Novel waveguide filters with multiple attenuation poles using frequency selective surfaces

This paper proposes a waveguide filter consisting of frequency selective surfaces (FSS) with an arbitrarily-shaped element, which can control not only a passband characteristic but also attenuation-pole frequencies at stopbands. In the present design method, the shape of each FSS is designed by a genetic algorithm (GA) so that the resonant curve of the FSS can be fitted to that obtained from an equivalent-circuit approach. By using such FSSs, we have constructed the bandpass filters with 4% bandwidth at the center frequency 10 GHz, in addition to multiple attenuation poles like an elliptic-function filter. The effectiveness of the waveguide filter with FSSs proposed here is validated by good agreement between the calculated and the measured results.