Improved modeling of wide-band linear phase SAW filters using transducers with curved fingers

The use of curved finger interdigital transducers (IDTs) is examined in wide band linear phase SAW filters. An improved modeling technique, in the form of a generalized impulse response model, is applied to equal input and output IDTs of this form. A finger curvature parameter p = -1/2 is found to be suitable for compensating the passband amplitude response of a 50-percent bandwidth filter against the effect of circuit factor loading at the input. This eliminates the need for an external compensating network, as previously reported for slanted-finger IDT geometries. Illustrative experimental results are given for a 70 MHz 50-percent bandwidth filter on YZ-lithium niobate, showing the improved response of the curved finger structure over that obtained using slanted finger IDTs.