AN APPROACH TO MEASURING THE DIRECTION OF ARRIVAL OF RADIO WAVES IN THE PRESENCE OF WAVE INTERFERENCE.

When two radio waves are reflected from the ionosphere and arrive at an antenna via two different elevation angles, the measurement of the angle of arrival of the stronger wave is influenced by the weaker interfering wave. This phenomenon is examined in detail, and an approach to measuring the elevation angle of the stronger wave is presented. In deriving completely general equations for the electric field in space, it is assumed that each wave is elliptically polarized and that they arrive at the antenna with a time phase difference, beta. An equation for the phase between the voltages induced in the antenna system is derived. This equation is analyzed using a digital computer to determine the effect of varying the relative field strength and beta. Assuming the angle of arrival of the stronger wave is desired, it is shown that the normal to the composite wavefront is in serious error with respect to this angle. The error is especially severe for beta near 180 degrees and for comparable field intensities. Since the polarization of each wave and beta are time dependent, the phase is averaged, assuming a random variation in beta and an arbitrary variation in polarization. It is shown that time averaging yields the phase associated with the elevation angle of the stronger wave, providing the stronger remained so throughout the averaging time. This is shown analytically and by use of a digital computer. Author