Weighted interdigital transducers for smoothing of ripples in acoustic-surface-wave bandpass filters

The transfer function of acoustic-surface-wave (a.s.w.) bandpass filters exhibits ripples in the passband and sidelobes in the stopband, owing to the finite length of the sin x/x-shaped interdigital transducer used for the filter´s impulse-response synthesis. A direct means of overcoming this inconvenience by weighting the interdigital transducer according to smoothing functions, such as those of Fejÿr and Lanczos, which were developed for the suppression of ripples due to the Gibbs phenomenon, has been devised. The reported results show the effectiveness of this simple approach to the improvement of a.s.w.-filter capabilities.