A novel substrate integrated waveguide‐fed low‐cost circularly polarized aperture coupled patch antenna array with wide impedance and axial ratio bandwidths, higher gain, and the stable radiation pattern is presented for millimeter‐wave frequency bands applications. A cut‐angle horizontal patch element and an aluminum plate are used to achieve the good performance of the circularly polarized aperture coupled patch antenna element. Besides, the antenna element is used to implement a wideband high‐gain circularly polarized patch antenna array. For demonstration, a proposed 2 × 2‐element antenna array with a SIW‐based sequential‐rotation feeding network is simulated, fabricated, and tested. The simulated −10 dB impedance bandwidth is 19.84% from 14.03 to 17.12 GHz, the operating bandwidth is 3.09 GHz, and the peak gain in the operating frequency band is 13.67 dBic.