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Analysis and optimized designs are presented of three types of single feed circularly polarized microstrip antennas, namely, a diagonal fed nearly square, a truncated-corners square and a square with a diagonal slot. The Green's function approach and the desegmentation methods are used. The resonant frequencies are calculated for two orthogonal modes which together yield circular polarization. Optimum feed locations are determined for the best impedance match to a coaxial feed line. Axial-ratio bandwidths, voltage standing-wave ratio (VSWR) bandwidths and radiation patterns are evaluated and verified experimentally.