Stepped-Impedance Defected Ground Structure

The negative image of a microstrip stepped-impedance lowpass filter (LPF) or hi-Z, low-Z filter is used on the ground plane to produce wide and deep stopband. This structure is simpler in design and more compact in size compared to conventional bandstop structures. The simulation and measured results show good agreement in 2.6 GHz 20-dB rejection bandwidth at 4 GHz center frequency. This distinct stopband characteristic can be applied to devices such as filters, antennas and coplanar waveguide to suppress harmonics and enhance performances such as better gain and isolation.