Antenna efficiency, Circularly polarized antenna, Decoupling technique, Envelope correlation coefficient (ECC), Isolation enhancement, Multiple-input multiple-output (MIMO), Engineering (General). Civil engineering (General), TA1-2040

In this article, a three-element circularly polarized multiple-input-multiple-output (CP-MIMO) antenna array with self-decoupled probing method is introduced. Three unidirectional radiated Guo-shaped patch antennas were arranged in a triangular lattice and excited by L-shaped feeding probes at different locations with respect to the patch center. Meanwhile, the patches themselves remained artistic and were placed in the upward position. Namely, the main motivation is to generate CP directional beams without requiring orthogonal placement. The contributions of this work account for (i) spatial diversity, (ii) pattern diversity, (iii) polarization diversity, and (iv) enhanced isolations (25 dB) between patch elements without inserting any external decoupling structures. As such, the antenna efficiency of Guo-patch elements can be raised in an order of 90 % within the band of interest at IEEE 802.11n/g/ac, viz., 2.4–2.5 GHz. The CP-MIMO prototype was fabricated and validated with experimental tests. Outstanding performance metrics such as an envelope correlation coefficient (ECC) of 0.005, mean effective gain (MEG) of −3.5 dB, channel capacity loss (CCL) of 0.18b/s/Hz, and a total active reflection coefficient (TRAC) of better than −15 dB were obtained. The measured results, which agreed with theoretical simulations, confirmed that the multi-element MIMO antenna with the spatial-, pattern- and polarization-diversity is a good candidate for the multi-user B5G-V2X.