Search

GF-3 is the first C-band multipolarization synthetic aperture radar (SAR) satellite in China. The SAR system is equipped with an active phased array antenna to electronically generate various antenna beams. The accuracy of SAR antenna patterns is of main importance for precise SAR image processing. The traditional method for antenna pattern measurement is the near-field method but it is unable to satisfy the demand for fast measuring in-orbit. In order to measure the SAR antenna pattern quickly with high accuracy, we propose the internal calibration method. The internal calibration uses calibration signals which are routed along the nominal signal path in SAR systems, thus monitoring the gain and phase variations for each T/R channel is possible. This paper will focus on this method, including its principle, operation steps, and results, compared to the near-field method. The internal calibration method provides a valuable solution for SAR antenna pattern measurement. [ABSTRACT FROM AUTHOR]

Delingha 13.7 m telescope is one of the most important radio telescopes in China. Since installing the superconducting spectroscopic array receiver (SSAR) and adopting the On The Fly (OTF) observation mode, the telescope has operated for nearly 10 years. During this period, a large number of astronomical observation projects have been carried out and completed, a large amount of astronomical data have been accumulated, and a series of important scientific results have been achieved. This paper introduces the operating status of SSAR in astronomical observations, the problems in operations, as well as the fault phenomena and solutions. The performance test and performance analysis of SSAR are described in detail, including the receiver noise temperature and telescope system noise temperature, image rejection ratio (IRR), receiver stability, beam performance and so on. The updating and development of SSAR are listed, including the automatic adjustment of LO (Local Oscillator) power, the updating of pre-amplification circuits of the sideband separation superconducting mixer, and the optimization of control program, etc. This paper summarizes the experiences and rules, and connects the past with the future, for applying the experiences of the maintenance and operation of SSAR to the next-generation large-scale receiver system. [ABSTRACT FROM AUTHOR]

Due to ionosphere absorption and the interference ofnatural and artificial radio emissions, astronomicalobservation from the ground becomes very difficultat the wavelengths of decametre or longer, whichwe shall refer to as the ultralong wavelengths. Thisunexplored part of the electromagnetic spectrum hasthe potential for great discoveries, notably in the studyof cosmic dark ages and dawn, but also in heliophysicsand space weather, planets and exoplanets, cosmicray and neutrinos, pulsar and interstellar medium(ISM), extragalactic radio sources, and so on. Thedifficulty of the ionosphere can be overcome byspace observation, and the Moon can shield the radiofrequency interferences (RFIs) from the Earth. A lunarorbit array can be a practical first step to openingup the ultralong wave band. Compared with a lunarsurface observatory on the far side, the lunar orbitarray is simpler and more economical, as it does notneed to make the risky and expensive landing, canbe easily powered with solar energy, and the datacan be transmitted back to the Earth when it is onthe near-side part of the orbit. Here, I describe thediscovering sky at the longest wavelength (DSL)project, which will consist of a mother satellite and6–9 daughter satellites, flying on the same circularorbit around the Moon, and forming a linearinterferometerarray.The dataarecollectedby the mother satellite which computes the inter ferometric cross-correlations (visibilities) and transmits the data back to the Earth. The whole array can be deployed on the lunar orbit with a single rocket launch. The project is under intensive study in China. [ABSTRACT FROM AUTHOR]