As we all know, the shielding box is just a large iron box, which can block radio signals indoors and outdoors. In layman's terms, the inside cannot get out and the outside cannot come in, but the electromagnetic waves inside will be reflected and superimposed on the inner wall.
The anechoic chamber is based on the shielded room, with absorbing materials laid on the inner wall to simulate the effect of an open field. The darkroom is much more expensive than the shielded room because it is more expensive to paste on these materials in the darkroom. The electromagnetic wave inside will be absorbed when emitted to the inner wall, and there will be basically no mixing effect of reflection and superposition. It is suitable for testing the radiated emission interference of the sample. The anechoic chamber is generally divided into full anechoic chamber and semi-anechoic chamber.
Tests that do not require high requirements for the experimental environment, such as conduction disturbance, electrostatic test, surge test, lightning test, etc., are all carried out through the power line, so only need to be carried out in a shielded room; and for space radiation and space disturbance, pass Space-borne harassment or anti-interference has special requirements for space, so it needs to be carried out in a dark room to simulate the space of an open field.
Radiation tests conducted in these three types of test sites in full anechoic chamber, semi-anechoic chamber, and open field can generally be considered to conform to the law of electromagnetic wave propagation in free space.
Full anechoic chamber
The full-wave anechoic chamber reduces the interference of external electromagnetic wave signals to the test signal. At the same time, electromagnetic wave absorbing materials can reduce the multipath effect caused by the reflection of walls and ceilings on the test results. It is suitable for emission, sensitivity and immunity experiments. In actual use, if the shielding effectiveness of the shield can reach 80dB~140dB, then the interference to the external environment can be neglected, and the situation of free space can be simulated in a full anechoic chamber. Compared with the other two test sites, the floor, ceiling and walls of the fully anechoic chamber have less reflection, less interference from the external environment, and are not affected by the external weather. Its disadvantage is that it is subject to cost constraints and limited testing space.