毫米波车地通信的小型化波导螺旋阵列天线设计

高速磁浮列车毫米波车地通信系统要求其车载天线具有小型化、宽频带、圆极化和辐射扇形波束等特点。为更好地满足这些要求，设计一种中心馈电的小型化波导螺旋阵列天线。该天线馈电系统采用同轴波导中心馈电、4路矩形波导并馈的形式，通过改变馈电波导尺寸、耦合探针长度以及末端采用波导同轴转换器等形式，实现了所有单元的等幅馈电；天线单元由低剖面螺旋天线构成，采用顺序旋转技术改善天线的圆极化性能。利用全波电磁仿真软件设计了一款中心频率为38 GHz的28单元波导螺旋阵列天线，并进行了实验测试。测试结果表明：在37~39 GHz频带范围内，天线驻波比小于1.41，增益大于21.7 dB，轴比小于3.6 dB，俯仰面波瓣宽度为4.5°~4.7°，方位面波瓣宽度为29°~29.7°，满足毫米波车地通信系统车载天线的设计需求。

Design of miniaturized waveguide spiral array antenna for millimeter-wave Vehicle-Ground Communication

In high speed maglev vehicle millimeter-wave communication systems, it is required that the vehicle antenna has the characteristics of miniaturization, wide band, circular polarization and radiating sector beam. To better meet these requirements, a compact waveguide spiral array antenna with center feed is proposed. The antenna feed system adopts the form of coaxial waveguide central feed and four rectangular waveguides joint feed. By changing the size of the feed waveguide, coupling the length of the probe and placing the coaxial converter at the tail of the feed waveguide, the uniform feed of each unit is realized; the antenna low-profile unit is constituted by the helical antenna, and the circular polarization performance of the antenna is improved by using sequential rotation technique. A 28-element waveguide spiral array antenna with a center frequency of 38 GHz is designed by using full-wave electromagnetic simulation software and tested experimentally. Test results show that: in 37-39 GHz band, the antenna standing wave ratio is less than 1.41, the gain above 21.7 dB, the axial ratio less than 3.6 dB, the beam width 4.5°-4.7° at the elevation plane and 29°-29.7° at the azimuth plane. It can meet the design requirements of the vehicle antenna for millimeter wave vehicle-ground communication system.