Design of a Wideband Circularly Polarized RFID Reader Antenna

The main objective of this paper is to design a circularly polarized patch antenna with a very large bandwidth covering the UHF (ultra-high frequency) RFID band of 860 MHz - 928 MHz. The objective is to obtain an axial ratio (AR) lower than 3 dB and a return loss (RL) lower than -10 dB for the entire band of interest. The patch antenna design must also possess attributes such as high gain, high efficiency, ease of fabrication, low-cost fabrication and small form factor. The design consists of two stacked patch antennas with truncated corners and a square slot in the center. A coaxial cable is connected directly to the main patch, which is positioned in between the ground plane and the parasitic patch on top. The main patch also has an open circuit stub attached to it to improve impedance matching. A laborious design procedure, along with numerous parametric studies, were conducted using ANSYS HFSS in order to optimize the design.