基于超材料的椭圆波束馈源技术研究

Metamaterial-based Feed Antenna with Elliptical Radiation Beam

摘要:

针对传统工程用椭圆波束馈源带宽窄、加工难度大等问题，设计了一种新型的椭圆波束馈源，即在角锥喇叭内壁加载超材料层，使得馈源在水平极化和垂直极化两个极化辐射相同椭圆外形的波束。根据阻抗匹配原理，当电磁波水平极化和垂直极化入射时波阻抗的乘积与真空中波阻抗乘积相等时，超材料单元的性能达到最优，将优化后的超材料单元周期排布为超材料层加载到喇叭内壁，即可形成椭圆波束馈源。在Grasp软件中仿真计算了该馈源作为前馈馈源和后馈馈源使用时，反射面天线的电气性能。仿真结果表明：在工作频带10.95GHz-14.5GHz内，基于超材料的椭圆波束馈源实现了良好的极化波束等化，波束宽度比在0.9-1.14之间，驻波小于1.55。前馈照射反射面时，天线效率在65%-75%之间，交叉极化电平低于-30dB；后馈照射反射面时，天线效率在61%-72%之间，交叉极化电平低于-30dB，验证了馈源设计的可行性。

Abstract:

Considering that the traditional elliptical beam feed is narrow bandwidth and is difficult to fabricate, a new type of elliptical beam feed is designed in this paper. The novel feed is obtained by loading metamaterial layers on the inner wall of a pyramid horn. This method makes the beams radiated by the feed show similar elliptical shape for both the horizontal and the vertical polarization. According to the impedance matching principle, when the product of the wave impedance in horizontal and vertical polarization is equal to the product of wave impedance in vacuum, the performance of the metamaterial unit cell is optimized. By periodically loading the inner wall of the horn with the optimized unit cells, the metamaterial layer is formed and the elliptical feed horn is achieved. The elliptical feed can be used as either prime focus feed or second focus feed. For both cases, the radiation performances are verified using GRASP software. The simulation results show that in the operating frequency band of 10.95GHz-14.5 GHz, the elliptical radiations of the feed are achieved. The beamwidth ratio is between 0.9 and 1.14, and the standing wave ratio is less than 1.55. When the feed is used for a prime focus reflector, the antenna efficiency is between 65% and 75%, and the cross-polarization level is lower than -30 dB. When the feed is used for a second focus reflector, the antenna efficiency is between 61% and 72%, and the cross-polarization level is lower than -30 dB. These results verify the feasibility of the feed design.