Design of output-taper for high power gyro-TWT

A new output-taper for Ka-band high power gyro-TWT is designed by a function of sine and cosine and using the coupled wave equation to analyze the radius changing circular waveguide. Using the MATLAB code and software HFSS, we analyze the transmission, the reflection coefficient and the coupling coefficient to TE02 mode and TE03 mode. When the length is 80 mm and the diameter changes from 14 mm to 32 mm, the results indicates its transmission coefficient more than -0.000 52 dB, reflection coefficient less than -65 dB, mode purity more than 0.995, the coupling coefficient to TE02 mode and TE03 mode less than -40 dB. Compared with Dolph-Chebyshev output taper, when the length and diameter are the same, the new output tapers transmission, reflection coefficient and mode purity are superior than those in 30 GHz to 33 GHz. The results of cold test for the test-sample show that S11＜-30 dB and S21＞-0.3 dB.