Wide tuning range dielectric resonator by optimizing the tuning stub characteristic impedance

A practical approach of getting a wide tuning range dielectric resonator given a small tuning voltage is presented. For this work, a dielectric resonator with resonant frequency of 3.6 GHz was used. The dielectric resonator is placed on a low dielectric constant ceramic standoff. A circular tuning stub coupled to a varactor at one end, is situated underneath the dielectric resonator. Two microstrip stubs are introduced tangential to the dielectric resonator to couple the response out. The tuning stub electrical length and characteristic impedance were varied and the varactor capacitance was swept using 0-10 V bias to find the widest tuning range. A tuning stub with an electrical length of λ/2 and a characteristic impedance of 28 Ω yielded 0.42% of tuning bandwidth or 15 MHz at 3.6 GHz.