Compact Elliptic-Function Low-Pass Filter Using Defected Ground Structure

A novel elliptic-function low-pass filter (LPF) is presented, which consists of a dumb-bell-shaped defected ground structure (DB-DGS), a spiral-shaped defected ground structure (SP-DGS) and a broadened microstrip line. The DB-DGS provides the required wideband attenuation in stopband, while the SP-DGS provides steep transition from passband to stopband. A 2.4 GHz five-pole LPF is developed and experimental results show that it has a sharp cutoff frequency response. The measured passband insertion-loss is below 0.3 dB, and the rejection band over 20 dB is from 2.95 to 8.25 GHz.