Low-loss SAW filters on NSPUDT orientations of a Li2B 4O7 substrate

Natural single phase unidirectional transducers (NSPUDT) have attracted much attention for implementing low-loss SAW devices. In this paper, we describe a low-loss SAW filter on NSPUDT orientation of a Li ₂B₄O₇ substrate previously reported by authors. Since the unidirectionality of NSPUDT is inherent to the substrate orientation, it is necessary to make the receiving transducer unidirectional in the opposite direction for obtaining a low-loss filter using two transducers with reverse directivity. A new transducer configuration to reverse the directivity of an NSPUDT substrate is proposed which utilizes reflector banks within the ladder transducer. The configurations has the advantage in that it can be fabricated through a single level and a single metallization with minimum electrode width of λ/4. The details of NSPUDT orientations on a Li₂ B₄O₇ substrate are shown with experimental verifications. The principle of operation of reversal of directivity transducer (RDT) is describe. The 200 MHz band low-loss SAW transversal filter with minimum insertion loss below 3 dB and low passband ripple is demonstrated with a theoretical filler response using coupling-of-modes theory