Research on Calibration Sources for a 35–40 GHz Millimeter-Wave Solar Radio Observation System

The microwave spectra in the optically thin regime provide unique information about the solar corona magnetic field; thus, a millimeter-wave solar radio observation system (35–40-GHz) in the Chashan observatory is newly established to obtain relevant data. Herein, we design and develop a blackbody calibration source employing a metal cone array and absorbing patch to calibrate the system and obtain accurate solar observation data for analysis and decision-making. The reflectivity of the calibration source is simulated and measured to characterize its emissivity. The reflectivity is obtained by the finite-integeral technique (FIT) method under various fitting conditions, i.e., the thickness of the absorbent patches and aspect ratios of the cone. The temperature gradient of cones is determined by the finite-element method (FEM). A
$5\times $
5 array microwave blackbody was developed based on a cone with a low scattering coefficient and excellent temperature uniformity. To reduce the influence of spurious signals, the time-domain gate technique is used to test the reflectivity of the target. The results demonstrate that the emissivity of the blackbody is higher than 0.9995 in the 35–40-GHz band. The temperature difference between the cone top and the cone bottom is 0.20 °C.