An Ultra-Wide Stop-Band LPF Using Asymmetric Pi-Shaped Koch Fractal DGS

Defected ground structure (DGS) with symmetrical geometry has been widely adopted in low-pass filter (LPF) designing, while asymmetrical geometry DGS can exhibit some specific features on transition band and stop-band. A novel asymmetrical Pi-shaped DGS with Koch fractal curve is proposed in this paper to design a low-pass filter (LPF). The designed LPF with a single resonator and two cascaded resonators are both simulated and tested. Simulation and experiment results demonstrate that the designed LPF has a very sharp transition and an ultra-wide stop-band performance compared with the existed similar symmetrical and asymmetrical DGS. The proposed LPF with two cascaded resonators is with a compact size of 36 × 22 mm2, a very low insertion loss of less than 0.7 dB from 0 Hz to 1.9 GHz, and a wide stop-band from 2.1 to 12 GHz with a rejection of greater than 25 dB.