GB1357193A - Acoustic surface wave devices - Google Patents

Abstract

1357193 Acoustic surface wave devices MULLARD Ltd 22 July 1971 34368/71 Heading H3U An acoustic surface wave i.f. bandpass filter for T.V. has a launching transducer 2 comprising arrays 4, 5 of interdigitated electrodes mutually disposed transverse to the surface wave propagation direction 6 on a ceramic piezoelectric body 1, receiving transducer 3 being wide enough to receive and combine the surface waves from both arrays 4, 5. The polarity and overlap of successive pairs of fingers, each finger being several wavelengths long, in each array are varied, so that, after combination of the respective array outputs at receiver 3, the distribution of effective source strength may be varied over a range of 10 : 1 with only a 10 : 4 variation within either one array, Fig. 4 (not shown). The arrays may be connected in series, with a corresponding overall reversal of polarity of one of them, Fig. 2 (not shown). To each finger 7 of array 4, there exists a corresponding finger of array 5 on the same transverse line although some fingers may be omitted. Alternatively, Fig. 3, the overlap of adjacent fingers may be invariant, the width of each finger 47 being variable, and the receiving transducer may comprise a similar pair of arrays 58, 59 in series, with, however, equal width and overlap of fingers 57. The polarities of arrays 45, 59, or 44, 58, may be reversed throughout if desired. The roles of launching and receiving transducers may be reversed. The transducers are made by a photolithographic process from vapour deposited gold, manufacturing errors in each respective array tending to cancel.