This paper presents a geodesic H-plane horn antenna with switchable circular polarization. The polarization diversity is realized by stacking two identical geodesic horn antennas and joining them at the aperture using a parallel plate waveguide septum polarizer. Depending on which of the two horns is fed, the antenna can radiate either left-hand or right-hand circular polarization. The proposed antenna operates in the K, -band, with a center frequency of 29 GHz and a 3 dB axial ratio bandwidth of 15 %.