Design of low-pass microstrip filters based on defected ground structure

An improved periodic defected ground structure (DGS) is investigated for low-pass filter (LPF) applications. The realization in microstrip configuration consists in making the equivalence between the geometry of a DGS structure and a parallel LC resonator circuit. Initially, one filter is designed using identical DGS, equally spaced. Varying empirically the dimensions of the DGS, we obtain an improvement of frequency responses. In order to verify the performances of the proposed changes in the filter, simulations were done between the uniform periodic DGS circuit and the improved non uniform periodic DGS. The results show that the latter exhibits better stopband performance, with suppressing ripples and enlarging the bandwidth. One modified DGS filter was designed and fabricated. The measurements show good consistency with the simulated results.