Acoustic surface wave devices

An acoustic surface wave device comprising a piezoelectric substrate able to propagate acoustic surface wave energy, first and second spaced apart transducers coupled to a surface of the substrate and each including an interdigitated array of two sets of parallel electrodes, one of said transducers comprising, a pair of elongated spaced apart conductive members extending generally in the direction of acoustic surface wave propagation through the transducer, and two sets of electrodes extending transversely to said propagation direction with one set of electrodes connected to a first one of said conductive members and the other set of electrodes connected to a second one of said conductive members, adjacent electrodes of said two sets of electrodes being spaced a half wavelength at a frequency f.sub.o and having a transverse overlap which varies along the propagation direction whereby the envelope formed by the ends of the overlapping electrodes defines the acoustic aperture of the transducer, and a group of conductive strips extending transverse to the propagation direction and located outside of said envelope and within the aperture and electrically connected together in common, adjacent strips within the group having an effective spacing of an odd integral multiple of a quarter wavelength of the acoustic surface waves at the frequency f.sub.o.

An acoustic surface wave device comprising a body of piezoelectric material one surface of which supports a transducer including an interdigital array of two sets of electrodes with each set connected to one of two opposed bus bars, each electrode having a part which overlaps a part of an adjacent electrode of the opposite set, the length of the overlapping electrode parts varying along the line of acoustic surface wave propagation through the transducer and with the limits of the envelope of the overlapping electrode parts normal to the propagation line defining the acoustic aperture of the transducer, said two bus bars being shaped to follow the overlap envelope formed by the overlapping electrodes, and at least one conductive area arranged on said one surface in a region outside of the envelope but within the acoustic aperture so that said conductive area compensates for wavefront distortion due to the varying lengths of the overlapping electrode parts, said conductive area extending over a distance, along the line of wave propagation through the transducer, that is proportional to the sum of the widths of those electrodes for whose varying lengths it provides compensation.