Miniaturized dual-mode spiral-ring resonator bandpass filter

A dual-mode ring resonator filter is devised to have a miniaturized size and its performance investigated. By placing an inductive perturbation at an asymmetric position, with respect to the input and output ports, two transmission zeros are created on the both sides of the passband. The miniaturization is achieved by folding the microstrip ring trace into a spiral configuration, incorporating with metallic via-holes and coplanar waveguide sections as the interconnection. The circuit size is only 20.5% of that of a conventional ring resonator. Measured results show good agreement with the simulation.