Analysis and design of circularly polarized capacitively-fed planar suspended antenna for universal UHF RFID applications

This research paper deals with the design of a circularly polarized reader antenna with a tennis ball-shaped radiating plate that operates at a frequency range of 860-960 MHz with the center frequency of 910 MHz. In the fabrication of the tennis ball-shaped radiating plate, a small annular-ring slot was first created on a circular radiating plate, followed by two diagonally opposite large arc-shaped annular-ring slots on either edge of the circular radiating plate and then the truncation of the corners of the remaining main element of the plate. A prototype antenna with the final tennis ball-shaped plate was subsequently assembled prior to excitation by the capacitively coupled feed technique to enhance |S11| bandwidth. The prototype antenna could achieve an average gain of 6.18 dBic, |S11| covering the frequency range of 837.6-966.2 MHz, and the circular polarization of 850.6-963.5 MHz, making it suitable for universal UHF RFID applications. In addition, simulations were carried out using CST Microwave Studio for comparison with the experimental results.