Compact CSRRs-Based Metamaterial Band Stop Filter with Controlled Rejection Band Ehab K. I. Hamad and Hany A. Atallah Electrical Engineering Department, Aswan Faculty of Engineering, South Valley University, Aswan 81542, Egypt e.hamad@ieee.org and hany.mohamed@asw-eng.svu.edu.eg Abstract— in this paper, a compact band stop metamaterial filter based on complementary split ring resonators (CSRRs) is presented using relatively low dielectric constant substrate material (Rogers RT/Duroid 5870 ε r = 2.33). The presented filter combines a conventional band stop filter characteristics and negative permittivity metamaterial to establish a metamaterial filter. The negative permittivity metamaterial is made of CSRRs, etched on the ground plane. The effects of varying the geometry of CSRRs with such resonant elements are analyzed. In addition a new method is proposed to design metamaterial dual BSF, broadband BSF and LPF by transmission zeros control to adjust the rejection band of the BSF. The CSRRs can be tuned to reject the signals at slightly different frequencies and thus, give rise to a rejection band with a certain bandwidth, which can be extent to some and controlled with the number of CSRRs. The important size reduction achieved with the use of CSRRs to create BSF, dual BSF, broadband BSF and LPF is obviously very convenient. The frequency characteristics of the proposed filters are successfully optimized using numerical experimentation techniques. The results show that the compact LPF has an insertion loss less than 0.5 dB and a controlled rejection bandwidth using periodic structures of CSRRs (up to 3.56 GHz with about 45 dB attenuation). Simulations results based on a 3D full-wave electromagnetic simulator are presented in this paper. Keywords - Complementary split ring resonators, Dual band filter, Transmission zeros, Periodic structures metamaterials. I. INTRODUCTION Recently, pioneer research of the complementary split ring resonator (CSRR) has been proposed in [1-2] and can be derived from the SRR structure in a straightforward way by using the concepts of duality and complementarin- ess. This CSRR structure provides negative effective permittivity. Because of their small size CSRRs are called sub-lambda structures. Due to this fact, a super-compact stop band structure can be implemented using CSRRs. The CSRRs are etched on the ground plane or the conductor line of planar transmission structure, such as microstrip or coplanar waveguide [3, 4], and provide a negative effective permittivity to the dielectric media [5]. The electromagnetic (EM) behaviors of the CSRRs are similar to those of the electromagnetic bandgap (EBG) structures and/or the defected ground structures (DGS) [6, 7]. However, it is difficult to design the dimension and finding the equivalent circuits of EBG and DGS. Although EBG structures, DGS and CSRR can provide the similarly stop band characteristics, it may be worth pointing out the attenuation produced by CSRR is better than EBG structures and DGS. Size miniaturization of microwave filters is of much demand in the today’s rapid changing communication world. Even those filters size are large at the lower end of microwave frequencies. These components for metamaterials can design filter with improved filter characteristics and size miniaturization. Many microstrip filter designs have been proposed for size miniaturization [8] and performance enhancement in the past few decades but there are still some areas for improvements when using metamaterials [9]. In this paper, a compact metamaterial BSF is designed in microstrip technology by using artificial left handed metamaterials implemented by means of CSRRs, we will do a detailed parametric study of CSRR to demonstrate the effects of the geometry of the CSRR. There are two important factors such as cell dimensions (split ring radius) and split ring gap widths have been discussed in this work. Although some literatures have been reported [10], it still requires different viewpoint. On the other hand, the dual-stop band characteristics of the CSRRs can effectively apply on the CSRRs BSF by means of two CSRRs periodic structure etched on the ground for dual band suppression with availability of controlling the two bands by adjusting the CSRRs cut-off frequency. Also, the effect of the number of CSRRs etching and periodicity on the stop band filter performance will be proposed for LPF design. Such techniques give a very good miniaturization filter performance viz; sharp cut-off, very high rejection level and complete harmonic suppression without compromising the in-band filter performance. II. CSRR-BASED METAMATERIAL BSF Fig. 1(a, b) show the 2-D views (top and side views) of the single CSRR on the substrate of RT/Duroid 5870 with thickness of t = 0.508 mm, dielectric constant İ r of 2.33 and loss tangent tan į of 0.0009 which is commonly used. The CSRR structure is etched in the ground plane exactly below the center of a microstrip line of width 1.4 mm. The width of the microstrip line is designed to match the characteristic impedance of 50 Ω. All etched gap widths of the CSRR are d = c = g = 0.4 mm. When the electric field (E-field), which is concentrated between the conductor line and ground plane is vertical to the ground with the CSRR, a negative real permittivity can be obtained [11]. Fig. 1(c) shows the S-parameters of the single CSRR. The presented BSF optimized through simulations using a commercial 3D full-wave analysis software package Ansoft HFSS [12]. A CSRR structure is designed to operate at transmission zero 5.8 GHz of the IEEE802.11a WLAN band microwave frequency region