GB1492766A - Surface acoustic wave couplers - Google Patents

Abstract

1492766 Dispersive surface wave devices MARCONI CO Ltd 15 Sept 1975 [30 Nov 1974] 51938/74 Heading H3U A dispersive surface wave coupler device comprises input and output transducers 2, 3 defining first and second wave tracks and arranged on the same side of wave redirecting means constituted by arrays of parallel coupling strips, each strip in the first track being connected to a respective strip in the second track. As shown in Fig. 1, the strips in both tracks are spaced by n#/2 and are aligned so as to form a single array, and dispersion is obtained by arranging the strips in bands 6, 7, 8 which reflect different frequencies. Alternatively the strip spacing may vary continuously along the device. The device may be used for pulse compression and expansion. The interconnection of the strips may be modified to reduce spurious signals due to reflections. In Fig. 2, pairs of strips in the first track are cross-connected to pairs in the second track, the connections being separated by an insulating region 37; the strips in each track are spaced by #/4. This arrangement is directional and the insertion loss is reduced as compared with the embodiment of Fig. 1. The cross-connections may be avoided by omitting half the strips, e.g. 20a, 21b, 22b, 23a, 24a and 25b (Fig. 3, not shown). In a further embodiment (Fig. 4, not shown) the strips are spaced by #/3 and aligned strips alternate with pairs of cross-coupled strips; again cross-connections may be avoided by omitting strips (Fig. 5, not shown). A directional modification, Fig. 6, may be obtained by omitting only some of the crossconnections. The strips in one track may be shifted longitudinally relative to the strips in the other track without affecting the performance of the device. In addition, the coupling strips may be weighted to control the surface wave amplitude. Also, coupling strips may be provided on both sides of transducers 2, 3.