Alternative Ways To Feed The Arecibo Spherical Reflector

Restricted (Penn State Only)
- Author:
- Alkhatib, Mohamed Redha
- Graduate Program:
- Electrical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 03, 2022
- Committee Members:
- Michael Lanagan, Outside Unit & Field Member
James Breakall, Chair & Dissertation Advisor
Julio Urbina, Major Field Member
Shizhuo Yin, Major Field Member
Thomas La Porta, Program Head/Chair - Keywords:
- Gregorian Sub-Reflector
Gain
Method of Moments
Optimization
Numerical Methods
Linefeed
FEKO
Electric Field - Abstract:
- The Arecibo Observatory 1000 spherical dish has been used for many years for astronomy, planetary radar, atmospheric radar, and other research. However, due to unfortunate and unforeseen events, the usage of such a monumental research instrument came to a halt as the whole feeding mechanism collapsed in December of 2020. The old feeding mechanism consisted of a Gregorian dome and a linefeed; the linefeed was essentially a tapered conical slotted leaky waveguide with fins separating each of its sections precisely placed in the focal region. While the original feed worked for many years, it had its issues, it was incredibly heavy and especially hard to maintain. With plans to rebuild the feeding mechanism, it is important to find a better and potentially cheaper feeding mechanism instead of rebuilding the original feeding mechanism on the heavy platform. The work on the Arecibo Observatory’s feeding system originally started when the linefeed was broken off except for about 15 feet from Hurricane Maria. This prompted the idea to rebuild the original linefeed, and by utilizing modern technological advancement in computers, possibly improve upon the design. During the optimization phase of the original linefeed, the whole platform collapsed at which point the focus of the work shifted from improving the original linefeed to designing a simpler and less expensive way to feed the damaged system. This dissertation will report on all that work on the linefeed up to the point of the collapse as well as new concepts for a lighter and less complex feeding system. In this dissertation, two alternative options of feeding the reflector are proposed and explored. Both methods are modeled in the electromagnetic modeling software FEKO. The first method is to use a single Gregorian sub-reflector placed in the region of least confusion and conical horn at the center of the main reflector. The horn is then excited by a waveguide feed that is provided by the modeling software which would ensure that the wave is circularly polarized. The second method is to use a combination of a single Gregorian sub-reflector in the circle of least confusion and another smaller parabolic dish placed at the center of the 1000 ft spherical dish. The parabolic dish is then fed to ensure that the wave is circularly polarized. The three-dimensional model and results of both methods will be presented in this dissertation. Furthermore, an optimization has been done and the results of the optimization will be shown. Finally, an angular tilt evaluation has been done and will be compared to actual measurements taken from Arecibo before it crashed.