A planar resonator of quasi-lumped elements and its application to band-stop filter

A compact band-stop filter (BSF) using quasi-lumped elements is proposed in this paper. The BSF consists of shunt resonators cascaded by quarter-wavelength transmission lines. The resonator using an inductor line and a parallel plate capacitor as quasi-lumped elements is represented by a series LC lumped resonator. The one plate of the capacitor is placed at the back side of the substrate and spaced by slots from the ground conductor. Due to the current flow of the bottom plate near the slots, the proposed resonator has an extra inductance element. The design of the BSF was performed by optimizing each resonators. The measured results of the BSF agreed well with the simulated ones.