Circular multi-usage RFID tag antenna with coding ability for chipless application

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