Survey of Transient Radio Sources with Digital Interferome

这六年来开发的64元无线电干涉仪使用新的HEMT接收器实现了比以前高三倍的灵敏度。它正在监测像Cyg X-3这样的瞬态射电源，并观察伽马射线类星体和快速变化的BL Lac物体。干涉仪使得世界上第一次以奈奎斯特速率获得无线电图像成为可能。目前世界上使用的无线电干涉仪都是傅里叶合成干涉仪（间接成像干涉仪），它可以制作精细的无线电地图。利用Wiener-Khinchin定理，对剑桥大学开发的方法进行了优化，以获得较少天线数量的精细图像。它要求接收信号的遍历性（时间平均值=可采样平均值）。由于天文射电源发出的信号通常变化不大，满足遍历性。然而，来自脉冲星或通信的信号是非遍历的，因此傅里叶合成不适合用于搜索脉冲星。早稻田大学开发的直接成像干涉仪使用空间FFT处理将空间接收的波转换为方向振幅，其中坐标表示与傅里叶变换的动量表示相关联。该处理器还可以对通信信号进行处理，在同时通信和多方向通信领域具有重要的应用价值。我们已经获得了处理器的专利。

64 element radio interferometer developed for these six years has achieved three times higher sensitivity than before with new HEMT receivers. It is monitoring transient radio sources like Cyg X-3, and watching gamma-ray quasars and rapidly varying BL Lac objects. The interferometer has made it possible to get radio images at Nyquist rate for the first time in the world.All radio interferometers currently used in the world are Fourier synthesis (indirect imaging interferometer), which could make fine radio maps. The method developed by Cambridge University is optimized to get fine images with less number of antenas, using Wiener-Khinchin theorem. It requires ergodicity(time average = ensamble mean) in received signals.Since signals from the astronomical radio sources usually do not change rapidly, and the ergodicity is satisfied. However signals from pulsars or comunication are non-ergodic, so Fourier synthesis is inapropiate to search pulsars.Direct imaging interferometer developed by Waseda University transforms the spatially received waves to the directional amplitudes using spatial FFT processing, in which cordinate representation is related to momentum representation by Fourier transform. Comunication signals could also be processed by this processor, and it is usefull in the fields of simultaneous and multi-directionai comunications. We have got a patent of the procesor.