准平面波辐射下的背景材料太赫兹后向散射特性的测量方法对测量结果影响很大。为减小连续激光器输出功率波动对测量结果的影响，在每次测量泡沫塑料板时，均先测量墙的后向散射。同时，为了消除墙对测量结果的影响，以最大后向散射为基准，给出不同泡沫塑料板及同种背景材料转动不同方位角的相对后向散射强度。实验结果显示，三种泡沫塑料板相对墙的散射测量误差明显降低，从而提高了后续的相对后向散射强度测量的准确性。

The methods of measuring the terahertz backward scattering characteristics of the background materials which are irradiated by quasi- plane wave have a great influence on the measuring results. To reduce the influence of the fluctuation of continuons wave laser output on measuring results, the backward scattering of the wall is measured before the foam plastic boards. Meanwhile, to eliminate the impact of wall on measuring result, the relative backward scattering intensity of different foam plastic boards and different azimuth angles of the same material are given, which is based on the biggest backward scattering intensity. The experimental results show that the scattering measurement errors of the three kinds of foam plastic boards which are relative to the wall have a significant decrease and thus the measurement accuracy of the relative backward scattering intensity in the follow-up parts is increased.