JOURNAL OF TELECOMMUNICATIONS, VOLUME 15, ISSUE 2, AUGUST 2012 56

Planar Monopole CPW Fed Slot Antenna with Modified H-Shaped Slot for RFID, WiMAX and

WLAN Applications Laxmi Ray, Chiranjib Goswami, Manimala Pal and Rowdra Ghatak

Abstract— In this paper a planar monopole antenna with dual wideband resonance characteristics is presented that simultane-ously satisfies RFID and Wi-MAX applications. The proposed antenna structure consists of a rectangular monopole bevelled at the base with an offset H shaped slot and occupies an area of 32×47 mm2. The measured realized gain is about 2.4dBi in the lower band (2.38 GHz -2.72 GHz) and about 3.8 dBi in the upper band (3.63 GHz – 6.15 GHz). .

Index Terms— Planar Monopole Antenna, RFID Antenna, Wi-MAX Antenna.

—————————— u ——————————

1 INTRODUCTION contact less automatic identification technology, the Radio Frequency Identification (RFID) became very popular in several applications such as electronic

toll collection, asset identification, retail item manage-ment, access control, animal tracking and vehicle security [1]. The RFID system consists of read/write device and a tag. The data is transferred between tag and read/write device using electromagnetic waves. The assign bands for RFID applications are 125 KHz, 13.56 MHz, 869 MHz, 902-928 MHz, 2.45 GHz and 5.8 GHz [2]. To accommo-date the antenna and microchip transmitter on RFID tag the antenna must be low profile, low cost and small size in order to make the system compact. Furthermore the tag performance can be degraded if a suitable antenna design is not adopted for microwave range operating frequency [3]. Most of the antenna developments in RFID paradigm have been focused on the UHF bands [4]. A number of antenna designs are proposed in several literatures in-cluding the aperture-coupled structure [5], the CPW-fed folded-slot structure [6] and CPW fed shorted F-shaped monopole antenna [7]. A microstrip to coplanar stripline transition based meander dipole with conformally cou-pled parasitic element is reported for RFID usage [8]. Me-ander PIFA structure for UHF RFID pervasive medical application is presented in [9]. These antennas are design for single RFID frequency. Recently multi-band antenna systems are the most attractive candidate for supporting multiple RFID standards simultaneously. Many of recent-ly published literature [10], [11] reported the dual band antenna for RFID standard. The main drawback of these antennas is very low gain. Recently some higher micro-wave bands like 2.45 GHz and 5.8GHz have been slated

for RFID application. In this domain certain antenna like coplanar Waveguide (CPW) fed slot antenna for 5.8 GHz is given in [12]. However, most of the development of multiband antenna for RFID is linked to one in UHF band and the other in 2.45GHz like that reported in [13], [14].

Fig. 1. The geometry of the proposed antenna. The slot dimensions are shown in the right hand top corner, which largely contributes to its resonance characteristics. The antenna is oriented in the yz plane.

In this paper, a novel high gain dual band antenna with

CPW fed structure for 2.45/5.8 GHz RFID application is proposed that merely occupies a compact size of 32×47 mm2 and consists of a rectangular monopole bevelled at the base with an offset H shaped slot. The proposed an-tenna satisfies the 10 dB return loss characteristics from 2.38GHz to 2.72 GHz (34 MHz) for 2.45 GHz and from

———————————————— • Microwave and Antenna Research Laboratory, Dept of ECE, National

Institute of Technology Durgapur, West Bengal, INDIA • Dept. of ECE/AEIE, Asansol Engineering College, West Bengal, INDIA • Dept. of ECE, NFET, NSHM Knowledge Campus Durgapur, INDIA • Microwave and Antenna Research Laboratory, Dept of ECE, National

Institute of Technology Durgapur, West Bengal, INDIA

A

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3.63 GHz to 6.15 GHz (2.52 GHz) for 5.8 GHz applica-tions, respectively. The measured antenna gain is about 2.4 dBi at 2.45 GHz and 3.8 dBi at 5.8 GHz.

2 ANTENNA DESIGN AND PARAMETRIC STUDY The antenna structure consisting of a bevelled rectan-

gular monopole with a modified H shaped slot as illus-trated in Fig.1. The substrate for realizing the antenna has !r=4.4, tan "=0.0022 and thickness of 0.787 mm. The an-tenna is analyzed using full wave electromagnetic simula-tion software IE3DTM.

Fig. 2. Variation of S11 (dB) of the proposed antenna for parametri-cally varying L1. Other parameters are L2=12.5, W1=6, W2=3, g=2.5. (All dimensions in mm).

Fig. 3. Variation of S11 (dB) of the proposed antenna for parametric variation in W1. Other parameters are L1=15, L2=12.5, W2=3, g=2.5. (All dimensions in mm).

The first step in the entire design process begins with

realization of a quarter wave monopole of length 30.61mm, corresponding to a frequency of 2.45 GHz. The length (L) and width (W) are further optimized to 27 mm for fine-tuning the allocated bands. To obtain the wide upper band; impedance matching is achieved by bevel-ling the bottom edges of the square patch to cover the

WLAN as well as RFID bands. Etching slots on the design as illustrated in Fig.1 brings about further adjustment of band allotment. The 50Ω coplanar waveguide (CPW) transmission line with finite ground plane Lg and Wg is used for feeding the antenna. Primary investigation of the antenna reveal that the dimensions of the slot L1, L2, W1, W2 and horizontal gap g, as shown in Fig.1 play a crucial role in resonant behaviour of the proposed antenna. Therefore these slot dimensions are put to parametric study. Symmetry about the vertical axis running along centre of the antenna is maintained. The dimension of left and right vertical slots is identical. It can be observed from Fig.2 that if length of the longer slot denoted by L1 is increased, simultaneously keeping the length of shorter slot L2 fixed, the lower and upper band gets shifted to higher frequency side in steps of 100MHz and 80 MHz respectively. Moreover impedance matching is improved in lower band compare to higher band.

Fig. 4. Variation of S11 (dB) of the proposed antenna for parametric study of horizontal gap g. Other parameters are L1=15, L2=12.5, W1=3, W2=3, (All dimensions in mm).

By keeping the dimensions of W2 unchanged, the change in slot width W1 results in 180 MHz right shift of the lower band at 2.45 GHz but upper band remains unaf-fected but impedance matching of the antenna is improve as observed from Fig.3. If the horizontal gap (g) is in-creased then lower band gets shifted to the right hand side of 2.45 GHz by 70 MHz and higher band gets re-duced by 110 MHz, but impendence matching is im-proved in both bands as shown in Fig.4. On the other hand when W2 is varied by keeping W1 fixed, negligible changes in resonance characteristics occur. The final di-mensions of the proposed antenna and the slot are tabu-lated in Table I and Table II respectively.

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3 RESONANCE AND RADIATION CHARACTERISTICS

A fabricated prototype of the proposed antenna, real-­‐‑ised using FR4 substrate is shown in Fig.5 (a). The meas-­‐‑ured S11 (dB) of the final design of the proposed antenna is given in Fig.5 (b) which show that it covers the 2.45 GHz (2.38 GHz -­‐‑2.72 GHz) and 5.8 GHz (3.63 GHz – 6.15 GHz) RFID band. The measured result and simulation are in good agreement. The slot dimensions are kept same along either side of vertical axis passing through centre of the antenna to keep the current distribution symmetrical on either side for all frequencies as shown in Fig.6. This manifests itself as symmetrical radiation pattern.

(a)

(b)

Fig. 5. (a) Prototype of the proposed antenna (b) Comparison be-tween simulated and measured S11 (dB) of the proposed antenna.

Fig. 6. Simulated current distribution of proposed antenna at (a) 2.45 GHz and (b) 5.8 GHz.

The comparison of measured and simulated principal plane patterns at 2.45GHz and 5.8GHz are shown in Fig.7 (a) and (b) respectively. It is noticed that computed radia-­‐‑tion pattern remains unaltered in each band. The pattern remains near omni-­‐‑directional in the azimuthal plane. The measured realized gain as shown in Fig.8 (a) and (b) remain about 2dBi lower band (around 2.45 GHz) and 3.8dBi in higher band (around 5.8 GHz) respectively. The measured impedance bandwidth in lower band is 34 MHz (2.42 GHz -­‐‑2.62 GHz) and in upper band is 2.52 GHz (3.63GHz-­‐‑6.15GHz).

4 CONCLUTION The proposed planar monopole antenna with offset H

shaped slot covers the 2.45 GHz and 5.8 GHz RFID bands as well as 5.2 GHz IEEE 802.11a WLAN band and 5.5 GHz WiMAX band. By properly choosing the dimensions of the slot dual band and tuneable impedance bandwidth characteristics for desire band can be achieved. Vertical

TABLE 1 LIST OF ANTENNA DESIGN PARAMETERS AND ITS

CORRESPONDING VALUES

Parameters Value (mm)

L 27 W 27 S 1.3 Lg 19.25 Wg 14.7

TABLE 2 LIST OF SLOT DESIGN PARAMETERS AND ITS COR-

RESPONDING VALUES

Parameters Value (mm) L1

15 L2

12.5 W1 6 W2 3 g 2.5

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(a)

(b)

Fig. 7. Principal plane simulated and measured radiation pattern at (a) 2.45 GHz and (b) 5.8 GHz.

length of the slots is responsible for improving imped -­‐‑ance matching in lower band of the antenna and band-­‐‑width can be control by horizontal width of slots. The horizontal gap is responsible for tuning the lower band as well as the upper band and improves the impendence matching in both bands. The radiation pattern remains unaltered from one band to other. The measured realized gain is about 2.4dBi in the lower band and on an average 3.8dBi in the upper band.

Fig. 8. Variation of measured realized gain with frequency of the proposed antenna in (a) 2.45GHz band and (b) 5.8 GHz band.

ACKNOWLEDGMENT One of the authors, Ms. Laxmi Ray, is grateful to Minis-

try of External Affairs, Government of India, for support-ing her Post graduate studies in India at National Insti-tute of Technology Durgapur through Dr. Homi J Bhabha Scholarship Scheme 2010-11 vide grant no. Kat/Edu/CP/233/13/2010 dated 02.08.2010.

REFERENCES [1] K Finkenzeller, ‘RFID handbook: fundamentals and application in

contactless smart cards and identification’, John Wiley and Sons Inc., UK, 2nd edn., 2003

[2] M. Keskilammi and M. Kivikoski, “Using text as a meander line for RFID transponder antennas”, IEEE Antennas Wireless Propa-gation Letters, vol.3, pp.372-374, 2004.

[3] P. Foster and R. Burberry, Antenna problems in RFID systems, IEE Colloq RFID Technology, London, 1999, pp. 3/1–3/5.

[4] Gaetano Marrocco, “The Art of UHF RFID Antenna Design: Impedance Matching and Size Reduction Techniques,” IEEE Antennas and Propagation Magazine, vol. 50 no. 1, pp.66-79, 2008.

[5] S.K. Padhi, N.C. Karmakar, and C.L. Law, “An EM-coupled dual polarized microstrip patch antenna for RFID applica-tions,” Microwave Optical Technology Letters, vol. 39, pp.354-360, 2003.

[6] S.Y. Chen and P. Hsu, “CPW-fed folded-slot antenna for 5.8-GHz RFID tags”, Electronics Letters, vol. 40, pp. 1516–1517, 2004.

[7] Wen-Chung Liu and Chao-Ming Wu, “CPW-fed shorted F-shaped monopole antenna for 5.8 GHz RFID application”, Mi-crowave Opt Technology Letters, vol.48, pp. 573–575, 2006.

[8] Reng Ching Hua and Tzyh-Ghuang Ma, “A Printed Dipole Antenna for Ultra High Frequency (UHF) Radio Frequency Identification (RFID) Handheld Reader,” IEEE Transactions on Antennas and Propagation, vol.55, no.2, pp.3742-3745, Decem-ber 2007.

[9] Andrea Sani, Marie Rajab, Robert Foster and Yang Hao, “An-tennas and Propagation of Implanted RFIDs for Pervasive Healthcare Applications,” IEEE Proceedings, vol. 98, no.9, pp.1648-1655, September 2010.

[10] You, B., Lin, B., Zhou, J., and Xu, W. ‘Dual-frequency folded dipole antenna with PBG structure’, Electronics Letters, vol. 45, no.12, pp. 584–588, 2009.

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[11] S M Hu, Y Zhou, C L Law and W B Dou, “Study of a uniplanar monopole antenna for passive chip less UWB-RFID localization system,” IEEE Trans. on Antennas Propagation, vol. 58, no. 2, pp. 271–278, 2010.

[12] W C Liu and Z K Hu, “Broadband CPW fed folded slot mono-pole antenna for 5.8GHz RFID Application,” Electronics Letters, vol41, no.17, pp.937-939, August 2005.

[13] S Jeon, Y Yu and J Choi, “Dualband Slot Coupled Dipole An-tenna for 900 MHz and 2.45GHz RFID Tag Application,” Elec-tronics Letters, vol42, no.22, pp.pp.1259-1260, October2006.

[14] H Kimouche, H Zemmour and B Atronz, “Dual Band Fractal Shape Antenna Design for RFID Applications,” Electronics Let-ters, vol.45, no.21, pp.1061-1063, 2009.

Laxmi Ray is a student of M.Tech (Telecommunication Engineer-ing) at ECe Dept., NIT Durgapur. Her area of interest lies in RFID systems and antenna. She did her undergraduate from Nepal from where she belongs. She is continuing her higher studies in India with the support of Ministry of External Affairs, Government of India, in India at through Dr. Homi J Bhabha Scholarship Scheme 2010-11 Chiranjib Goswami Received his B.Tech and M.Tech (Microwaves) degree from West Bengal University of Technology and the Universi-ty of Burdwan in 2006 and 2009, respectively. He is currently work-ing as an Assistant Professor in Asonsol Engineering College, Burdwan. His research interests are microwave antenna and met-amaterial. He is pursuing research work in the area of metamaterial and its application in microwave circuits and antenna. Manimala Pal received her M.Tech (Microwave Engineering) from The University of Burdwan in 2010. She started her research on microwave circuits at Radionics Laboratory. Presently she is an as-sistant professor in Electronics and Communication Engg Dept. of NSHM Knowledge campus, Durgapur Group of Institutions, Durga-pur, West Bengal. Her areas of interest lie in design and optimization of planar bandpass filters and couplers. She has twenty publications in various international and national journal as well as conferences. She is a member of microwave and antenna research group at NIT Durgapur as an external fellow. Rowdra Ghatak Received his M.Tech. (Microwave Engineering) from The University of Burdwan and Ph.D. (Engg.) from Jadavpur University in 2002 and 2008, respectively. He initiated his career in microwave engineering as a trainee at CEERI Pilani in fabrication and testing of S-band magnetrons. Thereafter, he has served at NationalInstitute of Science and Technology Berhampur, Odisha, and at the University of Burdwan. He is presently an associate pro-fessor in Electronics and Communication Engineering department of National Institute of Technology Durgapur. He is a recipient of the URSI Young Scientist Award in 2005. He has recently received sup-port under DST Young Scientist scheme for development of UWB antennas for imaging RADAR. He has more than 70 publications in various National/International journals and conferences. His research interest lies in the areas of fractal antenna, metamaterials, applica-tion of evolutionary algorithms to electromagnetic optimization prob-lems, RFID, computational electromagnetic and microwave passive circuit design.