This paper presents a microstrip lowpass filter with compact size, and ultra-wide stopband. The structure consists of a modified hairpin resonator loaded with tapered cells and the circular patches as the suppressing cell. The proposed lowpass filter has ¡3 dB cut-off frequency at 1.64 GHz. It also has suitable performances such as: ultra-sharp transition-band of 0.09 GHz that is from ¡3 to ¡20 dB, an extended stopband bandwidth from 1.73 to 21 GHz with the attenuation level more than ¡20 dB, low insertion-loss, flat group delay in the passband, and simple structure. The proposed lowpass filter is simulated and fabricated and there is good agreement between the simulation and measurement results.
