An estimation method of the 4-port S-parameters used for the E-MIMO approach

This paper investigates a novel method for deriving 4-port S-parameters for the E-MIMO approach. In this method, only the self-S-matrices of the transmitting antennas ($S_{TT}$) and receiving antennas ($S_{RR}$) need to be pre-calculated or measured. The coupling matrix ($S_{RT}$ or $S_{TR}$), which depends on the position of the receiving element, can be estimated using the proposed simplified method. Since the receiving antenna is positioned in the far-field, the Friis transmission formula is applied to estimate the amplitude of the elements in the coupling matrix ($S_{RT}$ or $S_{TR}$), while the array factor is used to estimate the phase of these elements. The S-matrices for a 3 × 1 array, obtained through conventional simulation, measurement, and the proposed estimation method, are compared. Furthermore, these matrices are applied to E-MIMO to compare their radiation patterns and power transmission efficiencies. The results demonstrate that the proposed estimation method achieves radiation patterns and power transmission efficiencies that are closely comparable to those obtained using the conventional method, confirming the effectiveness of the proposed method.