R. Hanbury Brown,
Boffin: a personal story of the early days of radar, radio astronomy and quantum optics
. Bristol: Adam Hilger, 1991, £17.50. ISBN 0-750-30130-9 It is doubtful if many scientists noticed the last paragraph of a mathematical paper published in 1954 by R. Hanbury Brown and R.Q. Twiss in the
Philosophical Magazine
. In this paper they gave the theory of a new type of interferometer for the measurement of the angular diameter of sources of radio emission. Unlike the Michelson type of optical interferometer extended to radio wavelengths, which depended on the combination of the signals from the two aerials
before
detection so that the relative phases were preserved, this new instrument was based upon the correlation between the
rectified
outputs of two independent receivers at each end of the baseline. Information about the relative phases was lost but in their
Philosophical Magazine
paper the authors showed that the cross correlation coefficient between the rectified outputs would be proportional to the square of the amplitude of the Fourier transform of the intensity distribution across the source.
Phased Arrays for Radio Astronomy, Remote Sensing, and Satellite Communications [Book Review]