Third order wideband bandpass filter for ISM band using stepped and hairpin composite

This work describes the design of wideband bandpass filter for ISM 2.4 GHz band. Using the hairpin and stepped impedance filters, filter bandwidth of approximately 800 MHz is obtained without the sacrifice of insertion loss. FR4 material with dielectric constant 4.4 and height 1.6mm material is used as substrate. The observed return loss at center frequency is approximately -34 dB while the insertion loss varies in the range of -0.7 to -1 dB and found to be reasonably stable over the filter bandwidth. The structure uses basic principle of third order maximally flat bandpass filter design using composite structure.