Side-coupled single-mode ring resonator with transmission zeros

A single-mode ring resonator which is fed along one of its quarter-wavelength sides is presented. The resonator's response presents transmission zeros whose frequencies can be modified by adjusting the line impedance of the ring and the coupling level of the feeding coupled-line. The proposed topology introduced much simpler bandpass filter configuration and reduced the number of control parameters. This idea is tested on FR4 microstrip substrate using the electromagnetic simulation. The measurement results are then presented in this paper to show its feasibility.