Coupled Surface-Acoustic-Wave Resonators

Abstract

Coupled Surface-Acoustic-Wave (saw) grating resonators are investigated analytically with a transmission-matrix technique, and the measured frequency responses at ∼145 MHz of devices on YZ-LiNbO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> with Ti-diffused gratings are compared with the theoretical results. Coupled-mode theory is applied to derive the two-by-two transmission matrix relating the acoustic wave amplitudes at the input and output of a surface wave grating. Using the transmission matrices, the external transmission through a saw resonator is found by matrix multiplication. Some fundamental aspects of resonator passband synthesis are introduced by considering the transmission through several acoustically cascaded resonators. Resonator filters where the transducers couple directly to the resonant cavities are treated by developing a description of the transducer that is compatible with the transmission matrix of the grating. The analysis technique is then applied to the familiar two-port resonator-filter. Next, coupled resonator-pairs with a transducer in each cavity are considered in detail for: (i) collinear acoustic coupling, (ii) multistrip coupling, and (iii) transducer coupling. Experimental results are presented for each configuration considered and good agreement with the analytical description is found in each case.