second dipole elements are designed to resonate slightly below and above the center frequency of the frequency band [5]. The length ratio of the second dipole to the ﬁrst one is 0.7, and that of the ﬁrst dipole to the ground reﬂector is 0.8. 3. EXPERIMENTAL RESULTS AND DISCUSSION The proposed antenna was simulated and the optimized parameters were obtained by using the commercial EM simulation software CST Microwave Studio. A prototype of the antenna was fabricated on an FR4 substrate with a dielectric constant of 4.4 and a thick- ness of 1.6 mm (loss tangent ¼ 0.025) as shown in Figure 2. Figure 3 shows the simulated and measured input reﬂection coefﬁcients of the antenna. For a voltage standing wave ratio (VSWR) < 2, the frequency band for the simulated data is 1.68–2.73 GHz and that for the measured data is 1.70–2.80 GHz. The antenna with no ground reﬂector behaves very similar to the proposed antenna with the reﬂector. The measured results agree well with the simulated ones, and the bandwidth is about 49% with respect to the center frequency of 2.25 GHz. The measured realized gain of the antenna is compared with the simulated ones, as shown in Figure 4, and it is clearly seen that the reﬂector improves the gain in the low-frequency band (1.7–2.3 GHz). The measured data range from 5.5 to 6.3 dBi with a varia- tion of 0.8 dB. Figure 5 compares the simulated and measured radiation patterns of the fabricated antenna at 1.8, 2.35, and 2.6 GHz in the E (xy plane) and H (yz plane) planes. The measured 3- dB beam widths in the E-plane are 60, 62, and 59  , respectively, and they are 113, 107, and 106  , respectively, in the H-plane. The front-to-back ratios (FBRs) in the E-plane are 12, 16.8, and 12 dB, and they are 12.9, 16.6, and 12.8 dB in the H-plane. 4. CONCLUSIONS A broadband series-fed two dipole array antenna with an inte- grated balun is proposed for mobile base station applications, covering the frequency bands of the 2G, 3G, and LTE systems. Two printed-strip dipole antennas with different lengths and an integrated balun consisting of an MS line and a slot line are used. For a VSWR < 2, the proposed antenna provides a 49% bandwidth in the range of 1.7–2.8 GHz, a stable gain of 5.5–6.3 dBi, and an FBR of 12–17 dB. A ground reﬂector is used to increase the gain in the low-frequency band and thus a stable gain is achieved in that frequency band. The antenna can be used as a broadband base station element antenna covering all the frequency bands of mobile systems or as an antenna for low-power repeaters and WLAN access points. REFERENCES 1. M. Barba, A high-isolation, wideband and dual-linear polarization patch antenna, IEEE Trans Antennas Propag 56 (2008), 1472–1476 2. X.P. Lu and Y. Li, Novel broadband printed dipole, Microwave Opt Technol Lett 48 (2006), 1996–1998 3. R.L. Li, B. Pan, T. Wu, K. Lim, J. Laskar, and M.M. Tentzeris, Equivalent-circuit analysis and design of a broadband printed dipole with adjusted integrated balun and a printed array for base station applications, IEEE Trans Antennas Propag 57 (2009), 2180–2184 4. L.C. Kretly and A.S. Ribeiro, A novel tilted dipole quasi-Yagi antenna designed for 3G and Bluetooth applications, Proceedings of the 2003 SBMO/IEEE MTT-S IMOC 1 2003, pp. 303–306 5. F. Teﬁku and C.A. Grimes, Design of broad-band and dual-band antennas comprised of series-fed printed-strip dipole pairs, IEEE Trans Antennas Propag 48 (2000), 895–900 V C 2012 Wiley Periodicals, Inc. DESIGN OF TRIPLE-BAND MONOPOLE ANTENNA WITH MEANDER LINE STRUCTURE FOR MIMO APPLICATION Nasser Ojaroudi, 1,2,3 Mohammad Ojaroudi, 1,2,3 and Khodadad Halili 1,2,3 1 Department of Electrical Engineering, Ardabil Branch, Islamic Azad University, Ardabil, Iran 2 Young Research Club, Ardabil Branch, Islamic Azad University, Ardabil, Iran; Corresponding author: m.ojaroudi@iauardabil.ac.ir 3 Department of Electrical Engineering, Aeronautical University of Science and Technology, Tehran, Iran Received 18 November 2011 ABSTRACT: In this article, a novel wireless local area network (WLAN) frequency range monopole antenna is designed and manufactured for multi-input-multi-output (MIMO) applications. The proposed antenna consists of three pairs of folded L-shaped strips are placed side by side and printed on a dielectric substrate to generate triple-band operation which is suitable for WLAN applications. In this structure, each pair of L-shaped strips monopole antenna can create additional resonances within the WLAN range, which the desired resonant frequencies are obtained by adjusting the dimension of the folded L-shaped strips. The operating frequencies of the proposed antenna are 2.4/5.2/5.8 GHz which covers WLAN systems frequency range. Various conﬁgurations of array of this meander line structure monopole antenna for MIMO application are also studied. Prototypes of the proposed antenna have been constructed and studied experimentally. Good return loss and radiation pattern characteristics are obtained in the frequency band of interest. Simulated and measured results are presented to validate the usefulness of this proposed small antenna structure for MIMO applications. V C 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2168–2172, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27008 Key words: meander line structure monopole antenna; folded L-shaped strip; wireless local area network; multi-input-multi-output 1. INTRODUCTION In the last few years, there have been rapid developments in wireless local area network (WLAN). The 2.4/5.2/5.8 GHz (2.4– 2.84 GHz/5.15–5.35 GHz/5.725–5.825 GHz) bands are demanded in practical WLAN applications. During the last few years, there are various antenna designs, which enable antennas with low-proﬁle, lightweight, ﬂush mounted, and WLAN devi- ces. These antennas include the planar inverted-F antennas [1, 2], and the slot antennas [3, 4]. Its plenty of advantages, such as simple structure, small size, and low cost due to have received increased attention, especially planar monopole are extremely attractive to be used in WLAN applications, and growing research activity is being focused on them application in multi- input-multi-output (MIMO) systems. Consequently, a number of planar monopoles with different geometries have been experi- mentally characterized [5–7]. In this article, we propose a printed omni-directional antenna using side by side folded L-shaped monopole radiators. Three pairs of folded L-shaped strips radiating patch are printed on a dielectric substrate to generate triple-band operation at 2.4, 5.2, and 5.8 GHz is reported, which is suitable for WLAN applica- tions. The proposed antenna shows advantages of small size, low-cost, and good omnidirectional radiation characteristics. The presented monopole antenna has a small size of 12  18 mm 2 . Good return loss and radiation pattern characteristics are obtained in the frequency band of interest. Details of the 2168 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 54, No. 9, September 2012 DOI 10.1002/mop