Proceedings of 2010 IEEE Asia-Pacific Conference on Applied Electromagnetics (APACE 2010)

Xplore Compliant @2010 IEEE

Multiband Microstrip Antenna for RFID Application #Fitri Yuli Zulkifli 1, Subroto Fajar Siddiq 2 , Eko Tjipto Rahardjo 2

1,2,3 Antenna Propagation and Microwave Research Group (AMRG) Electrical Engineering Department

Faculty of Engineering Universitas Indonesia, Depok 16424

e-mail: yuli@ee.ui.ac.id, sidiki_benarkan@yahoo.com, eko@ee.ui.ac.id

Abstract—A Multiband microstrip antenna for RFID application is proposed in this paper. The antenna design consists of two substrates with EMC feeding technique. The antenna design uses FR4 substrate and has dimension of 118 x 120 mm. Both simulation and measurement results show multiband characteristic at frequency bands 433 MHz, 923 MHz and 2.45 GHz.

Keywords-multibaband, microstrip antenna, RFID

I. INTRODUCTION

Recently, Radio Frequency Identification (RFID) application is widely used for vast areas of applications, such as for logistic distribution, library management, access control etc. The RFID system consists of tag, reader and processing system. Antenna is used to communicate between the tag and the reader.

In Indonesia, the standard frequency published by Directorate General Pos and Telecommunication for RFID is 923 - 925 MHz [1]. However, worldwide, there are many other common bands for RFID applications like microwave (2.45 GHz, ISO/IEC 18000-4) and UHF (433 MHz) [2]. These different standard of frequencies used for RFID application can be accommodated by one multiband antenna.

There are several techniques to embrace both UHF and microwave bands in one patch. One technique is using reactively loaded microstrip antenna. This technique can use notch, shorting pin or slots. The slot technique is used in this paper to excite multiband frequencies. Some shapes like S- and U- slot have been designed for WLAN application [3], while for RFID application, [4], [5] and [6] shows only dual band antenna characteristic. Therefore in this paper, a multiband antenna for RFID application is proposed for frequencies 433 MHz, 923 MHz and 2.45 GHz.

II. ANTENNA DESIGN

The proposed multiband antenna design is depicted in Fig.1. The antenna consists of two layered FR4 substrate with dielectric constant εr =4.3 with h = 1.6 mm. The dimension of the substrate is 118 x 120 mm. To excite multi-frequencies, the antenna design consists of two patches combined together on the first substrate. The patches are separated with a U-slot. The first patch is designed to excite the frequency 433 MHz, while the second patch to excite the 923 MHz and 2.45 GHz frequencies. The dimension of the first patch is 98 x 100 mm and the second patch is 57 x 38 mm.

(a)

Proceedings of 2010 IEEE Asia-Pacific Conference on Applied Electromagnetics (APACE 2010)

Xplore Compliant @2010 IEEE

(b)

Figure 1: Multiband Antenna Design (a) Top View (b) Side View

On the second substrate the T-junction microstrip line

feed is designed. The feeding technique used is Electromagnetically Coupled (EMC), where the first substrate is placed on top of the second substrate. In Fig. 1a, the feed is shown with dashed line, which means that the feed is on the second substrate beneath the first one. This is shown in Fig. 1b, which shows the side view of the antenna design.

The antenna feed is designed using T-junction as power divider to give excitation directly to the first and second patch. The width of the feed is designed to operate at 50 ohm. For the T-junction, the transformer λ/4 is used to achieve impedance matching and shown in Fig.2.

50 Ω 50 Ω

50 Ω

70 Ω

Figure 2: T-junction 50 ohm

III. RESULT AND DISCUSSION The proposed multiband antenna design is designed

using HFSSv11. The design is fabricated and measured. The results are discussed as follow.

A. Simulation Results

The simulation result of the proposed antenna shows multiband characteristic as shown in Fig.2. The bands excited are at 429.98 MHz – 435.98 MHz, 896 MHz –

929 MHz, and 2.39 GHz – 2.46 GHz. This bandwidth fulfills the frequency band for RFID application.

(a)

(b)

(c) Figure 2: Return loss Simulation Results (a) Band 433 MHz (b) 923 MHz (c) 2.45 GHz

Proceedings of 2010 IEEE Asia-Pacific Conference on Applied Electromagnetics (APACE 2010)

Xplore Compliant @2010 IEEE

Furthermore, the radiation pattern is shown in Fig.3. Fig.3a shows an omnidirectional pattern for the frequency 433 MHz and Fig.3b show a directional pattern at frequency 923 MHz. For RFID system, there is no specific desired radiation pattern. Each specific RFID application can need different specification with different radiation patterns.

(a)

(b)

Figure 3: Radiation Pattern Results (a) Band 433 MHz (b) 923 MHz

B. Measurement Results

The antenna design has been fabricated and measured. The measurement results are shown in Fig.4. Measured return loss shown in Fig.4 shows that the antenna has multiband characteristic with bandwidths at 426.95 – 433.7 MHz, 896.95 – 936.1 MHz and 2.43 – 2.49 GHz.

(a)

(b)

(c)

Figure 4: Return loss Simulation Results (a) Band 433 MHz (b) 923 MHz (c) 2.45 GHz

Proceedings of 2010 IEEE Asia-Pacific Conference on Applied Electromagnetics (APACE 2010)

Xplore Compliant @2010 IEEE

The measured smith chart results as depicted in Fig.5 show similar results as the measured return loss, that shows also multiband characteristic.

(b)

Figure 5: Measured Result of Multiband Antenna

IV. CONCLUSION

The multiband antenna has been simulated, fabricated and measured. Both simulation and measurement results

show multiband characteristic with bands at frequency 433 MHz, 923 MHz and 2.45 GHz. These bands can be used for RFID applications.

ACKNOWLEDGMENT

This work is partly supported by the Ministry of Research and Technology under applied research grant with the contract number 719/H2.R12/PPM.00 Penelitian/2010.

REFERENCES

[1] http://www.Radio-frequency identification.html [2] http://rfid-handbook.de/rfid/frequencies.html [3] F.Y. Zulkifli, H Halim,. and ET. Rahardjo, "A Compact

multiband microstrip antenna” IEEE International Symposium on Antennas and Propagation (APS), San Diego, 5 – 11 July, 2008

[4] T. Deleruyelle, P. Pannier, E. Bergeret, S. Bourdel, “Dual band UHF and microwave RFID antenna” 1st European Wireless Technology Conference, Amsterdam The Netherlands, pp. 342-345, October 2008

[5] Z. Xu, X. Li, “Aperture coupling two-layered dual-band RFID Reader Antenna Design”, ICMMT, 2008

[6] Y.D. Prasetya, F.Y. Zulkifli, E.T. Rahardjo, “ A Dual Band C-shaped Microstrip Antenna for RFID Application”, Indonesia Malaysia Microwave Conference 2010 (IMMAC 2010), ISSN: 2086-8308, Indonesia, 11-12 June 2010