Design techniques for SAW filters using slanted finger interdigitaltransducers

摘要

This paper describes useful design techniques for wide-band linearnphase SAW filters using slanted finger interdigital transducers (SFITs):nto increase stop band attenuation, to flatten the pass band response,nand to draw SFIT patterns for photo-masks. In order to increase stopnband attenuation, a withdrawal-weighted SFIT is employed. A combinationnof a withdrawal-weighted SFIT and an unweighted SFIT provides good stopnband responses, even though the number of finger pairs is small. Innorder to achieve a desired amplitude response in the pass band, annaperture-weighting technique for divided channels of SFITs is presented.nA design method for drawing SFIT patterns for photo-masks is alsondescribed. A linear-phase SAW filter using SFITs with a 50% fractionalnbandwidth is designed and fabricated on 128° y-x LiNbO3.nA sidelobe suppression of 40 dB and a 3 dB to 40 dB shape factor of 1.12nwere realized. Good agreement between theoretical and experimentalnresults is obtained