Design of compact multilayered quad-band bandpass filter

In this paper, we proposed a compact quad-band bandpass filter (BPF) using multilayer substrate technique. The filter is designed to have quad-band at 1.8, 2.4, 3.5 and 4.2 GHz. The four passbands are simultaneously generated by controlling the impedance and length ratios of the stub-loaded stepped impedance resonators (SIRs). By using the stub-loaded SIRs, the filter with closed passbands can be easily achieved. The frequency response of wide stopband is generated by using the defected ground structure (DGS) and having around -25 dB stopband from 4.2 to 12 GHz. The filter can provide the multi-path propagation to enhance the frequency response and achieving the compact circuit size. The measured results are in favorable agreement with the full-wave electromagnetic (EM) simulation results.