Mutual Coupling Modeling and Calibration in Antenna Arrays for AOA Estimation

In antenna arrays, mutual coupling is an undesired effect which degrades the array pattern and the performance of array signal-processing algorithms like for Angle-Of-Arrival (AOA) estimation. Various approaches for mutual-coupling compensation that evaluate the coupling in receiving and transmitting modes have been studied. In this paper, a definition of the mutual coupling in receiving mode from the scattering parameters is introduced. A dissimilarity factor is added on the signals after the coupling calibration to simulate amplitude and phase variations at the termination of array elements. The coupling model shows the role of antenna characteristics and distance between the elements. When the antennas are all connected to a matched load and there is no dissimilarity between the antennas, the coupling in the receiving mode assimilates to that in the transmitting mode. To validate this statement, the coupling of an array of two patch antenna elements in these two modes is calculated, which shows an adequate agreement. A simplified technique calibrating the coupling and the dissimilarity is also proposed. The application of these coupling-calibration techniques together shows many possibilities to improve antenna arrays processing.