Dual mode operation of a high-power, PPM-focused TWT

An existing, PPM-focused high-power traveling wave tube of the coupled-cavity type was mated to a dual-mode gun, capable of providing a perveance (pulse-up) ratio of 6 dB or higher. RF tests were performed at a beam voltage of 31 kilovolts and perveance of approximately 0.15 and 0.65 µpervs. With full RF drive, the beam transmission for the two modes was 0.98 and 0.92 respectively. At the midband frequency (f=9.5 GHz), the output power in the two modes was 2.2 kilowatts and 15.1 kilowatts, the saturated gain 15.5 dB and 30.3 dB, the basic tube efficiency 6.7% and 13% respectively. With a 50% collector depression, these efficiencies could be roughly doubled. By overdriving the high power mode amd slightly underdriving the low power modes, a power output ratio of 10 dB with constant RF can be achieved.