26-/39-GHz Low-Profile Dual-Circularly-Polarized Hybrid Antenna With Integrated Single Feed

A low-profile dual-band dual-circularly-polarized (dual-CP) antenna is proposed in this article. The proposed antenna hybridizes folded transmitarray (FTA) for the lower band and folded reflectarray (FRA) for the upper band. The top metasurface employs the receiver–transmitter (Rx–Tx) structure and works as a polarization grid to collimate electromagnetic (EM) waves at the lower band. In addition, this top metasurface realizes wave conversion from linear polarization to circular polarization for dual bands. Meanwhile, a double-layer bottom metasurface realizes wave collimation at the upper band and 90° polarization twisting in both bands. In this way, right-hand circular polarization (RHCP) at 26 GHz and left-hand circular polarization (LHCP) at 39 GHz are achieved simultaneously. Furthermore, the proposed hybrid antenna is fed by a wideband magneto-electric (ME) dipole with a single LP. This planar ME dipole is inherently integrated with the bottom metasurface. For validation, a dual-band antenna including a top metasurface and a bottom metasurface is designed, fabricated, and measured. The height-to-diameter ratio (H/D) is only 0.22 for FTA and 0.24 for FRA, while the 3 dB axial ratio (AR) bandwidths are 11.4% (24.9–27.9 GHz) and 4.2% (37.7–39.3 GHz), respectively. The proposed antenna features low cost, low profile, high gain, and planar integration. This single antenna covers two bands (26/39 GHz) for the fifth generation (5G) millimeter-wave applications.