Compact Dual-band Filter Based on Quarter-Wavelength SIRs with Grounded via coupling

A compact dual-band bandpass filter (DBF) based on quarter-wavelength (λ/4) stepped impedance resonators (SIRs) with miniaturized size is presented in this Letter. The compact size of this filter is realized by using the common grounded via hole and the folded λ/4 SIRs. Common grounded via is used to adjust the coupling coefficient of the dual-band filter. The coupling path to the input/output (I/O) ports of this dual-band filter are two different space thus external quality factor of single passband can be determined independently. Two transmission zeros (TZs) is introduced between passband to realize a sharp skirt characteristics. Finally, a prototype dual-band filter centering at 4.4GHz and 7.4GHz is designed and fabricated. Simulation and measurement results are in good agreement.