Passive RFID systems: Eigen-mode analysis

A numerical analysis method based on a combination of TE and TM eigen-modes is proposed for the study of the current distribution in a microstrip patch antenna devoted to passive Radio Frequency Identification (RFID) systems. The analysis is based on eigen-value and eigen-vector decomposition of the Method-of-Moments impedance matrix. The process of projection of incident plane waves on those eigen-modes is studied and a methodology is delineated to selectively excite certain modes using multiple plane waves.