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Dual-band operation and circular polarization are the main characteristics of the separated turnstile (ST) antenna that make it suitable for space applications. In this paper, we describe the design and optimization of a separated turnstile antenna to obtain a saddle-shaped pattern in the UHF band and an omnidirectional pattern in the VHF band, with simultaneous impedance matching in both bands. The antenna model and the effects of the body of the satellite and the solar panels were analyzed using the Moment Method. The effects of the physical parameters of the antenna on the radiation pattern, such as the length of the monopoles and their mounting angle, were investigated. A radio-frequency distribution unit - which included a diplexer, phase shifters, and a power divider/combiner for both bands - was also designed, analyzed, and measured. The test results agreed with the analysis results. The axial ratio and polarization efficiency of this antenna were calculated for incident waves with different polarizations. The antenna was fabricated and its radiation parameters were measured. The test results were compared with the analysis results to confirm the correctness of the design.