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BAND-NOTCHED LOW PROFILE MONOPOLE ANTENNA WITH ENHANCED BANDWIDTH BY USING AN INVERTED T-SHAPED PARASITIC STRUCTURE AND A PAIR OF G-SHAPED SLOTS M. Ojaroudi 1 and Y. Ojaroudi 2 1 Department of Electrical Engineerimg, Germi Branch, Islamic Azad University, Germi, Iran; Corresponding author: m.ojaroudi@iaugermi.ac.ir 2 Department of Mathematics, Germi Branch, Islamic Azad University, Germi, Iran Received 15 July 2011 ABSTRACT: In this letter, a novel printed monopole antenna for ultra wideband applications with variable frequency band-notch characteristic is presented. The proposed antenna consists of a forked-shaped radiating patch with an inverted T-shaped parasitic structure and a ground plane with a pair of G-shaped slots, which provides a wide usable fractional bandwidth of more than 130% (2.9–14.1 GHz). To generate frequency band-stop performance, the forked-shaped strips are folded back and result in a pair of coupled lines on the radiating patch that we can control band-stop performance characteristics such as band-notch frequency. By inserting an inverted T-shaped parasitic structure on the radiating patch and also by cutting a pair of G-shaped slots with variable dimensions on the ground plane, additional resonances are excited and hence much wider impedance bandwidth can be produced, especially at the higher band. The designed antenna has a small size of 10 Â 16 mm 2 while showing the band rejection performance in the frequency band of 5–6 GHz. Simulated and experimental results obtained for this antenna show that it exhibits good radiation behavior within the UWB frequency range. V C 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1123–1127, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/ mop.26770 Key words: monopole antennas; ultra-wideband applications; microstrip antennas 1. INTRODUCTION It is a well-known fact that planar monopole antennas present really appealing physical features, such as simple structure, small size, and low cost. Because of all these interesting characteristics, planar monopoles are extremely attractive to be used in emerging UWB applications, and growing research activity is being focused on them. Consequently, a number of planar monopoles with differ- ent geometries have been experimentally characterized [1–4]. The frequency range for UWB systems between 3.1 and 10.6 GHz will cause interference to the existing wireless communica- tion systems, for example, the wireless local area network (WLAN) for IEEE 802.11a operating in 5.15–5.35 GHz and 5.725–5.825 GHz bands, so the UWB antenna with a band-stop performance is required. Recently, to generate the frequency band-notch function, modified planar monopoles have been recently proposed [5–9]. In Refs. 5–7, different shapes of the slots (i.e., square ring with a pair of T-shaped strips protruded inside it, W-shaped and folded trapezoid) are used to obtain the desired band notched characteristics. Single and multiple [8] half-wavelength U-shaped slots are embedded in the radiation patch to generate the single and multiple band-notched func- tions, respectively. In Ref. 9, band-notch function is achieved by using a T-shaped coupled-parasitic element in the ground plane. In this letter, a new band-notched printed monopole antenna (PMA) is presented. The notched band, covering the 5–6 GHz WLAN band, is provided by using two forked-shaped strips. Unlike Refs. 5–9, in our model, the notched band, covering the 5–6 GHz WLAN band, is provided by using electromagnetically coupling between a pair of coupled lines on the radiating patch and also by inserting an inverted T-shaped parasitic structure in due to creating additional path for current distribution this per- formance is improved. In this structure, by inserting an inverted T-shaped parasitic structure and also by cutting a pair of C- shaped slots with variable dimensions on the ground plane, addi- tional resonances are excited and hence much wider impedance bandwidth can be produced, especially at the higher band. The size of the designed antenna is smaller than the UWB antennas with band-notched function reported recently [5–9]. Experimental and simulated results of the constructed prototype are presented. 2. ANTENNA DESIGN The proposed monopole antenna fed by a 50-X microstrip line is shown in Figure 1, which is printed on a FR4 substrate of thickness 0.8 mm, permittivity 4.4, and loss tangent 0.018. The proposed antenna is connected to a 50-X SMA connector for signal transmission. The optimal dimensions of the designed antenna are as follows: W sub ¼ 10, L sub ¼ 16, W ¼ 8, W f ¼ 1.5, L d ¼ 3, W S ¼ 1, L S ¼ 1, W S1 ¼ 1, L S1 ¼ 4, W S2 ¼ 1, L S2 ¼ 4.5, L S3 ¼ 1, W S3 ¼ 5, g ¼ 0.5, W g ¼ 2, L g ¼ 0.5, W g1 ¼ 3.5, L g1 ¼ 2.5, W g2 ¼ 0.5, L g2 ¼ 1, and L gnd ¼ 4 mm. DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 54, No. 5, May 2012 1123