Design of second order band-pass filter with inductive π-network coupling

This study presents a method of realizing second order band-pass filters with planar inductive π-network. The proposed filter is more flexible in practical implementation than those using magnetic or electric coupling methods. Electromagnetic simulation results show that the bandwidth of the filter is quite insensitive to the variation in substrate thicknesses and physical layout. A 5.2 GHz filter prototype is designed and fabricated. The measured insertion loss is less than 2.3 dB in the designed pass band and the attenuations at the stop bands are all greater than 30 dB.