Structure of surface acoustic wave filter

Details Structure of surface acoustic wave filter Structure of surface acoustic wave filter

1996-03-19

1997-09-09

Lee, Benny

Wave transmission lines and networks

Coupling networks

Electromechanical filter

310313A, 310313R, H03H 904

Patent

active

056660910

ABSTRACT:
Without increasing propagation loss or diffraction loss, (unlike conventional surface acoustic wave, SAW, filters which need many electrode finger pairs for constructing interdigital transducers, IDTs, to realize a steep cutoff frequency characteristic by conventional weighting or apodization that involves a high propagation loss and a high diffraction loss), there is provided a SAW filter with a very steep cutoff frequency characteristic on the low frequency side which uses three IDTs having N1, N2 and N3 electrode finger pairs, respectively. The filter is particularly applicable to a mobile radio communication device, such as a cellular radio. The relation between all the number of pairs N1+N2+N3 of the IDTs and the electromechanical coupling coefficient k.sup.2 of the piezoelectric substrate is N2<(N1+N3)<3.times.N2, and 2/k.sup.2 .gtoreq.(N1+N2+N3).gtoreq.0.8/k.sup.2.

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IEEE Transactions On Vehicular Technology, vol. 38, No. 1, Feb. 1989, "Miniaturized SAW Devices for Radio Communication Transceivers", by Hikita et al, pp. 2-8.

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