Experimental investigation of Ka-band harmonic multiplying gyro-TWT

To achieve high power millimeter waves at Ka-band, a harmonic-multiplying gyro-TWT is developed. The designed interaction circuit is a 2-stage waveguide that consists of input and output sections divided by severing. Both stages are linearly tapered rectangular waveguides in which the fundamental TE/sub 10/ mode is used. Tapering the waveguides increases stabilities and bandwidth by distributed interaction when the grazing condition along the taper is satisfied. In this study, each stage employs X-band and Ka-band frequencies, respectively. Through the fundamental and the 3rd electron cyclotron harmonics at each stage, a harmonic-multiplying interaction occurs. As a result, a saturated gain of 23 dB, an electronic efficiency of 10%, and a bandwidth of 3% were predicted by a self-consistent nonlinear calculation on the assumption of 4% axial velocity spreads of electrons when an axis-encircling electron gun at a moderate beam voltage of 30 kV and a current of 1 A is employed.