31st National Radio Science Conference (NRSC2014) April 28 – 30, 2014, Faculty of Engineering, Ain Shams University, Egypt
UWB Reflectarray Antenna for Chipless RFID Applications Maher Khaliel, A. Fawky, Mohamed El-Hadidy, Thomas Kaiser Digital Signal verarbeitung Institute, DSV, Duisburg Essen University, Duisburg, Germany,
[email protected]
ABSTRACT The main limitation of any chipless Radio Frequency Identification (RFID) system is the very short reading range. In this paper, we propose an Ultra Wideband (UWB) Reflectarray Antenna (RA) system with 2.2 GHz bandwidth centered at 6 GHz for the reader of chipless RFID applications. Four different antenna configurations presented in this paper to emulate different real case scenarios. The constructive guidelines for calculating the phase distribution of each configuration based on a mat lab algorithm is introduced. The proposed reader antenna system enhances reader sensitivity, reduces multipath effects, helps in tag localization and a lot of novel capabilities that cannot be provided by the conventional antenna systems. The cell used in the design is the double circular ring where the antenna panel consists of 100 elements (10x10). Simulations show that the proposed antenna system reaches fractional bandwidth (FBW) 37% covering all the feeder bandwidth. This achieved ultra wide bandwidth (UWB) satisfies the requirements of the frequency signature based chipless RFID systems.
Keywords: Reflectarray Antenna, Chipless, RFID I. INTRODUCTION The chipless radio frequency identification (RFID) systems expected to replace the barcode technology at 2020 [1]. The main limitation that faces any chipless RFID system is the very low reading range [2]. In [3] a novel reading methodology for increasing the reading range of the frequency signature based chipless RFID systems is presented. This methodology concludes that the reader sensitivity must be within -80dBw for 30cm detection range which is very low distance and very high sensitivity. These facts demand that the antenna used in tag detection must be very directive with high gain over ultra wide range of frequencies to improve reader sensitivity and reading range. Conventional antenna arrays cannot provide uniform functionality over a wide range of frequencies due to complex feeding network [1]. On the other hand, spatial feeding Reflectarray Antennas (RA) are best alternative to the bulky reflector and the complex feeding network phased array antennas, it combines a favourable feature of both antenna types. However, the main drawback of RA is the narrowband operation [4]. This problem results from the dependency of the compensated spatial distance on the frequency beside the used element to form the array. Several papers attempt to increase the antenna bandwidth such as using closely spaced stacked resonators [4], aperture coupled feeding antenna elements [5], or using dielectric resonator instead of microstrip resonator [6]. These mentioned solutions offer complexity and cost rise. Recently, using single layer concentric rings can enhance the antenna bandwidth [7]. However, these designs backed with a low permittivity substrate to linearize the slope of the reflection coefficient [7], [8]. This added substrate has to be assembled without air gabs, which add complexity to the design. In this paper, different RA design configurations investigated using single thick layer (Rogers RT 5880) substrate (h=6.35mm). With this single layer, we achieve a gentle phase slope and sufficient phase range (greater than 360 degree). The slower phase slope and the sufficient phase range reached, enhance the antenna bandwidth to reach a FBW of 37%. Design guidelines presented in section II, simulation results presented in section III and lastly the conclusion.
II. DESIGN GUIDELINES We begin our design by choosing an appropriate cell and feeder as shown in Fig. 1. Secondly, we obtain the best diameters and widths ratios that provide sufficient phase range, and linear phase slope as shown in Fig. 2. The used cell is double circular ring with outer ring radius (R 1), inner ring radius (R2 = 0.75*R1) and width (w=0.05*R1). The required phase distribution of each cell calculated based on eq. 1. Finally, the required physical dimensions for each cell obtained and simulation carried out. The used feeder is a commercial standard horn (4.97.1GHz) with11.4dBi gain -18dB side lobe level (SLL), its position and orientation are analytically calculated to produce a 10dB taper of the Reflectarray panel.
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31st National Radio Science Conference (NRSC2014) April 28 – 30, 2014, Faculty of Engineering, Ain Shams University, Egypt
R xij , yij k0 (dij ( xij sin 0 cos 0 yij sin 0 sin 0 ))
Where
R xij , yij ,
is the phase of the reflected field,
(1)
k 0 is the propagation constant in vacuum, d ij is the
distance from the feeder phase centre to the array cells,
x , y are the coordinates of element i, j and ij
ij
( 0 , 0 ) are the elevation and azimuth angles of the produced beam respectively.
Fig. 1: The Proposed Antenna System
Fig. 2: The Cell Phase Curve
III. SIMULATION RESULTS Four different RA configurations are shown in Fig. 3. These configurations are Centre Feed Centre Beam (CF-CB), Centre Feed Offset Beam (CF-OB), Offset Feed Centre Beam (OF-CB) and Centre Feed Dual Beam (CF-DB). The second and third configurations have the same purpose, which is to reduce blockage caused by feeder and to improve the feeder return loss using offset feeder or offset beam. It is shown from figures that the offset feeder is better than the offset beam configuration in terms of SLL. The CF-DB configuration purpose is to produce simultaneous dual beam to cover more than one region at the same time as shown in Fig. 3. In each configuration, the rings radiuses and widths calculated to produce such beam, furthermore the elements separation optimized to improve the SLL. In all of these different scenarios, the RA cover all the feeder bandwidth but the maximum gain is different from one to another as shown in Fig. 4. For sake of completeness, Fig. 5 shows the difference between horn antenna and our designed RA in terms of gain and beamwidth. Fig.5 shows that gain of the designed RA is 10dB greater than horn and the beam is four times narrower than horn antenna. This higher gain and narrower beamwidth help in solving the problem of low reading range and multi tag interference for RFID systems.
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31st National Radio Science Conference (NRSC2014) April 28 – 30, 2014, Faculty of Engineering, Ain Shams University, Egypt
Fig. 3: The Four Different Antenna Configurations. (a) Center Feed Centre Beam (CF-CB), (b) Center Feed Offset Beam (CF-OB), (c) Offset Feed Center Beam (OF-CB) (d) Center Feed Dual Beam (CF-DB)
Fig. 4: Gain with Frequency for the Four Different Antenna Configurations.
Fig. 5: The Feeder Versus RA 2-D pattern
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31st National Radio Science Conference (NRSC2014) April 28 – 30, 2014, Faculty of Engineering, Ain Shams University, Egypt
IV. CONCLUSION In this paper, an UWB Reflectarray antenna based on double circular ring resonator cell presented. We achieve a FBW of 37%. This achieved bandwidth make the antenna suitable for use with the frequency signature based chipless RFID systems. Four different antenna configurations introduced to emulate different real case scenarios. The proposed antenna system enhances the RFID reader reading range and solves the problem of multi tag interference with the help of achieved high gain pencil beam.
V. Acknowledgment The authors would like to thank the German Academic Exchange Service (DAAD) for funding the project ID4Egypt, which includes the research track, studied in this paper. REFERENCES [1] N. C. Karmakar, “Handbook of Smart Antennas for RFID Systems,” in John Wiley & Sons, Inc., 2010. [2] Y. F. Weng, S. W. Cheung, T. I. Yuk and L. Liu, “Design of Chipless UWB RFID System Using A CPW MultiResonator,” IEEE Antennas and Propagation Magazine, Vol. 55, No. 1, Feb. 2013, pp. 13–31. [3] M. El-Hadidy, B. Nagy, M. Khaliel, A. Fawky, E. Abdallah, H. Elhennawy, and T. Kaiser, “Novel Methodology for Increasing the Reading Range of the UWB Passive RFID Chipless Tags Considering Power Regulations,” in 34th PIERS, Stockholm, SWEDEN, 2013. [4] J. Huang and J. A. Encinar, “Reflectarray Antennas,” in John Wiley & Sons, Inc., 2008. [5] F. Venneri, S. Costanzo, and G. Di Massa, “Wideband Aperture-Coupled Reflectarrays with Reduced InterElement Spacing,” in Antennas and Propagation Society International Symposium, 2008. AP-S 2008. IEEE, 2008, pp. 1–4. [6] M. Abd-Elhady, S. Zainud-Deen, A. Mitkees, and A. Kishk, “Wideband Rectangular Dielectric Resonator Elements Reflectarray,” in Antennas and Propagation (MECAP), 2012 Middle East Conference on, 2012, pp. 1–5. [7] L. Guo, P.-K. Tan, and T.-H. Chio, “Design of an X-band Reflectarray Using Double Circular Ring Elements,” in Antennas and Propagation (EuCAP), 2013 7th European Conference on, 2013, pp. 2947–2950. [8] M. Hajian, B. Kuijpers, K. Buisman, A. Akhnoukh, M. Plek, L. de Vreede, J. Zijdeveld, and L. Ligthart, “Active Scan-Beam Reflectarray Antenna Loaded with Tunable Capacitor,” in Antennas and Propagation, 2009. EuCAP 2009. 3rd European Conference on, 2009, pp. 1158–1161.
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