Phase Principle for Measuring Location or Spectral Shape of a Discrete Radio Source

In many branches of science and technology observations of a discrete radio source provide fundamental knowledge. In the field of radar the illuminated target serves as the discrete radio source. In the field of space exploration the radio transmitter on-board the space vehicle serves as the discrete radio source. In the field of radio astronomy the "radio star" serves as the discrete radio source. The "radio star" is a remarkable example of a discrete radio source. In the past twenty years radio astronomers have discovered that nature provided many discrete radio sources or radio stars at certain locations in the sky. What are the locations of these radio stars? What is the power spectrum of the observed radiation from a particular radio star? Answers to such questions are of fundamental importance in the field of radio astronomy.1 415 416 T H E BELL SYSTEM TECHNICAL JOURNAL, MARCH 1968 In order to measure relatively small values of radiated power from a discrete radio source, one must compete with the inevitable background noise and the inevitable radio receiver noise. It is well known that one requires a method of measurement which is relatively insensitive to receiver gain fluctuations. The papers by Dicke2 and Ryle 3 discuss this important point in more detail. In fact, the present day method for measuring relatively small values of radiated power from a discrete radio source makes use of some form of the Dicke2 radiometer or the Ryle 3 interferometer. The purpose of this paper is to describe a phase principle for measuring the location or the spectral shape of a discrete radio source.