A DUAL-BAND WLAN/UWB PRINTED WIDE SLOT ANTENNA FOR MIMO/ DIVERSITY APPLICATIONS Sajad Mohammad, ali nezhad, Hamid Reza Hassani, and Ali Foudazi Department of Electrical and Electronic Engineering, Shahed University, Tehran, Iran; Corresponding author: hassani@shahed.ac.ir Received 10 June 2012 ABSTRACT: In this article, a dual-band WLAN/ultrawideband (UWB) printed wide slot microstrip-fed antenna is presented for multi-input multi-output (MIMO)/diversity applications. The proposed antenna consists of a U-shaped patch, a T-shaped monopole path, and a pentagonal wide slot in the ground plane. The antenna is designed to cover both the WLAN (2.4–2.485 GHz) and UWB (3.1–10.6 GHz) ranges, with value of S 11 below 10 dB. The antenna is constructed on a FR4 substrate with overall dimensions of 28  28  1 mm 3 . It is shown that the proposed dual-band antenna is suitable for diversity polarization applications. The simulation results show that the different conﬁgurations of the antenna in the MIMO/diversity have good S- parameters over the operating frequency bands. The simulation and measured results of the proposed dual-band antenna as well as that of the MIMO/diversity antenna conﬁguration agree well. V C 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:461–465, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27391 Key words: ultrawideband antenna; monopole antenna; multi-input multi-output; diversity 1. INTRODUCTION Multi-Input Multi-Output (MIMO) communication systems due to their ability to reduce multipath fading and increased channel capacity are of importance in wireless communication systems. Ultrawideband (UWB) MIMO communication systems can fur- ther increases the capacity of channel in comparison with nar- rowband MIMO systems [1]. From a MIMO antenna array one requires features, such as compact structure, high radiation efﬁ- ciency, low envelope correlation, and high isolation between the signal ports [2]. To achieve maximum channel capacity, the array with high gain and wide lobe pattern is required [3]. An important element in a MIMO/diversity system is the antenna structure. The printed antennas are strongly favored for their attractive features of low cost, easy fabrication, and their capability of integration with small terminal devices [3–7]. To design a UWB MIMO/diversity antenna, the mutual cou- pling between antenna elements should be low. Several techni- ques have been used in the literature to improve the isolation characteristics between the elements. Common to all these tech- niques is the use of external slits/strips in between the array ele- ments. By inserting slits in the ground plane of the structure, isolation is improved [4]. By introducing protruding strips in the ground plane in between the array elements mutual coupling can be reduced, [5, 6]. Printed monopole wide slot antennas can be more desirable as they can provide higher gain in comparison with printed monop- ole antennas. Design of a UWB antenna, using different shapes of printed microstrip-fed wide slot antenna is presented in Refs. 8 and 9. To obtain a multiband printed antenna which also includes the UWB range, Ref. 10has used an L-shaped resonant element at the corner of a UWB printed monopole antenna. This integrates the Bluetooth band with the existing UWB band and the overall dimension of antenna is 42  48  1 mm 3 . In this article, a new printed wide slot antenna conﬁguration suitable for the design of a multiband MIMO/diversity antenna that includes the UWB range and an extra band below the UWB range is presented. Unlike the previously reported methods, in the new design there is no need for any external slits/strips. Dif- ferent MIMO antenna array conﬁgurations are considered and S- parameter results are provided. The simulations are carried out using the commercially available software package HFSS and results are compared with those of measurement. 2. ANTENNA DESIGN To have a UWB diversity antenna, the antenna element should be designed in such a way that it has high gain, wide lobe pat- tern, and low mutual coupling. Printed UWB monopole antennas are able to provide a wide lobe pattern (omnidirectional), whereas printed wide slot antennas, due to their larger ground plane, can also provide a higher gain. In the printed slot anten- nas, there is a slot within the ground plane unlike the case of a monopole antenna with limited ground at the bottom of the structure. The presence of the ground edges in the slot can lead to a better reduction in mutual coupling when an array is formed as compared to that of a monopole structure. Thus, in this work, a printed wide slot antenna is used [11]. To design a UWB printed wide slot antenna, the structure of Figure 1 is considered which is simple and has a few parame- ters. The dimension of the antenna is 28  28  1 mm 3 and is fabricated on FR4 substrate with effective permittivity of 4.4 and loss tangent of 0.02. A simple pentagonal slot in the ground plane is used to obtain omnidirectional radiation pattern and wide impedance bandwidth. The slot is fed by a simple rectan- gular patch in which a half ellipse is removed, leading to a tapered U-shaped patch. The radius of the ellipse in the x- and y-directions is set at 5 and 8 mm, respectively. The patch is fed by a feed line of width ﬁxed at 1.86 mm that provides 50 X input impedance. Figure 1 Printed planar slot antenna with UWB/WLAN bands. [Color ﬁgure can be viewed in the online issue, which is available at wileyonlinelibrary.com] DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 55, No. 3, March 2013 461