Theory and experiment of wideband tunable forced‐mode ring resonator

For the first time a novel wideband tunable forced-mode ring resonator is proposed, which consists of a half guided-wavelength (λ g/2) ring resonator and two loading capacitors with different values. By controlling the respective values of the two capacitors, the fundamental resonant frequency (f fund) of the proposed ring resonator can be shifted up and down, resulting in a bi-directional tuning of f fund. With this new design, the tuning range of f fund can then be significantly extended to approximately double the range of the conventional tunable ring resonator. Meanwhile, no other resonance occurs in the wideband frequency-tuning range of f fund. The design equations of the proposed ring resonator are derived by using odd- and even-mode analysis, and the operating principle is investigated and presented. For demonstration, the proposed tunable technique is verified by the simulation and experiment, and the measured tuning range of f fund reaches 1.25 octaves, that is 0.68 → 1.53 GHz.