ADVANCED ELECTROMAGNETICS, VOL. 7, NO. 2, MARCH 2018 A Triple-band Suspended Microstrip Antenna with Symmetrical U- Slots for WLAN/WiMax Applications Seshadri Binaya Behera 1 , Debaprasad Barad 2 , and Subhrakanta Behera 3 123 School of Electronics Engineering, KIIT University, Bhubaneswar-24, India. *corresponding author, E-mail: subhrajsp@gmail.com Abstract In this study, a triple-band suspended microstrip antenna with symmetrical U-slots is proposed for modern wireless communication systems. The antenna is specifically designed to acquire application in WLAN and WiMAX communication. Symmetrical U-slots in the radiator patch increase the number of resonances and improve the gain response. An appropriate air height was maintained between the ground plane and the radiator patch layer for improving bandwidth operation. The impedance characteristics of the antenna are enhanced using probe feeding techniques. The proposed compact antenna is designed on a single dielectric substrate of (30×25×1.56) mm 3 . Parametric analysis of the proposed structure has been realized using IE3D software. This prototype exhibits maximum impedance bandwidth of 750 MHz and gain response of 7.28 dBi. The performance of the structure at three resonating bands i.e., at 3.3 GHz, 3.78 GHz and 5.3 GHz facilitate it to be applicable for WLAN/WiMAX systems. Keywords: High Gain; Microstrip Antenna; Multiband; U-Slots; Suspended antenna patch; WLAN/WiMAX. 1. Introduction Microstrip antenna offers extensive applications in wireless communication systems due to its low profile, light weight and ease of integration with the RF/Microwave systems [1]. Lately, many researchers have drawn their attention towards the design of compact microstrip antennas which can operate over a wide range of frequencies. In some cases it is desirable to incorporate a single antenna which can support two or more applications simultaneously. These types of antennas are referred as “Multiband” antennas; particularly, multi-frequency antenna for multi-standard communication. In 1978, G.G. Sanford [2] introduced the concept of using a microstrip antenna for achieving multiple resonances. Later, many authors [3-5] worked on the same concept and developed several multiband antenna models. S. Long and M. Walton [3], investigated a stacked circular- disc printed-circuit antenna for dual-frequency behavior. Single-feed microstrip antenna using multi-element radiator patch with a common input point was invented by C. kaloi [4] in 1981. A single-element microstrip antenna with shorting pins was investigated for dual-frequency operation [5]. However, narrow impedance bandwidth is a major disadvantage of using a microstrip antenna. Various techniques can be found in literature to overcome this problem. In [6], the authors used CPW feeding technique to enhance the impedance bandwidth of patch antenna. X.L. Sun, et al. [7] proposed a patch antenna structure with compact radiator patches which covered all the bands of WLAN i.e., 2.4/5.2/5.8 GHz with better impedance bandwidth characteristics. Use of meander lines[8] and PIFA related miniaturized antennas [9] are also found in literature for the same purpose. However, introduction of U- slots on patch antenna is a very popular method to achieve wideband characteristics. In 1995, T.Hyunh [10] first introduced U-slots on microstrip antenna and increased the impedance bandwidth up to 10-30 %. Later, several research works have been carried out using U-slots to obtain wideband characteristics [11-13]. Also, these U-slots create discontinuities in the current flow path, thus creating multiple paths for current flow of the patch surface. This enables the microstrip antenna to show multiband behavior. This work focuses on designing a compact patch antenna with simple structure which can operate in both WLAN (5150 MHz-5350 MHz) and WiMAX (3.2-3.8 GHz and 5.2-5.8 GHz) bands with good impedance bandwidth and good boresight gain. Some of the previously reported antenna structures in the literature are compared with the proposed antenna in Table 1. In this paper, a triple-band microstrip antenna with symmetrical U-slot and two half U-slots is investigated. The multi-resonance characteristics are achieved by introducing U-slots at appropriate positions with respect to the feeding point, which enables the antenna to first resonate at 3.3 GHz and later at 3.78 GHz, 5.3 GHz. The antenna patch is placed above the ground plane by maintaining a suitable air height in between the two layers to enhance the antenna performance. The impedance characteristics of the antenna are enhanced using probe feeding techniques. The antenna yields a maximum impedance bandwidth of 750 MHz with the maximum gain response of 7.28 dBi by optimizing the air layer height and the dimension of U-slot. A parametric study of various factors of the proposed antenna structure is executed. The simulation results obtained were validated with experiment and both the results match well. As observed in Table 1, the proposed antenna exhibits better