具有内场定相的相控阵观测
Phased array observations with infield phasing
摘要：
我们目前的结果，脉冲星观测使用巨型米波射电望远镜（GMRT）作为一个相控阵内场定相。通过应用基于天线的相位校正，天线在整个观察过程中保持同相，所述相位校正来自与相控阵列波束数据并行获得的vibration，并且使用目标场中的连续发射模型实时标记和校准vibration。我们发现，正如预期的那样，信噪比（SNR）不随时间而降低。相比之下，仅在观测开始时进行定相的观测示出了SNR随时间的明显退化。我们发现，这种退化是很好的拟合的函数的形式SNR（t）=a + b*exp（-（t/t0）^5/3），这对应的情况下，相位漂移所造成的柯尔莫哥洛夫型湍流在电离层。给出了相控阵天线的信噪比和合成波束尺寸的一般公式（包括相关天空噪声、非理想相位和自噪声的影响），以及非相干天线的相应公式。这将有助于规划大型阵列望远镜的观测。
英文摘要：
We present results from pulsar observations using the Giant Metrewave Radio Telescope (GMRT) as a phased array with infield phasing. The antennas were kept in phase throughout the observation by applying antenna based phase corrections derived from visibilities that were obtained in parallel with the phased array beam data, and which were flagged and calibrated in real time using a model for the continuum emission in the target field. We find that, as expected, the signal to noise ratio (SNR) does not degrade with time. In contrast observations in which the phasing is done only at the start of the observation show a clear degradation of the SNR with time. We find that this degradation is well fit by a function of the form SNR(t) =a + b*exp(-(t/t0)^5/3), which corresponds to the case where the phase drifts are caused by Kolmogorov type turbulence in the ionosphere. We also present general formulae (i.e. including the effects of correlated sky noise, imperfect phasing and self noise) for the SNR and synthesized beam size for phased arrays (as well as corresponding formulae for incoherent arrays). These would be useful in planning observations with large array telescopes.
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