Development of a new wideband heterodyne receiver system for the Osaka 1.85 m mm–submm telescope: Corrugated horn and optics covering the 210–375 GHz band.

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 as they improve observation efficiency and allow 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 210–375 GHz 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 matched frequency-independent optics, and simultaneous observations of ¹²CO, ¹³CO, and C¹⁸O (J = 2–1, 3–2) were successfully made. We describe the new design of the corrugated horn and report the performance evaluation results including the optics. [ABSTRACT FROM AUTHOR]