Novel SAW components for low-loss filters

Abstract

New SAW components are proposed and analyzed with help of the spectral theory. They are: closed and opened Modal Reflecting Structures (MRS), Magic Multistrip Mirror (MMM), and Reversing Transducer System (RTS), all of which can be applied to 2-channel SAW resonator filters, substituting Reversing MultiStrip Couplers (RMSC) there. The principle of operation of MRSs are similar to that of RMSCs, however, different connections between their electrodes results in only one mode of a pair of two that can propagate in the structure in a given direction being reflected in a stopband; the other mode is a propagating one for which the structure of MRS is transparent. Results of simple experiments verify the concepts of MRSs which, like RMSCs, have 3 strips per wavelength and similar stopband width, 2/3/spl Delta/v/v, relatively. In the RTS, appropriately connected IDTs are applied instead of strips in the RMSC (an analogue to IIDT). In the Magic Multistrip Mirror, which is also a double channel device, the track-changing phenomenon results from different phases (by 180/spl deg/) of Bragg reflected SAWs from short-circuited and opened metal strip gratings which, in the MMM, are accompanied by a shallow groove grating with the same period. Its relative working bandwidth is /spl sim/ 1/4 /spl Delta/v/v. Particular attention is paid to the admittances of one port double channel SAW resonators comprising the above reflecting structures which can be exploited in ladder filters utilizing SAW admittance elements.