Septum Horn Antennas at 47/48 GHz for High Altitude Platform Stations

The septum horns are aperture type antennas with the possibility to offer a circular polarization. The antenna can use both polarizations (left- and right-hand circular - LHC, RHC) simultaneously at the same time. Circular polarization has advantages in providing different services, e.g. coverage from HAPs, where better power budget is obtained by minimizing the polarization loss. A design of a septum horn antenna for frequency band 47.0-48.5 GHz (based on the studies and designs at 1.3 GHz and 2.4 GHz) is presented in the paper; possibilities of the septum horn antenna design and available parameters are discussed. Thanks to the circular polarization and rotationaly symmetrical aperture such antennas provide a pencil beam radiation pattern with a very low side lobes level. A 20 dBi gain septum horn antenna was developed and manufactured. Calculated data (radiation pattern, beamwidth, sidelobes suppression, gain and VSWR) were compared with measured data. Adaptations of the antenna design for possible deformations of the radiation pattern to get proper coverage footprint is discussed.