Transmission-line amplifiers

A wideband thermionic vacuum-tube power amplifier in which an extended and continuous grid and cathode serve as an input transmission line that excites a corresponding traveling-wave signal on a similar transmission line between the screen grid and anode is analyzed. The usual gain-bandwidth product limitation is avoided by making the input and output capacitances part of the transmission lines. The gain mechanism is the same as that in the usual power tetrode in that bunched charges are delivered to the anode at the proper time and location along the anode transmission line to enhance the traveling-wave signal. If line attenuation losses are small, the power gain increases as the square of line length. Part of the backward wave can be made a forward wave by tapering the impedance of the output line. This type of amplifier could potentially use a field-emission cathode and thus avoid the high heater power and slow transit time of the thermionic emitter. Its disadvantages are low gain and low input impedance