Design And Study Of Broadband Microwave Absorber Realized By Resistive Frequency Selective Surface

The absorbing material was firstly used in military to realize the weapon system electromagnetic invisible. The development of the technology of optical invisible further promotes the development of the absorbing materials. Therefore, the development of high-performance absorbing material has become an important topic in military filed. Frequency selective surface is a kind of periodic array structure, usually composed of the same unit-cells, which are usually patch printed on a dielectric layer or aperture etched out of a conductive surface. In recent years, the FSS has been widely used from microwave frequencies to the light spectrum and plays an important role in the field of radar detection and aircraft stealth. Periodic FSS structure can also process a lot of features which does not exist in the nature.In this paper, we report the design of broadband microwave absorber based on resistive frequency selective surface. The analysis show that the coupling between the FSS and the substrate can enhance the bandwidth with the reflectivity below-10dB in the frequency of 5-21GHz.The main contributions of this dissertation are listed below:(1) We study the physical properties of the resistive FSS, using an electron microscope to observe the characteristics of the FSS surface. We proposed an application of the open-terminal method to measure the conductivity of the resistive film. The conductivity as a function of reflection has been derived. The results are in good agreement with another technique.(2) The absorbing material is designed based on the resistive FSS. The equivalent circuit model is established due to transmission line. We explore the source of the resonance absorption by observing E-field pattern. On this basis, we put forward the cascade network method instead of the equivalent circuit model method, which will more truly reflecting the impedance of FSS. Moreover, we discuss the influence of dielectric constant, thickness of the dielectric substrate and surface resistance of FSS on the performance of the absorber. From simulation and experiment, it is showed that the material has the characteristics of polarization insensitive and wide-angle of incidence.(3)We use intelligent algorithm to design and optimize the existing absorbing material, through setting different fitness functions to meet different design requirements. Furthermore, we discuss different optimization strategies of absorbing material design under different requirements. In the condition of broadband and low profile, the designed absorbing material has the bandwidth with the reflectivity below-10dB in the frequency of 6.25 to 25.30GHz and its thickness is only 3.92 mm. Experiments have been carried out to verify the design results, which proves the effectiveness of particle swarm optimization algorithm.(4)On the basis of theoretical analysis and simulation calculation above, we did a series of experiments. On the basis of electromagnetic full-wave simulation, we designed the size of the FSS and the thickness of the dielectric substrate. We used bow test system to measure the reflection properties of samples with different dielectric substrates, different thickness and different electrical conductivities. The measure results were compared with the theoretical analysis. The experimental results show that the FSS materials have the characteristics of large incident angle, polarization insensitivity and wide-band.