Dual-Band BSF with Enhanced Quality Factor

Abstract

In the present work, a U-shaped CPW resonator (CPWR) with, generally, unequal arms is proposed to produce high Q-factor bandstop filter (BSF) based on broadside-coupling between the CPWR and a CPW through-line (CPWTL), which are printed on opposite faces of a thin substrate. The unequal arms of the U-shape and the finite width of the ground strips of the CPWR are shown to produce much higher Q-factor than that of equal arms and infinitely extending side ground planes. The dimensions of the CPWTL are optimized for impedance matching while the dimensions of the CPWR are optimized to obtain the highest Q-factor. The effect of the loss tangent of the dielectric substrate material on the Q-factor is investigated. It is shown that the difference between the lengths of the unequal arms of the U-shaped resonator can be used to control the Q-factor. Thanks to the computational efficiency of the employed electromagnetic simulator, enough number of trials has been successfully performed in reasonable time to arrive at the final design of the BSF. A prototype of the proposed BSF is fabricated for experimental investigation of its performance. The experimental measurements show good agreement when compared with the corresponding simulation results.