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
1
Outline
1. Introduction
2. OR-Patch Antenna
3. RFID Tag Antenna
4. Conclusion
2
Introduction
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.
3
Introduction
Impedance Matching
Circuit Model of an RFID Tag
Thevenin's equivalent circuit 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.
4
Introduction
Maximum Power Transfer
 Conjugate match between the
chip and the antenna
 Percentage power transferred to
the tag
4 Ra Rc
P
( Ra  Rc ) 2  ( X a  X c ) 2
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.
5
Introduction
Inductively-Coupled Feed
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
6
Introduction
Platform-Tolerant
 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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Patch Antenna
OR-Patch 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: 0.0021
Dielectric Constant: 3.38
Thickness: 1.52 mm
Top view of the OR-patch
where λ is the freespace wavelength at 915MHz
8
Patch Antenna
Current Distribution (IE3D)
At 915MHz,significant
current flows around the
“ O ” of the patch.
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Patch Antenna
Return Loss
 Measured resonance
frequency: 906MHz
Simulated resonance
frequency: 915MHz
 Percentage error: ~1%
Simulated and Measured S11 of the patch antenna
10
Patch Antenna
Simulated Radiation Pattern (IE3D)
E-Plane at 915MHz
H-Plane at 915MHz
11
Patch Antenna
Simulated Gain (IE3D)
4
3
Gain (dBi)
2
1
0
0.9
0.905
0.91
0.915
0.92
0.925
0.93
-1
-2
-3
Freq (GHz)
Simulated gain of the patch antenna
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RFID Tag Antenna
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RFID
Tag Antenna
Specifications
 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
14
RFID
Tag Antenna
Antenna Configuration
Side view of the antenna
Ground Plane:
W1 = 78mm (0.24 λ)
L1 = 108mm(0.33 λ)
OR-patch:
W2 = 50 mm (0.15 λ)
L2 = 82mm (0.25 λ)
Top view of the antenna
Duroid Substrate:
Loss Tangent: 0.0021
Dielectric Constant: 3.38
Thickness: 1.52mm
where λ is the freespace wavelength at 915MHz
15
RFID
Tag Antenna
Antenna Configuration
The C-loop is
directly connected
to the OR-patch
16
RFID
Tag Antenna
Range Measurement
 The read range was
measured inside an EMC
chamber
 Reader antenna was moved
inside the EMC chamber
RFID Tag range measurement using
EMC chamber
 Measure the maximum
readable distance that the
backscatter signal can be
detected.
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RFID
Tag Antenna
Platform-Tolerant Test
 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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RFID
Tag Antenna
Simulated Radiation Pattern (IE3D)
E-Plane at 915MHz
H-Plane at 915MHz
19
RFID
Tag Antenna
Measured Read Range
 Measured from 902MHz
to 928MHz, with a step
frequency of 1MHz.
 Minimum: 87 cm.
 Maximum: 448 cm.
Read range of the tag antenna mounted
on different surfaces
 Basically independent of
mouting surfaces
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RFID
Tag Antenna
Current Distribution
902MHz
21
RFID
Tag Antenna
Current Distribution
915MHz
22
RFID
Tag Antenna
Current Distribution
928MHz
23
RFID
Tag Antenna
Simulated Power Transfer
More than 65%
across the band.
Percentage power transfer to the tag
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Conclusion
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 902-928 MHz band.
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Thank You!
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