If they are ABSOLUTELY in phase, the far fields will add.

Typically, the fields will not be in phase, unless the signal SOURCE and
ALL cables are precisely controlled [phase locked and absolute phase
velocity controlled], and the resulting pattern will be the vector sum
of the individual fields. a distorted pattern will result.

AK

CD wrote:

Hi folks,

I have some questions. If I had two power amps at 15W each, 2 feet
apart, and they are connected to two similar isotropic antennas, would
the two far-field patterns add up? How would I calculate the power
received by a receiver at a certain distance?

I wonder since each antenna will have 0dB gain, then ideally the loss
that I would need to take into account would just be free space path
loss, eh? Will the antenna patterns change in terms of beamwidth and
gain? What other changes/factors do I need to know about?

Thanks!