Triple-Band L-ShapedMonopoleAntennawith Defected Ground Plane for WLAN and WiMAX Application

Yih-Chien Chen and Min-Zhe Weng

Triple-Band L-ShapedMonopoleAntennawith Defected Ground Plane for WLAN and WiMAX Application

Yih-Chien Chen and Min-Zhe Weng

—This paper presents the simulation and measured results of a triple-band L-shaped monopole antenna with defected ground plane for applications in wireless local area networks （WLANs） and worldwide interoperability for microwave access （WiMAX） bands. The triple-band L-shaped monopole antenna with defected ground plane was fabricated on a FR4 substrate. The lower band is associated with the shorted parasitic strip in the protruding stub of the ground plane； the middle band is expected to be controlled by the longer strip of L-shaped monopole in the front side，while the higher band is associated with the short strip of L-shaped monopole in the front side. The proposed antenna has a good agreement between the measured and the simulation results. It has a 10 dB return loss with the bandwidth of 250 MHz （2270 MHz to 2520 MHz） in the lower band， 600 MHz （3320 MHz to 3，920 MHz） in the middle band， and 1110 MHz （5030 MHz to 6140 MHz） in the higher band. The proposed antenna covers the ISM （industrial， scientific and medical），HIPERLAN （high performance radio local area network）， UNII （unlicensed national information infrastructure）， and WiMAX bands.

Index Terms—Bandwidth， monopole antenna，radiation， wireless local area network.

1. Introduction

Many commercial applications， including mobile radio and wireless communications， use monopole. The monopole is used extensively because it is reasonably compact， good efficiency， and very simple［1］，［2］. A conventional planar monopole is a straight shape of quarter-wavelength. Instead of a straight shape monopole， an inverted L-shape monopole owns the advantage of low profile. Recently，multiband monopole antennas for applications in WLAN（wireless local area network， 2.4 GHz to 2.484 GHz）， ISM（industrial， scientific， medical） and Bluetooth at the low band， HIPERLAN （high-performance radio local area network， 5.15 GHz to 5.35 GHz）， and UNII （unlicensed national information infrastructure， 5.725 GHz to 5.825 GHz） applied in the high band have been implemented. Simultaneously， associating with the rapid development of WiMAX （worldwide interoperability for microwave access，3.4 GHz to 3.6 GHz and 5.25 GHz to 5.85 GHz）， there is an increasing demand for antennas suitable for WLAN/WiMAX. Multiband monopoles have been realized by employing parasitic or shorted elements to the monopole［3］-［6］. The multiband monopoles are fed with a microstrip line， the structure of the antennas has two metal layers. Via holes are employed to connect the parasitic or shorted element on the front side to the ground plane on the back side of the substrate. However， this has increased the manufacturing cost and the difficulty in fabricating.

In this paper， a triple-band antenna with defected ground plane is proposed. The proposed antenna is simple in manufacturing because of single dielectric substrate，single metal layer， and without via holes. The proposed antenna is capable of operating in the ISM， HIPERLAN，UNII， and WiMAX bands simultaneously. The design considerations and experimental results for the proposed antenna are presented and discussed.

2. Antenna Design

The geometry and parameters of a triple-band monopole with defected ground plane are shown in Fig. 1. The triple-band monopole with defected ground plane is realized on a RF4 substrate of 1.6 mm in thickness， 4.4 in relative permittivity， and 0.024 in loss factor. A 50 Ω microstrip feed line is used to feed the triple-band monopole with defected ground plane. Dimensions of the microstrip feed line are calculated by the close-form formulas given in ［7］， assuming infinite ground plane and finite dielectric thickness.

The proposed triple-band monopole with defected ground plane comprises an L-shaped monopole in the front side and a parasitic strip in the protruding stub of the ground plane. The shorted parasitic strip in the protruding stub of the ground plane controls the lower band； the middle band is expected to be controlled by the longerlength of L-shaped monopole in the front side， while the short length of L-shaped monopole generates an operating band for the upper band. The effects of parameters on the resonant frequency are studied to understand the behavior of the triple-band antenna with defected ground plane.

Fig. 1. Configuration of the triple-band monopole with defected ground plane.

Fig. 2 shows the simulation return losses of the triple-band antenna with defected ground plane with different lengths of2gL ， Lf， and Ws， respectively. The first resonant frequency in the lower band decreases from 2.55 GHz to 2.27 GHz as the Lg2increases from 9.3 mm to 13.3 mm. The longer the2gL is， the lower the first resonant frequency is. The second and third resonant frequencies in the middle and higher bands also decrease as the length ofincreases. The second resonant frequency in the middle band decreases from 3.94 GHz to 3.30 GHz as Lfincreases from 25.0 mm to 25.9 mm. The first and third resonant frequencies in the middle and higher bands also decrease as the length of Lfincreases. The third resonant frequency decreases from 6.41 GHz to 4.62 GHz as Wsincreases from 4.5 mm to 8.5 mm. However， the influence of Wson the first and second resonant frequencies in the lower and middle bands is not evident. The resonant frequencies can be obtained through the following formulas. The first resonant length is calculated by

The second resonant length is calculated by

Fig. 2. Simulation return losses of the triple-band antenna with defected ground plane with different lengths of （a） Lg2， （b） Lf， and（c） Ws， respectively.

The resonant length is nearly equal to a quarter of the guided wavelength excited in the radiating structure， it can be obtained as

where λg1， λg2， and λg3are the corresponding guided wavelengths in the radiating structure at the first， second，and third resonant frequencies， respectively. The optimal parameters of triple-band monopole with parasitic elements are set as those in Table 1.

Table 1: Optimal parameters of triple-band monopole with parasitic elements

The current distribution of the proposed antenna is studied to understand the behavior of the proposed antenna. Fig. 3 shows the simulation current distributions of the proposed antenna at three resonant frequencies. As shown in Fig. 3， the shorted parasitic strip is in the protruding stub of the ground plane， the longer strip of L-shaped monopole is in the front side， and the shorter length of L-shaped monopole contributes to the first， second， and third resonant frequency， respectively.

Fig. 3. Simulation current distributions of the proposed antenna at three resonant frequencies: （a） 2.4 GHz， （b） 3.5 GHz， and （c） 5.5 GHz.

3. Results

Fig. 4 shows the measured and simulation return loss of the proposed antenna. The measured resonant frequencies are 2.37 GHz， 3.63 GHz， and 5.60 GHz. The measured resonant frequencies are close to the simulation resonant frequencies. The measured return losses are 18.59 dB，12.91 dB， and 22.12 dB at 2.37 GHz， 3.63 GHz， and 5.60 GHz， respectively. Furthermore， there is a 10 dB return loss with the bandwidth of 250 MHz （2270 MHz， 2520 MHz） in the lower band， 600 MHz （3320 MHz， 3920 MHz） in the middle band， and 1110 MHz （5030 MHz， 6140 MHz） in the higher band. The bandwidth of the proposed antenna is sufficient for the ISM band from 2.40 GHz to 2.484 GHz. It is also sufficient for the HIPERLAN， UNII， and WiMAX bands from 3.4 GHz to 3.6 GHz and from 5.15 GHz to 5.85 GHz. Compared with the results in ［8］ and ［9］， the monopole investigated in this study not only has a smaller size， but also has comparable bandwidth.

Fig. 4. Measurement and simulation return loss of the proposed antenna.

Fig. 5 displays the measured radiation patterns in the azimuth plane （x-z plane） and the elevation planes （y-z plane） at frequencies of 2.40 GHz， 3.58 GHz， and 5.50 GHz. The radiation patterns are similar to that of a monopole. Large cross-polarization is observed. Although large crosspolarization can be observed， it becomes an advantage for practical applications. The wave propagates with multiple reflections between the transmitter and receiver， especially in indoor applications. Fig. 6 displays the gain of the proposed antenna for operating frequencies in the ISM，HIPERLAN， UNII， and WiMAX bands. The peak gains are about 0.4 dBi， 1.3 dBi， and -0.6 dBi in the lower， middle，and higher bands， respectively. The gain variations are 0.6 dBi， 0.7 dBi， and 3.2 dBi for frequencies within the lower，middle， and higher bands， respectively.

Fig. 5. Measurements of the triple-band antenna radiation patterns in the azimuth plane （x-z plane） and the elevation planes （y-z plane） at frequencies of 2.40 GHz， 3.58 GHz， and 5.50 GHz.

Fig. 6. Gain of the proposed antenna for operating frequencies in the ISM， HIPERLAN， UNII， and WiMAX bands.

4. Conclusions

A triple-band antenna with defected ground plane for applications in WLAN and WiMAX bands was successfully realized. It was demonstrated that the triple-band antenna has a smaller size compared with that in literatures. The structure of the proposed antenna is simple and easily manufactured. The proposed antenna has a 10 dB return loss with the bandwidth 250 MHz， 600 MHz， and 1110 MHz in the lower， middle， and higher bands， respectively. The 10 dB S11 bandwidth of the proposed antenna covers ISM， UNII， HIPERLAN， and WiMAX bands.

Acknowledgment

The authors would like to thank the NSC funding for financially supporting this research under Contract No. 102-2622-E-262-009-CC3.

［1］ H. Jiang and H. Arai， “FDTD analysis of low profile top loaded monopole antenna，” IEICE Trans. Communications，vol. E85-B， no. 11， pp. 2468-2475， 2002.

［2］ J. Itoh， T. Hung， and H. Morishita， “Analysis of decoupling method between J-shaped folded monopole antennas for IEEE 802.11 b/g on handset，” IEICE Electron. Express， vol. 7，no. 18， pp. 1359-1363， 2010.

［3］ Y. C. Jan and L. C. Tseng， “Small planar monopole antenna with a shorted parasitic inverted-L wire for wireless communications in the 2.4-， 5.2-， and 5.8-GHz bands，” IEEE Trans. on Antennas and Propagation， vol. 52， no. 7， pp. 1903-1905， 2004.

［4］ N. M. Mohammad， H. Rousta， and B. S. Virdee， “Compact UWB planar monopole antenna，” IEEE Antennas Wireless Propagation Letters， vol. 8， pp. 1382-1385， Dec. 2009.

［5］ K. G. Thomas and M Sreenivasan， “A simple ultra-wideband planar rectangular printed antenna with band dispensation，”IEEE Trans. on Antennas and Propagation， vol. 58， no. 1， pp. 27-34， 2010.

［6］ J. H. Lu and Y. Y. Lee， “Planar C-shaped monopole antenna with multi-band operation for WiMAX system，” in Proc. of Int. Symposium on Antennas and Propagation， 2010， pp. 1-4.

［7］ K. C. Gupta， R. Garg， I. Bahl， and P. Bhartia， Microstrip Lines and Slotlines， 2nd Ed. Norwood: ArtecHouse， 1996.

Yih-Chien Chen received the B.S.， M.S.，and Ph.D. degrees in electrical engineering from National Cheng Kung University，Tianan in 1994， 1996， and 2000，respectively. He is currently a professor with the Department of Electrical Engineering， Lunghwa University of Science and Technology， Taoyuan. His research interests include microwave ceramic and antenna design.

Min-Zhe Weng was born in Taipei in 1991. He received the B.S. degree from the Lunghwa University of Science and Technology， Taoyuan in 2013. He is currently pursuing the M.S. degree with the Department of Electrical Engineering，Lunghwa University of Science and Technology. His research interests include microwave ceramic and antenna design.

Manuscript received November 7， 2014； revised January 13， 2015. The work was supported by the NSC under Grant No. 102-2622-E-262-009-CC3.

Y.-C. Chen is with the Department of Electrical Engineering， Lunghwa University of Science and Technology， Taoyuan （e-mail: ycchenncku@ yahoo.com.tw）.

M.-Z. Weng is with the Department of Electrical Engineering， Lunghwa University of Science and Technology， Taoyuan （Corresponding author e-mail: k01223059@yahoo.com.tw）.

Color versions of one or more of the figures in this paper are available onlineat http://www.journal.uestc.edu.cn.

Digital Object Identifier: 10.3969/j.issn.1674-862X.2015.02.009