You mean wide-aperture? This averages out the local distortions which would normally be much more noticeable with the more narrowly focussed CVOR antenna (at about half a wavelength as opposed to about 5), so a theoretical tenfold reduction in site errors is possible (something to do with space diversity).
The Doppler shift comes from the relative motion of the antenna and the receiver. It is used because the wide aperture system needs Doppler to work properly, in that it creates the direction-dependent FM signal. The frequency change observed as the antenna rotates towards or way from an observer on the same circle is in proportion to the azimuth.
Phil
Last edited by paco; 6th Jul 2016 at 16:22.