Dual-mode filter using ring resonator with non-uniform linewidth
A dual-mode bandpass filter is proposed using a single ring resonator with non-uniform linewidth. The proposed filter consists of a circular patch with a circular hole and two chip inductors loaded into the gap in the ring. The non-uniform linewidth ring resonator can be realised by moving a circular hole in the circular patch. This asymmetric structure creates a pair of degenerate modes, and thus acts as a dual-mode filter. Two inductors applied to the gap generate one transmission zero on each side of the passband, improving the skirt characteristics of the filter. In addition, a dual-mode filter with the same characteristics is implemented by replacing the chip inductor with a meander line.
