezo-electric regions are polarized in the same transverse direction. In each piezo-resonator used in a parallel branch, the piezo-electric regions are polarized in alternately opposite transverse directions. In addition, the divisional electrodes of the parallel branch piezo-resonators are bridged over with a suitable conductor, such as conductive paint, or the like.

Dependencies are inferred from the claim text.