Transcript 下載/瀏覽Download

Impedance Characterization of RFID Tag
Antennas and Application in Tag Co-Design
RFID Tag 天線的阻抗特性和應用在Tag共同設計
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
1
2009/12/2
Outline
 Introduction
 Paper review
 Purpose
 Methods & Materials
 Results
 Conclusions
 Future works
 References
2
2009/12/2
Introduction
 RFID (Radio Frequency Identification)
Reader
3
(135K／13.56M／868M
／915M／2.45G…etc. )
※ RFID - 無線射頻辨識
Tag
2009/12/2
Introduction
 Tag
Antenna
Chip
Tag
4
2009/12/2
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
5
2009/12/2
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.
6
※ UHF -超高頻率
dipole antenna –雙極天線
2009/12/2
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.
7
※ balanced antenna -平衡天線
2009/12/2
Principle
A typical asymmetrical balanced dipole antenna
The driven voltage can be split as V1 and
V2 with a virtual ground plane
8
2009/12/2
Principle
Each terminal of the antenna radiators and
the ground plane can be considered as a “port.”
9
2009/12/2
Principle
Network representation of the asymmetrical dipole antenna.
The impedance of the antenna can be
10
2009/12/2
Principle
Based on the definition of Z-parameters , the port
voltages and currents are related as
Considering I1=I0 and I2=-I0 , the differential voltage is
given by
Impedance is
11
2009/12/2
Principle
Converting the Z-parameters to S-parameters and considering
~
Zd  Z0  Z d
For the symmetrical balanced antenna , S11=S22 , and S12=S21 , can be
simplified to
Z0 is the characteristic impedance of the connected transmission
lines, which is 50 Ω for most of measurement systems.
12
2009/12/2
Methods
 Measurement Setup
Schematic configuration
13
2009/12/2
Measurement Procedures
Conduct standard VNA parameters
setting and calibration
Shift the calibration plane through the portextension technique to deembed the influence of
the text fixture.
Connect the test fixture to the test cables and
carry out the port extension to shift the
calibration plane to the tips of the fixture.
Connect the antenna to the fixture and measure
the S-parameters.
Calculate the impedance of the antenna using
14
2009/12/2
Measurement Procedures
 Measurement setup using Agilent N5230A network
analyzer
15
2009/12/2
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.
16
2009/12/2
Materials
 Antennas under test
Asymmetrical dipole antenna
FR4 PCB
dielectric constant ：4.4
thickness：0.504 mm
17
Symmetrical meander line dipole antenna
2009/12/2
Results
 Measured and simulated impedance of the asymmetrical
dipole antenna
Real part
18
Imaginary part
2009/12/2
Results
 Measured and simulated impedance of the symmetrical
meander line dipole antenna
 dipole antenna
Real part
19
Imaginary part
2009/12/2
Example in RFID tag co-design
 The specific RFID application in a Sushi restaurant.
 The tag is required to be designed at the UHF band of
the 920–925 MHz.
 The ASIC used here is Impinj - Monza 2 with an
impedance of 59 –j242 Ω
20
※ ASIC -特殊應用IC
2009/12/2
 RFID applications in Sushi restaurants: plate tracking.
21
2009/12/2
Tag Antenna Design Without Considering Plate Effect
 The tag was prototyped on a 0.5-mm thin FR4
substrate.
L1=38
L2=38
L3=33
L4=33
L5=18
L6=6
L7=18
L8=6
L9=15.5
L10=7
22
W1=5
W2=2
W3=2
W4=1
S =3
Unit:mm
Geometry of the proposed omnidirectional tag antenna
2009/12/2
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.
23
Comparison of reading patterns of the RFID tag without/with plasticplate.
2009/12/2
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.
24
2009/12/2
Co-Design and Optimization
 Impedance measurement of the tag antenna together
with the plastic plate.
25
2009/12/2
Co-Design and Optimization
 Impedance measurement results
 A frequency shift of 120 MHz is observed.
Real part
26
Imaginary part
Comparison of the calculated and measured impedance of the tag antenna
2009/12/2
together with the plastic plate
Co-Design and Optimization
 The antenna was retuned and validated by measurement
27
Comparison of reading range patterns of the initial/co-designed
RFID tags with the plastic plate.
2009/12/2
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.
28
※ conjugate matching -共軛匹配
2009/12/2
Future works
 Production a fixture prototype
 Measured and simulated dipole antenna
 Measured and simulated RFID tag
29
2009/12/2
References
 [1] K. V. S. Rao, P. V. Nikitin, and S. F. Lam, “Impedance matching concepts in RFID
transponder design,” in 4th IEEE Automat. Identification Adv. Technol. Workshop, Oct.
2005, pp. 39–42.
 [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.
848–851.
 [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.135–138.
 [5] J. D. Griffin, 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. 247–250,May 2006.
 [6] L. Ukkonen, L. Sydanheirno, and M. Kivikoski, “A novel tag design using inverted-F
antenna for radio frequency identification of metallic objects,” in Proc. Int. IEEE Adv.
Wired and Wireless Commun. Symp.,2004, pp. 91–94.
30
2009/12/2
Thank You For Your Attention
31
2009/12/2