Compact microstrip lowpass filter based on defected ground structure and compensated microstrip line

An improved defected ground structure (DGS) with compensated microstrip line is investigated for low-pass filter (LPF) applications. With this structure, the basic resonant element exhibits the elliptic-function low-pass responses. The use of introduced resonant elements allows sharp cutoff frequency response and high harmonic suppressions together with small size to be obtained with less number of periodic structures. An equivalent lumped L-C circuit model is presented and its corresponding L-C parameters are also extracted by using parametric relationships. Based on the equivalent circuit model, a 3-pole LPF, using 3 DGS units cascaded, is optimally designed and implemented; measurements show good consistency with calculations.