International Journal of Electrical and Computer Engineering (IJECE) Vol.
No.
August 2017, pp.
ISSN: 2088-8708.
DOI: 10.
11591/ijece.
Design of Compact Tri-Band Fractal Antenna for RFID Readers Mohamed Ihamji1.
Elhassane Abdelmounim2.
Hamid Bennis3 Mostafa Hefnawi4.
Mohamed Latrach5 LASTI.
Faculty of Sciences and Techniques.
Hassan 1st University.
Settat.
Morocco TIM Research Team.
EST of Meknes.
Moulay Ismail University.
Morocco Dept.
of Electrical and Computer Engineering.
Royal Military College of Canada.
Canada RF-EMC research group.
ESEO-IETR.
Angers.
France Article Info
ABSTRACT
Article history:
In this paper, a multiband and miniature rectangular microstrip antenna is designed and analyzed for Radio Frequency Identification (RFID) reader The miniaturization is achieved using fractal technique and the physical parameters of the structure as well as its ground plane are optimized using CST Microwave Studio.
The total area of the final structure is 71.
94 mm2.
The results show that the proposed antenna has good matching input impedance with a stable radiation pattern at 915 MHz, 2.
45 GHz, and 5.
GHz.
Received Jan 1, 2017 Revised Mar 20, 2017 Accepted Apr 4, 2017 Keyword:
Koch fractal
Microstrip antenna
Miniature antenna
Multiband antenna
RFID
Copyright A 2017 Institute of Advanced Engineering and Science.
All rights reserved.
Corresponding Author:
Mohamed Ihamji.
ASTI Labotary.
Faculty of Sciences and Techniques.
Hassan 1St University.
Settat.
Morocco.
Email: mihamji@gmail.
INTRODUCTION
Radio Frequency Identification (RFID) is the wireless use of electromagnetic field to identify tagged objects and is used in a variety of fields such as access control, transport, banks, health, and logistic.
RFID system is generally composed of a reader and tags.
The communication between the reader and the tags is achieved by modulated backscattering of the readerAos carrier wave signal.
Most RFID systems operate in either the low frequency band .
Ae300 kH.
, the high frequency band .
Ae30 MH.
, the ultra-high-frequency band .
MHzAe3 GH.
, or the microwave band .
GHzAe40 GH.
One major consideration for handheld and portable RFID reader applications is the compact size.
Therefore, the design of miniature reader antennas is important.
In this circumstance, fractal antennas are very attractive choice because of their well-known advantages of low profile, lightweight, and easy There are many popular fractal geometries, such as the Koch fractal, the Sierpinski fractal, the Hilbert fractal, the Minkowski, and the Square Curve fractals.
The Koch fractal microstrip patches are attractive because of their small size and multiband capabilities .
In this paper, a miniature low cost microstrip multiband antenna, based on the Koch fractal structure, is proposed.
Using CST-MW Studio, the antenna is designed and optimized to operate at 915 MHz, 45 GHz, and 5.
8 GHz frequencies.
Journal homepage: http://iaesjournal.
com/online/index.
php/IJECE IJECE
ISSN: 2088-8708
RESEARCH METHOD
The proposed antenna is a rectangular radiating patch fed by a 50 ohms microstrip line and uses an FR4 substrate with dielectric constant Ar = 4.
4, loss tangent tanA = 0.
025, thickness H = 1.
60 mm, and metal thickness t = 0.
035 mm.
Conventional Patch Antenna Rectangular patch antenna has two dimensions, the length Lpatch and width Wpatch, which are related to the resonant frequency, to the permittivity and to the thickness of substrate by the following conventional equations discussed in .
WPatch = .
LPatch = Leff - 2 A DL where c is the speed of light, f is the resonant frequency and effective length given by:
Leff = 2 f e eff is the substrateAos dielectric constant Leff is the .
and iL is the length extension, given by:
yW DL = 0.
Aur A 1 Aur A1E yW .
eff - 0.
A yy h 0.
8yy where, h is the height of substrate and Au reff A .
A yy h 0.
264 yy is the effective dielectric constant which can be determined by:
E h EE 2
EE1 A 12E E EE
EW EE
In this case, the dimensions of the conventional patch antenna at frequency 915MHz are:
Lpatch = 76 mm.
Wpatch = 99 mm.
Fractal and Slots Techniques Fractals antennas use the space-filling properties to miniaturize the classic antenna elements.
The line that is used to represent the fractal can meander to fill the available space.
This line is electrically long but compacted into a small physical space .
The size reduction of the proposed microstrip antenna is achieved by etching the patch edges according to Koch curve.
Multiple iterations of the Koch fractal are shown in Figure 1.
To form the first iteration, the original line segment is partitioned into n=9 equal line segments of 1/5 the original length.
This corresponds to a reduction of 9/5 for the first iteration, .
2 for the second iteration, and so on.
Three slots are inserted into the patch antenna in order to adjust the other resonances generated by the fractal technique.
By this insertion the current is forced to flow through a long path around the slots and change the additional resonance around 2.
45 GHz and 5.
8 GHz.
Figure 2 shows the proposed patch antenna with fractal side of length L and width W, a microstrip feed line of length Lf and width Wf, and three inserted slots.
The conducting ground plane with length Lgnd, which is placed on the other side of the substrate, is optimized to have a good gain.
The width Wf of the microstrip feed line is fixed at 2.
7 mm.
Design of Compact Tri-Band Fractal Antenna for RFID Readers (Mohamed Ihamj.
A ISSN: 2088-8708 Figure 1.
The three iterations of the Koch Curve .
Figure 2.
Geometry of the proposed antenna: .
Top Face and .
Back Face The dimensions of the proposed antenna are presented in Table 1.
TABLE I.
Antenna Dimensions Antenna Dimensions Optimized Value .
Lsub Wsub Ls1 Ws1 Ls2 Ws2 Lfc Wfc IJECE Vol.
No.
August 2017 : 2036 Ae 2044
IJECE
ISSN: 2088-8708
RESULTS AND ANALYSIS
Simulation Results Using the fractal structure and the slots technique to minimize the patch size, we have proposed an antenna structure with fractal side and three slots.
The influence of different parameters of the proposed antenna has been studied by using CST simulation software which is based on the Finite Integration Technique.
Figure 3, shows the influence of different slots lengths values (Ls1.
Ls2.
Ls.
to adjust the resonance antenna at 915 MHz, 2.
45 GHz and 5.
8 GHz.
Figure 4 shows the return loss S11 of the proposed antenna after many optimizations, which has good matching input impedance at the three resonant frequencies of 915 MHz, 2.
45 GHz, and 5.
8 GHz.
It is also noted that a return loss of less than -10 dB was achieved for all three frequencies with a bandwidth varying from 68 MHz to 168 MHz.
Figure 3.
Return loss S11 of the proposed antenna with different slots length Figure 4.
Return loss S11 of the proposed antenna On the other hand.
Figure 5 to Figure 7 show the 2D E-plane and H-plane radiation patterns at 915 MHz, 2.
45 GHZ, and 5.
8 GHz.
The proposed antenna has an omni-directional radiation pattern for both Hplane and E-plane at 915 MHz.
The angular width is 85 degrees at 915 MHz, 50.
9 degrees at 2.
45 GHz, and 27 degrees at 5.
8 GHz.
The achieved bandwidths and gain, which are summarized in Table 2, are very suitable for RFID applications.
Design of Compact Tri-Band Fractal Antenna for RFID Readers (Mohamed Ihamj.
A ISSN: 2088-8708 .
Figure 5.
2D radiation pattern at 915 MHz in the: .
E-plane, .
H-plane .
Figure 6.
2D radiation pattern at 2.
45 GHz in the: .
E-plane, .
H-plane .
Figure 7.
2D radiation pattern at 5.
8 GHz in the: .
E-plane, .
H-plane Figure 8 and Table 3 compare the size of the proposed patch structure .
6 x 72 mm .
with the size of a traditional rectangular patch antenna .
6 mm.
at the same operating frequency of 915 MHz.
This corresponds to 34.
77% reduction in size.
This antenna is also smaller than the fractal antenna proposed in IJECE Vol.
No.
August 2017 : 2036 Ae 2044
IJECE
ISSN: 2088-8708
which has a size of 72 x 96 mm2 and has approximately the same FR4 substrate and operates at the same frequency bands .
MHz, 2.
4 GHz and 5.
8 GH.
Table 2.
Performance of the Proposed Antenna Frequency S11 .
B) Bandwidth (MH.
Gain .
Directivity .
915 MHz - 32.
45 GHz - 20.
8 GHz - 24.
Figure 8.
Ordinary Patch Antenna, .
Proposed Patch Antenna Table 3.
Patch Antennas Size Comparison Patch Antenna 915 MHz W .
L .
Conventional Patch Antenna Proposed Patch Antenna Patch size reduction (WxL) Experimental Results A prototype of the antenna has been realized as shown in Figure 9.
Figure 9.
The antenna prototype achieved: .
Top Face, .
Back Face Design of Compact Tri-Band Fractal Antenna for RFID Readers (Mohamed Ihamj.
A ISSN: 2088-8708 Figure 10 compares the simulated and measured return loss of the antenna and the results, which are summarized in Table 4, show good agreement with a return loss of approximately -10 dB at the tri-band frequencies of 915 MH, 2.
45 GHz, and 5.
8 GHz.
Figure 10.
Measured and simulated return loss of the proposed antenna Table 4.
Resume of Simulated and Measured Results Frequency S11 .
B) S11 .
B) Bandwidth (MH.
Bandwidth (MH.
Simulated Measured Simulated Measured 915 MHz - 32.
- 11.
45 GHz - 20.
- 10.
8 GHz - 24.
- 18.
CONCLUSION
This paper proposed a new tri-band patch antenna for RFID readers.
The design was based on fractal structures and slot techniques to achieve a size reduction of 35% when compared with a conventional rectangular patch.
The antenna was designed using a standard FR4 substrate and realized with conventional Printed Circuit Board (PCB) techniques.
A return loss of less than -10 dB was achieved with a bandwidth varying from52 MHz to 370 MHz and a gain between 2.
62 dBi and 3.
31 dBi.
ACKNOWLEDGEMENTS
We gratefully acknowledge Professor Mohamed Latrach for his assistance, guidance and for allowing us to use the experimental equipment of his laboratory.
REFERENCES