A wideband millimeter‐wave circularly polarized (CP) antenna based on metasurface (MS) is proposed. The antenna consists of a two‐layer substrate integrated waveguide (SIW) feed structure and a layer of MS with a 2 × 2 rectangular truncated corner. As a polarization conversion structure, the MS converts the linearly polarized wave generated by the SIW into a CP wave, and four metal pins are placed in the middle to improve the impedance and the axial ratio (AR) bandwidth. Based on this antenna element, a SIW‐fed 2 × 2 array using the sequentially rotating phase (SRP) feed technique is designed, which further improves the AR bandwidth and the gain level of the antenna. The results of the measurements show that the array maintains a low profile with an impedance bandwidth of 40.3% from 25.05 to 37.14 GHz, and an AR bandwidth of 31.3% from 23.14 to 32.54 GHz, and a peak gain of 14.3 dBi.
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