RFID ROSE READER

Document Sample
RFID ROSE READER Powered By Docstoc
					       INTERNATIONAL JOURNAL OF ELECTRONICS AND
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 1, January- June (2012), © IAEME
COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)

ISSN 0976 – 6464(Print)
ISSN 0976 – 6472(Online)
Volume 3, Issue 1, January- June (2012), pp. 83-91
                                                                     IJECET
© IAEME: www.iaeme.com/ijecet.html
Journal Impact Factor (2011): 0.8500 (Calculated by GISI)          ©IAEME
www.jifactor.com




    GROUND SLOTTED HAMMER SHAPE COMPACT CP UHF
             RFID ROSE READER ANTENNA

            T. G. Abo-Elnaga 1, *, E. A. F. Abdallah 1, and H. El-Hennawy2
                1
                  Microstrip Circuits Dep., Electronics Research Institute
                              El-Tahrir Street, Dokki 12622
                Cairo, Egypt, +(202)1006751840, tgaber010@yahoo.com
             2
               Faculty of Engineering, Ain Shams University, Cairo, Egypt

ABSTRACT

A compact rose shaped circularly polarized (CP) microstrip antenna is
presented for ultra high frequency (UHF) radio frequency identification (RFID)
reader applications. Fourier series analysis is used for the thin wire circular
loop antenna radii prediction in free space at the 900 MHz. The printed rose
antenna (RA) is optimized to radius R= 28.275 mm instead of 41.37 mm for
the conventional one. A hammer shaped slot is cut onto the ground plane for
circularly polarized CP radiation and compact size. The effect of ground plane
size and the offset length effect on the bandwidth and 3 dB axial bandwidth is
investigated. The proposed antenna has an overall antenna size of 62 × 61.37 ×
1.5 mm3. The 3 dB axial-ratio (AR) bandwidth of 15 MHz and bandwidth of 73
MHz are achieved.

 1. INTRODUCTION

Radio Frequency Identification (RFID) is the technology that uses radio
frequency (RF) signals for automatic identification of objects and items. RFID
has become very popular in many services industry, distribution logistics,
manufacturing companies and goods flow systems. In these application systems
data are transferred to a local reader from a remote transponder (tag) including
an antenna and an application specific integrated circuit (ASIC). RFID systems
use frequency ranges that have been reserved specifically for industrial,
scientific or medical applications, known as the ISM frequencies, such as 2.45
GHz, 5.8 GHz, and UHF frequency band (860 MHz – 960 MHz) [1]. RFID
systems operating at UHF frequencies have received considerable attention for
various commercial applications, such as supply chain management or

                                             83
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 1, January- June (2012), © IAEME

inventory control. In this regard, a great demand of UHF RFID system is
expected to replace the current position of barcode system. Deferent
frequencies ranges are adopted in deferent countries at UHF frequencies such
as 920.5-924.5MHz in China, 920-926MHz in Australia and 920-925MHz in
Singapore, 952-955MHz in Japan and 902-928MHz in USA, Canada, Mexico,
Puerto Rico, Costa Rica, Latin America, etc. [2]. In practical usage, the tag
antennas are normally linearly polarized and the RFID tags are always
arbitrarily oriented. So, circularly polarized (CP) reader antennas have been
used in UHF RFID systems for ensuring the communications reliability
between readers and tags [3]. Circular polarized operation could be obtained
through applying inclined slot [4], L-shape slot [5], single H-shaped copper
plate and circular fan-shaped slot [6]. Many designs were introduced for the
RFID reader applications such as, [3] where the proposed antenna achieves the
universal UHF RFID band with gain of 8.3 dB and dimensions of 250 x 250 x
35 mm3, [7] where 3 dB AR bandwidth of 893 MHz - 948 MHz but with
dimensions of 220 x 220 x 14 and gain of 8.9 dB, [8] where 865- 925 MHz 3
dB axial-ratio bandwidth and 6 dB gain are obtained but with diameter of 80
mm and height of 130 mm, [9] where an antenna had an overall antenna size of
90 × 90 × 4.572 mm3, 3 dB axial-ratio (AR) bandwidth of around 8.0 MHz and
10 dB return loss bandwidth of 24.0 MHz and gain of 3.7 dBi were achieved
and [10] where a circularly polarized RFID reader antenna for worldwide UHF
(860-960 MHz) applications was proposed. This antenna had a total size of 225
× 250 × 12.8 mm3. Also, some antenna designs where a size reduction was
achieved regardless the circular polarization such as [11], where an antenna
dimension of 100 mm×100 mm×1.6 mm was proposed. The antenna had
maximum gain of 5.3 dBi and bandwidth of approximately 70 MHz (860 - 930
MHz). The main objective of this paper is to present a compact circular
polarized UHF RFID reader antenna with low cost and simple antenna
structure. This paper is organized as follows: first, UHF wire loop antenna is
analyzed and resonant radii at 900 MHz are predicted. Second, UHF circular
polarized rose antenna is proposed. Third, experimentally circular polarized
rose antenna is introduced and discussed. Finally, conclusions are introduced.

2. UHF WIRE LOOP ANTENNA ANALYSIS

In this section, Fourier series analysis for the equivalent half-loop antenna
excited with a transverse electromagnetic (TEM) mode assumed in the
aperture of the coaxial line was used to obtain the input admittance of the wire
loop antenna [12]. This method is rearranged and programmed for the wire
circular loop antenna radii prediction in free space at the 900 MHz resonant
frequency. The antenna has radius R, resonant wavelength λo , constructed from
a perfectly conducting wire of radius ai ,                      and β o = 2π λo .
The wire circular loop input admittance Yin is found as:




                                             84
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 1, January- June (2012), © IAEME

Yin = G + jB = I (0) Vo ) =  I o + 2∑ I n  Vo
                                      ∞                                                           (1)
                                          
                                    n =1  
      − jVo bn
In =                n = 0,1,2,...                                                                 (2)
       ξ oπ a n

       βoR                             n2                                                         (3)
an =           (K n +1 + K n −1 ) −        Kn
           2                          βo R

       1   a             2     a                2  1        2      2 2
                                                                             (         )
                                                                                       0.5
                                                                                             
Kn =  B0  i n 2 − (βo R )  H 0  i n 2 − (β o R )  + γ + ln 4 n − β o R                 
    π R                    R                      π                                    
                    2β R
    2 n −1    1    1 o
   − ∑            − ∫ [Ω2 n ( x) + jJ 2 n ( x)]dx                                                 (4)
    π m = 0 2m + 1 2 0


                     a
bn =
           1
                 ( B0 i      (n + 1)2 − (βo R )2  ⋅ {H 0  ai (n + 1)2 − (βo R )2 
       ln(ao ai )  R
                                                 
                                                       R
                                                          
                                                                                  
                                                                                   

        a
   − H0  o       (n + 1)2 − (βo R )2 } + B0  ai (n − 1)2 − (β o R )2 
                                                                                               (5)
        R                                     R                      
          a
   ⋅ {H 0  i     (n − 1)2 − (βo R )2  − H 0  ao (n − 1)2 − (βo R )2 })
                                                                     
          R                                R                        

In Eqs. (1) to (5), G and B are the input conductance and susceptance
respectively, B0 and H 0 are the modified Bessel functions of the first and
second kinds and order zero, Ω 2 n is the Lommel-Weber function of order 2n,
 J 2 n is the Bessel function of the first kind and order 2n, Euler's constant γ =
0.57722 and ξ o = µ o ε o with µ o and ε o are free space permeability and
permittivity, respectively. Matlab code was built to calculate the input
admittance using image equivalent half-loop antenna over ground plane. The
code accuracy was checked through calculating the input admittance of an
antenna with R = 40.36 mm, 2ai = 3.25 mm and outer to inner coaxial line feed
radius ratio a o a i = 2.174 and compared with the experimental results
published in [12], Fig. 1. Good agreement between measured and calculated
results was obtained. The code was modified to calculate different radii with
input impedance at 900 MHz as shown in Fig. 2, with a o = 1.57 mm and ai =
0.6825 mm for coaxial line characteristic impedance Z c = 50 Ω .The thin-wire
circular loops with R= 80 mm and R= 31 mm which almost have a real input
impedance, were used as a prototype circular loop antenna. The wired loop
antenna is transformed to a printed circular loop with width w = 4ai [13]. FR4
material with relative dielectric constant ε r = 4.65 and thickness h = 1.5 mm
was used as antenna substrate. Microstrip line on a finite ground plane was
used for feeding purpose. Fig. 3 shows the proposed RFID reader antenna in
which a microstrip feeding line is connected directly with the radiating element
on the top, below laid a finite ground plane. The IE3D simulator is used to test


                                                             85
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 1, January- June (2012), © IAEME

the wire to planar transformation formulae accuracy, [13] of the
aforementioned wire loop radii in the presence of partial ground plane. The
optimized conventional printed loop antenna has width w = 2.73 mm, ground
line with width wg = 1.46w, Lg = 54.16 mm and optimized radius R = 84.55
mm. The simulated conventional printed loop antenna reflection coefficient
versus frequency is shown in Fig. 4. The optimized conventional printed loop
antenna with radius R= 41.37, width w = 2.73 mm, ground line with width wg =
1.46w, Lg= 51.16 is simulated. The simulated reflection coefficient versus
frequency is shown in Fig. 4. These discrepancies between the aforementioned
radii which were initially predicted in Fig. 2 and that used in the simulator may
be attributed to the approximated transformation from wire to printed shapes
and the presence of ground plane under the radiator element.
                                                                                    BExp [12]                        4000
                20                                                                  GExp [12]                                                                                            Real
                                                                                                                                                                                         Imag
                18                                                                  GCom
                16                                                                  BCom                             3000

                14
                12
                                                                                                                     2000
                10
                 8



                                                                                                     Impedance (Ω)
   G, B (mS)




                 6
                                                                                                                     1000
                 4
                 2
                 0
                                                                                                                             0
                 -2
                 -4
                 -6                                                                                                  -1000
                 -8
                -10
                      0.5   0.6   0.7   0.8   0.9   1.0   1.1   1.2   1.3   1.4   1.5   1.6
                                                                                                                     -2000
                                                                                                                          20                 30   40     50            60   70     80           90
                                                      βR
                                                                                                                                                              R (mm)




  Fig. 1 Input admittance of loop antenna                                                        Fig. 2 Input impedance of loop antenna versus
                 versus                                                                          radius           R,
                                                                                                                                   .
                                        Y                                                                                                                                               R= 84.55 mm
                                              Copper Conventional                                                                 5                                                     R= 41.37 mm
                                                Loop Antenna
                                                                                                                                  0


                                                                                                                                  -5
                                                                                                                |S11| (dB)




                                                                                                                                 -10


                                                                                                                                 -15
                                                                                        X
                 w
                                                                                                                                 -20
                                                     R
                                                                                                                                 -25

                            Lg           wg                                                                                      -30
           εr                                                                                                                          0.7        0.8            0.9         1.0          1.1
                                                                                                                                                        Frequency (GHz)
                                               w
           h

                                            Finite Ground Line

Fig. 3 Conventional printed loop antenna.                                                        Fig. 4 Conventional printed loop antenna
                                                                                                 reflection coefficient versus frequency.




                                                                                                86
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 1, January- June (2012), © IAEME

3. UHF CIRCULAR POLARIZED ROSE ANTENNA (CPRA)
Fig. 5 shows the Rose Antenna (RA) in which the radiating loop element is
meandered in the shape of a rose figure. The printed rose antenna was
optimized to radius R= 28.275 mm, width w = 2.73 mm, L1= 26.254 mm and
L2=19.309 mm. The effect of ground plane size was studied in Fig. 6 and Fig. 7
which indicate that, as ground plane length increases the resonant frequency
increases and as ground plane width increases the resonant frequency
decreases, respectively. So, the resonant frequency could be controlled by the
ground plane geometry. The offset length         effect on the bandwidth and 3 dB
axial bandwidth is investigated, table 1. As the offset length increases the 3 dB
axial bandwidth increases too till 5 mm and then it began to vanish. It is worth
to mention that a size reduction of 53.3 % is obtained when a rose antenna
shape is used as compared to the conventional loop antenna with radius R=
41.37 mm. The schematic diagram of the proposed circularly polarized rose
antenna (CPRA) is illustrated in Fig. 8 and (b) where the rose antenna is placed
on the top and a finite ground plane with a hammer slot shape at the bottom of
the proposed antenna. The hammer slot initiates the circular polarization
operation of the proposed antenna. The antenna is fabricated on FR4 substrate
with relative permittivity ε r = 4.65, tanδ = 0.02 and thickness h = 1.5 mm. The
optimized printed rose antenna with radius R= 28.275 mm, width w = 2.73
mm, L1= 26.254 mm, L2=19.309 mm, ground plane with width wg = 62 mm,
Lg= 20.58 mm is simulated. The CPRA introduces a bandwidth of 73 MHz
(874 MHz - 947 MHz), Fig. 9 with 3db axial band width of 15 MHz (909 MHz
- 924 MHZ) and 6 dB axial bandwidth of 34 MHz (900 MHz - 934 MHz), Fig.
10.

Table 1 Offset length       effect on bandwidth, 3 dB bandwidth and gain.
  Offset length              BW (MHz)        3dB BW (MHz)          Gain (dB)
        (mm)
          0                    892-960                   0                     0.85
          1                    888-957                   0                     1.148
          2                    885-954                905-915                  1.175
          3                    883-951                906-917                   0.95
          4                    874-947                909-924                    1
          5                    874-944                911-928                  0.69
          6                    868-904                   0                      0.59

At 900 MHz the CPRA introduces gain of 1 dB and directivity of 2.67 dB, Fig.
11 and 12, respectively. Radiation pattern is shown in Fig. 13 where right and
left hand circular polarization are obtained for the upper and lower space,
respectively.




                                             87
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 1, January- June (2012), © IAEME
                                                                                                                                                             Lg= 8 mm
                                                                                                 0                                                           Lg= 12 mm
                                                                                                                                                             Lg= 16 mm
                                                                                                                                                             Lg= 24 mm
                                                                                                 -5
                        εr
                                                                                                -10




                                                                                     |S11| dB
                                                                                                -15



                                                                                                -20



                                                                                                -25



                                                                                                -30
                                                                                                  0.850   0.875          0.900   0.925    0.950      0.975    1.000
                                                                                                                            Frequency (GHz)




Fig. 5 Printed rose loop antenna.                                                   Fig. 6 Proposed antenna ground plane length
                                                                                    effect on resonance frequency ( =62mm).
                                                                      W g = 62 mm
                                                                      W g = 58 mm
               0                                                      W g = 54 mm
                                                                      W g = 50 mm
              -10



              -20
   |S11| dB




              -30



              -40



              -50



                0.850        0.875   0.900   0.925    0.950   0.975    1.000
                                        Frequency (GHz)




  Fig. 7 Proposed antenna ground plane                                          Fig. 8(a) Proposed CPRA top view.
   width effect on resonance frequency
               ( =25mm).

                                                                                                  0




                                                                                                 -5
                                                                                     |S11| dB




                                                                                                -10




                                                                                                -15




                                                                                                -20
                                                                                                   0.80           0.85            0.90            0.95          1.00
                                                                                                                             Frequency (GHz)




  Fig. 8(b) Proposed CPRA bottom view.                                              Fig. 9 Proposed CPRA reflection coefficient
                                                                                                 versus frequency.




                                                                                88
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 1, January- June (2012), © IAEME




Fig. 10 Proposed CPRA axial ratio versus      Fig. 11 Proposed CPRA gain versus frequency.
               frequency.




Fig. 12 Proposed CPRA directivity versus Fig. 13 Proposed CPRA radiation pattern at 900
frequency.                               MHz.

4. EXPERIMENTALLY CIRCULAR POLARIZED ROSE ANTENNA

CPRA with offset length of 4 mm is fabricated using FR4 substrate, Fig. 14.
CPRA reflection coefficient is measured and shown in Fig. 15. Discrepancy of
2% between the measured and simulated reflection coefficients of the proposed
CPRA is observed. The discrepancy between numerical and experimental
results is mainly because of the fabrication difficulty in precise alignment
between the rose antenna and the hammer shape slotted ground plane and the
SMA soldering process before measurement.




                                             89
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 1, January- June (2012), © IAEME

                                                                                               Sim
                                                      5                                        Mes



                                                      0




                                                      -5




                                          |S11| dB
                                                     -10




                                                     -15




                                                     -20
                                                        0.80   0.85        0.90         0.95    1.00
                                                                      Frequency (GHz)


Fig. 14 Fabricated CPRA photo.       Fig. 15 CPRA measured and simulated reflection coefficients.

5. CONCLUSIONS

In this paper CPRA was introduced for UHF RFID reader. The proposed
antenna was fabricated on FR4 substrate. The CPRA input impedance and
resonant frequency were controlled by the ground plane length and width. The
obtained bandwidth covers the UHF frequency band of 73 MHz (874 MHz -
947 MHz), 3 dB axial bandwidth of 15 MHz (909 MHz - 924 MHZ) and 6 dB
axial bandwidth of 34 MHz (900 MHz - 934 MHz). The antenna had an area of
radius 28.275 mm compared to 41.37 mm and 84.55 mm for the conventional
printed loops. Also, the proposed antenna introduced a small area compared to
previous published work. Other antenna parameters were found to be at
acceptable level. It is worth to mention that any UHF RFID stander could be
met by controlling the loop radius and the partial ground plane size with
hammer slot geometry. Finally, the proposed antenna is cheap, simple and
suitable for CP RFID reader antenna applications.

REFERENCES

1.     Barthel H., “Regulatory status for RFID in the UHF spectrum,” EPC
       Global, Brussels, Belgium, March 2009.
2.     Abo-Elnaga T. G., Abdallah E. A. F. and El-Hennawy H.,” Analysis and
       design of universal compact flexible UHF RFID tag antenna”, Progress
       In Electromagnetics Research B, Vol. 35, 213-239, 2011.
3.     Chen Z., Qing X. and Chung H., ''A universal UHF RFID reader
       antenna'', IEEE Trans. Microwave Theory Tech., vol. 57, no. 5, pp.
       1275-1282, May 2009.
4.     Bernard L., Chertier G., and Sauleau R.,” Wideband circularly polarized
       patch antennas on reactive impedance substrates,” IEEE Antennas and
       Wireless Propagation Letters, vol. 10, pp. 1015-1018, 2011.
5.     Mousavi P. , Miners B., and Basir O. ,” Wideband L-shaped circular
       polarized monopole slot antenna,” IEEE Antennas and Wireless

                                                     90
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 1, January- June (2012), © IAEME

       Propagation Letters, vol. 9, pp. 822-825, 2010.
6.     Lin S. and Lin Y., “A broadband leaky-wave aperture antenna of circular
       polarization,” IEEE International Symposium on Antennas Propagation
       (APSURSI), pp. 789 –792, 2011.
7.     Chen X., Fu G., Gong S., Y. Yan, and W, Zhao,” Circularly Polarized
       Stacked Annular-Ring Microstrip Antenna With Integrated Feeding
       Network for UHF RFID Readers,” IEEE Antennas and Wireless
       Propagation Letters, vol. 9, pp. 542-545, 2010.
8.     Nikitin P.V, Rao K.V.,” Helical antenna for handheld UHF RFID
       reader,” IEEE International Conference on RFID, pp. 166-173, 2010.
9.      Chen Z. N.; Qing X.,” Compact arc-shaped slotted circularly polarized
       microstrip antenna for RFID readers,” International Workshop on
       Antenna Technology (IWAT), pp. 340 – 343, 7-9 March 2011.
10.    Mireles E., Sharma S.K., ”A broadband microstrip patch antenna fed
       through vias connected to a 3dB quadrature branch line coupler for
       worldwide UHF RFID reader applications,” IEEE International
       Symposium on Antennas and Propagation (APSURSI), pp. 529-532, July
       2011.
11.    Kaki S., Chakravarty T.,” Compact Printed Yagi Antenna for Handheld
       UHF RFID Reader,” International Conference on Devices and
       Communications, pp. 1-3, 2011.
12.    Guangping Z., Glenn S. S., “An accurate theoretical model for the thin-
       wire circular half-loop antenna,” Antenna and Propagation Symp. (APS),
       vol. 39, no. 8, pp. 1167-1177, 1991.
13.    Hejase H. N., “Analysis of a printed wire loop antenna,” IEEE Trans.
       Microwave Theory Tech., vol. 42, no. 2, pp. 227-233, Feb. 1994.




                                             91

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:0
posted:11/20/2012
language:
pages:9