Sensitivity of Antenna Arrays for Long-Wavelength Radio Astronomy
Sensitivity of Antenna Arrays for Long-Wavelength Radio Astronomy
复制标题
长波长射电天文学天线阵列的灵敏度
DOI：
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发表时间：
2010
影响因子：
5.7
通讯作者：
S. Ellingson
中科院分区：
文献类型：
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作者：
S. Ellingson
许多新的和计划中的射电望远镜将由大型低增益天线阵列组成，工作频率低于300兆赫兹。在这个频率范围内，银河噪声可能是总噪声的重要或主要贡献。这一点，再加上天线之间的相互耦合，使得很难预测这些仪器的灵敏度。本文描述了一个系统模型和估算系统等效通量密度（SEFD）的程序，SEFD是射电望远镜灵敏度的一个有用和有意义的度量。该方法应用于长波阵干涉仪的第一个“站”LWA-1。LWA-1由512个领结型天线组成，在110 × 100 m的椭圆占地面积内，设计工作在10 MHz和88 MHz之间，使用噪声温度约为250 K的接收器。结果表明，对于不接近天顶的波束指向，天线间的星系噪声相关性显著地降低了阵列的灵敏度。研究还表明，在这些条件下，采用优化信噪比的波束形成系数可以显著改善系统的性能。发现相互耦合发挥了重要作用，但并不具有一致的积极或消极影响。特别是，我们证明了模式乘法（假设阵列中嵌入的单个天线的行为与那些相同的天线本身相同）不会产生可靠的SEFD估计。
A number of new and planned radio telescopes will consist of large arrays of low-gain antennas operating at frequencies below 300 MHz. In this frequency regime, Galactic noise can be a significant or dominant contribution to the total noise. This, combined with mutual coupling between antennas, makes it difficult to predict the sensitivity of these instruments. This paper describes a system model and procedure for estimating the system equivalent flux density (SEFD)-a useful and meaningful metric of the sensitivity of a radio telescope-that accounts for these issues. The method is applied to LWA-1, the first “station” of the Long Wavelength Array (LWA) interferometer. LWA-1 consists of 512 bowtie-type antennas within a 110 × 100 m elliptical footprint, and is designed to operate between 10 MHz and 88 MHz using receivers having noise temperature of about 250 K. It is shown that the correlation of Galactic noise between antennas significantly desensitizes the array for beam pointings which are not close to the zenith. It is also shown that considerable improvement is possible using beamforming coefficients which are designed to optimize signal-to-noise ratio under these conditions. Mutual coupling is found to play a significant role, but does not have a consistently positive or negative influence. In particular, we demonstrate that pattern multiplication (assuming the behavior of single antennas embedded in the array is the same as those same antennas by themselves) does not generate reliable estimates of SEFD.