Compact, Low Insertion Loss and Ultra-Wide Rejection Bandwidth Microstrip Low- Pass Filter M. Challal 1 , A. Boutejdar 2 , M. Dehmas 1 and A. Azrar 1 1 Signals and Systems Laboratory, Institute of Electrical Engineers and Electronics, University of Boumerdes 35000 Boumerdes, Algeria E-mail: mchallal@gmail.com 2 Chair of Microwave and Communication Engineering, University of Magdeburg Magdeburg, 39106, Germany ABSTRACT In this paper, an ultra-wide rejection bandwidth compact microstrip low-pass filter with low insertion loss using two identical etched shapes in the ground plane and a compensated line is investigated. Its circuit model is as well presented. The proposed filter offers a low insertion loss of 0.1 dB and ultra-wide rejection bandwidth of more than 20 dB up to 20 GHz. The simulated results are found to be in good agreement with the measured ones. KEYWORDS Low-pass filter (LPF); Defected ground structure (DGS); Ultra-wide rejection bandwidth. 1 INTRODUCTION The rapid development of the advanced RF/Microwave wireless communication systems has generated an increasing research interest in performance improvement and size miniaturization. The design of low-pass filters (LPFs) with low cost, low insertion loss (IL), sharp rejection, wide stopband and compact size are greatly required in modern communication systems for suppressing the unwanted signals. One of the techniques that can be applied in microstrip LPF is using a defected ground structure (DGS) technique instead of cascading several resonator cells. Many types of LPF for performance improvement have been introduced [1-5]. Nevertheless, their performances such as stopband bandwidth, insertion loss and filter area do not completely achieve the communication systems requirements. In this work, an ultra-wide stopband compact LPF with low IL is designed using a novel shape of DGS and a microstrip compensated line. The proposed LPF offers a wide and deep stopband and, compact size than the conventional LPFs [2- 4]. Moreover, circuit model based on lumped elements is used to characterize the proposed filter. The substrate material used for the design is RO4003 material with a dielectric permittivity of 3.38 and a thickness of 0.813 mm. The electromagnetic (EM) and circuit model simulations show good agreement to the measurement results. 2 DGS-LPF DESIGN CONCEPT AND CIRCUIT MODELING The proposed LPF with its circuit model is shown in Figure 1. It is composed of a defected area etched in the ground plane under a 25 Ω compensated microstrip line (w 1 = 4.93 mm). The conductor strip of the 50 Ω microstrip line on the top plane has a calculated width w of 1.92 mm. The filter dimensions, r and g, are considered to be 5 and 2.5 mm, respectively. The structure can be modeled as one resonator along with two shunt capacitors Cp as shown in Figure 1.b. The circuit elements are extracted using the following expressions [5]: ) ( Z 2 C 2 c 2 0 0 0      (1) ISBN: 978-0-9891305-3-0 ©2013 SDIWC 127