Compact printed monopole tag antennas for UHF RFID applications

In this paper, three compact printed monopole antennas are designed for use in UHF RFID that contain a chip with input impedance of 8.2-J61Ω. The challenges in the design of these antennas are conjugate matching of the antenna to the chip while achieving a small layout area. Inductive coupling via a printed loop is employed to eliminate the need for a matching circuit with lumped components. For each antenna, the loop area and proximity of it to the radiating body is optimized to obtain a relatively wide band (on the order of 940 MHz, from 530 MHz to 1.47 GHz) matching. Of the three designs, the proposed 3D meander monopole offers the smallest foot print and yields a 70% area reduction in comparison to a folded printed dipole that is commonly used in RFIDs.