FEKO Modeling for an Alternative Feed Method for Arecibo Incoherent Scatter Radar

The Arecibo Observatory 1000 foot spherical dish has been used for many years for 430 MHz incoherent scatter radar (ISR) for probing the ionosphere. This all came to a halt in December 2020 when the whole feeding infrastructure collapsed also damaging the iconic 1000 spherical dish. The old feeding mechanism for ISR consisted of a Gregorian dual reflector system and a 96 foot leaky waveguide linefeed. While there is currently no clear indication on what the future holds for the Arecibo telescope, it is interesting to explore alternative ways to feed the Arecibo spherical reflector for ISR and other applications if it is to be rebuilt in the future. In this paper, we first show how FEKO was used to model the linefeed and then show an alternative option of feeding the 1000 foot dish with a lightweight sub-reflector. FEKO is the perfect solution with its hybrid techniques of Physical Optics - Large Elements (PO-LE), Multilevel Fast Multipole Method (MLFMM), and spherical mode excitation. The simple ISR solution shown in this paper serves to propose a possible feasible design that can be developed and optimized for possible construction to rebuild Arecibo. This design can be further enhanced for other research uses involving radio astronomy, planetary radar, and others.