Compact multimode bandpass filters with wide upper stopband using dual-mode DGS resonators

A novel compact dual-mode DGS resonator (DMDGSR) is proposed, which is composed of a folded slot line resonator (FSLR) and a coplanar stepped impedance resonator (CSIR), each of them controls one resonant mode. By adding end-coupled microstrip feeding lines, a simple compact dual-mode bandpass filter (BPF) can be designed with two transmission zeros beside the passband and behaves a wide upper stopband to as far as 12 GHz with rejection better than 20 dB. As extensions, a quad-mode BPF as well as a hex-mode one is designed and fabricated by simply series connecting two or three such DGS segments. The two BPFs have a simple structure, wide upper stopband and good selectivity.