This paper presents design considerations and measured results for a two element 8 to 12 GHz horn antenna array for transmit/receive applications requiring high isolation. Circular polarization is achieved by incorporating a five layer meanderline circular polarizer over the aperture of the horn antenna. The measured axial ratio for operational antennas including protective radomes is less than 0.85 dB over the entire frequency band. The antennas are fitted with waveguide-to-coax adapters and achieve a VSWR ≤ 1.5:1 in the fully assembled condition. Installed isolation of better than 78 dB is achieved over most of the frequency band at a prescribed antenna separation of 500 mm.