Surface wave device with capacitance

Details Surface wave device with capacitance Surface wave device with capacitance

1997-05-08

1998-10-13

Mottola, Steven

Wave transmission lines and networks

Coupling networks

Electromechanical filter

333194, 310313B, H03H 964, H03H 925

Patent

active

058218343

ABSTRACT:
A surface wave device filter comprises two 2-pole waveguide coupled double mode resonators (WCRs) electrically connected together in cascade. To permit narrowing of the filter passband for improved out-of-band rejection, e.g. for use of the filter as an intermediate frequency channel filter in a wireless communications system, while maintaining good matching for low ripple in the passband, a shunt capacitance is connected in parallel with the static capacitances of the two WCRs. The shunt capacitance is constituted by interdigital fingers provided on the same piezoelectric substrate as one or both of the WCRs, perpendicularly to the WCR fingers to avoid surface wave interference, conveniently in space otherwise used by rails of the WCRs, optionally with oppositely phased fingers to cancel surface waves generated by these fingers. A capacitance can be similarly provided on the same substrate as any other type of surface wave device.

REFERENCES:
patent: Re33957 (1992-06-01), Nakazawa et al.
patent: 5365138 (1994-11-01), Saw et al.
patent: 5581141 (1996-12-01), Yamada et al.
"Narrow Bandpass Filter Using Double-Mode SAW Resonators on Quartz", M. Tanaka et al., IEEE 38th Annual Frequency Control Symposium, 1984, pp. 286-293.

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