The Gas-Discharge Transmit-Receive Switch

HE gas-discharge transmit-receive switch has become an accepted part of every modern radar set. Indeed, without such a device, an efficient single-antenna micro-wave radar would be nearly impossible. M a n y of the early radar sets made in this country employed separate antennae for the transmitter and receiver. T h e advantages of single antenna operation are so apparent as hardly to require discussion. T h e saving in space or, if the same space is to be occupied, the increase in gain and directivity of a large single antenna is, of course, apparent. B u t even more important, perhaps, is the tremendous simplification in tracking offered by a single antenna, particularly where a very rapid complex scanning motion is desired. T h e fact that the receiver needs to be operative only during periods between the transmitting pulses makes single antenna operation possible if four conditions are satisfied. These are: (1) the receiver must not absorb too large a fraction of the transmitter power during the transmitting period, (2) the receiver must not be permanently damaged by that portion of the transmitter power which it does absorb, (3) the receiver must recover its sensitivity after any possible overload during the transmitting pulse in a time interval shorter than the interval required by the reflected pulse to arrive back to the receiver from the nearest target, and (4) the transmitter must not absorb too large a fraction of the received power. At frequencies of the order of 700 megacycles and at low power levels these conditions are not impossible of attainment without recourse to any special switching mechanism other than that provided automatically by the usual circuit components.