Acoustic surface wave devices

DETAILED DESCRIPTION What is claimed is: 1.
An acoustic surface wave resonator device comprising, a substrate having a surface layer of piezoelectric material, a pair of spaced apart reflectors on the piezoelectric surface forming a resonant cavity capable of supporting an acoustic surface standing wave at or near a predetermined frequency, and means for coupling with acoustic surface standing wave energy in the resonator, the coupling means including two similar arrays of parallel conductive strips on the piezoelectric surface transverse to the length of the cavity and located between the pair of reflectors, the strips of each array having a centre-to-centre spacing of half a wavelength or an odd integral multiple of half a wavelength of acoustic surface waves at said predetermined frequency, the spacing between the two arrays being a quarter wavelength or an odd integral multiple of a quarter wavelength of acoustic surface waves at said predetermined frequency, and a point mid-way between the two arrays being at the centre of the resonant cavity or displaced from the centre of the resonant cavity by half a wavelength or an integral multiple of a half wavelength of acoustic surface waves at said predetermined frequency.
2.
An acoustic surface wave resonator device as claimed in claim 1 wherein said coupling means comprises an interdigital transducer within the cavity.
3.
An electrical filter comprising two acoustic surface wave resonator devices as claimed in claim 2, in which said interdigital transducer in one of the resonator devices forms input transducing means arranged to launch acoustic surface wave energy into the resonator of that device which thereby forms an acoustic surface standing wave therein, means for coupling the two resonator devices whereby an acoustic surface standing wave is formed in the other resonator device, and in which said interdigital transducer in the other device forms an output transducing means arranged to receive acoustic surface wave energy from the other resonator device