This paper presents a compact circularly polarized microstrip antenna for radio frequency identification (RFID) readers. The dimensions of the proposed antenna are reduced by etching a cross slot in the radiation patch and loading four grounded coupling patches on the four corners of the radiation patch. An inverted Z-shaped coupling feedline is used to realize circularly polarized operation. The measured −10 dB |S 11 | bandwidth, 3-dB axial ratio bandwidth and maximum gain are 872−1095 MHz, 888−933 MHz, and 5.52 dBi, respectively, at 922 MHz frequency. The overall dimension of the proposed antenna is 0.36 λ g × 0.36 λ g × 0.05 λ g (λ g is the guide wavelength at the center frequency of 915 MHz). The proposed antenna has small size with good overall performance and is suitable for compact RFID devices. INDEX TERMS Circular polarization (CP), coupling patch, coupling feedline, microstrip antenna, radio frequency identification.