Design of start part of slow wave structure in relativistic backward wave oscillator

Spatial harmonic coefficients are theoretically calculated for transverse magnetic TM01 mode in slow wave structure (SWS) of relativistic backward-wave oscillators(RBWO). It is proved that there are four means to construct resonant SWS cavities whose electromagnetic properties are the same as those of infinite SWS cavities. According to the field distribution in SWS and computer simulation results, it is suggested that the SWS generally begin with the deepest location of corrugation in order to increase the conversion efficiency.