Smith-Purcell radiation of oversized backward wave oscillator

Smith-Purcell (SP) radiations of oversized K-band backward wave oscillator (BWO) are examined. By injecting an annular beam in the weakly relativistic region less than 100 kV, a beam mode with harmonic number n = 1 excites BWO radiations based on the TM₀₁ surface wave. The same beam mode excites higher order modes leading to SP radiations in the U- and E-bands. For a beam mode with n = 2, SP radiations are in the F- and D-bands, up to about 100 GHz, which is about four times higher than the frequency of the TM₀₁ surface wave. The SP radiation in the U-band can be enhanced by using a serf-bunching of K-band BWO. (author)