How Does Antenna Spacing Affect Signal Intensity at a Distance?

[nahanksh]

Homework Statement

The four antennas are arranged in a square with side length d and each of the antennas has an adjustable phase of the radiation emitted. The intensity of radiation emitted by each antenna is I1 with wavelength λ. A receiver is placed at locations A (at the center of the antenna array), B (much farther from the array than d, due east), and C (much farther from the array than d, due south-east). http://online.physics.uiuc.edu/cgi/courses/shell/common/showme.pl?courses/phys214/oldexams/exam1/sp08/fig5.gif

How should the distance d be adjusted so that the maximum possible intensity is received at position B? (Assume φ1 = φ2 = φ3 = φ4 and remember that B is far away.)

Homework Equations

The Attempt at a Solution

I am not even getting close to the question..

Could anyone give me a hint or help approach to this question..?

 

[kuruman]

Think constructive and destructive interference.