LOW-LOSS SURFACE-ACOUSTIC-WAVE FILTER ON NATURAL-SINGLE PHASE UNIDIRECTIONAL TRANSDUCTER ORIENTATIONS OF A LI2B4O7 SUBSTRATE

Natural-single phase unidirectional transducers (NSPUDT) have attracte d much attention for the implementation of low-loss surface acoustic w ave (SAW) devices: In this paper, we describe a low-loss SAW filter us ing NSPUDT orientations of a Li2B4O7 substrate previously reported by the authors. Since the unidirectionality of NSPUDT is inherent to the substrate orientation, it is necessary to make tile receiving transduc er unidirectional in the opposite direction in order to obtain a low-l oss filter using two transducers with reverse directivity. A new trans ducer configuration to reverse the directivity of an NSPUDT substrate is proposed, which utilizes reflector banks within the ladder transduc er. The configuration has the advantage that it call be fabricated thr ough a single level and a single metallization with minimum electrode width of lambda/4. Tile principle of the operation of a reversal of di rectivity transducer is described. A 200-MHz-band low-loss SAW transve rsal filter with minimum insertion loss below 3 dB and low passband ri pple are demonstrated with a theoretical filter response using couplin g-of-modes theory.