SAW DEVICE TAPPED DELAY LINES

摘要

A SAW (surface acoustic wave) device tapped delay line comprises a continuous pattern of bifuecated inter-digital fingers (48) having a constant pitch of .lambda./2 and forming a first IDT (interdigital transducer) (12), a plurality of second IDTs (14); substantially identical to one another and arranged with a predetermined pitch P for consecutively receiving a SAW propagated from the first IDT with respective propagation delays, and grounded dummy fingers (42) in regions between adjacent IDTs. The first IDT is apodized in accordance with a Hermitian response to provide it with a pass band (58) centered at a first frequency (140 MHz) and .lambda. is the wavelength of a SAW at a second frequency (143.36 MHz) different from the first frequency and within the pass band. P is an integral multiple of .lambda./2; so that there is a constant fingerperiodicity throughout the SAW device whereby reflections between the second IDTs are avoided: The SAW device tapped delay line is used in an adaptive time delay equalizer of a high capacity microwave radio communications system, with the first frequency equal to the receiver intermediate frequency and the second frequency being an integral multiple of half the symbol rate of the system.