A Mutual Coupling-Based Full Self-Online Calibration Method for Antenna Arrays in Uplink

Abstract

This paper proposes a mutual coupling based self-calibration method for transmit mode large scale antenna arrays. In accord with the proposed active antenna array model, gain/phase uncertainties, antenna element position errors and mutual coupling effects are reduced to an error matrix. The expansion of equations of the proposed calibration method are presented. The proposed calibration procedure is capable of compensating the error matrix while the system is operating and is suitable for off-line, on-site and online calibration procedures. The calibration procedure relies on the measurements of the error signal related to scan reflection coefficient while the system is operating, and the premeasured inter-element couplings. The calibration system takes pre-measured couplings, the geometry of the antenna array, the antenna weights and pointing direction as input, then, during the operation it combines input with the measured feedback signals to construct an array manifold. The coefficients of the error matrix are later estimated from the array manifold. The antenna weights are compensated by direct inversion of the estimated error matrix which involves division operator, yielding possible inaccurate coefficient estimation in hardware. Therefore, a globally convergent generalized inverse matrix approximation method is adopted. Simulation results with worst case errors and a simple experimental study are presented. The results show that with the proposed method, accurate calibration can be made with couplings only in the first and second order neighbors of an antenna element.INDEX TERMS Active antenna array, inverse matrix approximation, mutual coupling effect, self-calibration, up-link antenna arrays.