Preface [to the Special Issue

Abstract

The title of this issue should really be "Partial Coherence and Other Correlations of the Electromagnetic Field." Sorting out the various types of correlations that radio engineers have found useful - of which the coherence functions form but a prominent subclass - is one of the purposes of this special issue. The first three contributions in this issue, and the first communication, are tutorial. Even so, some modestly new material will be found in them, for example, a nonstatistical approach to coherence theory, a first experimental demonstration of spectral impurity effects and the unmodulated Alford and Gold effect, a novel aspect in the measurement of the coherency matrix, and a unified treatment of randomness in sources and media. The following three contributions, and the second and third communications, develop various aspects of coherence theory and experiments. An optical paper is included because of incipient microwave interest in holography. Two contributions, and the fourth through sixth communications, deal with antennas and interferometry. The nine contributions, and the last two communications, on propagation through random media, contain a gratifying amount of experimental data in an area that has been and will continue to be in urgent need of them. Two contributions are on plasma diagnostics by means of correlation measurements, a subject that has for understandable reasons received more attention from optical than microwave engineers. The last two contributions deal with the communications aspects of coherence and scattering, a topic that will surely receive increasing attention in the future.