Development of an antenna system to observe the circularly polarized radio emission from the solar corona at low frequencies

Abstract

The corona is the outer most atmosphere of the Sun, overlying the photosphere and the chromosphere. It extends to several millions of kilometers into space and is about 106 times fainter compared to the photosphere. At optical wavelengths, it is observed primarily during a total solar eclipse. The solar corona is also observable with coronagraphs wherein the bright light from the photosphere is occulted artificially. Outside the optical window, the solar corona is also observable at radio and Xray wavelengths. Observations of the solar corona at Xray wavelengths are carried out from space since the Earth's atmosphere doesn't allow the Xrays from the outer space to pass through it. The primary advantage of radio astronomy in observing the solar corona is that the observations can be carried out from the ground as compared to the optical and Xray wavelengths. Depending on the frequency of observation, one can image different altitude levels in the solar atmosphere. Also it is possible to observe polarized radio emission from the solar corona with a simple observing setup and derive the magnetic field there, as compared to other wavelengths. In this project, a Cross polarized Log Periodic Dipole Antenna (CLPD) has been designed, where 0o and 90o oriented arms are mounted on the same axis. The receiver system is used for both orientations is same to minimize the instrumental errors. Using the correlation interferometry technique, observations of the Sun and the calibrator sources are carried out to test the performance of CLPD.