High-gain traveling-wave amplifiers

Modern techniques make it possible to build traveling-wave amplifiers with stable gains as high as 60 or 70 db. Such tubes can have relatively flat frequency response, and high gain over frequency ranges well in excess of two to one. In design it is necessary to pay strict attention to adequate isolation of the input and output so that spurious feedback paths do not cause oscillation or excessive variation of gain with frequency. In many practical applications, such tubes are required to operate with source and load impedances which produce large reflections of energy. Special design techniques result in tubes which are stable under such conditions. Another feature which can be achieved in modern tubes is a high ratio of backward loss to forward gain, so that the amplifier can very effectively isolate an oscillator.