A Characteristic Mode Based Multiport Antennas for MIMO Base Station Applications

A novel multiport multi-input multi-output (MIMO) antenna for 4G/5G base station application is developed based on the theory of characteristic modes (TCM). The solved characteristic modes illustrate that it is possible to excite five modes simultaneously with a properly designed patch in the 1.7-2.7 GHz frequency band. The characteristic modes also provide clear guidelines for selecting feeding places and designing excitation for the characteristic modes. The natural orthogonality property of characteristic modes guarantees high isolations among the many ports in a MIMO antenna system. The developed MIMO antenna is comprised of two layers. The top layer is the radiating aperture, while the bottom layer is the feeding circuit. The working frequency band of the developed MIMO antenna is 1.64-2.74 GHz, which can be used in 4G Long-Term Evolution and sub-6 GHz 5G networks. By using TCM and orthogonality of characteristic modes, a compact four-port MIMO antenna is designed with at least 20 dB isolations. The four ports excite different shapes of radiation patterns with diverse polarizations and radiation patterns. The envelope correlation coefficient is extremely low between the four ports, which makes it attractive for MIMO diversity systems. Both simulated and measured results are presented to demonstrate the proposed design. In addition, the ergodic channel capacity is also evaluated to demonstrate the enhanced capability in communication system applications.