RHINO: A large horn antenna for detecting the 21cm global signal

TL;DR

RHINO is a large horn antenna designed to detect the faint 21cm global signal from neutral hydrogen, employing innovative calibration and shielding techniques to improve measurement accuracy during Cosmic Dawn and Epoch of Reionisation.

Contribution

The paper introduces RHINO, a novel horn antenna system with continuous calibration for improved 21cm signal detection, addressing challenges of foregrounds and instrumental artefacts.

Findings

Simulation shows limited bandwidth affects signal recovery.

Continuous wave calibration improves gain stability.

Prototype construction is underway at Jodrell Bank.

Abstract

The sky-averaged brightness temperature of the 21cm line from neutral hydrogen provides a sensitive probe of the thermal state of the intergalactic medium, particularly before and during Cosmic Dawn and the Epoch of Reionisation. This `global signal' is faint, on the order of tens to hundreds of millikelvin, and spectrally relatively smooth, making it exceedingly difficult to disentangle from foreground radio emission and instrumental artefacts. In this paper, we introduce RHINO, an experiment based around a large horn antenna operating from 60-85 MHz. Horn antennas are highly characterisable and provide excellent shielding from their immediate environment, which are potentially decisive advantages when it comes to the beam measurement and modelling problems that are particularly challenging for this kind of experiment. The system also includes a novel continuous wave calibration source to control correlated gain fluctuations, allowing continuous monitoring of the overall gain level without needing to rapidly switch between the sky and a calibration source. Here, we describe the basic RHINO concept, including the antenna design, EM simulations, and receiver electronics. We use a basic simulation and analysis pipeline to study the impact of the limited bandwidth on recovery of physical 21cm global signal model parameters, and discuss a basic calibration scheme that incorporates the continuous wave signal. Finally, we report on the current state of a scaled-down prototype system under construction at Jodrell Bank Observatory.