This study describes about a Ku-band antenna with almost circular polarization in omnidirectional azimuth direction. The antenna structure contains two sections of inclined slotted array on a circular waveguide, and the waveguide is terminated with a matched load. The structure is fed a rectangular waveguide and a rectangular-to-circular waveguide transition. The designed antenna has 10 dB return loss bandwidth is about 3 percent, which is usually sufficient for the most of the satellite communication applications in Ku-band. Besides, the axial ratio of the antenna is also sufficiently low within the most of the frequency band as providing circular polarization. Besides, the radiation pattern of the antenna at azimuth plane is uniform such that the designed antenna is said to have the omnidirectional characteristics at this plane.