Gain and Bandwidth Improvement Studies of Millimeter Wave Periodically Dielectric Loaded Gyro-Twystron Amplifier

In this article, the spurious oscillations in the output section of gyro-twystron have been analyzed and the design and modeling of its various subassemblies also been presented. The periodic dielectric loading (PDL) technique has been adapted in the output waveguide section to improve the device gain by suppressing the backward wave oscillations (BWOs). Further, to improve the performance of the amplifier all the cavities were staggered tuned. The particle-in-cell (PIC) simulation of the present PDL gyro-twystron predicted an RF output power of ~120 kW in the fundamental TE01 mode at 94 GHz. The conversion efficiency, 3-dB bandwidth, and saturated gain were calculated as ~34%, ~2.2 GHz, and ~51 dB, respectively. A triode magnetron injection gun (MIG) was designed for 60 kV and 6 A gyrating electron beam and optimized for the velocity spread of ~2.2% with a velocity ratio of 1.6. A single-stage depressed (SSD) collector has also been designed to enhance the efficiency of the amplifier to ~57%. A double-disk window was designed and optimized for the broader bandwidth of ~8 GHz.