Abstract: The direction and/or distance between a fixed point and a vehicle or between two vehicles located on a common vehicle way are measured by an intermediate frequency interferometric technique wherein signals are transmitted from a single antenna to a receiver system comprising three equally spaced linearly arranged antennas. The technique encompasses determination of the path length differences between the transmitting antenna and each of the receiving antennas. The path length differences are thereafter employed to compute the distance to and/or direction between the transmitting antenna and the linearly aligned receiving antennas.

Abstract: An intermediate frequency interferometric technique and apparatus for the measurement of angles, for example the measurement of the elevation and azimuth bearing angles between an aircraft installed transmitter and a ground based receiver, are disclosed. Carrier and sideband signals emitted by a mobile transmitter are received by at least a pair of fixed position antennas, spaced at a nominal distance equivalent to the wavelength of the frequency separation between the transmitted carrier and its associated sideband, and the angle related path length difference between the transmitter and the spaced receiving antennas is measured in wavelengths at the carrier modulation frequency.