platform-tolerant rfid tag antenna

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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.

E-mail: 50450664@student.cityu.edu.hk E-mail: eekleung@cityu.edu.hk

(2). EE Department, Pennsylvania State University, 319 Electrical Engineering East University Park, PA 16802-2705

E-mail: mittra@engr.psu.edu

(3). RFID Intellitag Engineering Department, Intermec Technologies Corporation, Everett, WA 98203 USA

E-mail: kvs.rao@intermec.com

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Outline

1. Introduction

2. OR-Patch Antenna

3. RFID Tag Antenna

4. Conclusion

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Objectives

Design an OR-shaped patch antenna.

Design a platform-tolerant RFID tag antenna with the patch antenna (902-928 MHz).

Measure the read range of the tag antenna.

Test the platform-tolerant ability.

Introduction

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Impedance MatchingIntroduction

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.

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Maximum Power TransferIntroduction

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

22 )()(

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caca

ca

XXRR

RRP

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Inductively-Coupled FeedIntroduction

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

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Platform-TolerantIntroduction

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.

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OR-Patch AntennaPatch Antenna

Ground Plane: W1 = 55 mm (0.17 λ) L1 = 109mm(0.33λ)

OR-patch:W2 = 50 mm (0.15 λ) L2 = 83 mm (0.26 λ)

Duroid Substrate: Loss Tangent: 0.0021Dielectric Constant: 3.38Thickness: 1.52 mm

where λ is the freespace wavelength at 915MHzTop view of the OR-patch

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Current Distribution (IE3D)Patch Antenna

At 915MHz,significant current flows around the “ O ” of the patch.

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Return LossPatch Antenna

Measured resonance frequency: 906MHz

Simulated resonance frequency: 915MHz

Percentage error: ~1%

Simulated and Measured S11 of the patch antenna

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Simulated Radiation Pattern (IE3D)Patch Antenna

E-Plane at 915MHz H-Plane at 915MHz

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Simulated Gain (IE3D)Patch Antenna

Simulated gain of the patch antenna

-3

-2

-1

0

1

2

3

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0.9 0.905 0.91 0.915 0.92 0.925 0.93

Freq (GHz)

Gai

n (

dB

i)

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RFID Tag Antenna

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SpecificationsRFID 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

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Antenna ConfigurationRFID Tag Antenna

Top view of the antenna

Side view of the antennaGround Plane: W1 = 78mm (0.24 λ) L1 = 108mm(0.33 λ)

OR-patch:W2 = 50 mm (0.15 λ) L2 = 82mm (0.25 λ)

Duroid Substrate: Loss Tangent: 0.0021Dielectric Constant: 3.38Thickness: 1.52mm

where λ is the freespace wavelength at 915MHz

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Antenna ConfigurationRFID Tag Antenna

The C-loop is directly connected to the OR-patch

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Range MeasurementRFID 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

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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)

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Simulated Radiation Pattern (IE3D)RFID Tag Antenna

E-Plane at 915MHz H-Plane at 915MHz

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Measured Read RangeRFID 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

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Current DistributionRFID Tag Antenna

902MHz

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Current DistributionRFID Tag Antenna

915MHz

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Current DistributionRFID Tag Antenna

928MHz

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Simulated Power TransferRFID Tag Antenna

Percentage power transfer to the tag

More than 65% across the band.

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ConclusionConclusion

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 902-928 MHz band.

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Thank You!