A stepped impedance resonator (SIR) based wideband bandpass filter (BPF) with a good rejection level in the extended upper stopband is presented in this article. The proposed SIR is found to have the ability to introduce two transmission poles in the passband. By appropriately selecting the impedance ratio and length ratio (α) of the SIRs, the BPF can provide a wide passband and a sharp rejection over a broad stopband. Based on SIRs, a bandpass filter is designed with two transmission zeros. To improve the stopband, two stubs have been introduced in input/output (I/O) lines. The susceptibility test has been accomplished to check whether the filter will be able to operate satisfactorily in the presence of interfering signals. The filter has been fabricated and measured. Both simulated and measured results are presented.

Keywords: Defected ground structure (DGS), Electromagnetic bandgap (EBG), Microstrip bandpass filter (BPF), Susceptibility