A New Method to Prevent Spurious Oscillations in Coupled Cavity TWT's

Self- and drive induced oscillations are prevented in Coupled Cavity Power Travelling Wave Tube Amplifiers (TWTA's) by introducing frequency dependent R.F. losses at the upper cutoff. This paper describes a new method to realize the requested lossed by means of the cutoff properties of loaded waveguides coupled to the circuit. The losses introduced do not interfere in the working band, so that the tube efficiency and gain are not affected. A Coupled Cavity R.F. circuit is designed according to this method with the aim to obtain stable operations in a 400 MHz hot band at 3 GHz. Experimental results showed excellent stability with 50 dB saturated gain