Guided-Wave Dispersive Delay Lines

Abstract

A variety of new delay devices having delay times which are functions of frequency have been developed. These devices are based on waveguide propagation of ultrasonic waves in solid rectangular strips or circular wires. In contrast to the usual delay networks composed of many electrical sections, these dispersive delay lines are less expensive, occupy less space, and provide smoother delay characteristics. A linear delay network has the property that it transforms a short AM pulse into a long FM pulse. This makes possible the design of radar systems with increased range without requiring a corresponding increase in peak power. Existence of an inflection point in the delay versus frequency characteristic of the lowest longitudinal mode in a strip or a wire makes possible delay lines having an approximately linear delay characteristic. A typical example is a delay line operating in the lower megacycle region which has a product of time variation times bandwidth equal to about 100. Delay lines having various types of curvature can be designed by utilizing certain longitudinal, flexural, or shear modes in wires or strips.