Design of Low Pass Filters Using a Symmetrical T-Shaped Defected Microstrip Structure

This paper describes the design of microwave low pass filters (LPF) using a symmetrical T-shaped defected microstrip structure (DMS). The equivalent inductance and capacitance are extracted from the electromagnetic simulation of the unit DMS pattern. After designing a microstrip prototype LPF at a normalized frequency, scaling to LPF is performed. The size of the DMS pattern corresponding to the required inductance and capacitance for the LPF design is determined by the established equations or curve-fitting process. Afterwards, open stubs are connected for shunt capacitance to complete the design. As a design example, a 9-pole DMS LPF with 3 GHz of cutoff frequency is designed and measured. The proposed DMS LPF has better attenuation characteristics, wider rejection band and miniaturized layout by 17% compared to the LPF designed according to conventional design. It is also suggested that the measured performances agree excellently with the prediction without any additional tuning. Copyright © The Korean Institute of Electrical Engineers.