Ceyhan TurkmenMustafa Secmen2025-10-062016978-8-8907-0186-32164-3342https://gcris.yasar.edu.tr/handle/123456789/6061This study describes about Ku-band antennas with circular polarization in hemispherical radiation pattern for telemetry and telecommand applications of satellite communication. The first section of antenna contains a septum polarizer structure which converts linear-polarization to circular-polarizations (left-hand and right-hand). This structure feeds a circular aperture waveguide which is the second part. The axial ratio performance of the antenna is improved by adding some metallic rings with optimized dimensions. Therefore circular polarization is achieved in wider azimuth and elevation angles. Two different designs are carried out for 11.35-11.8 GHz and 14.3-14.65 GHz. The return losses are greater than 15 dB in the given frequency bands. Besides the axial ratio of the antenna is under 3 dB throughout 1700 at azimuth and elevation which proves circular polarization property in hemispherical region. The gain at the broadside is almost 9.3 dB and it is higher than -10 dB throughout 170 degrees angle coverage.Englishcircular polarization, Ku-band, telecommand, telemetry, waveguide antennaDESIGNConference Object