Abstract: Based on the mode coupling theory, the design of TM₀₁-TE₁₁，TE₀₁-TM₁₁，TE_0n-TE₀₁，TE₀₁-TE₁₁ overmoded circular waveguide mode converter geometric configurations with different phase rematches and structures is given to obtain more acceptable geometry parameters. This result contributes to teh design of a corresponding circular waveguide mode converter with compactness high efficiently and a wideband.

Key words: circular waveguide, bent waveguide, mode conversion, coupled wave equations