Gain vs. frequency characteristic of very broadband crossed-field amplifiers

Because of the rapid impedance variation with frequency encountered in the space-harmonic slow-wave structures normally employed in high power, broadband injected-beam crossed-field amplifiers, a flat gain vs. frequency characteristic is very difficult to achieve if one is limited to a single synchronous velocity. This paper will present a new method of adjusting this characteristic to any desired degree of flatness or any other reasonable frequency-gain variation. The adjustment is made externally during hot test and may be modified at any time during the life of the amplifier. This method makes use of a slightly dispersive slow-wave structure (i.e., the wave phase velocity varies slightly with frequency) and an electron beam velocity programmed to vary along the interaction space. By making various portions of the structure synchonous at various frequencies, any portion of the gain vs. frequency characteristic may be emphasized relative to any other portion.