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An UHF RFID tag antenna which is comprised of a trapezoidal loop and a dual-dipole radiator with an L-slit for omnidirectional polarized reading patterns is designed, fabricated and measured. For a conjugate match to the Monza 3 microchip impedance of 44-j231 at 915 MHz, an orthogonal dual-dipole tag antenna (91 mm × 91 mm) with L-slit on each dipole arm was designed. Simple size adjustments of the L-slit and dipole radiator of the antenna allow for easy control of the antenna resistance and inductive reactance, from which the microchip impedance requirement may be readily satisfied. The read range of the prototype attached on a different glass can reach more than 9 m, which has been tested for an RFID reader with 4.0 W of EIRP. Good tag sensitivity and near omnidirectional radiation patterns were obtained in the desired frequency band.