聚焦透镜天线焦斑宽度估算

Analytical calculation of focal spot size for lens antenna

根据惠更斯-菲涅耳原理,通过简单的推导,得出聚焦透镜天线焦平面上焦斑宽度的近似计算公式,并讨论了与焦平面平行的平面上的焦斑场.为证明该方法的计算精度及效率,设计了一个Ka波段聚焦透镜天线,并加工了两个天线样品进行比较.对两天线进行了平面近场扫描测试,采用近似公式计算得到的Ka波段聚焦透镜天线半功率点宽度与实验数据接近,表明文中给出的公式有一定工程参考作用.

An analytical method was presented to calculate the focal spot size of the focal lens antenna. Firstly, the formulation for the 3 dB focal spot size on the focal plane of the focal lens antenna was derived by Huygens-Fresnel principle. Then this formulation was simplified for convenience and the approximate expression was obtained. Secondly, the field distribution on the plane that parallels the focal plane was discussed. In order to demonstrate the accuracy and efficiency of this new method, a focal lens antenna at Ka band was designed and simulated as an example. Moreover, two focal lens antennas were fabricated for comparison. And these two lens antennas were measured by the planar-near-fields （PNF） method. Finally, the results obtained by the proposed method were compared with those of numerical method and measured data. It is found that the results of 3 dB focal spot size computed by the approximate expression are in good agreement with the experimental data.