A Novel Waveguide Bandpass Filter with Multiple Attenuation Poles Using Four-Armed Square-Loop FSSs

摘要

This paper presents a waveguide filter loaded with frequency selective surfaces (FSS) that can realize multiple attenuation poles. As the FSS resonant element, a square-loop FSS with arms is proposed. The authors have studied the design of the shape of the resonant element for the FSS by using the genetic algorithm (GA). There have been problems, namely, that the shape obtained by GA is complex and that the optimization design by GA requires a considerable amount of time. In this paper, these problems are eliminated by means of a square-loop FSS with arms. The proposed resonant element has a resonance (full transmission) at the center frequency while it has antiresonances (full reflection) on both sides. By means of these antiresonances, attenuation poles can be created. The resonant frequencies can easily be controlled by adjusting the element shape. As an example, a three-stage waveguide filter loaded with FSSs with a total of six attenuation poles in the X band is designed. By comparison of the numerical results and the experimental results, effectiveness of the proposed shape is verified.