Presenter: HsuanHan Chiang

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Impedance Characterization of RFID Tag Antennas
and Application in Tag Co-Design
RFID Tag ???????????Tag????
Xianming Qing Chean Khan Goh Zhi Ning Chen
Impedance Characterization of RFID Tag Antennas
and Application in Tag Co-Design IEEE
TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES,
VOL. 57, NO. 5, MAY 2009 

• Presenter Hsuan-Han Chiang
• Adviser Dr. Hung-Chi Yang
• Date 12.2.2009

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Outline

• Introduction
• Paper review
• Purpose
• Methods Materials
• Results
• Conclusions
• Future works
• References

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Introduction

• RFID (Radio Frequency Identification)

Reader
(135K/13.56M/868M /915M/2.45Getc. )
Tag
? RFID - ??????
4
Introduction

• Tag

Antenna
Chip
Tag
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Paper review

• Xianming Qing Chean Khan Goh Zhi Ning Chen
  Impedance Characterization of RFID Tag Antennas
  and Application in Tag Co-Design IEEE
  TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES,
  VOL. 57, NO. 5, MAY 2009 

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Purpose

• Propose an experimental methodology for the
  impedance characterization of balanced RFID tag
  antennas.
• An asymmetrical dipole antenna.
• A symmetrical meander line dipole antenna.
• The co-design of an (UHF) RFID tag for the plate
  tracking in a Sushi restaurant.
• The impedance of the tag antenna can be measured
  accurately.
• The significant enhancement of read range can be
  realized.

? UHF -???? dipole antenna ????
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Methods Materials

• The impedance of a balanced antenna cannot be
  measured directly by most measurement
  instruments.
• Unbalanced ports such as coaxial ports
• The currents fed to the two radiators of the
  antenna are unequal, the impedance of the
  balanced antenna cannot be characterized
  accurately.

? balanced antenna -????
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Principle
A typical asymmetrical balanced dipole antenna
The driven voltage can be split as V1 and
V2 with a virtual ground plane
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Principle
Each terminal of the antenna radiators and the
ground plane can be considered as a port.
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Principle
Network representation of the asymmetrical dipole
antenna.
The impedance of the antenna can be
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Principle
Based on the de?nition of Z-parameters , the
port voltages and currents are related as
Considering I1I0 and I2-I0 , the differential
voltage is given by
Impedance is
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Principle
Converting the Z-parameters to S-parameters
and considering
For the symmetrical balanced antenna , S11S22 ,
and S12S21 , can be simpli?ed to
Z0 is the characteristic impedance of the
connected transmission lines, which is 50 O for
most of measurement systems.
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Methods

• Measurement Setup

Schematic con?guration
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Measurement Procedures
Conduct standard VNA parameters setting and
calibration
Shift the calibration plane through the
port-extension technique to deembed the in?uence
of the text ?xture.
Connect the test ?xture to the test cables and
carry out the port extension to shift the
calibration plane to the tips of the ?xture.
Connect the antenna to the ?xture and measure the
S-parameters.
Calculate the impedance of the antenna using
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Measurement Procedures

• Measurement setup using Agilent N5230A network
  analyzer

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Materials
Fixture prototype
Using two sem-ridge coaxial cables with a length
of 100 mm and an outer conductor diameter of 2.2
mm. The coaxial cables are soldered together on
their outer conductors.
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Materials

• Antennas under test

Asymmetrical dipole antenna
FR4 PCB dielectric constant 4.4 thickness0.504
mm
Symmetrical meander line dipole antenna
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Results

• Measured and simulated impedance of the
  asymmetrical dipole antenna

Real part
Imaginary part
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Results

• Measured and simulated impedance of the
  symmetrical meander line dipole antenna
• dipole antenna

Imaginary part
Real part
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Example in RFID tag co-design

• The speci?c RFID application in a Sushi
  restaurant.
• The tag is required to be designed at the UHF
  band of the 920925 MHz.
• The ASIC used here is Impinj - Monza 2 with an
  impedance of 59 j242 O

? ASIC -????IC
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• RFID applications in Sushi restaurants plate
  tracking.

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Tag Antenna Design Without Considering Plate
Effect

• The tag was prototyped on a 0.5-mm thin FR4
  substrate.

L138 L238 L333 L433L518 L66 L718 L86 L91
5.5 L107
W15 W22 W32 W41 S 3 Unitmm
Geometry of the proposed omnidirectional tag
antenna
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Tag Antenna Design Without Considering Plate
Effect

• The performance degradation of the tag when
  attached to the plastic plate is caused by the
  loading effect of the plastic plate.

Comparison of reading patterns of the RFID tag
without/with plasticplate.
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Co-Design and Optimization

• The tag antenna must be co-designed with the
  plastic plate by taking the loading effect of the
  plastic plate into consideration.
• A plastic substrate was added underneath the tag
  antenna in simulation to imitate the plastic
  plate.
• The plastic substrate was assigned a thickness of
  5 mm, a dielectric constant of 2.

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Co-Design and Optimization

• Impedance measurement of the tag antenna together
  with the plastic plate.

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Co-Design and Optimization

• Impedance measurement results
• A frequency shift of 120 MHz is observed.

Real part
Imaginary part
Comparison of the calculated and measured
impedance of the tag antenna together with the
plastic plate
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Co-Design and Optimization

• The antenna was retuned and validated by
  measurement

Comparison of reading range patterns of the
initial/co-designed RFID tags with the plastic
plate.
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Conclusions

• Using a two-port VNA and the port-extension
  technique, the impedance of the symmetrical and
  asymmetrical balanced tag antennas can be
  extracted from the measured S-parameters
  directly.
• The impedance characteristics of the tag antenna
  together with a plastic plate has been accurately
  characterized.
• The conjugate matching between the tag antenna
  and the ASIC has been realized so that the
  reading range of the RFID system has been greatly
  enhanced.

? conjugate matching -????
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Future works

• Production a fixture prototype
• Measured and simulated dipole antenna
• Measured and simulated RFID tag

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References

• 1 K. V. S. Rao, P. V. Nikitin, and S. F. Lam,
  Impedance matching concepts in RFID transponder
  design, in 4th IEEE Automat. Identi?cation Adv.
  Technol. Workshop, Oct. 2005, pp. 3942.
• 2 Z. N. Chen, Antennas for Portable Devices,
  1st ed. New York Wiley,2007, ch. 3.
• 3 P. Raumonen, L. Sydanbeimo, L. Ukkonen, M.
  Keskilammi, and M.Kivikoski, Folded dipole
  antenna near metal plate, in Proc. Int. IEEE
  AP-S Symp., Jun. 2003, pp. 848851.
• 4 D. M. Dobkin and S. M. Weigand,
  Environmental effects on RFID tag antennas, in
  IEEE MTT-S Int. Microw. Symp. Dig., Jun. 2005,
  pp.135138.
• 5 J. D. Grif?n, G. D. Durgin, A. Haldi, and B.
  Kippelen, RFID tag antenna performance on
  various materials using radio link budgets,IEEE
  Antennas Wireless Propag. Lett., vol. 5, no. 5,
  pp. 247250,May 2006.
• 6 L. Ukkonen, L. Sydanheirno, and M.
  Kivikoski, A novel tag design using inverted-F
  antenna for radio frequency identi?cation of
  metallic objects, in Proc. Int. IEEE Adv. Wired
  and Wireless Commun. Symp.,2004, pp. 9194.

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Thank You For Your Attention