Tuning circuit based on varactor for tunable filter

A tuning concept of a quarter wavelength side-coupled ring resonator is proposed by introducing varactor diode as tuning device at the four corners of the ring resonator to allow modification of the ring electrical length. This modification is typically used to allow the variation of the capacitance as a function of bias voltage thereby resulting in center frequency tuning. A complete tunable circuit is simulated using electromagnetic (EM) circuit simulator involving the integration of microstrip technology and lumped elements on Taconic substrate. The proposed tunable ring resonator manages to achieve13% of tuning range.