A Wideband Circularly Polarized Transmitarray Antenna for Millimeter-Wave Applications

A wideband circularly polarized (CP) transmitarray antenna (TA) is presented for millimeter-wave applications. First, a wideband CP TA element is designed by combining two wideband antennas, one of which is a linearly polarized (LP) magnetoelectric (ME)-dipole antenna, and the other is a CP antenna with orthogonal electric-dipole mode and patch mode. Both of the two antennas are fed by a probe from the center of the unit cell; thus, the CP antenna can be rotated freely to realize the required phase shift. Then, a CP TA with $15\times 15$ elements is designed based on the unit cell proposed here. To excite the proposed TA, a fully metallic ME-dipole-based antenna array featuring wide operating bandwidth with a low profile and ease for assembling is used as the source antenna. Finally, by integrating the CP TA with the source antenna, a prototyped millimeter-wave CP TA is designed, fabricated, and measured. Experimental results show that the gain of the proposed CP TA is up to 25.6 dBic at 33 GHz with a peak aperture efficiency of 44%. The 3 dB gain bandwidth is 33.8%, and the axial ratio (AR) is smaller than 2 dB within a bandwidth of 37.5% from 26 to 38 GHz.