1.2 Meter Shielded Cassegrain Antenna for Close-Packed Radio Interferometer

TL;DR

This paper introduces a lightweight, 1.2-meter Cassegrain antenna with shielding and optimized design for close-packed radio interferometers, enabling efficient millimeter-wave observations of cosmic microwave background and galaxy clusters.

Contribution

It presents a novel 25 kg carbon-fiber antenna design with high structural integrity, low sidelobe levels, and effective shielding, suitable for dense interferometric arrays.

Findings

A 25 kg carbon-fiber antenna with excellent structural behavior.

Shielding reduces inter-antenna coupling below -135 dB.

Estimated 60% overall efficiency with ~50 cluster detections per year.

Abstract

Interferometric millimeter observations of the cosmic microwave background and clusters of galaxies with arcmin resolutions require antenna arrays with short spacings. Having all antennas co-mounted on a single steerable platform sets limits to the overall weight. A 25 kg lightweight novel carbon-fiber design for a 1.2 m diameter Cassegrain antenna is presented. The finite element analysis predicts excellent structural behavior under gravity, wind and thermal load. The primary and secondary mirror surfaces are aluminum coated with a thin TiO$_2$ top layer for protection. A low beam sidelobe level is achieved with a Gaussian feed illumination pattern with edge taper, designed based on feedhorn antenna simulations and verified in a far field beam pattern measurement. A shielding baffle reduces inter-antenna coupling to below $\sim$ -135 dB. The overall antenna efficiency, including a series of efficiency factors, is estimated to be around 60%, with major losses coming from the feed spillover and secondary blocking. With this new antenna, a detection rate of about 50 clusters per year is anticipated in a 13-element array operation.