Various multiple-input multiple-output (MIMO) antenna systems for vehicles are presented in this paper usingtwo uniquely designed elements: low profile wideband Planar Inverted-F antenna (PIFA), and compact wideband monopole for automotive application in the sub-6 GHz 5G systems and Vehicle-to-Everything (V2X) communications that operate on the frequency range from 617 MHz to 6 GHz. This paper presents different MIMO configurations to be used in a low-profile housing or a shark fin style on the vehicle's roof. Each MIMO system achievesa satisfactory MIMO performance across the whole band withsuitable physical dimensions. The envelope correlation coefficient (ECC) and diversity gain (DG) are calculated using MATLAB in each MIMO configuration as they represent the two key factors in the MIMO performance. Simulation results are presented along with measured data on 1-meter rolled-edge ground plane (GND) and on vehicle's roof from properly cut metal sheet prototypes. The results are discussed in terms of VSWR, passive isolation between elements, combined radiation patterns, port-efficiencies, ECC and DG.
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