For the protection requirements of the microwave diagnostic systems from damage by stray radiation, the microwave diagnostic systems on J-TEXT need a planar, lightweight, and low-cost notch filter structure. Without protection, this stray radiation can significantly damage the performance of the microwave diagnostic systems. To protect the microwave diagnostic systems, a frequency selective surface (FSS) is the suitable choice as a notch filter to attenuate stray radiation. The FSS notch filter should be located between the lenses of the microwave diagnostic systems. This paper presents a 105 GHz FSS notch filter for the microwave diagnostic systems on J-TEXT, and the S-parameters of FSS are calculated based on the equivalent circuit model. The parameters of FSS were determined using the particle swarm optimization (PSO) algorithm and full-wave analysis method optimization, and the factors influencing FSS have been examined. The research results of this paper provide a standard design flow.

frequency selective surface,notch filter,equivalent circuit model