THE INSTITUTE OF ELECTRONICS, VJMW 2015 INFORMATION AND COMMUNICATION ENGINEERS Copyright ©2015 by IEICE X-band Broadband Array Antenna Design For Radar Applications Using Defected Ground Structure (DGS) Nguyen Ngoc Lan†, Duong Thi Thanh Tu‡ and Vu Van Yem† † School of Electronics and Telecommunications, Hanoi University of Science and Technology ‡Post & Telecommunications Institute of Technology E-mail: †{dtvt2006@gmail.com, yem.vuvan@hust.edu.vn}, ‡tudtt@ptit.edu.vn Abstract This paper proposes a broadband array microstrip antenna design at X-band. The antenna comprises a 4-element linear array and it is based on FR4 substrate (hsub = 1.6 mm, εr = 4.4 and tanδ = 0.02). The antenna is designed, simulated and implemented at 9.7 GHz by using Defected Ground Structure (DGS). The bandwidth of antenna is 700 MHz. Moreover, the array antenna has high gain (approximate 12 dB) and small size (75 x 60 mm). Therefore, it is enough for X-band applications. The antenna has advantages: small size, light weight, low cost and fabrication. All results are simulated in CST Microwave Studio software. Keyword: array antenna, Defected Ground Structure (DGS), microstrip patch antenna, antenna geometry, radar 1. Introduction Nowadays, modern wireless communication system requires low profile, light weight, high again, and simple structure antennas to assure reliability, mobility, and high effciency characteristics[1]. Microstrip technology satisfies all requirements above. However, two main disadvantages of microstrip antenna is narrow bandwidth, low gain. Therefore, this paper using Defected Ground Structure (DGS) to extend bandwidth and increase gain for antenna. There are many ways to improve the bandwidth and gain for antenna was introduced[2-5]. However, one of simple and effective way is using DGS. DGS is an etched periodic or non-periodic cascaded configuration defect in ground of a planar transmission line which disturbs the shield current distribution in the ground plane cause of the defect in the ground[6]. Therefore, this is increasing capacitance and inductance. Depeding on the frequency, the size and shape of ground, we have the diffenrent of DGS size. Besides, antenna geometry also contributes miniaturization and increasing gain. The different radar systems operate in L, C, and X bands. X-band (8-12 GHz) is used for missile guidance, short-range tracking, mapping, marine radar, airborne intercept[7]. In this paper, the antenna is designed at the center frequency of 9.7 GHz. The array antenna includes an 4-element linear array, based on FR4 substrate with parameters: hsub = 1.6 mm, εr = 4.4 and tanδ = 0.02. The distance The distance between antennas is λ0/2 (λ0 is the wavelength in free space). The remained part of this paper is organized as follow. The antenna parameters and its structure will be presented in Section II. The simulated and measurement results are shown in Section III, while some conclusions are given in Section IV. 2. Antenna design 2.1 DGS The dumbbell DGS are composed of two a × b rectangular defected areas, g × w gaps and a narrow connecting slot wide etched areas in backside metallic ground plane as shown in Figure 1. DGSs have the characteristics of stopband, slow-wave effect and high impedance [6]. Figure 1: Dumbbell DGS unit The DGS has the property of single pole low-pass, so the equivalent circuit parameters of DGS are easier to obtain. The DGS has main two types, that is DGS unit and periodic DGS. The type of DGS unit has different shapes, and some shapes is shown in Figure 2. While the period DGSs care about parameters including the shape of unit DGS, distance between two DGS units and the distribution of the different DGSs[7].