Design of a SIR bandpass filter with spurious passband suppression using defected ground structure and Spurline

A new structure of compact microstrip bandpass filter with wide out of band suppression has been proposed and implemented in this letter. It is proposed by using stub-loaded resonator, quarter-wavelength stepped impedance resonator (SIR), Dumbbell-Shape Defect Ground Structure (DGS) and symmetrical Spurline. By utilizing two forms of the SIR, the second harmonic can be eliminated. In order to suppress higher harmonics, the Spurline is needed. A dumbbell shape DGS which is etched in bottom-layer of the substrate, provides bandgap and slow-wave characteristics to improve the filter's performance. The BPF was fabricated, the measured results show that the proposed filter could obtain 20 dB rejection level in the stopband from 1.2 f₀ to 3.2 f₀. The experimental results show excellent agreements with theoretical results and the validity of the modeling method for the proposed compact bandpass filter.