Study On Performances Of Reverberation Chamber And Anechoic Chamber At Low Frequency

Both as typical radiation test sites, the performances of Reverberation Chamber (RC) and Anechoic Chamber (AC) at low frequency are deteriorated, which cannot be predicted accurately by ray-tracing method and so on. Therefore, this thesis focuses on this problem.A systematic study is made on the basic reverberating theory, geometrical shapes of RC and diffusers, in order to develop intrinsic reverberation chamber, which has lots of advantages over mechanical-stirring reverberation chamber.1) Expressions for electromagnetic fields in various regular cavities are deduced. An original expression is derived analytically for the electromagnetic field in current-active cylindrical cavity, and the expression is very convenient for application; the singularity, in the formula of reference [107] for 3D current-active rectangular cavity, is resolved. The mode density, as well as mode structure in diverse cavities is studied, too. These studies lay a theoretical foundation for optimizing the geometrical shape of RCs.2) Since it is very difficult to deduce electromagnetic formulae for irregular or asymetrical cavities, two numerical methods are adopted to study the effects of different geometrical shape of RCs on the field uniformity (FU), under the guidance of above mode density theory. The simulation results show that "truncated wedge" overmatch other shapes of chambers in acquiring better FU.3) The effects of different diffusers/diffractors on the FU are studied. The mode density theory, as well as simulation results shows that specific ball crowns (SBCs) are superior to other planar diffusers/diffractors, such as Schroeder diffusers/diffractors, because the FU improvement from SBC is more remarkable, and what's more, SBCs will not load the RC notably.The above findings show a way to IRC (Intrinsic Reververation Chamber); what's more important, the findings are useful to improve the performances of MSRC (Mechanical Stirring Reverberation Chamber) and EMSRC (Electronic Mode Stirring Reveration Chamber) at low frequency.Then, an improvement is made for time-domain method to evaluate rapidly the quality factor of RCs, which is good for industrial test.The second part of this thesis focuses on the problems of AC. First, an efficient method is put forward to calculate accurately the reflectivity of radio-frequency (RF) absorbers. These conclusions can be a good guide for manufacturing absorbers.The effects of RF-absorbers on the floor, on long-side-wall and on short-side-wall, on the performance of ACs are studied by Finite Element Method, with regard to the relation between sizes of shielding enclosure, the height of RF-absorbers and the incident angle. The cause of disputation occurred during radiation immunity test is illustrated visually by three-dimensional graph in the zone of EUT. The key RF-absorbers in AC area also found by comparing the effects of absorbers on different side walls. Such full-wave analysis method is valuable that the performance of a specific AC can be predicted accurately before practical construction.