S.A.W. bandpass filter with −50 dB sidelobes using unweighted i.d.t.s

Abstract

The use of a resonantly loaded i.d.t. (r.l.i.d.t.) as an s.a.w. track changer in bandpass filter design is described. A filter with 3dB fractional bandwidth (f.b.w.) of 11.5% and −50 dB sidelobes is realised using unweighted input/output i.d.t.s of 5½ finger pairs each and a 7½ finger pair r.l.i.d.t. as the s.a.w. track changer. The scheme is expected to be useful in realising low-shape-factor low-sidelobe bandpass filters using relatively short i.d.t.s.