Research On Multi-band Frequency Selective Surface Based On Coupling Technology

A frequency selective surface is a kind of 2-D periodic structure composed of patch or aperture elements. It can let some certain electromagnetic wave pass or reflex as a spatial filter. With the rapid development of public communication and military radar, the application of FSS is becoming wider and wider, so the request of the performance of FSS is higher and higher.To meet the needs of working in higher frequency and integrated module of communication and radar, FSS tends to be multi-band, miniaturization and broadband. The filtering characteristics of traditional FSS are riot so good that low selectivity and narrow band often occurs; FSS which uses the method of fractal or complementation to realize the performance of multi-band can't be flexible to turn every band solely when a certain structure parameter changed.To solve problems above-mentioned, we study, analysis and apply the mutual-coupling,self-coupling and mixed coupling of FSS. The work includes several aspects below:1. Beginning with the basic theory and structure of the FSS, we discussed the factors which make great influence on the performance of the FSS. And then we expounded the mathematical model and equivalent model for analysis of the FSS. In addition, we displayed the general process of designing the FSS.2. Beginning with the phenomenon of "Separation of the center frequency",we discussed the factors of the phenomenon as the results of mutual-coupling of the two layers of the FSS, whose strength of coupling depends on the area of the metal of the two layers which face to face to each other. Then we reach a simplified equivalent circuit of the mutual-coupling FSS,and explained the factor of "Separation of the center frequency" from microscopic view of charge distribution.3. According to the theory of mutual-coupling, we make use of the phenomenon of"Separation of the center frequency" to design a double layers FSS based on assembly unit.This FSS have one pass-band and two stop-bands, and there are two transmission zeros or poles in each working band so that the FSS can have sharp sidebands, and better filter property.4. According to the theory of self-coupling, we designed an FSS based on the quasi-snap-ring of windmill structure. This FSS constructs two pass-bands and stop-bands because of the self-coupling stripes. And then we change the special parameters to prove the working band of the FSS can change independently of each other. What's more, we turn the FSS to double layers to make an addition of mixed coupling factors. Then we get an FSS working with two pass-bands and stop-bands which have multi-zeros and multi-poles in each working band.5. Basing on nesting and connecting with loops, we get a new multi-band FSS, which have three stop-bands and pass-bands. Also its working bands can be moved independently with the change of special parameters. Then we turn it to double layers to get a mixed coupling FSS, and get a new double-layer FSS which have three stop-bands and pass-bands with multi-zeros and multi-poles.