Patent ID: 7772942

Claim:
An elastic wave filter of a resonator type comprising: a piezoelectric substance; and at least one IDT electrode arranged so as to contact the piezoelectric substance; wherein 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 in the sub-propagation mode being capable of propagating simultaneously with the elastic wave in the main propagation mode; an electromechanical coefficient K 2 of the elastic wave in the sub-propagation mode is within a range from about 0.1% to about one third of an electromechanical coefficient K 2 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 so as to cause a response for the sub-propagation mode to occur at a location related to a frequency at which an attenuation amount is desired to be increased and which is located outside a band.