A Grid-Shaped Microstrip Traveling Wave Antenna With Selective Differential Feeding Networks for CM-Level Position Detection Systems

In this paper, a near-field ultrahigh-frequency radio frequency identification (RFID) system, which has cm-level 2-D positioning precision, is proposed. The system consists of a grid-shaped microstrip traveling wave antenna (TWA) and four-port switched differential feeding networks. To selectively form tag-read sections, opposite directional currents (ODCs) are used. To introduce a microstrip TWA for cm-level 2-D positioning, the influence of $H_{z}$ fields in microstrip TWAs is theoretically analyzed. In addition, to utilize field reinforcement and achieve precise 2-D localization, a grid-shaped microstrip TWA with four-port selective switched differential feeding networks is proposed and investigated. The proposed antenna and feeding network were fabricated on FR-4 substrates. The simulated and measured results demonstrate that precise 2-D tag positioning is achieved using the proposed system utilizing ODC along two selected adjacent microstrip lines in the TWA.