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 the 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 0.5λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is built. Decoupling air notches are designed to improve the isolation between the same polarization. The measured results show that the designed phased array realizes a working bandwidth of 22% covering 24 GHz to 30 GHz and an 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.