UHF RFID Technologies for Identification and Traceability

2

Design of UHF RFID Tags

2.1. Tag antenna design

Radio frequency identification (RFID) tag antennas present unique design challenges to satisfy heavy constraints due to cost and size. The antenna miniaturization on inexpensive materials is only one of several problems that a designer needs to solve, others being the wideband impedance matching to the RFID integrated circuit (IC) and the sensitivity to the environment. Section 2.1.1 describes the fundamental circuit parameters of the dipole antenna. As most ultra high frequency (UHF) RFID tags are dipole-based structures, dipole issues regarding the input impedance, radiation resistance, efficiency, quality factor (Q-factor) and impedance will be of practical interest in the design of tag antennas. For polarization, radiation pattern and propagation issues, readers can refer to [BAL 05] and [DOB 12]. Then, miniaturization strategies based on fat dipoles, tip loading and meanders are presented in sections 2.1.2 and 2.1.3. The last section (section 2.1.4) addresses the influence of the dielectric and metallic environments on the tag performance.

2.1.1. Fundamental circuit parameters of the dipole antenna

2.1.1.1. Equivalent electrical circuit

The dipole forms the basis of most tag antenna designs. It can be built with either metallic wires or strips. Considering the dipole in Figure 2.1, when a potential is applied to the antenna inputs, there is opposite charge buildup on the ends. Essentially, the dipole ends can be viewed as open ...