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Abstract-This paper proposes two methods for increasing the Gain of Vlasov Antenna. The first method, using a Parabolic Cylinder Reflector, results in a 7 dB increase in the Gain. The second method, constructing a Horn on the aperture, increases the Gain by about 5 dB. The results were checked using a prototype antenna and there was a close agreement.

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.