Razi University

   In this thesis a microstrip low-pass filter with a cutoff frequency of 2.4 GHz is designed using modified split-ring resonators. The proposed structure consists of a main transmission line two open-circuited stubs and two modified split-ring resonators. In the proposed resonator the outer ring features one gap while the inner ring features four gaps.       The filter is designed and fabricated on an FR4 substrate with a relative dielectric constant of ?r = 4.6 and a thickness of 1.6 mm. The overall dimensions of the structure are 29?97×18?86 mm . To analyze the electrical behavior of the structure, LC equivalent circuits were developed for the initial structure, the resonator, and the final structure; their responses were then compared with the results obtained from layout simulations.       Layout simulation results indicate that the filter's cutoff frequency at the -3 dB level is 3.318 GHz; the S11   lot remains below -20 dB up to approximately 1.5 GHz, and transmission zeros are located around 3.2 GHz, 3.6 GHz, and 5.0 GHz. Furthermore, measurement results confirmed the low-pass filter behavior and the transmission zeros, and the discrepancies relative to the layout simulation were analyzed.       Keywords:Microstrip Low-Pass Filter – Modified Split-Ring Resonator – Transmission Zero – Compact Dimensions – Stopband