Very thin open ring resonator BPF with flexible control of bandwidth

A new use of broad-side coupled resonators has been proposed. It is a low-profile BPF that has versatile bandwidth control ability of almost several hundred times. Against the common understanding that broad-side arrangement of resonators only gives a strong coupling and thus a broad-bandwidth BPF, we found the narrower distance rather results a weaker coupling if the relative rotation angle of each resonator is adjusted to be around zero.