Design of Planar Low Pass Filter with Razor-sharp Roll-off

The design and development of a microstrip low pass filter with sharp selectivity and wide fractional stop band bandwidth by employing high and low impedance resonators is presented in this paper. The designs of individual resonators are studied with equivalent circuit. The measured results validate the simulated results. Filter exhibits a razor-sharp roll-off of 289 dB/GHz after 1.98 GHz cut-off and achieves a wide relative stop band bandwidth of 147% with suppression level better than 20 dB.