Assume a 2D problem. Given a linear antenna array, lets say 3 antennas distributed around the z axis, how could we extract the incidence angle of the received wave? Having 3 antennas equally spaced by λ/2 in the z axis and connected to each other, the result gain would be a function of ϑ (angle of incidence). The problem is that there are 2 values of ϑ between 0 and 90 degrees where I would get the same gain. I want to have a bijective function so that given a gain we can extract the incidence angle. Can I achieve that by changing the space between the antennas?