Evaluation of vehicle-level MIMO antennas: Capacity, total embedded efficiency, and envelope correlation

The paper describes an approach to estimate 2×2 MIMO channel capacity of a shark-fin radome antenna designed for multiple LTE bands by using channel matrices measured from drive tests in a real driving environment with a commercially available LTE radio network analyzer. The nonproduction shark-fin radome antenna that is mounted on the roof of a sedan is treated as a black box, and the estimated channel capacity is compared with that of a reference MIMO antenna consisting of identical monopoles tuned at 750 MHz. The two element λ/4 monopole array was also measured in a rich isotropic multipath environment at a reverberation chamber so that it can be used as a reference with known channel capacity. Total embedded efficiency and envelope correlation derived from measured s-parameters for the black box and the reference antennas are presented and discussed. The results show that the channel capacity depends on both the embedded efficiency and the correlation, and the approach estimating the MIMO throughput based on the channel matrices measured from the drive tests is shown to be useful to evaluate multiple MIMO antennas in a real driving environment.