Optimization Of Low Frequency Characteristics Of Mechanical Stirred Reverberation Chamber

Mechanical stirred reverberation chamber was initially applied to the electromagnetic compatibility(EMC)test of large-scale equipment such as automobiles and aircraft.With the development of research,reverberation chamber has been applied in the OTA test of small antenna,Bluetooth,WLAN,Internet of Things and other devices.Compared with the microwave anechoic chamber test method,reverberation chamber test method has the advantages of fast test speed and low test cost.Because the number of electromagnetic modes in the reverberation chamber is small at low frequencies,the performance of the reverberation chamber is poor at low frequencies.The test range of reverberation chamber is limited by the lowest usable frequency(LUF).LUF is one of the most important indexes in reverberation chamber,which is mainly determined by the chamber size,shape,quality factor and the effectiveness of mechanical stirrer.The IEC standard determines the LUF of reverberation chamber by measuring the electric field intensity at the vertex of the working area and calculating the electric field uniformity in the working area of the reverberation chamber.In practice,it is found that the electric field distribution in reverberation chamber is still far behind the ideal model even at frequencies higher than LUF.In recent years,some methods have been proposed to determine a more rigorous and reliable minimum frequency.When the working frequency is higher than this frequency,the reverberation chamber is in an ideal working state.After comparing and analyzing the latest methods,this paper adopts the method of determining the frequency fwsc which satisfies the "Well Stirred Condition" in reverberation chamber by measuring the parameters of transmitting antenna S11.By studying the influence of optimization method on frequency fwsc,the optimization of low frequency characteristics of reverberation chamber is studied.In detail,the main research focus on the following issues:First,in this paper,the effect of synchronous step and staggered step of two stirrers on reverberation chamber frequency fwsc is studied quantitatively.The previous test methods determing fwsc are suitable for one-dimensional scene of single stirrer step or double stirrer step synchronously in reverberation chamber,but this test involves two-dimensional scene of double stirrer staggered step,so the test method needs to be improved.After analyzing the relevant literature,the method of two-dimensional autocorrelation function is used to improve the test method,which makes it better applicable to the staggered step tuning of two stirrers.The data processing results show that the improved method has certain advantages.The test results show that the frequency fwsc of reverberation chamber can be significantly reduced by staggered step tuning compared with synchronous step tuning.Second,this paper presents a method to find the optimal step position of stirrers.Different from the traditional uniform stepping,the fwsc obtained by non-uniform stepping is compared with the fwsc obtained by uniform stepping.The results show that the fwsc of reverberation chamber can be slightly reduced by "Perturbation" modification near the uniform step position.Third,the simulation study of intrinsic reverberation chamber is also carried out in this paper.Because the intrinsic reverberation chamber can not be measured in practice,the lowest usable frequency(LUF)is calculated by the method specified in IEC standard.The results show that the lowest usable frequency(LUF)of the reverberation chamber can be reduced by combining the source with the quadrilateral scatterer in a prism reverberation chamber with the same volume as the rectangular reverberation chamber.