Probing and resolution of multipath fields

One of the difficulties commonly encountered in field strength measurements of the VHF-UHF spectrum is the prevelance of multipath propagation, In order to make meaningful measurements it becomes necessary to resolve the various components of the multipath field. The problem of determining the amplitude, time phase, polarization and direction of arrival of the various multipath components in such a field is the subject of discussion of this paper. A direct method of making the measurements could be to use a very large aperture antenna and receive the various components separately. However, this requires an impractically large antenna in the VHF-UHF range. An aperture synthesis technique introduced by Ryle (1960) for radio astronomical measurements has been adapted by Watterson (1962) for probing a multipath field. In one possible form of the scheme a small probe is moved along three linear orthogonal axes. In an alternative scheme the probe movement is along circular paths. The paper discusses various ways of processing the probed data and resolving the various components in a multipath field.