Compact microstrip dual-band bandpass filter with quarter-wavelength stepped impedance resonators

In this paper, a compact microstrip dual-band Chebyshev bandpass filter based on λ/4 stepped impedance resonators is designed, which are serially coupled by the alternative J and K inverters. Appropriate impedances and lengths of λ/4 stepped impedance resonators are synthesized based on the values of chosen dual-band K inverter. The dual-band coupled-line is then synthesized to render required J couplings at two central frequencies. Finally, a 4^th-order Chebyshev dual-band bandpass filter centering at 1.8 and 5.8 GHz with respective fractional bandwidths of 15.0% and 8.0% is designed and fabricated, and measured results show consistent match with the theoretical ones.