Adaptation of an unused paraboloidal reflector for L-band drift scan observations

This thesis presents the design and fabrication of a feed antenna for a deep 4.5m reflector, with a focal ratio of 0.34, in an L-band radiometer system targeting observations of the neutral hydrogen 21cm line. A coaxial cavity feed horn was implemented using cost-effective manufacturing techniques. The horn is comprised of sheet metal sections and standard aluminum pipe. The antenna’s radiation pattern approximates a sec2(θ/2) amplitude distribution, which is optimal for illuminating rotationally symmetric paraboloidal reflectors and reduces the effects of feed blockage. The horn is excited by a dual coaxial-to-cylindrical waveguide excitation structure fabricated using standard N-type connectors and 3mm brass rod. Average reflection coefficients and crosscoupling of the dual polarized excitation was measured to be below−20dB over a 40MHz band. An average aperture efficiency of 79% was achieved, representing a nearly 10% improvement over comparable coaxial cavity horn designs reported in the literature. The average antenna noise temperature of 16K is approximately half that of comparable designs. This thesis also serves as a comprehensive resource for the theory of prime focus reflectors in radio astronomy applications. All design decisionswere motivated by fundamental principles. Topics presented include the definition and calculation of antenna temperature, the gain to system noise temperature ratio as the standard figure of merit for feed antenna evaluation, geometric analysis of rotationally symmetric paraboloidal antennas, and an analysis and study of different designs of horn antennas for prime focus feeds.

Grantor dc:publisher

Stellenbosch : Stellenbosch University

Year dc:date.issued

2026

Author dc:creator

• Le Roux, Phillip Hugo

Advisor dc:contributor.advisor

• Steyn, Werner

Language dc:language.iso

en

Repository record dc:identifier.uri

https://scholar.sun.ac.za/handle/10019.1/136290

OAI identifier oai:identifier

oai:scholar.sun.ac.za:10019.1/136290