Analyze Of Microwave Absorbing Characteristic Of Artificial Periodic Structure

Artificial periodic structure can be considered as a structural material with periodic unit cells to achieve various electromagnetic (EM) propoerties. Frequency selective surface (FSS) as one of the structures can act as a spatial electromagnetic wave filter, which fully reflect or let pass the coming EM wave with the frequency close to its resonate frequency of the patch or solt. This character is widely used in the field of microwave and optical engineering. EM absorbers known as the circuit analog absorber are composed by FSS and dielectric layers, and such absorber has good performance due to the high equivalent surface impedance, which attracts much attention and has been wideiy studied. In this paper, two different kinds of EM absorbers based on FSS absorber are analyzedThe first one is formed by two layers of resistive Hilbert curve arrays. The characteristic of Hilbert curve was introduced first, and its ability of absorbing was analyzed in theory to point out that this absorber has narrow bandwidth and has different effects with different polarizations, Then the structure of two layers of resistive Hilbert curve arrays was put forward, and numerical simulation was carried out providing that this absorber has wide bandwidth for both TE and TM polarizations. At last, the effect of different parameters of the structure was simulated to show how they influence the ability of EM absorbing. The conclusion is that wide bandwidth only exists with appropriate parameters.The other one comprises an array of metal patches over a grounded dielectric slab, and the patches are connected with vias to ground, which is also called the mushroom structure. Analyze in theory shows that the structure without vias has different absorb for different incidence angles, and vias only influence TM-polarized incidence waves. Then simulation of different relative permittivity confirms that vias have different effects on TE and TM polarized incidences, and can expand the bandwidth of TM polarization.