1 Platform-Tolerant RFID Tag Antenna Y. C. Or (1), K. W. Leung * (1), R. Mittra (2), and K.V.S. Rao (3) (1). Wireless Communications Research Centre and Department of Electronic Engineering, City University of Hong Kong, Kowloon Tong, Hong Kong. (2). EE Department, Pennsylvania State University, 319 Electrical Engineering East University Park, PA (3). RFID Intellitag Engineering Department, Intermec Technologies Corporation, Everett, WA USA

2 Outline 1. Introduction 2. OR-Patch Antenna 3. RFID Tag Antenna 4. Conclusion

3 Objectives  Design an OR-shaped patch antenna.  Design a platform-tolerant RFID tag antenna with the patch antenna ( MHz).  Measure the read range of the tag antenna.  Test the platform-tolerant ability. Introduction

4 Impedance Matching Introduction Thevenin's equivalent circuit of an RFID tag Circuit Model of an RFID Tag where Ra and Rc are the input resistances of the tag antenna and of the chip, respectively, and Xa, Xc are their corresponding input reactances.

5 Maximum Power Transfer Introduction Power transfer formula where Ra and Rc are the input resistances of the tag antenna and of the chip, respectively, and Xa, Xc are their corresponding input reactances.  Conjugate match between the chip and the antenna  Percentage power transferred to the tag

6 Inductively-Coupled Feed Introduction Inductively-coupled feed structure * * H. W. Son, C.S. Pyo “ Design of RFID tag antennas using an inductively coupled feed ”, Electronics Letters, vol 41. no. 18, Sep, 2005

7 Platform-Tolerant Introduction  Use a patch antenna as the resonating element.  The ground plane isolates the tag antenna from the surface material.  Stable performance regardless of the mounting surface.

8 OR-Patch Antenna Patch Antenna Ground Plane: W 1 = 55 mm (0.17 λ) L 1 = 109mm(0.33λ) OR-patch: W 2 = 50 mm (0.15 λ) L 2 = 83 mm (0.26 λ) Duroid Substrate: Loss Tangent: Dielectric Constant: 3.38 Thickness: 1.52 mm where λ is the freespace wavelength at 915MHz Top view of the OR-patch

9 Current Distribution (IE3D) Patch Antenna At 915MHz,significant current flows around the “ O ” of the patch.

10 Return Loss Patch Antenna  Measured resonance frequency: 906MHz  Simulated resonance frequency: 915MHz  Percentage error: ~1% Simulated and Measured S 11 of the patch antenna

11 Simulated Radiation Pattern (IE3D) Patch Antenna E-Plane at 915MHz H-Plane at 915MHz

12 Simulated Gain (IE3D) Patch Antenna Simulated gain of the patch antenna

13 RFID Tag Antenna

14 Specifications RFID Tag Antenna  RFID Chip: Philips Electronics  Chip-on-board Impedance at 915MHz: 16-j380Ω  Chip’s Minimum Operating Power at 915MHz: -13dBm  Frequency Band: UHF, 902MHz- 928MHz  Transmitting Antenna Gain (Reader): ~ 6dBi  Transmitting Power (Reader): ~ 30dBm

15 Antenna Configuration RFID Tag Antenna Top view of the antenna Side view of the antenna Ground Plane: W 1 = 78mm (0.24 λ) L 1 = 108mm(0.33 λ) OR-patch: W 2 = 50 mm (0.15 λ) L 2 = 82mm (0.25 λ) Duroid Substrate: Loss Tangent: Dielectric Constant: 3.38 Thickness: 1.52mm where λ is the freespace wavelength at 915MHz

16 Antenna Configuration RFID Tag Antenna The C-loop is directly connected to the OR-patch

17 Range Measurement RFID Tag Antenna  The read range was measured inside an EMC chamber  Reader antenna was moved inside the EMC chamber  Measure the maximum readable distance that the backscatter signal can be detected. RFID Tag range measurement using EMC chamber

18 Platform-Tolerant Test RFID Tag Antenna  Following surfaces were used in the test:  Aluminium plate(200 x 200 x 3 mm)  Acrylic resin plate (200 x 200 x 3 mm)  Wood (200 x 200 x 3 mm)

19 Simulated Radiation Pattern (IE3D) RFID Tag Antenna E-Plane at 915MHzH-Plane at 915MHz

20 Measured Read Range RFID Tag Antenna Read range of the tag antenna mounted on different surfaces  Measured from 902MHz to 928MHz, with a step frequency of 1MHz.  Minimum: 87 cm.  Maximum: 448 cm.  Basically independent of mouting surfaces

21 Current Distribution RFID Tag Antenna 902MHz

22 Current Distribution RFID Tag Antenna 915MHz

23 Current Distribution RFID Tag Antenna 928MHz

24 Simulated Power Transfer RFID Tag Antenna Percentage power transfer to the tag More than 65% across the band.

25 Conclusion  An OR-patch antenna has been investigated.  A platform-tolerant RFID Tag antenna has been designed with the OR-patch.  The feeding loop is connected to the OR-patch directly.  Tests have been carried out using different materials, e.g., metal, plastic, and wood, with little adverse effect on its performance.  The minimum and maximum read ranges are 87cm and 448cm, respectively, across the MHz band.

26 Thank You!