The corrugated horn antenna is investigated for the application of TE11 to HE11 mode converter. Two types of structures, i.e. sin-parallel and tanh profile are designed and verified by using commercial software. It is showed that the Gaussainity is more than 98.6% over a bandwidth of 10 GHz centered at 94 GHz. The Gaussianity can reach 99.2% at the central frequency. It is also seen that the beam waist of the sin-parallel type is located at the aperture of the structure. The tanh type bears advantages of a low-profile and stable phase center.