Progress of Cosmic Dawn global spectrum experiments

Exploring the Dark Ages, Cosmic Dawn, and Cosmic Reionization is of great significance to understand the evolution of the Universe and has been an important research direction in astronomy. From around the year of 2000, people began to try to use 21 cm neutral hydrogen radiation below 200 MHz to detect the early evolution of the Universe, mainly in two ways, one is to use large-scale array for three-dimensional imaging of neutral hydrogen radiation, and the other is to measure the average power spectrum of 21 cm neutral hydrogen through a single antenna. The latter type of measurement has a small equipment scale and only requires a single antenna, but requires the receiver to have a high-precision calibration capability. This paper mainly focuses on the experiments of global spectrum experiment conducted at Hongliuxia observation station of National Astronomical Observatories in Xinjiang in recent years, including a variety of frequency-independent antenna designs, innovative multi-channel cross-validation receiving system design, and preliminary experimental progress. The experimental results show that the residual error of system calibration accuracy obtained by antenna simulator is less than 0.025 K, which reaches the international level of self-calibration accuracy. The development of these devices and the implementation of experiments will strongly promote China’s future lunar orbit or lunar base global spectrum exploration project in China.