RADIOHELIOGRAPH OF ROYAL-OBSERVATORY-OF-BELGIUM

Research work has shown that a fruitful comparison is possible between optical and radio wavelength observations of the sun. The radioheliograph at Humain in Belgium was built using the Mills-Cross interferometer principle. Using a T antenna array, ground area and costs were kept to a minimum while the resultant pencil beam, in combination with well designed circuitry, provided a highly satisfactory system performance as shown by experimental results. The radioheliograph is able to record at relatively high rates a radio image of the sun. The resultant film is compared with similar recordings obtained with the solar equatorial table. The working frequency of the system is 408 MHz with 32 antennas in EW direction and 16 antennas in a NS direction, the crossover being asymmetrical at the 23rd EW antenna. The pencil beam created is only slightly elliptical at 4 prime multiplied by 4 prime 36 double prime . The system can be operated in 3 modes: scanning the sun, drift, and aperture synthesis. The scanning provides a raster of 80 lines, the frame frequency being 125 Hz and the line frequency of 10 kHz. An alignment procedure has been devised that requires less than the usual distance separation between antennas and transmittr, 30 km being reduced to 13 km. A sophisticated system of alarms ensures immediate awareness of any fault in the system and modular construction of all electronic equipment means fast replacement.