Wideband, Closely-Spaced, High-Isolated MIMO Microstrip Antenna Array for Vehicular Communication

This paper presents the wideband, closely-spaced, and high-isolated multiple-input multiple-output (MIMO) microstrip antenna (MPA) array for vehicular communication. The close proximity, identical polarization, and wide frequency range lead to stronger mutual coupling between antennas, resulting in the degradation of the original antenna's (Ant. A) fractional bandwidth (FBW) and isolation to 27.8% and 9.1 dB, respectively. As a result, the cross-type capacitor-loaded fence and quarter-wavelength open-ended slots are explored to gradually improve impedance matching and enhance the port isolation, thereby realizing the first prototype. Additionally, by loading four shorting vias on patch corners, the second wideband prototype is implemented, demonstrating better isolation and reduced H-plane cross polarization, even with closer spacing. As a validation of the concept, these two prototypes are fabricated and experimentally tested, showing good consistency between simulations and measurements. More importantly, the 2×6 MIMO MPA array achieves a wide 20-dB decoupling bandwidth of 43.5%, demonstrating good isolation in both the E-plane and H-plane arrays simultaneously. The proposed antenna shows potential usages for vehicular communication and wideband high-isolation MIMO applications.