Second-order effects in acoustic surface-wave filters: design methods

摘要

Second-order effects, which may be defined as those effects which prevent acoustic surface-wave filters from behaving as ideal transversal filters, are described systematically. Explicit exact and approximate formulas are given for the effect of acoustic multireflections and external matching circuits on both the main signal response and triple transit echoes. The effect of non-uniform tap coupling across the acoustic beam is described, and weighting methods thatprovide a more uniform coupling are presented. Other secondary effects like electrostatic or quasistatic end effects, beam diffraction, mass loading and bulk wave excitation are briefly described. A method for the correction of positioning errors or delay errors by experimental means is described.