A way to improve the field of view of the large aperture radiotelescope

There is a limitation in the field of view (FOV) of large aperture radio telescopes, which is usually unavoidable. In order to enlarge the FOV, we may place several discrete feeds at the focal plane of the telescope. When all of the feeds work at the same time, we can achieve an FOV extended to several times, which equivalently increases the functions of the telescope. The disadvantage of this solution is the sparseness of the sampling at the FOV, which is not desirable for a continuous imaging process. Moreover, the number of the feeds mounted at the focus is restricted by the F/D (focal length to diameter) ratio of the telescope. We investigate an innovative technology to realize a simultaneous and continuous large FOV for the FAST (five-hundred-meter aperture spherical radio telescope). The new feed is proposed to be made of a focus array whose elements are microstrip antennas, so called Vivaldi antennas. An electromagnetic property of the Vivaldi element and the Vivaldi array is introduced, which is essential to the formation of the focus array. The focal field distribution (FFD) of the FAST for different illuminated portions is simulated using the GRASP8 software package. The results give critical information for the layout design of the focus array, especially the weighting system of the Vivaldi array. Cursory configurations of the array structure are suggested, and illumination patterns are estimated. Finally, some remarks on the feasibility of applying the Vivaldi array to FAST are made.