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| Paper: |
Radio Telescopes and Measurements at Radio Wavelengths |
| Volume: |
278, NAIC-NRAO School on Single-dish Radio Astronomy: Techniques and Applications |
| Page: |
45 |
| Authors: |
Goldsmith, Paul F. |
| Abstract: |
We present an overview of how single--dish radio telescopes collect energy in an astronomical context. We begin with a discussion of key radio astronomical terminology, including specific intensity, flux density, antenna temperature, and point--like and extended sources. In order to analyze radio telescope system performance, we discuss single mode transmission lines, the feed system which couples the receiver to the antenna, and the concept of the antenna as a phase transformer. Using the distribution of the electric field in the aperture plane, we calculate the sensitivity of the radio telescope to a point source. This discussion is based on the antenna aperture efficiency and includes its dependence on the characteristics of the feed system, on the blockage, on systematic errors due to feed or secondary reflector defocus, and on random errors. The aperture plane field distribution is also the starting point for the Fourier transform relationship used to compute the far--field response, or power pattern, of the antenna. We analyze the effects of the telescope characteristics on the beam width and sidelobe level of the antenna's power pattern, and on the coupling efficiency to an extended source. Understanding this basic behavior allows us to determine what measurements are needed to calibrate the antenna, and to determine whether the system is performing properly. |
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