A Compact VHF Circular Eleven Feed for FAST: Design, Mechanical Solution and Measurement

Paper in proceeding, 2026

A Compact VHF (Very-High-Frequency) circular Eleven feed has been designed and manufactured for the Fivehundred-meter Aperture Spherical radio Telescope (FAST). This Eleven feed operates over 50-250 MHz with its main astronomical purpose of detecting new pulsars and investigating critical pulsar emission processes at these frequencies. The dipole order N (amount of all dipole-pairs on each petal) is also taken into account as a variable during optimization in order to restrict the feed size and meanwhile still maintain the predicted performance. The four radiation petals of the feed are finally manufactured with a solid 4 mm-thick metal plate instead of the conventionally-used Printed-Circuit-Board (PCB), so as to reduce the possible deformation over such a large span. Measured reflection coefficients of both linear polarizations are better than -12 dB and a predicted aperture efficiency of ~70% in average could be achieved. The feed has a compact size of only 3.8 m in diameter as well as a weight of 300 kg, making itself mechanically compatible with the FAST cabin. Measured and observation results will be also shown in the paper.