Surface acoustic wave filter device having a cascade filter structure and a piezoelectric substrate having mirror-polished surfaces

摘要

A surface acoustic wave filter device includes a piezoelectric substrate having mirror-polished surfaces on both sides, so that it is essentially free from warping. One surface of the substrate is provided with two filter stages which are cascade connected with each other thereby to sufficiently attenuate bulk wave spurious noise below a practically negligible extent. The filter device can be manufactured with an improved yield.