XPD Enhancement of Dipole Antenna Arrays by Inducing Coherent Current From Feeding Line

Cross-polarization discrimination (XPD) is a critical parameter in designing dual-polarized antennas, particularly for multiple-input–multiple-output (MIMO) base station (BS) antenna arrays. A high XPD level leads to high isolation between two polarized waves and a high input signal-to-noise ratio of the system. In this article, a new scheme for enhancing XPD of a ±45° dual-polarized dipole antenna pair, the most prevalent antenna element form for MIMO BS antenna arrays, is proposed and is applied to a dipole antenna array. The new scheme induces the required coherent currents on a pair of vertical monopoles from the feeding line. Specifically, a 3-U structure that is printed on the circuit board of the feeding line is proposed. The structure couples the signal from the feeding line and excites two opposite currents on the vertical monopoles, whose radiated fields effectively compensate the
$\theta $
-component of electric field in a wide scanning angle. The working principle of the scheme is elaborated in detail with a simplified analytic model. The scheme is applied to a dipole array, in which each 3-U structure is personally designed to accommodate the complex array environment. Simulation and experimental results are presented to demonstrate the effectiveness of the proposed scheme.