Radio receiver opens wider window to exploring universe

The receiver, created by a team of researchers at Osaka Prefecture University (OPU) and the National Astronomical Observatory of Japan (NAOJ), can capture radio waves at frequencies over a range several times wider than conventional ones. It is also expected to enable significant signs of progress in studying the evolution of the Universe and the mechanisms of star and planet formation.

Interstellar molecular clouds of gas and dust provide the material for stars and planets. Each type of molecule emits radio waves at characteristic frequencies and astronomers have detected emissions from various molecules over a wide range of frequencies.

By observing these radio waves, astronomers and scientists can learn about the physical properties and chemical composition of interstellar molecular clouds. This has been the motivation driving the development of a wideband receiving system.

The range of radio frequencies that can be observed simultaneously by a radio telescope is very limited. This is because of the characteristics of the components that make up a radio receiver. But the researchers in Japan have widened the bandwidth of various components, such as the horn that brings radio waves into the receiver, the waveguide (metal tube) circuit that propagates the radio waves, and the radio frequency converter.

By combining these components into a receiver system, the team said they have achieved a range of simultaneously detectable frequencies several times larger than before. The receiver system was mounted on the OPU 1.85m radio telescope in NAOJ’s Nobeyama Radio Observatory and captured radio waves from actual celestial objects. This shows that the results are extremely useful in actual astronomical observations, the research team said.

“It was a very emotional moment for me to share the joy of receiving radio waves from the Orion Nebula for the first time with the members of the team, using the receiver we had built,” said OPU graduate Yasumasa Yamasaki, lead author of the paper describing the development of the wideband receiver components. “I feel that this achievement was made possible by the cooperation of many people involved in the project.”

When compared to the receivers currently used in the Atacama Large Millimetre/sub-millimetre Array (ALMA) in northern Chile, the breadth of frequencies that can be simultaneously observed with the new receivers is striking, the team said. To cover the radio frequencies between 211 and 373GHz, ALMA uses two receivers, Band 6 and 7, but can use only one of them at a given time.

In addition, ALMA receivers can observe two strips of frequency ranges with widths of 5.5 and 4GHz using the Band 6 and 7 receivers, respectively. The researchers also said the new wideband receiver can cover all the frequencies with a single unit. The receiver can detect radio waves in a frequency range of 17GHz at a time, especially in a higher frequency band.

“It was a valuable experience for me to be involved in the development of this broadband receiver from the beginning to successful observation,” said graduate student Sho Masui, lead author of the research paper reporting the development of the receiver and the test observations. “Based on these experiences, I would like to continue to devote further efforts to the advancement of astronomy through instrument development.”

According to the team, this wideband technology has made it possible to observe the interstellar molecular clouds along the Milky Way more efficiently using the 1.85m radio telescope.

Widening the receiver bandwidth is also listed as one of the top priority items in the ALMA Development Roadmap, which aims to further improve the performance of ALMA. This achievement is expected to apply to ALMA and other large radio telescopes, and to contribute significantly to enhance our understanding of the evolution of the universe.