Virtual Impedance Method for Mutual Coupling Compensation

The radiation pattern of an antenna within an array environment is modified by mutual coupling to neighboring elements, which can create unknown phase and amplitude variation on the order of 10° and 5 dB. This uncertainty in the element patterns results in beamforming errors, which can be particularly problematic for applications requiring precise pattern control. A new approach is reported to compensate for the mutual coupling of single-mode radiators using only the measured S-parameters and received signal from several far-field sources. The technique relies on the fact that dominant mode scattering from each antenna can be removed by terminating it with the proper impedance. Optimized beamforming weights are derived that compensate for mutual coupling. It is shown that implementing these optimized weights is equivalent to terminating all elements with a “virtual” impedance that cancels scattering from neighboring antenna elements (i.e., mutual coupling). Simulations of perfectly uniform and nonuniform linear dipole arrays show that compensating for mutual coupling using the proposed technique reduces the variation of the embedded element patterns by an order of magnitude compared to more conventional techniques. The proposed approach could be useful for a wide variety of antenna arrays and may even lend itself to self-calibration in the field using signals of opportunity.