Broad band low loss input coupling system in W-band gyrotron

The design principle of a TE□10-TE○01 broad band cruciform mode converter was addressed in this paper, and the scheme of a set of W-band low loss input coupling system was presented. According to this scheme, the 3-D model was optimized and simulated by HFSS. A TE□10-TE○01 broad bandmode converter with a loss of less than 0.14 dB, a maximum VSWR of 1.388, and a band width of 10 GHz was obtained through simulation. For the whole system, a calculated loss of less than 1 dB, which was far less than that of TE10 mode in the rectangle waveguide(about 15 dB), was given. It leaded to the increase of the transmission efficiency and reduction of the energy loss. A pair of manufactured mode converters was tested in the experiment, and the loss was about 1 dB. So the loss of the whole system was equal to 3 dB, which was greatly improved compared with the loss in the rectangle waveguide.