A tunable filter which may include at least one resonator. The at least one resonator may comprise a ring resonator made on a dielectric substrate placed in a waveguide, wherein the waveguide may contain a cut-off portion which houses and shields at least one resonator containing at least one tunable capacitor therein. A DC Bias circuit may be connected to the at least one resonator and may be capable of providing DC bias to the at least one tunable capacitor.