Using MoM To Analyze The Electromagnetic Scattering Characteristic Of Frequency Selective Surfaces

Frequency selective surfaces(FSS) which is a two-dimensional periodic array structure, usually consists of many passive conductor patches (band stop) or periodic apertures unit (band pass). It can be used to effectively control the transmission and reflection of the microwave. Since the immediate design of FSS is rather difficult, the structure analyzing plays an important role in FSS development. The main structures this paper analyzes are square unit, circular unit, ring unit, cross unit, square loop unit, and Jerusalem cross unit. Besides, the paper employs a new type of unit patch—unit of square embedded loop, which is combined with square loop unit theoretically. Then, with the increasing angle of the incident wave, the paper calculates the variations of the electromagnetic scattering.There are various methods to analyze FSS, such as Finite Element Method(FEM), Finite Difference Time Domain(FDTD), Method of Moment(MoM), etc. Base on the rooftop basis function, the author aims to analyze the scatter of periodic frequency selective structure. First of all, the infinite unit cycle is reduced to a single computing cycle using the concept of Floquet theorem. After that, with the help of Green function, operator equation is built. At last, the currents and reflectance are presented by the method of moment. When analyzing the FSS, the author treats it as an ideal conductor which is infinite and zero thickness. The incident electromagnetic waves can be assumed as uniform plane wave, and be broken down to polarized wave, whose directions of transfer are TE and TM. In order to get any unit of FSS, the author unfolds the unknown induced currents, by utilizing the rooftop basis function, which is belong to the subdomain basis function. In the case of large unknowns, the computation speed can be improved by using a fast Fourier transform based iterative approach (conjugate gradient method, FFTCG).By comparison, the combined unit will not only achieve the merits of the single unit patch, but also increase the bandwidth of the frequency sharply. So, it possesses a good application value. In addition, when the angle of incident wave is increasing, the reflection characteristic of ring unit is steady. Most of the results in the paper, accord perfectly with those that present in other literature.