A novel single-layer passive RFID tag antenna for the resonant frequency 2.45/2.41 GHz using a square microstrip patch with a pair of U and T slots is proposed, which is suitable for attaching to metallic objects. The proposed antenna was fabricated with a thin copper layer printed on a thin lossy FR4 substrate for low-cost production. The dimensions of the proposed antenna are around 35 times 35 mm. The antenna shows near-linear phase characteristics, 250 MHz bandwidth under the condition of voltage standing-wave ratio less than 2 and it covers all RFID microwave bands. The gain of the proposed antenna is 2.0 2.2 dBi for worldwide RFID microwave bands. Half-power bandwidth is about 108.