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Mode selective circuits with waveguide structures for gyro-TWTs Y.S Yeh, T. Y. Lin * , C.H. Lai, C. H. Chen Department of Electro-Optical Engineering,Southern Taiwan University of Science and Technology 1 Nan-Tai St., Yung-Kung City, Tainan County, Taiwan, 710 Abstract 研究方向 The gyro-TWA also suffers from the disadvantages of the small radius of the waveguide, leading to the increment of the wall loss of the waveguide significantly. The stability and performance of the gyro-TWA operating at the high order mode are enhanced because of the large radius of the waveguide. The second harmonic component TE02 (s=2) of the beam current initiates a wave to be amplified by amplifying a TE01 (s=1) drive wave. In this study, new mode selective circuits are employed for suppressing non-TE0n competing modes while distributed wall losses or attenuation severs are employed for suppressing TE0n competing modes. B. a improved mode selective circuit for the 200 GHz gyro-TWT I.THEORY multiple reflection rs TE02 ∆L incident wave rw transmitted wave coupling wave TE01 TE02 TE21 dispertion II. RESULTS AND DISCUSSION A. a improved mode selective circuit for the 35 GHz gyro-TWT TE02 structure III. CONCLUSION TE21 dispertion This study presents a transverse sliced interaction structure for the 35 GHz second harmonic TE02 multiplying gyro-TWT. Because the wall surface current for the TE0n mode is in the azimuthal direction only, the TE02 operating wave isn’t affected as it travels through the transverse slice. In contrast, the TE21(1) competing mode (f~24.3 GHz) with axial surface current are significantly affected. A novel mode selective circuit with waveguide bandstop filter provides the bandwidth of 10 GHz at the insertion loss -10 dB while the other one can provide the bandwidth of 8 GHz at the insertion loss -20 dB. For the 200 GHz second harmonic TE02 multiplying gyro-TWT is proposed. A novel mode selective circuit with a waveguide structure provides the insertion loss -15 dB at the TE21(1) competing mode (f~86.4 GHz) and the insertion loss -100 dB at the TE51(2) competing mode (f~179 GHz) z) and the insertion loss -84 dB at the TE22(2) competing mode (f~187 GHz). This work was supported by the National Science Council under Contract No. NSC 101-2221-E-28-033.The authors are also grateful to the National Center for High-Performance Computing (NCHC) for providing computing facilities and technical supports. Reference structure 1. Chen, Nai-Ching,“TE01 Gyrotron Backward-Wave Oscillator with Mode Selective Circuit”, Physics of NTHU,2009. 2. N. C. Chen, C. F. Yu, C. P. Yuan, and T. H. Chang, “A mode-selective circuit for TE01 gyrotron backward-wave oscillator with wide-tuning range, ” APPLIED PHYSICS LETTERS 94, 101501 2009.