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Low-loss surface-acoustic-wave (SAW) ring filters without matching elements

S. A. Dobershtein, E. B. Korzhinskii, V. A. Malyukhov


Several methods are in use for the creation of low-insertion-loss SAW filters. A traditional way of reducing insertion losses is through the use of various constructions of unidirectional counter-stub converters (CSC); this technique encounters numerous difficulties. The principal difficulty resides in the fact that the complexity of the spherical construction and topology of such CSC substantially reduces flexibility in the development of SAW filters and the guarantee of their ultimate electrical parameters (see [1]). In this connection the utilization of a ring construction consisting of input and output bidirectional CSC situated in parallel acoustic channels, plus two multistrip reflecting gratings which ensure transmission of the SAW between these channels (see [2]; Fig. 1) is promising. In such a construction, it is fairly simple to implement the stipulated selectivity and the low losses, since the amplitude-frequency response (AFR) of the filter is determined by multiplication of the AFR of the grating and the AFR of the input and output CSC in this case, while the low insertion losses are determined by the reflection coefficient of the grating and are ensured by the choice of its construction. In addition, the creation of filters with self-matching (see [3]) is possible in ring constructions.

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