An Introduction to Radio Astronomy

A radio telescope intercepts the radiation coming from celestial sources, usually separating it into its two polarization components. The telescope sends the energy it receives through transmission lines to a receiving system where the signals are amplified and transferred to the detection system. The radio telescope must meet two basic requirements, sensitivity and angular resolution. The following three chapters are concerned with optimizing these two fundamental parameters. Sensitivity depends on having the largest collecting area possible, while minimizing the contributions of extraneous noise; this depends upon both the telescope design and the quality of the receiving system. The angular resolution is determined by the overall dimensions of the telescope.

In this chapter, we consider single-aperture telescopes, for which large area and high angular resolution go together. It is economically impossible to get the highest angular resolution by extending the size of a single aperture indefinitely, so it is necessary to use widely spaced single-aperture telescopes in an array. Such arrays, and the means by which their data are analysed, are discussed in Chapters 5 and 6. Arrays, which are now usually aperture-synthesis arrays, are made up of individual elements, usually paraboloidal radio telescopes, although they may themselves be arrays of dipoles if intended for long wavelengths. The individual elements instantaneously observe a patch of sky, determined by the beam pattern; this is called the field of view (FOV).When the elements are steerable, as they usually are for paraboloids, their design (or the horizon) defines the available sky.