A Two-element Interferometer for Millimeter-wave Solar Flare Observations

• Published in: The Astrophysical journal. Supplement series Vol. 267; no. 1; pp. 14 - 23
• Main Authors: Yu, YongLin, Xu, Shuo, Zhang, Lei, Shang, ZiQian, Qiao, ChengLong, Li, ShuQi, Wu, Zhao, Su, YanRui, Song, HongQiang, Chen, Yao, Yan, FaBao
• Format: Journal Article
• Language: English
• Published: Saskatoon The American Astronomical Society 01.07.2023; IOP Publishing
• Subjects: Antennas; Astronomical instrumentation; Cassegrain antennas; Cloud cover; Cross correlation; Fluctuations; Flux density; Interferometers; Low level; Millimeter waves; Noise factor; Nulling interferometry; Quiet Sun; Radiation; Radiation flux; Radio emission; Radio interferometers; Sensitivity; Solar flares; Solar radio emission; Time constant; Wavelengths
• ISSN: 0067-0049; 1538-4365
• DOI: 10.3847/1538-4365/acd9af

Abstract In this paper, we present the design and implementation of a two-element interferometer operating in the millimeter-wave band (39.5–40 GHz) for observing solar radio emissions through nulling interference. The system is composed of two 50 cm aperture Cassegrain antennas installed on a common equatorial mount, with a separation of 230 wavelengths. The cross-correlation of the received signals effectively cancels out the quiet solar component of the high flux density (∼3000 sfu) that reduces the detection limit due to atmospheric fluctuations. The system performance is as follows: the noise factor of the analog front end in the observation band is less than 2.1 dB, system sensitivity is approximately 12.4 K (∼34 sfu) with an integration time constant of 0.1 ms (default), the frequency resolution is 153 kHz, and the dynamic range is ≥30 dB. Through actual testing, the nulling interferometer observes a quiet Sun with a low level of output fluctuations (up to 50 sfu) and has a significantly lower radiation flux variability (up to 190 sfu) than an equivalent single-antenna system, even under thick cloud cover. As a result, this new design can effectively improve observation sensitivity by reducing the impact of atmospheric and system fluctuations during observation.