Design of Microwave Filter

Abstract

The purpose of this final year project was to design a microwave filter using defected ground structure (DGS) technique. In this project, a novel turtle-shaped defected ground structure with three transmission zeros and a sharp selectivity was designed firstly. After that, the microstrip line was modified to obtain a good lowpass response. Therefore, a compact wideband DGS lowpass filter with good passband performance, good stopband performance and sharp selectivity was designed using one proposed DGS unit and the modified microstrip line. The lowpass filter was fabricated on a 3cm x 2cm printed circuit board. The substrate used was Duroid 6002-0300. A network analyzer was used to measure the filter. A reasonable agreement between the simulated and measured results was obtained. An equivalent circuit model of the filter was then analyzed and presented in this project. The agreement between the circuit simulated and electromagnetic simulated results is acceptable. According to the measured result, the proposed microwave lowpass filter operates from 1GHz to 10GHz. Its cut-off frequency, selectivity and stopband bandwidth are 2.8GHz, 96.4dB/GHz and 6.79GHz respectively.