H - Electricity – 04 – R
Patent
H - Electricity
04
R
333/89, 349/59.1
H04R 1/28 (2006.01) H03H 9/02 (2006.01) H03H 9/25 (2006.01) H03H 9/64 (2006.01)
Patent
CA 1126829
ABSTRACT A substrate has a pair of spaced apart reflectors forming a resonant cavity capable of supporting an acoustic standing wave at a plurality Or distinct resonant mode frequencies, a pair of terminals, and a transducer connected to said terminals and disposed on a surface of substrate between the pair of reflec- tors. An array Or electrodes which is interdigitally connected in the transducer is symmetrically arranged with respect to A central point or the cavity so as to form a plurality Or pairs of electrodes with the electrodes of each pair being equally spaced in opposite directions from that central point, If the two electrodes of each pair are connected to the same terminal then the transducer has zero net coupling with one set or alternate modes of the cavity whereas if the two electrodes Or each pair are connected opposite terminals then the transducer has zero net coupling with the other set of alternate modes. Thus the transducer can be considered as made up of two equal halves one in each half of cavity. Two transducers in the cavity can have equally suppression of the two quired sot Or alternate modes with the two halves of one transducer of being adjacent in a region between the two halves Or the other transducer. A transducer coupled sur- face acoustic wave coupled resonator electrical filter designed to have a low loss narrow passband may have a low stepband level outside that passband by design of the resonators such that the combined reflective frequency passband of the resonator reflectors includes only three resonant modes and by a symmetrical arrangement of the transducers with respect to the centres of the resonator cavities so that they couple to only the middle one of those three modes. Fie. 1 is suitable for abridgement.
312548
Mitchell Richard F.
Redwood Martin
Stevens Richard
White Philip D.
Fetherstonhaugh & Co.
N.v. Philips Gloeilampenfabrieken
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