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In this letter, a high-isolation dual-polarization microstrip patch antenna with omnidirectional radiation patterns is proposed. The radiation elements of the antenna are a combination of an annular-ring patch and four curved branches. The annular-ring patch is fed by a modified capacitive coupling structure to radiate a vertically polarized omnidirectional pattern, while the four curved branches that are set around the annular-ring patch with a suitable distance for high isolation are fed in phase to radiate a good horizontally polarized omnidirectonal radiation pattern. The isolation between the two ports is better than a high degree of - 40 dB to limit the interference of the signals. A prototype of the proposed antenna is fabricated and measured to verify the predictions, and the measured results are in good agreement with the simulated ones. The proposed antenna is a good candidate for wireless communication for its extremely low profile, high port isolation, and omnidirectional radiation property.