Fabrication of the double-layer millimeter wave frequency selective surface by femtosecond laser

With the rapid development of communication technology, frequency selective surface (FSS) operating at higher frequencies is required and it is necessary to design and fabricate new FSS. In this paper, a broadband double-layer FSS is proposed which is composed of one layer of foam, two metal layers, and four layers of substrate. The simulation result shows that a high transmission in the band of 60.03-89.33 GHz (covering the E band) with a relative bandwidth up to 29 % is achieved. In addition, the effects of the key structural parameters, oblique incidence angle, and TE/TM polarization on the transmission performance are further explored. The results indicate that the proposed FSS has good oblique incidence angular stability and polarization insensitivity up to 60 degrees. Finally, the proposed FSS is fabricated by the femtosecond laser and measured by the waveguide method. Experimental results show that the machined sample has high precision and the machining error is within 1 mu m, and good agreement between the simulated and measured results is observed. Therefore, the proposed FSS could be used as spatial filters or sub-reflectors of multiband antennas and the corresponding processing method could be extended to other millimeter wave functional devices, such as absorbers, radomes, etc.