Design of Bandwidth-Enhanced and Multiband MIMO Antennas Using Characteristic Modes

Recent work has shown that, with the help of the Theory of Characteristic Modes (TCM), minor modifications of the terminal chassis can facilitate the design of orthogonal multiple-input-multiple-output (MIMO) antennas with viable bandwidth at frequencies below 1 GHz. Herein, a new framework is proposed to further exploit TCM to enhance the performance of the orthogonal MIMO antennas. By correlating the characteristic currents and near fields of modes with high modal significance in a given frequency band, a single feed may be designed to excite multiple modes, leading to enlarged bandwidth. Similarly, the correlation of characteristic currents and near fields across different bands provides candidate modes that can be excited for multiband operation using a single feed. Moreover, the impedance matching of these modes can be improved by additional structural manipulation. As proof of concept, a dual-band (818-896 MHz, 1841-2067 MHz), dual-antenna prototype was designed on a 130 × 66-mm² chassis for Long Term Evolution (LTE) operation. Full-wave simulation results were experimentally verified with a fabricated prototype.