Development of a high power - High efficiency - Wideband traveling-wave tetrode

The traveling wave tetrode is a unique device which can provide multi decade bandwidths in the VHF-UHF frequency range. The device consists basically of two isolated transmission lines which are coupled by the transverse electron beam. The beam is rf modulated by the signal on the input line and collected on the output line. The two lines are designed to have equal phase velocity at a given frequency in the operating band so that the rf currents will continue to add up in the direction of propagation. Two basic types of device have been developed. The first device which utilizes uniform input and output transmission lines produces the maximum gain - bandwidth product. Using this approach a bandwidth from 6 to 600 mc has been demonstrated at the 100 watt output level and 15 db gain (17% eff.). In the second type of device the impedance of the output line is tapered after a Short buildup section to maintain a constant rf voltage swing. This approach produces a device with optimum efficiency. An efficiency in excess of 40% has been demonstrated. Power output capability is in the 500-700 watt range with a bandwidth from 6 to 300 mc. The gain is 13 db. Both devices use the same vacuum envelope ( ) and weigh 7 1/2 lbs. Because of the high efficiency, extreme bandwidth, and small size and weight, this approach offers tremendous advantage over beam type devices for applications in VHF-UHF frequency range.