A Wideband Quad-Port 3-D MIMO Antenna Decoupled With DGS Structure for Roadside Units

A wideband quad-port three-dimensional multiple-input--multiple-output (MIMO) antenna for intelligent transportation roadside units is proposed. The MIMO antenna adopts a cube-shaped metal box as its ground, with microstrip patch elements vertically placed on each side of the cube. Therefore, omnidirectional coverage is realized. A concave metal patch is added on the back layer of the dielectric substrate, and two rectangular metal pillars are soldered to both sides of the substrate. These structures significantly improve impedance matching, generating a wideband of 4.69 GHz to 8.92 GHz. Several slots are cut along the edges of the metal box to alter the surface current distribution of the metal, thereby enhancing the port isolation. The interport coupling coefficient is better than −24 dB in the entire frequency range. Particularly, the coupling coefficient is better than −31.2 dB in the vehicle-to-everything (V2X) band [(5.905 to 5.925) GHz]. The microstrip patch antenna measures 15 mm × 13.2 mm × 1.6 mm, and the metal box has a side length of 44 mm and a thickness of 1 mm, indicating a miniaturized design. The envelope correlation coefficient is below 0.002. The diversity gain reaches 9.98 dB. The channel capacity loss is less than 0.4 b/s/Hz.