Elastic wave filter utilizing a sub-propagation mode response to increase out of band attenuation

摘要

An elastic wave filter of a resonator type includes at least one IDT electrode arranged so as to contact the piezoelectric substance. The elastic wave filter is arranged such that an elastic wave in a main propagation mode for obtaining target frequency characteristics and an elastic wave in a sub-propagation mode propagate, the elastic wave being capable of propagating simultaneously with the elastic wave in the main propagation mode, an electromechanical coefficient K² of the elastic wave in the sub-propagation mode is in the range from about 0.1% to about one third of an electromechanical coefficient K² of the elastic wave in the main propagation mode, and a sound velocity of the elastic wave in the sub-propagation mode differs from a sound velocity of the elastic wave in the main propagation mode.