Redesign of a Dual-mode Ring Resonator Using Composite-Right/Left-Handed Line

This paper considers a redesign of a dual-mode ring resonator with suppression of the second harmonic. The suppression is achieved by incorporating a composite- right/left-handed (CRLH) line in the ring resonator. It is shown that the phase shift expression for the CRLH line cannot explain ring resonance. Further, it is shown that the earlier design produces resonance at a frequency which is about half the frequency of the first harmonic of the ring resonance. A redesign, reducing the sub-harmonic resonant frequency as well as eliminating lumped inductors, is proposed. It is shown that the frequency difference between the dual modes is determined by the mismatch of the image impedance of the left-handed (LH) line and the characteristic impedance of the right-handed (RH) line.