A novel miniaturized lowpass filter on Defected Ground Substrate for IEEE 802.16a applications

Miniaturized stepped impedance lowpass filters employing defected ground substrates (DGS) are proposed for IEEE 802.16a applications. The DGS slots are applied to the high impedance sections of the lowpass filter increasing the effective inductance of the circuit. A suitable combination of DGS slot, high impedance line and step discontinuity bring about an increase in the series inductance and result in a reduction in the filter length. The proposed model is validated by fabricating a lowpass filter for a cut-off frequency of 1.35 GHz on a glass epoxy substrate. The filter shows an insertion loss of around 0.5 dB and a return loss of around 20 dB in the desired cut-off frequency.