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相控阵天气雷达波束特性
Beam Characteristics Analysis on Phased Array Weather Radar
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摘要: 为了缩短雷达的探测周期, 相控阵天气雷达必须采用宽波束发射, 多波束接收。该文在天线口径为均匀分布和非均匀分布情况下讨论了相位扫描天线的方向图, 对波束特性进行分析, 提出采用非均匀划分子空间方法可对相位扫描天线带来的波束展宽效应和增益减小进行补偿, 并模拟设计了一个相控阵天气雷达天线方案, 给出宽波束和多个窄波束方向图及波束参数。结果表明:海明加权方法可使副瓣电平降低到-25 dB, 能基本满足天气探测需求; 采用非均匀划分子空间能够对波束宽度和天线增益进行补偿; 文中所设计的天线方案不仅能够缩短雷达的探测周期, 还能充分利用雷达的照射能量。Abstract: The current NEXRAD system completes a volume coverage pattern in a minimum of approximately 5 minutes for 14 elevation steps. Phased array radar, with easily designed multi beams and processing of signals, offer the prospect of routinely sampling the atmosphere with volume scan rates an order of magnitude faster than the fastest(5 minutes)operational scan mode of the Doppler radars. Therefore, phased array weather radar is to form a wider transmitted lobe and receive backward radar signal using multiple narrower beams in order to save radar scanning time. The directional diagrams of the phased array antenna are derived respectively under the uniform and the non uniform circumstances, then their characteristics are analyzed and discussed. Changes of beam width and antenna gain will bring observation errors, therefore, a method of using non uniform partitioning subspace to correct the beam width and antenna gain is derived to overcome the shortcoming of phased array radar. An antenna scheme of phased array weather radar is designed using 144 array element numbers based on one dimensional linear array, meanwhile, a wider transmitted beam and multi narrow beams patterns are derived. Results show that, under the circumstances of uniform antenna caliber, side lobe level of antenna is higher. The methods of Hamming weighting can decrease the electrical level of side lobes to-25 dB, which can fundamentally meet the requirements of weather observation. The designed antenna scheme can not only save the scanning time of antenna, but also sufficiently utilize the radar resource.
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图 1 一维相位扫描天线方向图的模拟(d=0.5λ, sinθB=0)
Fig. 1 Simulation of the antenna directional pattern of one-dimension phase scanning(d=0.5λ, sinθB=0)
图 2 波束宽度随扫描指向角的变化曲线(a)修正前,(b)修正后
Fig. 2 Graph of beam width versus scanning direction angle(a)the original,(b)the corrected
图 3 天线增益随扫描指向角的变化曲线(a)修正前,(b)修正后
Fig. 3 Curve of the antenna gain vs the angle of scanning direction(a)the original,(b)the corrected
图 5 多个接收波束形成原理示意图(T :发射, R:接收)
Fig. 5 Principle illustration of multiple beam reception(T : transmit; R: receive)
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