Compact quad-band filter using stub-loaded quarter-wavelength resonators and stub-loaded half-wavelength SIRs

This paper presents a quad-band filter using a set of stub-loaded quarter-wavelength resonators operated at the first and fourth passbands (1.8/5.8 GHz) and a set of stub-loaded half-wavelength SIRs operated at the second and third passbands (2.4/3.5 GHz). Furthermore, both of the loading stub are used to generate another passband. This study provides an effective method to design a quad-band filter with low insertion loss and compact size. Finally, the proposed filter is successfully fabricated and measured. It is shown that the measured and simulated performances are in good agreement.