Study On Multi-band Frequency Selective Surfaces Based On Lumped Element Loadings And Fractal Structure

Frequency selective surfaces (FSS) are very popular for their spatial filtering characteristics. They have been used in many applications, such as sub-reflectors of antennas, radomes and wireless security. Recently, the multi-band components are in great demand for wireless communications and multi-mode compound guidance technology, and the research of multi-band FSS has attracted many attentions. In this dissertation, the study of the miniaturization and reducing the sensitivity of resonant frequency has been carried out by loading with lumped elements or using fractal structures. The main contributions of this dissertation are list as fellow:1. The split-field FDTD method for analyzing periodic structures has been discussed. In order to deal with the FSS structure with lumped elements loadings, the equations of considering different lumped elements are deduced.2. For eliminating the coupling between FSS units, the Faraday cage structure is firstly adopted to design square loop slot FSS, thus the resonant frequency of FSS could be designed exactly just by analyzing one FSS unit.3. Single-layer miniaturized FSS for low frequency band is proposed by loading lumped elements on traditional square loop slot FSS. Both simulated and measured results shows that the dimension of the FSS units is miniaturized to 0.083λ(λrefer to the resonant wavelength), and the max shifting of the resonant frequency is no more than 0.5% as the angle of the incident wave change from 0 to 60 degree.4. A novel equivalent circuit model is proposed for square loop slot FSS loaded with lumped elements. The frequency response can be calculated directly based on the dimension of the FSS units and the parameter of the lumped elements, which greatly simplify the process of the loaded FSS design.5. Single-layer miniaturized multi-band FSSs for low frequency band are proposed by using concentric square loop slot units loading with lumped capacitors. The FSSs with dual-band, tri-band are realized, Both simulated and measured results shows that the dimension of the FSS units is miniaturized to 0.09λ, and the max shifting of the resonant frequency is no more than 2.5% as the angle of the incident wave change from 0 to 60 degree. Furthermore, single-band and dual-band loaded FSS with enhanced bandwidth are proposed, the relative bandwith of single-band is enhanced from 4.57% to 22.3% while that of dual-band are enhanced from 3.7%, 4.3% to 11.1% and 11.5%, respectively. 6. The dichroic beam combiner is used in MMW/IR compound hardware in the loop (HWIL) system for transmitting MMW wave while reflecting IR signal. And a FSS based on Y-loop fractal elements with dual-band at 8mm and 3mm MMW band is designed and fabricated. Both simulated and experiment results show that the proposed FSS takes the advantages of stable and good frequency domain response, insensitive to the incident angle and polarization. Besides, the tiptop reflectivity at IR band reaches 90%. Besides, this FSS can be used in both 8mm and 3mm band MMW/IR compound hardware in the loop system.