The factors that affect its performance index mainly include darkroom parameters, antenna measurement errors and other errors.
The electrical performance of microwave anechoic chamber is mainly characterized by the characteristics of static zone. The characteristics of the static zone are described by the size of the static zone, the maximum reflection level in the static zone, cross polarization, field uniformity, path loss, inherent radar cross section, operating frequency range and other indicators.
The factors that affect the darkroom performance index are diverse and complex. When using the light emission method and the energy physics law to simulate the darkroom performance, it is necessary to consider the effects of radio wave transmission decoupling, polarization decoupling, the pattern factor of the standard antenna, the vertical incidence performance and oblique incidence performance of the absorbing material, multiple reflections and so on. However, in the actual engineering design process, the performance of the absorber is often taken as the key determinant of the darkroom performance.
1) Cross polarization degree: due to the non strict symmetry of the darkroom structure, the inconsistency of the absorption of various polarization waves by the absorbing materials, the darkroom test system and other factors, the polarization of electric waves in the darkroom propagation process is not pure. If the polarization surface of the antenna to be tested is orthogonal and parallel to that of the transmitting antenna, and the tested field strength ratio is less than -25db, it is considered that the cross polarization meets the requirements.
2) Multipath loss: uneven path loss will cause the polarization surface of the electromagnetic wave to rotate. If the antenna to be tested rotates in the direction of the incoming wave, and the fluctuation of the received signal does not exceed +-0.25 dB, the multipath loss can be ignored.
3) Field uniformity: in the quiet area of the darkroom, move the antenna to be tested along the axis, and the fluctuation shall not exceed +-2db; On the section of the static area, move the antenna to be tested horizontally and up and down, and the fluctuation of the received signal shall not exceed +-0.25 dB.