In this paper, a modified semi-circle patch and a semi-circle stepped impedance resonator are cascaded to design a compact lowpass filter with sharp response and wide stopband. This filter has 3-dB cutoff frequency at 1.55GHZ. The transition band is only 0.29GHZ from 1.55 to 1.84GHZ with -3dB and -20dB respectively. Maximum insertion loss is 0.4dB in the passband and stop bandwidth with attenuation level better than -20dB extends from 1.84GHZ up to 12.5GHZ and up to 15GHZ is greater than -10dB, hence wide stopband is achieved. Simulation and measurement results are presented and good agreement between them is achieved. Results show that we have obtained a high Figure-of-Merit (FOM) of 30433.