Abstract In this paper at first, the ordinary septum polarizer has been designed and used for parabolic reflector feed in Ground station antenna. Next, a novel design of modified septum polarizer with wider beam-width is proposed for satellite antenna. Compactness, low weight, large bandwidth, high TX/RX isolation, low axial ratio as well as low loss are the advantages of the septum polarizer. The designed antenna has high purity circular polarization ( $\left| {AR} \right| \le 1.6dB$ ) and low return loss. The frequency bandwidth of the antenna is about 27 % in the center frequency 11 GHz and the TX/RX isolation is better than 32 dB. Finally the septum polarizer, modified septum polarizer and reflector are fabricated and tested and there were good agreement between simulation and measurement results.