compact low pass filter using sharp roll-off ultra-wide stopband t-shaped resonator

In this paper, an ultra-wide stopband microstrip low pass filter (lpf) with sharp roll-off and compact size is designed and fabricated. to provide very small dimensions, t-shaped and stepped impedance have been used. the cut off frequency at -3db is 3.1ghz. in the proposed structure, the insertion loss is lower than 0.12db and the return loss is greater than 15db. in order to achieve a -20db attenuation level in the stopband, a modified l-shaped structure is utilized. this filter has an ultra-wide stopband that is expanded from 3.37ghz to 37.5ghz. also, the suppression level is greater than -20db. the fabricated lpf has a size about 16.6 × 13.5 mm² which is equal to 0.28ƛg × 0.22ƛg, where ƛg is the guided wavelength at 3.1ghz, which is very small. the proposed filter is designed, simulated, optimized, fabricated and measured and we can see a good agreement between the simulations and measured results.