| In the wake of progress in radar technology and the extensive in its application, the requirement of radar data is becoming more precise than ever. Radar cross section (RCS) is an important argument and parameter in recognizing the target and receiving more and more attentions. Terahertz (THz) which locates in a special place among the waves, between the micro and infrared waves, is more suitable to compact antenna test range as well as the detecting the detailed data of target. However, nowadays the THz waves sent by the existing resources are usually a Gaussian distribution one which is not able to be shaped into a perfect plane one. So it is necessary to discuss the condition that influence of the incident beam is a Gaussian one instead of a plane one that most of the radar utilize. in this paper, the formula calculating several targets by different method according to the characters of the targets themselves are given and the comparement of the RCS using different incident beam, Gaussian one and plane one, are made.Flat plate is a common target in radar detection and sometimes will be used as a calibration objects, therefore, it is worth-while to analyze the effects of Gaussian beam to scattering. Physical optics(PO) is chosen as the method to calculate scattering field becase of its high precision in calculating the scattering field of plate. First, simplified the target as a two dimensional one which means that the width of the plate is certain but the length is infinite. Such kind of simplification can help short the calculation time. While the Gaussian beam is axisymmetric, it is still needed to consider the condition that both of the width and the length are certain and calculating the influence of two variable respectively, in the meantime, the precision of two dimensional approximation.The semicircular and hemispherical boss on the plate can be viewed as the mathematical model of welded joint or rivet as well as a consist of a rough surface. On the method of images, the origional problem is reduced to the scattering of a cylinder or a sphere. In the paper, the scattering field of such kind of model is also calculated by applying the spectrum method and superposition principle. The spectrum is utilized to expand the incident Gaussian beam, while the superposition principle is utilized to get the total scattering field. By comparing the scattering field of Gaussian beam and plane wave, the deviation distribution along with different characters is given and analyzed.Sometimes a periodic array of target may bring the scattering field an unpredicted effects and can be used as an analog of rough surface. In the paper, two methods, lattice sums and T-matrix, are introduced to calculate the scattering field of a periodic array of objects, and cylinders are used as an example to show the distribution of the scattering field. Meanwhile, analyzing the results and discussing the influence of Gaussian beam as an incident beam. After that, a brief introduction about the possibility of using the two methods to calculate other periodic array of objects and array of objects is given. |
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