A voltage tunable delay line

This paper discusses a novel device capable of delaying an RF pulse over a wide frequency band with the delay continuously adjustable over a wide limit and with low insertion loss. Fundamentally, the device is a C-band traveling-wave tube with a portion of the helix replaced by a length of drift tunnel. A low perveance cylindrical beam is made to interact with a helix slow-wave structure upon which is impressed a pulsed RF signal. Before entering the drift tunnel, the slow space-charge wave on the beam is transformed into a fast space-charge wave mode. The desired RF delay can be obtained by varying the accelerating potential on the drift region. The fast mode then is transformed back to the slow wave mode. A short helix coupler strips off the transformed slow wave velocity/current information in the usual manner. Data is presented showing the delay as a function of frequency and delay potential as well as insertion loss, noise figure and other operating parameters.