为了实现低频段太赫兹高斯波束整形为大尺寸平顶波束，提出了一种利用双相位板结构设计大尺寸平顶波束整形系统的方法。基于Input-Output算法，利用角谱理论计算系统参数，同时对所设计系统进行了数值仿真并搭建了实验系统，验证了出射光场的横向强度分布是否符合预期。结果表明，所设计的双相位板整形系统能够成功将0.1 THz高斯波束转换为百毫米尺寸的平顶波束，仿真结果与理论较为接近，证明了设计系统的合理性。实验中波束直径达到228 mm，虽存在部分能量泄漏，但是平坦程度很好，相对均方根甚至优于理论和仿真结果，可达89%以上，充分说明了设计方法的有效性。

We present a new compact radar system to measure a terahertz radar cross section (RCS) of metal plates, trihedral corner reflectors, and an aircraft scaled model with a 0.1 THz continuous wave. We both numerically and experimentally investigate the terahertz RCS of the metal plates and trihedral corner reflectors. The numerical simulations are obtained by using commercial software, i.e., computer simulation technology, which agree well with the experimental results. Then, the RCS of an aircraft scaled model is measured, and the experimental results are in good agreement with the physical characteristics of the scaled model. The effectiveness of our compact radar system is verified to get the RCS of complex targets, such as the scaled models of the tactical targets.