principle
The antenna collects the radio radiation of the celestial body, the receiver processes and transforms these signals into a form that can be recorded and displayed, and the terminal equipment records the signals, and performs certain processing according to specific requirements and then displays them. The basic indicators to express the performance of a radio telescope are spatial resolution and sensitivity. The former reflects the ability to distinguish two radio point sources close to each other on the celestial sphere, and the latter reflects the ability to detect weak radio sources. Radio telescopes usually require high spatial resolution and high sensitivity.
The objects studied by radio astronomy include a continuous-spectrum radio source as strong as the sun, quasars with very strong radiation but extremely remote and small angular diameters, stars with small angular diameters and flux densities, and narrow spectrums. Celestial masers sources with small angular diameters, etc. In order to detect the signal of the radio source under study, distinguish it from nearby background sources, and then observe its structural details, the radio telescope must have sufficient sensitivity and resolution.
Sensitivity and resolution are two important indicators to measure the performance of radio telescopes. Sensitivity refers to the “lowest measurable” energy value of the radio telescope. The lower the value, the higher the sensitivity. Common methods to improve sensitivity include reducing the inherent noise of the receiver itself, increasing the antenna receiving area, and extending the observation integration time. Resolution refers to the ability to distinguish two radio sources close to each other. The higher the resolution, the closer the two radio sources can be separated. So, how to improve the resolution of radio telescopes? For a single antenna radio telescope, the larger the antenna diameter, the higher the resolution. However, it is difficult to make the diameter of the antenna large. At present, the maximum diameter of a single antenna is less than 300 meters, and the resolution of the long-wavelength radio band is still low. Therefore, a radio interferometer composed of two radio telescopes was proposed. For radio interferometers, the larger the maximum distance between the two antennas, the higher the resolution. In addition, when the diameter of the antenna or the distance between the two antennas is constant, the shorter the received radio wavelength, the higher the resolution. Has high sensitivity. Only with high-resolution radio telescopes can we “see” farther and clearer cosmic objects in the radio band.
Resolution refers to the ability to distinguish two identical point sources that are close to each other. Because the angular distance between the two point sources must be greater than the half-power beam width of the antenna pattern, the resolution of the radio telescope should be specified as The half power width of the main beam. Limited by the diffraction of radio waves, for a simple radio telescope, it is determined by the physical size D of the antenna aperture and the wavelength λ.
refractor