DESIGN TECHNIQUE FOR NONLINEAR PHASE SAW FILTERS USING SLANTED FINGERINTERDIGITAL TRANSDUCERS

This paper describes a useful design technique to achieve a nonlinear phase SAW filter using slanted finger interdigital transducers (SFITs) or tapered interdigital transducers which are suitable for wide-band filters in intermediate frequency stages. A required nonlinear phase r esponse in the passband can be obtained by changing center-to-center d istances between input and output SFITs along an axis perpendicular to the SAW propagation axis. The design is based on a building-block app roach in the frequency domain. A nonlinear phase SAW filter with a cen ter frequency of 70 MHz and a fractional bandwidth of about 10% is dem onstrated on x-cut 112.2 degrees y-propagating LiTaO3. Because the sub strate has a power flow angle of 1.55 degrees, the SFIT pattern is til ted along that angle. Good agreement between theoretical and experimen tal results is obtained.