The Research Of VHF Band Antenna Array Used In Solar Observations

Karl Jansky first discovered electromagnetic waves from universe, and it opened the study of radio astronomy. There have been many import discovers in decades of research in radio astronomy, such as pulsars, cosmic microwave background radiation and so on. In order to explore the universe further, and to obtain a more accurate search result, radio astronomy technology has been made tremendous development.The diameter of parabolic antenna has only few meters at first, but now the few hundreds diameter antenna has been designed. It has increased the sensitivity and resolution of antenna. Based on the technique of Very long baseline interferometry(VLBI), the whole world will be a big telescope through combine the telescopes separated in all over the world. At the same time we can form a complete image from all single telescopes through the techniques of Synthesis aperture imaging. As technology advances, many countries began to build the antenna array to explore universe, such as the Very Large Array(VLA) in America, Square Kilometer Array(SKA) in South Africa and Australia, which more than 20 countries have took part in the design.The VHF band antenna array studied in this paper will receive electromagnetic waves and preprocessing and store the data. The operation frequency of the antenna in low frequency band, and the center frequency is 60 MHz. The receiver of antenna array will receive the microwaves and transmit it to the acquisition system, and then the analog signals will be converted into digital signals. The data stored by different station will conduct the coherent processing at the later step, and antenna array requires a stable time and frequency system.Two functions of the time and frequency system is:(1)NTP(Network Time Protocol) server provides reference time to computer which control data sampling(2)GPSDO generates a 10 MHz signal and converted to 200 MHz by PLL, as a precise external clock signal of acquisition board.The NTP server will produce standard time through receiving GPS signal, and transmit the time to computers in LAN(Local Area Network). Through programming in LabView can get the time of different computers' system time deviation occurs and making the time strategy best.