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Radio frequency identification (RFID) excelled in automatic identification and data collection industry through its speed, agility, and endurance. In this letter, an improved uniplanar antenna for handheld RFID reader applications covering free ISM bands of 2.45 and 5.8 GHz is presented. The antenna is composed of a microstrip feeding line, two unsymmetrical ground planes, and a folded strip with a small top branch. The folded strips generate radiations in resonances and the ground, which act as reflectors, force the radiation in the endfire direction. The impedance matching and bandwidth of the antenna is improved by inserting optimized triangular periodic open-end stub (POES) cells on the top edge of the coplanar ground. A good impedance bandwidth of 320 MHz is achieved in measurement (from 2.35 to 2.67 GHz for the lower band), while the upper band covers 310 MHz (from 5.60 to 5.91 GHz). Also, good polarization purity, front-to-back ratio, and gain are found, which makes the antenna a strong candidate for compact handheld RFID reader applications.