A Novel Compact Microstrip Low-pass Filter with Sharp Transition band using Stepped-Impedance and Semi-circular Units

A novel compact microstrip low-pass filter (LPF) has been proposed using stepped impedance and semi-circular units, which are symmetrically loaded as resonator. The proposed LPF has achieved a sharp transition band and improved pass-band and stop-band characteristics. The filter with -3 dB cut-off frequency at 2.25 GHz has been designed, fabricated and measured. The proposed LPF has been fabricated on a RT/Duriod 5880 substrate (r = 2.2, thickness = 15 mil, loss tangent of 0.0009). Physical size of this work is only 18.2 mm × 10.67 mm. The low-pass filter has an insertion loss of less than 0.05 dB in the pass-band. The rejection bandwidth is from 2.5 to 8.8 GHz for attenuation level of -20 dB. The simulated and measured results are in good agreement and validate the advantages of the proposed lowpass filter. According to the mentioned advantages, the proposed LPF can be a good choice to suppress the unwanted signals and harmonics in modern communications systems

Keywords:

Low-pass filter , Microstrip , Wide stopband