Design of a Passive RFID Tag Antenna with a Modified T-match Structure

This paper presents design of a printed dipole antenna suitable for RFID applications. The RFID chip of Farsens Rockyl00 with the input impedance of 64 - j 469 Ω at 868 MHz was used to develop a passive RFID sensor tag. The antenna was etched on an FR4 dielectric substrate with a relative permittivity of 4.4, loss tangent of 0.02, and thickness of 1.6 mm. Initially, a simple dipole antenna with a single T-match structure was designed having overall dimensions of 163 mm × 16 mm × 1.6 mm. The antenna was simulated in ANSYS High Frequency Structure Simulator (HFSS) and found that its impedance is 63.66 + j 130.56 Ω. Then the T-match was modified by adding another bridge parallel to the T-match and by folding the dipole. The dimensions of its structure were optimized by using parametric optimization to match the impedance. The impedance match between the proposed antenna and the chip concerning the power transmission coefficient is 0.998. The simulated S
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≤ -10 dB bandwidth is 690 MHz - 970 MHz. The radiation patterns are omnidirectional with a gain of about 1.7 dB. The read range of the proposed antenna was computed and found as 2.36 m.