Single-phase unidirectional transducers employing uniform-width dithered electrodes

Abstract

A new family of Dithered Single-Phase Unidirectional Transducer (DSPUDT) configurations is described. These structures are comprised of uniform width single-level electrodes on a non-uniform grid. They are an extension of the uniformly-sampled 3/spl lambda//8 and 5/spl lambda//8 double-level SPUDT configurations introduced in 1992. Instead of employing a double-level metalization, unidirectionality is achieved in these new structures by dithering the position of the electrodes. This technique is very powerful as it allows the reflectivity function in the transducer to be implemented in a near analogue fashion, rather than a discrete approximation. In addition to mean sampling rates of 3/spl lambda//8 and 5/spl lambda//8, other sampling rates are considered of the general form m/spl lambda//n and (1-m/n)/spl lambda/, where m and n are integers and m/spl les/n/2. These additional sampling rates provide additional flexibility for making design tradeoffs in the minimum critical geometry, implemented coupling and reflection coefficients, and undesired out-of-band responses in the transducer. Using combinations of these sampling rates, filters with excellent rejection characteristics can be constructed. The large critical geometry's possible with these new transducers permits low-loss filters to be easily fabricated at frequencies in excess of 1 GHz with very linear group-delay and high out-of-band rejection.