Dual circularly polarized antenna of compact structure for RFID application

A compact structure is proposed to realize dual circularly polarized antenna for RFID system. In this paper, a cross-shaped aperture in the ground plane provides coupling between the patch and a single microstrip line with two ports underneath the ground plane, the means of feeding is constructed. For system requirements, some modifications are made to improve the performance. This design realizes low profile, separating the radiating patch and the feeding layer, particularly saving space by avoiding the traditional scheme based on microstrip branch line coupler. In the wireless communication system for RFID applications, circular polarization modulation (CPM) is implemented, which reduces the requirement for bandwidth effectively, and simplifies the data communication. Therefore, a dual circularly polarized antenna is an indispensable key part of this RFID system, and in some case the compact structure is necessary. In this design process, the dimensions and performance of this antenna are calculated and optimized by HFSS (High Frequency Structure Simulator). The results agree well with the measurement, and show the practicability of this scheme.