Design of Reconfigurable Defected Ground Structure (DGS) for UWB Application Z. Zakaria, N. A .Shairi, R. Sulaiman and W. Y. Sam Department of Telecommunication Engineering, Faculty of Electronic and Computer Engineering, Universiti Teknikal Malaysia Melaka (UTeM), Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia. E-mail: zahriladha@utem.edu.my,noorazwan@utem.edu.my, rushilawaty@gmail.com, samwengyik2@hotmail.com Abstract—This paper presents the design of reconfigurable defected ground structure (DGS) resonator that can be integrated with ultrawide-band (UWB) microwave filter to produce bandpass and bandstop response simultaneously. The reconfigurable DGS is designed based upon coplanar waveguide (CPW) technology to exhibit bandstop characteristic at 3.5 GHz and 5.5 GHz using FR-4 on a 1.6 mm dielectric substrate thick with dielectric constant   = 4.6. The simulation performance shows promising results that could be further validated during the experimental works. This topology of reconfigurable DGS is useful for applications when the undesired signals need to be removed such as in wideband systems. Keywords-Defected Ground Structure (DGS); Coplanar Waveguide (CPW); Ultra-wideband (UWB) I. INTRODUCTION The increasing development of wireless applications introduces new requirements for transceiver architecture that feature excellent performance and enhanced integration density. Since 1998, photonic band gap (PBG) structures [1] and defected ground structures (DGS) [2] have attracted the interest of many researchers. The used of DGS technology into coplanar waveguide transmission lines (CPW-TL) [3] compared to conventional transmission lines have many advantages such as to allow a simple reconfiguration as well as it is a very compact solution [4-7]. Furthermore, high performance, compact size and low cost often meet the stringent requirements of modern microwave communication systems. In 2002, the Federal Communication Commission (FCC) authorized the frequency band from 3.1 GHz to 6.1 GHz for commercial applications [8]. Since then, there have been considerable research efforts put into ultra-wideband (UWB) radio technology worldwide. The UWB frequency band of 3.1 GHz to 10.6 GHz are interfering with the wireless local network signals such as WiMAX frequency at 3.5 GHz [9], and the WLAN systems operate in the 5.0 GHz frequency bands, e.g., 5.15 to 5.35 (IEEE 802.11a lower bands) and 5.725 to 5.825 GHz (IEEE 802.11a upper bands). Hence, a compact microwave bandpass filter working in the UWB system requires a design of reconfigurable bandstop filter in order to avoid being interfered by the undesired signals such as the WLAN radio. In this paper, the design of reconfigurable defected ground structure (DGS) using coplanar waveguide (CPW) technology based on the study investigated in is presented. II. DESIGN OF DGS The design of the DGS is realized using coplanar waveguide (CPW). The procedures of realizing the structure can be found in [10] and [11]. Fig. 1 shows the layout for the dumbbell-shaped DGS resonator. It consists of a single square resonator whose pattern is etched in the ground plane of the CPW with a slot width, c. Figure 1. Schematic diagram of DGS (half symmetrical view) This structure is designed using FR4 substrate with dielectric constant,  r = 4.6, dielectric thickness, h = 1.6 mm, copper thickness = 0.035 mm, and loss tangent 0.019. CPW parameters are G/W/G = 0.715/4/0.715 mm in order to attain 50 Ω of input line impedance. The dimensions of A, B, C and D can be determined depending on resonant frequency and can be calculated according to the literature in [4]. A. Design of DGS at 3.5 GHz Fig. 2 (a) shows the geometrical layout for the DGS to resonate at 3.5 GHz. The design is based on a single square resonator and constructed using Momentum Advanced Design System (ADS). The dimensions of the structure: A = 7 mm, B = 7 mm, C = 0.5 mm and D = 1 mm. The structure produces a single transmission zero at 3.5 GHz. The photograph of the fabricated DGS is shown in Fig. 2 (b), whilst the simulated and measured responses are shown in Fig. 2 (c). It can be observed that the insertion loss of -18 dB and a -10 dB bandwidth of 0.65 GHz are obtained particularly in the stopband. The Top-layer (copper) Square resonator 2012 IEEE Asia-Pacific Conference on Applied Electromagnetics (APACE 2012), December 11 - 13, 2012, Melaka, Malaysia 9978-1-4673-3115-9/12/$31.00 ©2012 IEEE 195