A circular tag antenna for the ultra-high frequency radio frequency identification band, with an outer radius of 25 mm is proposed. The proposed design consists of a loop radiation element, two symmetrical microstrip feed lines, resonant rings, and resonant arms. Simulation and measurement results show that the proposed antenna can operate steadily in free space, and on the surface of the human body, water-filled container, and metal along with good conjugate impedance matching. The maximum measured reading range of 3.6 to 6.9 m can be achieved depending on the background. Utilizing a matching circuit, parallel combination of an inductor and capacitor at the feeding port, a point frequency working state at any frequency can be realized. Consequently, it can be used as a frequency signature chipless tag with coding capability. K E Y W O R D S chipless, coding, multi-usage, RFID, tag antenna 1 | INTRODUCTION Many radio frequency identification (RFID) tag antennas for ultra-high frequency (UHF) band have been designed in the previous work. 1-5 With these designs, some of the tag antennas can be mounted on metallic surfaces directly, 6,7 other reported designs can work on the human body, organs, blood bag and water-filled