Optimal Design Of Frequency Selective Surface Using Equivalent Circuit Model

The rapid development of wireless communication technology not only brings convenience to daily life,but also has problems such as electromagnetic radiation and electromagnetic interference.Frequency selective surface（FSS）is a periodic microstructure array composed of metal patch or metal aperture unit cell.Because of its selectivity to the frequency and polarization mode of electromagnetic wave,it is often used as a spatial filter of electromagnetic wave and is widely used in wireless communication,electromagnetic shielding and other fields.As a spatial filter,the transmission characteristics of FSS are not only related to internal factors such as its topology,arrangement,structural parameters and the dielectric constant of the loaded dielectric layer,but also affected by external factors such as incident angle,polarization mode and energy of electromagnetic wave.Due to the numerous influencing factors and complex influence mechanism,it is very difficult to design the FSS structure driven by performance.In particular,how to quickly complete the FSS unit cell design according to the target transmission characteristics is the key problem to be solved in the engineering application.Aiming at the problem of fast optimization design of FSS structure,a FSS design method based on equivalent circuit model（ECM）and multi-objective particle swarm optimization（MOPSO）algorithm is proposed in this paper.This method starts from the perspective of circuit analysis and synthesis,determines the ECM topology from the target frequency response characteristics,realizes the accurate inversion from the target frequency response characteristics to the equivalent circuit parameters with the help of the MOPSO algorithm,completes the mapping from the ECM topology to the FSS structure topology based on the equivalent circuit principle,and then realizes the structural parameter optimization by HFSS-MATLAB co-simulation.On this basis,taking the typical engineering background as the traction,this paper designs three high-performance FSS structures.Firstly,in order to improve the utilization of Cassegrain antenna,a miniaturized bandstop-bandpass FSS operating in S-band and C-band is designed.Its transmission zero is located at 2.73 GHz,the transmission pole is located at 4.59 GHz,and the unit period is only 0.073λ₀×0.073λ₀,thickness is only 0.009λ₀,the angular stability of the resonant frequency is up to 80^°.Secondly,according to the multi-frequency communication requirements of wireless devices,a dual-bandpass FSS operating in S-band and C-band is designed.The structure has two independently adjustable transmission bands（the center frequencies are 3.39 GHz and 4.48 GHz respectively）.Both transmission bands have double-sided roll-off characteristics,which can effectively avoid the frequency interference of the multi-frequency communication system.Finally,in order to meet the requirements of high-order bandpass transmission characteristics of the radome,a low profile second-order bandpass FSS operating in X-band is designed.Its-3 d B fractional bandwidth is 13.06%and the profile thickness is only 0.026λ₀.The filtering performance of the above three FSSs is verified by full-wave simulation and prototype test.At the same time,the frequency response of ECM is in good agreement with the full-wave simulation results of FSS,which proves the effectiveness of the proposed design method.The design method based on ECM and MOPSO algorithm proposed in this paper can be used to design FSS structures with different frequency response characteristics.It has good accuracy and universality,and provides a feasible technical scheme to solve the problem of FSS structure design.