Design and Experimental Study of a High-Gain W-Band Gyro-TWT With Nonuniform Periodic Dielectric Loaded Waveguide

Abstract

Gyrotron traveling wave tubes (gyro-TWTs) are of considerable interest for high-power millimeter and submillimeter radiation sources. The analytical design and experiment of a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> -band gyro-TWT loaded with nonuniform periodic lossy dielectric rings is presented in this paper. The gyro-TWT is operating in the circular TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> mode at the fundamental cyclotron harmonic, and driven by a 60 kV, 8-A gyrating electron beam with velocity ratio 1.2. Hot test results were: 1) maximum peak output power 112 kW; 2) 69.7-dB saturated gain; and 3) 23.3% efficiency at 93.5 GHz. The measured bandwidth with peak power greater than 90 kW is about 4 GHz in the range of 93–97 GHz. The hot test results show excellent agreement with the theoretical prediction. The potential backward wave oscillations involving the spurious modes TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> , TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> , and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> are effectively suppressed by the nonuniformly loaded periodic lossy dielectric rings. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> -band gyro-TWT is zero-drive stable at the operating points. It demonstrates that a nonuniform loaded lossy dielectric structure is excellent for suppressing potential spurious oscillations.