A NOVEL LOW-LOSS SURFACE ACOUSTIC WAVE TRANSDUCER

THE NUMBER OF FREQUENCY CHANNELS WHICH MAY BE ASSIGNED WITHIN A GIVEN GEOGRAPHICAL AREA IS LIMITED BY INTERFERENCE BETWEEN THE CHANNELS. THIS GREATLY REDUCES THE NUMBER OF CHANNELS WHICH MAY BE ALLOCATED AND THUS LEADS TO AN INEFFICIENT UTILIZATION OF THE RADIO FREQUENCY SPECTRUM. RECENTLY CONSIDERABLE INTEREST HAS ARISEN IN DEVELOPING MOBILE COMMUNICATIONS SYSTEMS FOR THE CONSUMER. SO-CALLED "CELLULAR RADIO" SYSTEMS ARE CURRENTLY BEING DEVELOPED TO MEET THIS NEED. THESE SYSTEMS HAVE BEEN ALLOCATED TO FREQUENCY BANDS A LITTLE OVER 800 MHZ. TO INCREASE THE EFFICIENCY OF FREQUENCY UTILIZATION THERE IS A NEED TO DEVELOP HIGHLY SELECTIVE BANDPASS FILTERS. THESE FILTERS IDEALLY SHOULD BE LOW COST, SMALL AND LIGHT-WEIGHT, AND HAVE LOW INSERTION LOSS. CURRENT SURFACE ACOUSTIC WAVE (SAW) FILTERS COME CLOSE TO MEETING THESE REQUIREMENTS. HOWEVER, LOW-LOSS SAW FILTERS ARE CURRENTLY EXPENSIVE AND RESTRICTED TO FREQUENCY BANDS BELOW THOSE OF CELLULAR RADIO. IT IS PROPOSED, HEREIN, TO DEVELOP A NOVEL LOW-LOSS SAW UNIDIRECTIONAL TRANSDUCER FOR FILTERING APPLICATIONS AS HIGH AS 1.2 GHZ, BASED UPON A COMPLETELY NEW CONCEPT. THE STRUCTURE PROPOSED HAS NOT PREVIOUSLY BEEN DISCLOSED IN THE LITERATURE. IT HAS SIGNIFICANT ADVANTAGES IN TERMS OF BOTH COST AND PERFORMANCE FOR HIGH-FREQUENCY LOW-LOSS FILTERING APPLICATIONS.