A Dual-polarized Endfire Antenna with Wideband and Enhanced Isolation for 5G Millimeter-wave Phased Array

This letter presents a wideband, high isolation dual linearly polarized (LP) endfire antenna, which is implemented using a high isolation substrate integrated waveguide (SIW) magic-T to feed the proposed dual circularly polarized (CP) antenna. High substrate profile of the conventional dual CP antenna deteriorates reflection coefficient of the SIW magic-T. To address this problem, a folded SIW structure was proposed for the antenna design, leading to a 38% reduction in the substrate's height. The lower substrate height ensures good impedance matching of the SIW Magic-T and facilitates phased array design. Then, a metasurface and a plate dipole are introduced to solve the impedance mismatching caused by the reduced substrate height. Based on this scheme, the presented dual polarized antenna realizes an operating bandwidth of 22% and an isolation level higher than 35 dB, which is improved by 20 dB compared with the same type of design. To realize the beam scanning, a 1×4 phased array with an element spacing of 0.5λ0 is built. Decoupling air notches are designed to improve the isolation between same polarizations. The measured results show that the designed phased array realizes a working bandwidth of 22% covering 24 to 30 GHz and the overall isolation level of more than 22 dB. A wide scanning angle of ±40°, with a scanning loss of less than 3 dB, is validated at 27 GHz. The proposed phased array is an attractive candidate for 5G millimeter-wave applications.