1. The problem statement, all variables and given/known data I am trying to understand how the total directivity of an array of antennas is calculated. 2. Relevant equations 1. A_e = (D * lambda^2)/(4 * pi) where: A_e = effective aperature (or area of antenna) D = Directivity of one antenna lambda = wavelength 2. D_t = (4 * pi * A_t) / (lambda^2) where: D_t = directivity of array A_t = effective aperature (of array) lambda = wavelength 3. The attempt at a solution What I am confused on is how aperature comes into play because if I have X antennas spaced Y wavelengths apart for the array, total aperature (A_t in eqn #2) is what will change. I just don't know how to get A_t from A_e if I know what the antenna spacing is. As an example, let's say I know the directivity of one antenna is 10 (which 10 dBi). But if I have 3 of them and let's say they're spaced 0.25 wavelengths apart, what is the directivity of the array? From eqn #1, A_e would be (10 * (.25L)^2) / (4 * 3.14) = 0.0497L^2 = 0.05L^2 (I'm using L for lambda) So what is the aperature of the array if I know the aperature of one antenna is 0.05L^2 ? Once I have that I would be able to use eqn #2 to figure out the array's total directivity. But the relationship between A_e and A_t is unknown to me. Thanks.