Surface-wave dispersion with a time bandwidth of 1000

Experimental results are presented that were obtained in the initial evaluation of a multifunction surface wave delay line designed for a time bandwidth product of 1000. Two types of lines that operate on ST-cut quartz substrates are described. One type utilizes three identical coded 25-Ms transducers symmetrically arranged so that both positive and negative chirp slopes are obtained in addition to zero slope or flat delay. The other type of line provides positive and negative slopes with separate transducer pairs approximately coded. Lines of both types are designed to operate at a center frequency of 60 MHz with a 20-MHz bandwidth and a 50-μs time delay. Tests demonstrated time-bandwidth product capabilities of 785 and 900, with time dispersions of 45 and 50 μs, respectively, and bandwidths of 18 MHz. Time multiplexing and spectrum inversion were used to measure pulse compression performance. Measured sidelobe levels of -9 to -18 dB indicated nonlinearity and incidential weighting present in these lines. In addition, surface-wave delay-line performance was measured with a 56-μ delay, a nominal 10-MHz bandwidth, and -15-dB time sidelobes. The lines were also temperature tested for center frequency time-delay stability. Results indicated time-delay variations of less than 2 ppm/°C, which is an order of magnitude improvement over those in YX-cut quartz substrates lines.