Highly Selective Planar Filters with Shielded Split-Ring Resonators

This paper presents two novel high-selectivity filters at 2.4 GHz with coupled square split-ring resonators. Metallized via holes are added around the filter forming a shielded cavity configuration which increases the Q factor. By introducing cross coupling, a pair of transmission zeros are introduced and the selectivity of the filter has been substantially improved. In the improved version, four stubs are added at the end of square open-loop resonators to enhance the miniaturization. For verification, the filters are fabricated and measured. Simulated and measured results are in good agreement. The experimental results demonstrate that the filter realizes a -3dB absolute bandwidth of 180 MHz in the passband with good stopband suppression and high selectivity.