Miniaturized Triple-Band Bandpass Filter Using Coupled Lines and Grounded Stepped Impedance Resonators

A triple-band bandpass filter with good selectivity based on modified grounded stepped impedance resonators (SIRs) is presented. The fundamental and first higher order resonances of the two λ/4 grounded SIRs are utilized to obtain dual-band response. Moreover, bandwidths of the two passbands can be controlled by tuning the distance between the two grounded vias. Owing to the use of two λ/2 fork resonators, another passband can be realized without increasing additional feedlines, which can be designed independently while other passbands are not affected. Several transmission zeros (TZs) are generated on each side of the passbands to obtain good selectivity. The λ/4 SIRs are embedded inside of the λ/2 fork resonators to realize miniaturization. The measurement and simulation results show good agreement.