Surface acoustic wave filter with attenuated spurious emissions

Abstract

A surface acoustic wave filter includes a piezoelectric substrate. On the surface of the piezoelectric substrate, an input transducer and an output transducer are formed at a predetermined interval. The input transducer and the output transducer are respectively formed with a pair of IDT (interdigital electrode transducers) disposed oppositely. A pair of IDT which construct at least one transducer of the input transducer and the output transducer are formed on the piezoelectric substrate in the following manner. That is, a first impulse train is determined by inverse Fourier transformation of desired transmission characteristics (where, center frequency is f.sub.0 and surface wavelength is .sub.0), a second impulse train is determined by double over-sampling of the first impulse train along its envelope at a half period, wherein the number of unit impulses of the first impulse train is doubled, a third impulse train is determined by dividing the second impulse train into four impulse trains each, among which second and third impulses are made zero, and the IDT are formed on the piezoelectric substrate corresponding to the third impulse train.