为了提高对远场方向性调控的灵活性，提出双蝶形银纳米光天线，基于时域有限差分的方法研究了天线不同结构与尺寸的变化对远场方向性产生的影响。研究发现，由于局域表面等离激元的存在，偶极子源垂直放置于双蝶形银结构下表面一定距离时，远场方向图出现明显的旁瓣。天线长度的增加是方向图出现旁瓣的关键因素。天线臂之间夹缝的减小，使远场方向图中旁瓣增大，同时主瓣增益增大。天线厚度的增加使远场方向图出现旁瓣，主瓣增益先增大后减小。结果表明，双蝶形银纳米光天线能够改变与其相耦合的偶极子源的辐射方向性。

In order to improve the flexibility of the control to far-field directivity, the double butterfly-shap silver nanostructure optical antenna is put forword. The influence of the far-field directivity caused by different structures and sizes is researched based on finite difference time domain method. The research demonstrates that, because of the exist of localized surface plasmon, far- field pattern shows a significant side lobe when the dipole is placed beneath the structure vertically. The increase of length is the key factory to make the side lobe appears in the farfiled pattern. The decrease of the gap between antenna arms can make the side lobe and the main lobe gain increase in the far-field pattern. The increase in antenna thickness causes a side lobe in the far-field pattern and the main lobe gain first increases then decreases. The results show that double butterfly-shap silver nano optical antenna can change the radiation directivity of the coupling dipole source.