The design of closed loop type BPF with two attenuation poles at the upper side of passband

In this paper, a new design method of a BPF which has two attenuation poles at the upper side of the passband, using closed loop type resonator and perturbation elements, is presented. The closed loop resonator based on the TEM mode is analyzed by the network analytical method, and the effect of the perturbation element is investigated. The advantage of this method is the high attenuation at the upper side of the passband because of the two attenuation poles. To prove the usefulness of the proposed synthesis method, the simulation data are compared with the experimental result measured by a vector network analyzer (VNA). There is good agreement between them.