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A novel aperture-coupled circularly polarized metallic patch antenna for UHF RFID reader is proposed. In the particular configuration studied, a square patch is placed above a common plane and is fed by means of an aperture-coupled feed network, which adopts sequential rotation technique. The aperture-coupled configuration and multilayer dielectric substrates have the advantage of miniaturizing the antenna's size and enhancing the antenna bandwidth. By means of electromagnetic simulation, the impedance bandwidth and 3 dB axial-ratio bandwidth of the circularly polarized patch antenna presented achieve 58 MHz and more than 1%, respectively. Peak antenna gain across the overall operating band is designed to be 6 dB. Because of taking factors such as cost and weight into account by the selection of dielectric substrates, it's very easy to get the low-cost and light-weight antenna.