Estimating polarization information using vector antennas is of great significance in signal processing. However, the antenna patterns are normally assumed ideal without considering practical factors, such as cross polarization. Moreover, pattern calibration is required in data processing. In this work, we first illustrate the polarization estimation method, taking into account the cross polarization of antennas. To simplify the estimation, we introduce a practical co-located antenna pair comprising a sleeve monopole and a windmill loop, which share mostly identical radiation patterns but orthogonal polarizations. The cross polarizations of both antennas are below -20 dB. Besides, the phase and amplitude patterns of both antennas are almost omnidirectional in the azimuth plane, avoiding complicated calibrations. Attributed to orthogonal polarizations, good isolation is achieved, and the envelope correlation coefficient is below 0.01. With the proposed antenna, the axis ratio and phase difference of the incoming wave are reasonably estimated without pattern calibration and compensation. The co-located antenna pair was fabricated, using which the polarization information of a commercial WLAN antenna has been measured.
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