Phase rematch on overmoded waveguide mode converter for BWO

The overmoded transmission line is often adopted by high-power millimeter wave system, so the influence of various distortion has to be evaluated. The distortion of waveguide can be utilized if we know its influence to the modes. So, the questions of mode coupling should be studied which arising from waveguide distortion. For the output mode of Backward wave oscillator and Virtual cathode oscillator is often TM₀₁ mode and TM_0n mixed modes. The TM_0n-TM₀₁ mode converter can adopt gradual radius changes of the waveguide, and TM₀₁ mode radiate outside only converter to TE₁₁ mode, so the thorough study of the structure and characteristic of TM₀₁-TE₁₁ mode converter is needed. The size of a waveguide is large under a high-power situation, thus it is necessary to take account more waves and their mutual coupling as well as the attenuation of circular waveguide and the option of coupling mode etc. Heavy considerations have been given to the influence of multimode factor, backward wave, ohmic losses carried from metal wall, modes choice and phase rematch.