Characteristic Mode Analysis for Pattern Diversity and Beamforming: A Survey

With the rapid development of space-air-ground integrated communications, diverse requirements have been imposed on antenna radiation patterns. In addition, increasingly compact platforms brings significant challenges to the deployment of antenna arrays normally used for beamforming. This article comprehensively surveys characteristic mode analysis (CMA)-based pattern diversity realizations in past years. Specifically, exciting multiple characteristic modes independently achieves pattern reconfigurability and element-reduced multiple-input and multiple-output systems. We furthermore overview a series of works on modes superposition. Various methods have been explored for modal weights decision, and therefore specific patterns are synthesized. The weighted modal combination also fulfills single-element beamforming. A recent study on an antenna design for electrically small unmanned aerial vehicles (UAVs) is summarized, and the desired reconfigurable radiation patterns of the conformal radiator are realized based on CMA. Moreover, a formation-based beamforming technique, which takes advantages of the electromagnetic coupling among conformal radiators and the agility of UAVs, is introduced.