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1 Design of RFID Antennas for UHF Band ε ε This paper reports the characteristics and designs of RFID antennas operating at UHF band. Antennas for RFID application should work with high efficiency, a low return loss and a good antenna gain to achieve the required readable range with the restricted system power. Especially, for reader antennas, the high quality of a circular polarization (CP) in a wide range of frequency is strongly required and the proper radiation pattern is needed to broaden the readable range of the system. For tag antennas, the small and planar profile is desired to be easily attached to an object and the stable radiation performance nearby various dielectric materials is required. In addition, the readable range of the tag should not change much depending on its rotation angle. In this paper, we propose a novel reader antenna, called multi-layered polygonal helix, on which the wire is wound around multi-layered polygons causing the pitch angle to both increase and decrease. We also propose two different types of tag antennas. One is to miniaturize the electrical size of the tag and the other is to achieve an omni-directional readable range so that the tag can be stably detected irrespective of its rotation angle. The detail design parameters for the both the reader and tag antennas are determined using a Pareto Genetic Algorithm in conjunction with numerical simulation code such as Numerical Electromagnetics Code (NEC) and IE3D. Then, we fabricated the samples of the optimized antennas on the low cost substrate materials and compared the measurement results to the simulations. Keywords: characterisitcs of the RFID antenna, Pareto genetic algorithm, multi-layered polygonal heix antenna, small tag antenna, isotropic tag antenna.

2 I µ S 11 θ kr S 11 kr S 11 II

3 λ R P r,tag P T η D λ (ηd) Tag (ηd) Reader λ 2 1 P r,tag P T Re[V r,tag I r,tag * ] (4πR) 2 2 (1) P r,chip P r,tag P r,chip P r,chip(max) P r,chip Re[V Chip I * Chip ] V Chip 2 Re [ 2 2 Z Chip ] 1 Z Chip 1 V r,tag 2 Re [ 2 Z ] 2 Tag Ant Z Chip Z Chip 1 R Chip V r,tag 2 2 (D Tag Ant Z Chip ) 2 (X Tag Ant X Chip ) 2 (2) 1 V r,tag 2 P r,chip(max) (3) 8 R Tag Ant q q

4 P r,chip 4R Tag Ant R Chip q P r,chip(max) (R Tag Ant R Chip ) 2 (X Tag Ant X Chip ) 2 Z Chip Z * Tag Ant 2 1 (4) Z Chip Z Tag Ant P r,chip P r,tag P r,chip P r,chip,min Z Chip Z * Tag Ant 2 P r,chip qp r,tag ( 1 Z Chip Z Tag Ant ) Z Chip Z * Tag Ant 2 (ηd) Tag (ηd) Reader λ2 P r,tag ( 1 ) ( ) P T ZChip Z Tag Ant (4πR) 2 (5) Ω Ω P r,chip,min P Chip,loss (ηd) Tag (ηd) Reader λ 2 P r,reader (P r,chip P chip,loss ) (4πR) 2 Z chip Z * ant 2 (ηd) Tag (ηd) Reader λ 2 (P T ( 1 ) ( Z chip Z ant (4πR) ) 2 (ηd) Tag (ηd) Reader λ 2 P chip,loss ) ( ) (6) (4πR) 2 P Chip,loss P r,chip,min P R,min R max P R,min P r,chip,min R max P R,min P r,chip,min P T (ηd) 2 Reader (ηd)2 Tag λ P R,min 4π R max ( ) 4 (P r,chip P r,chip,min ) (7-1) P T (ηd) Reader (ηd) Tag λ 2 (7-2) R max ( P r,chip,min 4π ) III

5 1 Eff Reader BWReader COST 1 ( 1 ) RQ (8) 2 BW RFID 1 CPBW Reader COST2 ( 1 ) AQ (9) 2 BW RFID COST3Size Norm (10) RP Reader COST41 (11) RP RFID Eff Reader BW RFID BWReader CPBW Reader S 11 RQ AQ RQ AQ r kπλ kr θ φ (RR Reader ) RR RFID RR RFID

7 P T P R,min (ηd) Tag (ηd) Reader θ φ A(Region A) B(Region B) kr ε

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10 µ µ IV (M 2 )

11 Eff Tag BWTag Cost 11 (12) BW Theory Γw/o,material Γw, material Cost 2 ) (13) Γw/o,material Cost 3Size NORM (14) h b h l h f w b w f d w d h d Cost 1 kr S 11 BW Theory Eff Tag BW Tag Cost 1 Cost 2 Cost 3 kr S 11 kr rλ Linewidth µ ε kr S 11

13 θ θ θ θ θ θ θ θ θ θ Cost 1 Cost 2 Cost 3 G maxg min Cost 31 (15) G dev,ref G max G min θ φ h l h f h d w f w l w d Linewidth G dev,ref (kr) λ kr kr

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15 S 11 θ kr kr S 11 kr S 11 [1] (Ministry of Information and Cumunication Republic of Korea), ''Notice '' [2] K. Finkenzeller, RFID Handbook, Reading, MA: Addison Wiley, [3] W. Rankl and W. Effing, Smart Card Handbook, New York: John Wiley & Sons, [4] RFID system [5] H. A. Wheeler, ''The radiansphere around a small antenna,'' Proc. IRE. Aug.,1959, pp [6] J. S. McLean, ''A re-examination of the fundamental limits on the radiation Q of electrically small antennas,'' IEEE Trans. Antennas Propagat., Vol. 44, May. 1996, pp [7] U. Karthaus and M. Fischer, ''Fully integrated passive UHF RFID transponder IC with 16.7-µW minimum RF input powoer,'' IEEE J. Solid-State. Circuits, Vol. 38, Oct. 2003, pp [8] C. A. Balanis, Antenna theory analysis and design, New York: John Wiley & Sons, [9] W. L. Stutzman and G. A, Thiele, Antenna theory and design, New York: John Wiley & Sons, [10] D. M. Pozar, Microwave engineering, New York: John Wiley & Sons, [11] H. E. King and J. L. Wong, ''Characteristics of 1 to 8 wavelength uniform helical antennas,'' IEEE Trans. Antennas Propagat., Vol. 28, Mar. 1980, pp [12] A. Safaai-Jazi and J. C. Cardoso, ''Radiation characteristics of a spherical helical antenna,'' Proc. Inst. Elect. Eng. Microwave and Antennas Propagat., Vol. 143, Feb. 1996, pp [13] J. M. Tranquilla and S. R. Best, ''A study of the quadrifilar helix antenna for Global Positioning System applications,'' IEEE Trans. Antennas Propagat., Vol. 38, Oct. 1990, pp [14] D. Goldberg, Genetic Algorithms in Search, Optimization and Machine Learning, Reading, MA: Addison Wesley, [15] Y. Rahmat-Samii and E. Michielssen, Electromagnetic Optimization by Genetic Algorithms, New York: John Wiley & Sons, [16] H. T, Hui, K. Y. Chan and E. K. N. Yung, ''The input impedance and the antenna gain of the spherical helical antenna,'' IEEE Trans. Antennas Propagat., Vol. 49, Aug. 2001, pp [17] H. Choo and H. Ling, ''Design of electrically small planar antennas using an inductively coupled feed,'' Electron. Lett., Vol. 39, Oct. 2003, pp [18] H. D. Foltz, J. S. Mclean and G. Crook, ''Disk-loaded monopoles with parallel strip elements,'' IEEE Trans. Antennas Propagat., Vol. 46, Dec. 1998, pp [19] E. Newman, P. Hohley, and C. H. Walter, ''Two methods for the measurement of antenna efficiency,'' IEEE Trans. Antennas Propagat., Vol. 23, Jul. 1975, pp

THE JOURNAL OF KOREAN INSTITUTE OF ELECTROMAGNETIC ENGINEERING AND SCIENCE. vol. 29, no. 10, Oct ,,. 0.5 %.., cm mm FR4 (ε r =4.4)

THE JOURNAL OF KOREAN INSTITUTE OF ELECTROMAGNETIC ENGINEERING AND SCIENCE. 2018 Oct.; 29(10), 799 804. http://dx.doi.org/10.5515/kjkiees.2018.29.10.799 ISSN 1226-3133 (Print) ISSN 2288-226X (Online) Method