Acoustic-surface-wave dispersive delay line

The requirements for a dispersive delay line, for pulse-compression radar, capable of operating at v.h.f. and microwave frequencies, suggest the use of an acoustic-surface-wave system. The basic structure consists of a thin film supported on a substrate. It is shown how a required delay characteristic can be synthetised by tapering the thickness of the film. Experiments carried out at relatively low frequencies are in good agreement with the theoretical results produced by the synthesis programme. The attainment of a high compression ratio demands a very precise control, and hence measurement, of the dispersion characteristic. A new technique which is capable of achieving the required precision has been developed. It is based on a continuous-wave (c.w.) bridge method, in which a small modulation of the surface wave enables one to achieve a very high discrimination against spurious modes. The materials problems for high-frequency delay lines are discussed, and a number of suggestions based on computer analysis are advanced.