Implementation of an Optimised Cassegrain System for Radio Telescopes

TL;DR

This paper details a cost-effective, high-efficiency radio telescope antenna design using a modified Cassegrain system with a shaped secondary mirror, improving gain and reducing ground-spill.

Contribution

It introduces a novel shaped secondary mirror design for Cassegrain antennas that enhances gain and reduces ground-spill while maintaining low manufacturing costs.

Findings

Antenna gain increased by approximately 10%.

The design maintains low ground-spill across 12-18GHz.

Antennas are simple to manufacture and cost-effective.

Abstract

We present the antenna design for a radio interferometer, the Arcminute Microkelvin Imager, together with its beam pattern measurement. Our aim was to develop a low-cost system with high aperture efficiency and low ground-spill across the frequency range 12-18GHz. We use a modified cassegrain system consisting of a commercially-available paraboloidal primary mirror with a diameter of 3.7m, and a shaped secondary mirror. The secondary mirror is oversized with respect to a ray-optics design and has a surface that is bent towards the primary near its outer edge using a square term for the shaping. The antennas are simple to manufacture and therefore their cost is low. The design increased the antenna gain by approximately 10 per cent compared to a normal Cassegrain system while still maintaining low contamination from ground-spill and using a simple design for the horn.