A signal input selective device for a high-current relativistic Cherenkov amplifier

Selective unidirectional excitation of a cylindrical waveguide through the side wall has been studied in application to the signal entry of a millimeter-wave high-current relativistic cherenkov amplifier. The found ratio of the input structure parameters ensures maximum transfer from the fundamental mode of the rectangular waveguide to the unidirectional lowest circular mode of the cylindrical waveguide. The transfer efficiency in absence of ohmic loss reaches 97.5%. The input structure adapted to the 35.5 GHz-amplifier construction has been realized with an efficiency of 75%.