Surface acoustic wave and surface skimming (shallow bulk) acoustic devices with any of the following: (a) A carrier frequency exceeding 6 GHz; (b) A carrier frequency exceeding 1 GHz, but not exceeding 6 GHz and having any of the following: 1. A ‘frequency side-lobe rejection’ exceeding 65 dB; 2. A product of the maximum delay time and the bandwidth (time in μs and bandwidth in MHz) of more than 100; 3. A bandwidth of greater than 250 MHz; or 4. A dispersive delay of more than 10 μs; or (c) A carrier frequency of 1 GHz or less and having any of the following: 1. A product of the maximum delay time and the bandwidth (time in μs and bandwidth in MHz) of more than 100; 2. A dispersive delay of more than 10 μs; or 3. A ‘frequency side-lobe rejection’ exceeding 65 dB and a bandwidth greater than 100 MHz;