A Fast Computational Method for Characteristic Modes and Eigenvalues of Array Antennas

In this article, an efficient and systematic method for fast and accurate computation of characteristic modes (CMs) and eigenvalues of the entire array antenna as a whole is proposed. This technique benefits from the symmetry and Toeplitz property of the method of moments (MOM) impedance matrix of the array structure. Using this technique, we are able to directly obtain CMs of a large-scale array structure with minimal computational resources. First, the self-impedance matrix of a radiating element and the mutual-impedance matrices between that element and the remaining ones are calculated numerically using MOM. Then, the theory of characteristic modes (TCM) is applied to the entire array. Using the proposed method, we decompose the coefficient matrix of the CM equation into smaller matrices. In addition, interesting and meaningful relations between currents flowing on elements associated with each CM of an array are derived and used to significantly reduce the computational complexity in the CM extraction. Moreover, numerical results and computation time are reported to validate the proposed method.