Far field zone of a single antenna can be determined by using the equation below.
Where D is the biggest dimension of the antenna.
This equaiton is suitable for single antenna. But what if there are more antennas than one?
How can we determine rayleigh distance, far-field distance, of an array antenna? For example, how can I determine far-field distance of an two element (aperture type antennas) linear array antenna as shown below?