Sidelobe levels of a large radio telescope employing a combination of physical and resistive tapering

The main beam, sidelobe levels, and effective collecting area of a proposed radio telescope array, operating at 12 MHz, are considered. The telescope consists of two large rectangular arrays containing several thousand half-wave dipoles arranged horizontally in a tee shape above a ground plane. A narrow beam is formed by cross-correlating the outputs of the individual arms of the tee. The possibility of sidelobe reduction using a form of physical tapering consisting of reducing the width of each rectangular arm at appropriate intervals along the array is assessed, by comparing the performance achieved with this type of taper to that obtainable with the more common resistive taper. It is concluded that when the effects of random errors in element excitation are considered the performance of the physically tapered and resistively tapered arrays compares favorably.