Decoupling of Axial Symmetric Three Antennas Based on Active Impedance Matching

In this article, a novel decoupling scheme based on active impedance matching is proposed for the decoupling of axial symmetrical three antennas. Three simultaneous excitation modes with the same amplitude and different phase relationships are utilized to analyze the decoupling problem. In the perspective of simultaneous excitations, the decoupling of the three antenans can be transformed into active impedance matching. Theoretical demonstration reveals that achieving decoupling for axial symmetrical three antennas necessitates matching the active impedances under the three excitations. The active impedance matching can be solved intuitively in a clear step-by-step process by exploiting the impedance characteristics of the coupled three-line and the unique field distribution under different excitation modes. To validate the effectiveness of the proposed method, the decoupling of axial symmetric three inverted-F antennas (IFAs) is presented as an example. The achieved isolation exceeds 17 dB in the desired band with a peak isolation of 31 dB. With good isolation and a straightforward design process, the approach holds promise for future multi-input-multi-output (MIMO) antenna systems. Furthermore, the proposed method provides a new physical intuition for solving the decoupling problem of multiple antennas without the need for numerous optimizations.