Radio direction finder with means for reducing sensitivity to multipath propogation errors

A radio direction finder having a plurality of consecutively numbered antenna elements in an array, for determining the angle of arrival of an electromagnetic wave from the phases of received energy at said elements, comprising:

• first means including at least two selected pairs of said antenna elements each including two elements, said elements of each pair being equally spaced and arranged so that a line joining the elements with even ordinal numbers is parallel to the line joining elements with odd ordinal numbers;
• second means for separately measuring the amplitudes m1, m2, m3 and m4 and the phases .alpha.1 and .alpha.2 of the rf voltages picked up by each element;
• and third means including a computer responsive to said second means for determining the phase .beta. of the desired wave in the condition of unequal values in amplitude and phase measured values denoting the presence of a spurious signal of the same frequency as the desired wave, said third means operating to solve the equation:
• m1.sup.2 + m2.sup.2 -2m1 m2 cos (.alpha.1-.beta.) =m3.sup.2 + m4.sup.2 -2m3 m4 cos (.alpha.2-.beta.)
• for the value of said .beta..