In this letter, a new design method of ultra wideband bandpass filter (UWB BPF) is proposed. Based on a symmetrical structure of a simple uniform line loaded by a stepped-impedance open stub (SIS) connected at its center, the proposed design method employs simultaneously the optimization of a defined objective function in the range of frequency 3.1-10.6 GHz and the transmission zeros at cut-off frequencies for a rapid convergence.

Obtaining different filter sizes with good performance, the compact UWB BPF is simulated, fabricated, and measured. A good agreement between simulation and measurement is obtained while achieving good performances such as a return loss better than 10 dB, an upper stopband attenuation higher than 20 dB up to 17.6 GHz, and a sharp selectivity.