A Self-Decoupling Method for Antenna Arrays Using High-Order Characteristic Modes

In this article, a self-decoupling method is proposed for antenna arrays by exploring the coupling path through high-order characteristic modes (CMs) of the antenna elements. Mathematical formulas for coupling energy calculation are developed by combining the equivalent circuit of a receive mode antenna with the CM theory. With the CM analysis, radiating mode (RM) and decoupling mode (DM) of the antenna element are identified. An effective loading technique is proposed to enhance the modal significances of the DMs. The coupling between the DMs and the adjacent antenna element is enhanced, while the coupling with the dominant rms of the antennas is suppressed. Because of the coupling energy dispersion in the DMs, the corresponding unwanted induced currents flowing into the feed ports of the antenna element are suppressed, and the port isolations are efficiently improved. The decoupling structure composed of a simple metal ring and an impedance matching layer could be directly introduced into an antenna element, and the radiation performance of the previously optimized antenna element is preserved. Both simulated and measured results demonstrate that the port isolations are improved from 15 to 20 dB, and the radiation pattern distortion due to the mutual couplings is eliminated.