Research On The Model Of Absorber And Performance Of Anechoic Chambers

With the technology development of building an Anechoic Chamber, the mature schemes of chamber design are much expected. Numerical calculation can be applied to this procedure to make it convenient. However, because of large electrical size and complex absorber's model structure, completely simulating chamber's structure with numerical method will lead to intensive computation and time consuming, which couldn't be tolerable. During low frequency range, the dimension of absorber array is far smaller than wavelength. We can consider the steady-state fields of this situation as a periodic distribution with array structure. By replacing the periodic unit(cell) of absorbing array with homogenization, it can be replaced by a uniform media with a effective electromagnetic properties in transverse direction, and divided a proper number of layers in longitudinal direction, and computation can be simplified enormously.By generalizing the theory of properties' test and effective properties' conclusion, for the first time, translation/reflection method is used to compute the effective properties of periodic structure and then to found equivalent model of absorbing array in this paper. In order to obtain the effective properties of each layer, a two-port network model of period cell based on transmission/reflection method (NRW) will be founded. Groups of effective properties are calculated through the scattering parameters on two ports, and then substitute each group into corresponding layer model to get reflectivity. According to comparing the reflectivity among the model founded by NRW, the model by Hasin-shtrikman (HS) bound and the model of initial pyramid array, it can be proved that the method in this paper can get a better approximating result especially in low-frequency range(below 100MHz). Finally, the equivalent layer model is introduced into Anechoic Chamber model to implement the full-wave simulation of Anechoic Chamber.In simulation, the main indicator for the performance of the semi-Anechoic Chamber is normalized site attenuation (NSA). A half-wave dipole is chosen as emission antenna, and receiving antenna is used by receiving points. Other requirement is according to the relevant standards. Using similar methods, transmission loss and field uniformity can be obtained too, and in transmission loss (NSTL) calculation, the height of transmission antenna and receiving points are fixed. In field uniformity (FU), the position of receiving points is in accordance with standards.The simulation tool selected in this paper is high-frequency structural simulation software HFSS developed by Ansoft. The tool, based on the finite element method, can get very high precision to solve the high-frequency fields, and currently it's widely used in microwave fields.