A 50-75 Gc power backward-wave oscillator

A power backward-wave oscillator for a minimum power output of one watt c.w. over the 50-75 Gc band has been designed and tested. Maximum powers of 2.5 watts c. w. and approximately 20 watts peak have been measured with this tube operating in a permanent magnet. This tube uses an electron gun having an area convergence of 100:1 and a coupled-cavity circuit with a cold bandwidth of 385%. Very low circuit losses, of the order of 0.2 db per wavelength at 70 Gc have been achieved in this circuit, as well as Pierce impedances approaching 10 ohms. Some detailed measurements of the characteristics of this tube and its circuit are presented, such as start-oscillation current, power output, tuning characteristics and circuit losses. Some predictions based on this data are made regarding power output and frequency coverage which can be obtained using other versions of the beam and circuit combination described in this paper. Also presented will be measured data of the attenuation vs frequency of some commercially available microwave components, as measured by this tube in the 50-75 Gc range.