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In this paper, the design, production, and results of an omnidirectional and circularly polarized antenna for satellite communication applications such as telemetry or telecommand are explained. The antenna is fed by a special transition structure between rectangular waveguide to circular waveguide in order to provide symmetrical circular waveguide mode of TM01 and eliminate dominant but asymmetric mode of TE11. The radiation part on the antenna has the geometry of inclined waveguide slots placed in a rotationally symmetric way on a circular waveguide and two radially outward parallel cylindrical plates in order to provide circular polarization. In the design of the antenna, nonidentical slots are used on the circular waveguide where half of the total number of slots is reduced to increase the bandwidth of the antenna. The realized antenna is found to give about 5–6% impedance bandwidth around 12 GHz where it is just approximately 2.5% when all slots in array are identical. The usage of nonidentical slots results in degradation of gain variation and axial ratio performances as compared to the antennas with identical slots; however, it still performs gain variation less than 3 dB over full azimuth plane, and axial ratio under 3 dB over full azimuth plane and elevation beamwidth of minimum 50° for the given bandwidth.

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This study is related with the design of a ± 45° dual polarized base station antenna with improved cross-polarization discrimination (XPD) values. Parasitic elements are added to antenna design formed by orthogonal two compact meandered dipole above ground plane. The antenna designed with CST Microwave Studio program has VSWR ≤ 2 within 1.71-2.69 GHz frequency band, which covers GSM 1800/3G/LTE bands. The antenna has minimum of 0 dBi gain in the beamwidth of 120° ( 60°) at azimuth plane (ϕ = 0°) along the band, and XPD values being minimum of 2 dB at 1.71-2.4 GHz for  60° without parasitic elements are improved to 10 dB with parasitic elements. This design initially had two horizontal straight monopoles on the ground plane perpendicular to each other. Afterwards, antenna with microstrip balun feed applied but the XPD values were not appropriate to expected results. Because of that, by using image theory, vertical parasitic elements were added to get appropriate XPD values. Later, meandered structure used to make antenna smaller. Finally, according to base station applications, antenna frequencies optimized to 1.71 GHz and 2.69 GHz. The designed and optimized antenna produced and measured in laboratory environment. Return losses for port 1 and port 2 are measured above the 10 dB and isolation between the port 1 and port 2 are measured above the 20 dB. In addition, the maximum gain values are measured between 3 dB and 7 dB in 1.71 GHz and 2.69 GHz frequency band.  Finally, XPD values are measured more than 10 dB in bandwidth.