Design Of Active Test Method For The Reflectivity Of Microwave Anechoic Chambers

The microwave anechoic chamber is a test equipment commonly used in the communication industry.With the development and popularization of 5G technology and Internet of Things technology,the number of wireless portable devices has experienced a blowout growth and the volume of devices has also tended to be miniaturized.Facing the huge test demand of wireless portable equipment,compared with the traditional large-scale anechoic chamber,the small-scale microwave anechoic chamber is widely welcomed by the market due to its small size,easy disassembly,and low construction cost.The reflectivity measurement is a critical method to evaluate the performance of the anechoic chamber.However,when the current standard method is applied to the reflectivity measurement,it will be found that there are great limitations.This article will conduct an in-depth study on the reflectivity measurement of a small microwave anechoic chamber.The main research contents of this article are as follows:1.Analyze the existing methods for evaluating the performance of the quiet zone of the microwave anechoic chamber.2.Research on a passive test method for the reflectivity measurement of small anechoic chambers.This method is modified on the principle of the VSWR method stipulated by the standard.The main difference between this method and the standard method is that the test antenna in the quiet zone is changed from a high-gain directional antenna to an omnidirectional antenna Dipole antenna,which solves the problem that the directional antenna cannot meet the test requirements due to its large size.This article first derives the method theoretically,then uses electromagnetic simulation software to verify it,and at the end of the article carries out a large number of experiments to prove it.3.Uncertainty analysis of the passive measurement method.Due to the commonmode current problem of small-sized antennas such as Dipole antennas,the cable routing during the test process will bring great uncertainty to the reflectivity measurement.This article designs two experiments to verify the influence of commonmode current on the reflection level test.Corresponding electromagnetic simulation verification was also made for one of the experiments.At the same time,the experiment also verified the actual effects of the common-mode current suppression schemes,namely the scheme of adding ferrite beads and the scheme of increasing the Choke structure.It can be concluded that the cable routing can cause the standing wave to fluctuate by 1.25 d B,and the uncertainty of the corresponding reflectivity result can reach the order of 10 d B.4.The design of an active reflectivity test method.Aiming at the problems of passive test method,a method of using OTA test system for testing is proposed.Through the test,it can be proved that the uncertainty of the standing wave caused by the active test can be within 0.2d B,which is much lower than the uncertainty of the active test of 1.25 d B.This paper designs a complete test plan,including theoretical derivation,performance evaluation of the device under test,test environment construction,test specific steps and analysis of test results.5.The reflectivity test experiment was carried out on a small microwave anechoic chamber using active and passive test schemes.The experiment covers multiple frequency points and covers most of the quiet zone of the anechoic chamber,which can reproduce the real reflectivity mearsurement scene well.In the analysis of the results of the experiment,many details that need to be paid attention to in the actual test are discussed and the conclusion is drawn that the active test scheme has higher accuracy and more reliable results than the passive test scheme.