Abstract: This paper describes an advanced design systems (ADS) approach of stepped impedance microstrip low pass filter design for maximally flat or Butterworth responses. The cut-off frequency is 4 GHz with source and load impedances of 50 Ω. The insertion loss at passband is 0.5 dB and stopband is 20 dB. In this filter design, an order N=7 was chosen for maximally flat (Butterworth) filter prototype. Substrate properties such as relative dielectric constant ∈_r = 4.2, loss tangent tanδ=0.02, height of dielectric material h=2.0 mm and conductor thickness of 0.01 mm were used in calculation of the length and width of the transmission line. Design of lumped circuit for microwave filter prototype scaled in frequency and impedances is discussed. Equivalent transmission line was obtained by converting lumped circuit into certain lengths and characteristic impedances. ADS simulation software was used to plot maximally flat filter characteristics. The plots show variation of incident wave S(1,1) and forward gain S(1,2) with frequency in GHz.