The Model ATH18G27-1 is a wide band, low gain, wide beamwidth, high power microwave horn antenna. With a minimum gain of 8.8dB over isotropic, the Model ATH18G27-1 supplies the high intensity fields necessary for RFI/EMI field testing within and beyond the confines of a shielded room. The Model ATH18G27- 1 is extremely compact and light weight for ready mobility, yet is built tough enough for the extra demands of outdoor use and easily mounts on a rigid waveguide by the waveguide flange. Part of a family of microwave frequency antennas, the Model ATH18G27-1 provides the 18.0-26.5GHz response required for many often used test specifications. The ATH18G27-1 is ideally suited for use with the AR Models 40T18G26A and other high power amplifiers in this frequency range.