Development of a new wideband heterodyne receiver system for the Osaka 1.85 m mm–submm telescope: Receiver development and the first light of simultaneous observations in 230 GHz and 345 GHz bands with an SIS-mixer with 4–21 GHz IF output

Abstract

We have developed a wideband receiver system for simultaneous observations in CO lines of J = 2–1 and J = 3–2 transitions using the Osaka 1.85 m mm–submm telescope. As a frequency separation system, we developed multiplexers that connect three types of diplexers, each consisting of branch-line couplers and high-pass filters. The radio frequency (RF) signal is eventually distributed into four frequency bands, each of which is fed to a superconductor–insulator–superconductor (SIS) mixer. The RF signal from the horn is divided into two frequency bands by a wideband diplexer with a fractional bandwidth of $56\%$, and then each frequency band is further divided into two bands by each diplexer. The developed multiplexers were designed, fabricated, and characterized using a vector network analyzer. The measurement results showed good agreement with the simulation. The receiver noise temperature was measured by connecting the SIS-mixers, one of which has a wideband 4–21 GHz intermediate frequency (IF) output. The receiver noise temperatures were measured to be ∼70 K in the 220 GHz band, ∼100 K in the 230 GHz band, 110–175 K in the 330 GHz band, and 150–250 K in the 345 GHz band. This receiver system has been installed on the 1.85 m telescope at the Nobeyama Radio Observatory. We succeeded in simultaneous observations of six CO isotopologue lines with the transitions of J = 2–1 and J = 3–2 toward the Orion KL as well as on-the-fly mappings toward the Orion KL and W 51.

First Detection of the Molecular Cloud Population in the Extended Ultraviolet Disk of M83

“…Again using Orion A as a reference, the velocity width of the bulk gas, measured in CO(1-0) and averaged over the whole cloud, is about 5 km s −1 at 50% of the peak brightness (from Figure 5 of Nakamura et al 2019). The full CO(3−2) velocity width over the OMC-1 clump (size of about 2 pc) is not found in the literature; toward Orion KL (the brightest region), it is about 7 km s −1 at 50% of the peak brightness in a 134″ (∼0.3 pc) beam (from Figure 15 of Masui et al 2021). Hence, the dense part has a broader linewidth than the entire cloud.…”

Development of a wideband multi-channel receiver for simultaneous observations in 230 and 345 GHz bands with dual-polarization

“…The prototype multiplexer was already developed and installed in the Osaka 1.85-m radio telescope. Then, we succeeded in preliminary simultaneous observations in 230 and 345 GHz bands with single-polarization [2]. We are currently working on improving the multiplexer and developing a 90° differential phase shifter [3] and a wideband orthomode transducer (OMT).…”

“…and 345 GHz bands with dual-polarization Sho Masui* (1), (2) , Sana Kawashita (1) , Yasumasa Yamasaki (1), (2) , Yutaka Hasegawa (1) , Takafumi Kojima (2) , Hideo Ogawa (1) , and Toshikazu Onishi (1) (1) Osaka Metropolitan University, Osaka, Japan; e-mail: s_s.masui@omu.ac.jp…”

A Broad-Band Dual-Polarization All-Metal Dichroic Filter for Cryogenic Applications in Sub-THz Range

“…In continuum observations, increasing the instantaneous bandwidth directly enhances the power of the received signal. For spectral line observations, a wider instantaneous frequency band enables quicker spectral line surveys or simultaneous observations of astronomically important CO lines, such as J = 2→1 and J = 3→2 transitions at 230 GHz and 345 GHz [2]. Moreover, multi-frequency Date of submission: July 14, 2023.…”

“…One possible implementation of a multi-band receiver system relies on duplexing and filtering techniques using waveguide technology, as presented in [2]. However, the inclusion of diplexers and filters between the feed and the receivers, along with the associated signal (RF) transmission loss, inevitably contributes to an increased system noise.…”