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

A compact dual-band bandpass filter (DBF) based on quarter-wavelength (lambda/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 lambda/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 he 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.