Patent ID: 6570471
Filing Date: 2003-05-27
Classification: H03H

Abstract:
A surface acoustic wave filter comprising a piezoelectric substrate having formed thereon a plurality of surface acoustic wave resonators electrically connected in a ladder form for exciting a surface acoustic wave, wherein each of the surface acoustic wave resonators includes an interdigital transducer and reflectors arranged closely on both sides of the interdigital transducer in a direction parallel to a propagation direction of an excited surface acoustic wave;wherein the interdigital transducer of at least one of said surface acoustic wave resonators consists of a prescribed number of pairs of comb form electrodes arranged in a sequence of the pairs along the propagation direction; and wherein each pair of the sequence further comprises a first electrode extending from an upper terminal part of the interdigital transducer and a second electrode extending from a lower terminal part of the interdigital transducer, whereby each of the pairs in the sequence has a regular orientation or an inverted orientation depending on whether the second electrode follows the first electrode along the propagation direction or the first electrode follows the second electrode along the propagation direction; wherein at least one pair of comb form electrodes in the regular orientation exists between pairs of comb form electrodes in the inverted orientation; whereby the surface acoustic wave excited by the pairs of comb form electrodes in the regular orientation proceeds in the propagation direction and a surface acoustic wave that differs in phase by 180Â° is excited by the pairs of comb form electrodes in the inverted orientation.