Examples of manufactured dispersive delay lines using acoustic surface waves

Two kinds of dispersive delay lines operating in radars at the present time are described as examples of manufactured acoustic surface-wave components. These lines were designed some yearsago for a non-linear chirp impulse response and they are used as pulse expander and weighting matched pulse compressor. These dispersive delay lines consist of metallic interdigital transducers deposited on piezoelectric quartz substrates. The first kind of line, which was produced in quantity, (about 180 units) has a compression ratio equal to 23.5. The relative sidelobe level of the compressed pulse is ¿26 dB. The delay varies by 4 ¿s in a 7 MHz frequency range, the centre frequency being 30 MHz. A sampled transducer with variable finger pair spacing is used for the second kind of line in order to limit the number of fingers. The delay change is 25 ¿s for a 1 MHz frequency range centred at 30 MHz. The compression ratio and the relative sidelobe level of the compressed pulse are 19.2 and ¿24 dB respectively.