本文对VHF（Very High Frequency）频段天线及其配套地网的设计和优化进行了研究，使天线系统的性能达到了低频射电观测的要求，主要工作为：首先重点阐述了低频射电观测的特点和观测系统模型，根据低频段银河背景噪声和后端接收机噪声温度，计算出了天线所满足的技术指标要求；根据半波振子天线的原理和振子天线扩展工作频率的方法；使用电磁仿真软件设计出了刀片型半波振子天线，并且对天线的结构进行优化，通过增加天线面板宽度增加天线工作带宽，通过改变天线馈电部分的形状改善天线在工作带宽内的阻抗匹配情况，最终确定天线臂长1.8m，臂宽宽0.4m，馈电部分为等腰三角形，顶角为90度。然后仿真模拟了天线在四种不同地面上时的辐射特性，无地网条件下，天线在干燥土壤和沙地上增益分别是3.06dB和1.44dB,且存在明显的旁瓣和后瓣；在两种潮湿地面上，分别是4.33dB和4.25dB。针对这个问题，设计了一种金属地网，增加地网后，天线在干燥土壤和沙地地面的增益分别为4.87dB和4.97dB，潮湿土壤和沙地地面分别是4.39dB和4.40dB。并且方向图不存在明显的后瓣和旁瓣，谐振点稳定在27.0MHz和69.5MHz处，有效的稳定了天线在不同环境下的性能。最后，根据仿真结果使用铝板制作了刀片型振子天线和配套的不锈钢材料的地网，结合空心扼流巴伦对天线进行了测试，测试结果表明，天线的第一谐振频点为25.9MHz，第二谐振频点为79.4MHz，虽然与仿真结果有一些偏差，但是天线在工作频段内的电压驻波比低于仿真结果，阻抗匹配情况完全满足低频射电观测要求。
其他摘要
This paper introduced the design and optimization of VHF (very low frequency) band antenna and ground screen, finally the performance of the antenna system satisfied the requirements of low-frequency radio observation. The main work is: Firstly, based on the characteristics of the low-frequency radio observation and the observation system model, the Galaxy background noise and the back-end receiver noise temperature were studied, and we calculated the technical specifications of the antenna. According to the principle of the half-wave dipoles and the method of broadening working frequency, we used the electromagnetic simulation software design the blade-type half-wave dipoles. The bandwidth was increased by increasing the width of the antenna panel, and the impedance matching was improved by changing the shape of the feeding part. Finally, the antenna arm length is 1.8m, the arm width is 0.4m, the feeding part is an isosceles triangle, and the apex angle is 90 degrees.Then we simulated the radiation characteristics of the dipoles on four different grounds. Without ground screen, the gain of antenna on the dry grounds are 3.06 dB and 1.435 dB, on the moist grounds are 4.327 dB and 4.246 dB. After placing the ground screen, the gain of the antenna on the dry grounds are 4.869 dB and 4.971 dB, on the moist grounds are 4.286 dB and 4.403 dB. The ground screen can not only stabilize the performance of antenna, but also effectively improve the radiation characteristics of the antenna.Finally, according to the simulation results, we made the blade-type dipoles and the stainless steel ground screen with aluminum plate, and tested dipoles in combination with the hollow balun. The test results show that the first resonant frequency of the dipoles was 25.9MHz, and the second resonant frequency was 79.4MHz. Although there are some deviations from the simulation results, the voltage standing wave ratio of the dipoles in the working frequency band is lower than the simulation result, and the impedance matching completely satisfies the low frequency. radio observation requirements.
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