Reduced-size circularly polarised square microstrip antenna for 2.45 GHz RFID applications

This study proposes a new design of circular polarised (CP), microstrip (patch) antenna using a set of slits and slots to effectively reduce the area of patch by 67% compared with the conventional, corner truncated, circular polarised square patch. The antenna is designed to operate at 2.45 GHz in the Industrial-Scientific-Medical (ISM) band and has many applications in short-range data communications such as in wireless sensors, radio frequency identification and personal area networking. The proposed antenna has been simulated using HFSS. The design has been fabricated and an extensive measurement campaign has confirmed simulation results. The proposed antenna has a low bore-sight axial ratio of 0.77 dB and a 10 dB bandwidth of 70 MHz. The overall antenna size is 19.6 mm x 19.6 mm on a substrate of thickness 1.59 mm. A second design with a more complex network of slots and slits achieves similar performance in simulation with an overall side length of 13.2 mm, but at the cost of a much larger input impedance.