A STUDY ON THE MODE-BASED ANALYSIS OF NEAR-FIELD COMMUNICATION COMPRISED OF SMALL ANTENNAS

Abstract

This thesis presents the novel mode-based analysis method for estimating some important characteristics of near-field communication (NFC) systems comprised of small antennas. In order to analyze the interaction of coupled antennas, the coupling model has been proposed by using the equivalent circuit representation based on the addition theorem, and it can be applicable for the general conditions including asymmetrical cases where non-identical antennas are employed. Firstly, the optimum operating frequency for NFC is investigated. From the mode-based analysis, the existence of the optimum frequency can be inferred from the frequency dependence of the mutual impedance and radiation efficiency of the antenna. In addition, it is shown that the optimum frequency can be accurately estimated under the condition that the EM simulation results of a single antenna are given. Secondly, the method for estimating the 3 dB bandwidth of NFC is proposed. In this method, in order to consider the impedance characteristics of the forced-resonant solenoidal or open-ended helix antennas, the correction factors are also proposed. By using the proposed method, the values of 3 dB bandwidth for the near-field coupled antennas are investigated, and then it is found that the proposed analysis yields data that are in good agreement with those of EM simulation. Furthermore, variation in the 3 dB bandwidth with respect to the relative position and orientation of the NFC system is investigated using the proposed method. Finally, a new mode-based method for estimating the channel characteristics of a near-field MIMO is proposed. When an antenna array composed of a short electric dipole and a small solenoidal loop is used, TM10 and TE10 modes generated from each antenna element can be considered as an independent channel, respectively, due to the orthogonality of spherical mode. Therefore, a 2´2 near-field MIMO can be effectively constructed. By using the proposed method, the transmission characteristics of the MIMO and the mutual coupling effects at the antenna arrays can be easily calculated. In addition, the capacity of the MIMO can also be calculated by using the analysis results.