Abstract: This invention relates to a radio wave angle of incidence measurement apparatus which is applicable to radar and other detection systems, and which utilizes an antenna array with radiator elements distributed at a spacing larger than one half of the propagation wavelength. A radio signal is received by an antenna array that exhibit at least two different values of d/.lambda. (where d is the inter-element spacing of the radiator elements, .lambda. the propagation wavelength), and the resultant inter-element phase differences, of which there are at least two sets, are digitally measured. A phase difference converter circuit receives the digital signals representing the inter-element phase differences and processes them and generates an output signal that varies monotonically as the incident angle of the radio signal incident on the antenna array varies.