Wideband, high-gain, variable time-delay techniques for array antennae

The purpose of this paper is to present two improved techniques for obtaining a wideband, high-gain, non-dispersive, variable time-delay device to steer array antennae. The first time-delay technique utilizes two wideband helix structures separated by a cylindrical drift tube to obtain a variable delay of 20 ns or more with a gain of 20 to 30 dB. An electron beam passes through the two helices and drift region. Signal energy coupled on to the beam at the input helix is decoupled at the output helix. A variable delay is obtained by controlling the beam velocity through the drift region by varying the drift tube potential. Gain variation is minimized by maintaining constant beam velocity through the helices. The gain of the device is proportional to output helix length. The second method for obtaining a variable time-delay is realized by switching different time-delay elements into the signal path. Such a technique is controlled digitally and is referred to as a digital delay line. In this technique each switch is replaced by a wideband amplifier. It is the bandwidth of these amplifiers that determines the system bandwidth (200 to 800 Mc/s). Each bit is capable of producing 12 dB gain. The amplifiers can be easily gated on or off.