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A novel structure for the transition from the dominant mode in circular waveguide to that in circular groove guide is presented. The mode converter based on this structure which has low reflection coefficient is designed. The numerical result shows that the performance of this new type of transducer is improved.

Abstract: This paper gives a structure on the mode converter from TE 0nO mode of gyrotron output to the MediaObjects/10762_2007_BF02678395_f2.jpg main mode of the circular groove guide. The design consists of two parts: the first part is to convert TE 0nO to TE 01O using an advanced periodic wall perturbation technology, the second part is to convert TE 01O to MediaObjects/10762_2007_BF02678395_f3.jpg mode basing on the method of gradually changing the wave guide cross section. An example at 37.5Ghz is given. For the first part, the efficiency is 94.71%, the length is 1.868m. For the second part, the theoretic figure of reflectance coefficient vs. frequency is given.