Microsonic pulse filters - Replacements for traditional Butterworth designs

Microsonic filter response characteristics are analyzed under CW, pulsed, and transient input conditions. Previous CW formulations had to be extended for pulsed and transient response calculations because the acoustic waves generated are not, in general, spatially long enough to encompass the entire transducer pattern. A synthesis procedure is also developed and used for the successful design of six pulse filters employed in a practical airborne collision-avoidance system, SECANT VECAS GM/A. The microsonic filters replace six standard lumped-element five-pole Butterworth filters required to distinguish various 1-microsec pulses received from nearby aircraft. Each microsonic filter (on ST-cut quartz) comprises one uniform interdigital transducer with 35 to 39 lambda/4 fingers and one Gaussian apodized transducer with 221 to 257 fingers, depending on the synchronous frequencies (53 to 64 MHz) that match the frequencies contained in the different i-f input pulse envelopes.