A way to improve the field of view of large aperture radio telescopes

There is a limitation on the field of view (FOV) of a large aperture radio telescope: the FOV decreases with increasing resolution and sensitivity of the telescope and the greater the aperture, the smaller the FOV. In order to enlarge the FOV, we may place several discrete feeds on the focal plane of the telescope. When these feeds work simultaneously, the FOV and therefore the operating efficiency of the telescope will be increased by several times. A disadvantage of this solution is the discontinuous character of the resulting FOV. Moreover, the number of feeds mounted on the focal plane is restricted by the F/D ratio of the telescope. We investigate in this paper an innovative technique for realization of simultaneous and continuous large FOV for the FAST (Five-hundred-meter Aperture Spherical radio Telescope). oposed new feed is a dense focal-plane array of microstrip antenna elements, the so called Vivaldi antennas. The electro-magnetic properties of the Vivaldi element and Vivaldi array are briefly introduced, which are essential for this application. The focal-field distributions (FFD) of FAST are simulated by using the software package GRASP8 for different illuminations. The simulation results give important information for the layout design of the array, especially for the weighting system of the Vivaldi array. A preliminary configuration of the array structure is suggested, and the illumination patterns are estimated. Finally, some remarks on the feasibility of applying the Vivaldi array to FAST are made.