Development of a new wideband heterodyne receiver system for the Osaka 1.85-m mm-submm telescope -- Corrugated horn & Optics covering 210-375 GHz band

TL;DR

This paper presents a novel wideband corrugated horn design for millimeter/submillimeter telescopes, enabling simultaneous multi-line observations with improved efficiency and performance in the 210-375 GHz range.

Contribution

The study introduces a new conical corrugated horn with 56% fractional bandwidth optimized for short wavelengths, enhancing wideband receiver capabilities.

Findings

Achieved a 56% fractional bandwidth in the horn design.

Successfully installed and tested the horn on the Osaka telescope.

Performed simultaneous observations of multiple CO emission lines.

Abstract

The corrugated horn is a high performance feed often used in radio telescopes. There has been a growing demand for wideband optics and corrugated horns in millimeter and submillimeter-wave receivers. It improves the observation efficiency and allows us to observe important emission lines such as CO in multiple excited states simultaneously. However, in the millimeter/submillimeter band, it has been challenging to create a conical corrugated horn with a fractional bandwidth of ~60% because the wavelength is very short, making it difficult to make narrow corrugations. In this study, we designed a conical corrugated horn with good return loss, low cross-polarization, and symmetric beam pattern in the 210-375GHz band (56% fractional bandwidth) by optimizing the dimensions of the corrugations. The corrugated horn was installed on the Osaka 1.85-m mm-submm telescope with the matched frequency-independent optics, and simultaneous observations of 12CO, 13CO, and C18O (J = 2-1, 3-2) were successfully made. In this paper, we describe the new design of the corrugated horn and report the performance evaluation results including the optics.