Saw filter device for radio tranceiver utilizing different coupl

Details Saw filter device for radio tranceiver utilizing different coupl Saw filter device for radio tranceiver utilizing different coupl

1997-01-13

1998-03-10

Pascal, Robert

Wave transmission lines and networks

Plural channel systems

Having branched circuits

333193, 333196, 310313R, 310313B, H03H 972

Patent

active

057266107

ABSTRACT:
A full duplex radio (10) having improved properties is obtained by using asymmetric surface acoustic wave (SAW) filters (70, 92, 100, 100', 112). The filters (70, 92, 100, 100', 112) are composed of series (50.sub.1, 50.sub.1 ') and parallel (50.sub.2, 50.sub.2 ') coupled SAW resonators. Asymmetry is obtained by covering either of the series (50.sub.1, 50.sub.1 ') or parallel (50.sub.2, 50.sub.2 ') resonators of each filter (70, 92, 100, 100', 112) with a dielectric layer (96) to increase the SAW coupling coefficient (Cs, Cp) of the covered resonators (50.sub.1 ', 50.sub.2 ') relative to the uncovered resonators (50.sub.1, 50.sub.2). The filters (70, 92, 100, 100', 112) are desirably in pairs arranged with mirror image frequency asymmetry such that the steeper skirts (87, 79) of the frequency response (91', 91") are adjacent. Greater pass-band bandwidths (77, 77', 77") can be obtained without adverse affect on transmitter and receiver isolation.

REFERENCES:
patent: 3965444 (1976-06-01), Willingham et al.
patent: 4243960 (1981-01-01), White et al.
patent: 5091051 (1992-02-01), Greer
patent: 5115216 (1992-05-01), Hikita et al.
patent: 5471178 (1995-11-01), Hickernell

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