A new form of X-band pre-t.r. cell

A simple plug-in discharge tube for high-power transmit-receive switching is described. The tube, which is of precision-bore silica, contains a rare-gas filling optimized for low arc loss and long life. The problem of lengthening recovery time during life is overcome by the use of silica wool as an agent for surface recombination, and initial breakdown is assisted by the inclusion of a trace of tritium, which is a safe source of low-energy ß-particles. The application of this form of discharge tube at X-band wavelengths is discussed. Loss of power by propagation along the discharge is overcome with microwave chokes, and sparking at high powers is minimized by ensuring a close fit between the chokes and the tube. This is achieved with precision-bore silica tubing, accurately ground on the outside. Tubes have been tested at power levels up to 1 MW peak without breakdown. The arc loss at 200 kW is less than 0.3 dB, the recovery time is less than 10 microsec to an attenuation of 6 dB and the striking power is less than 15kW. The insertion loss is less than 0.1 dB. Nineteen tubes have been tested for at least 3000 hours each without failure in duplexers operating at 800 kW peak and 600 watts mean power.