Making my brain work again!! (So some of this may be through my hat!)

The far field pattern would no longer be isotropic. You didnt specify
the frequency in use but genenerally speaking you would get more
radiation perpendicular to a line between the two antennas than in line
with them. As you go lower in frequency this effect becomes less and
less. As you go higher than frequencies where the distance between
become more than a wavelength (or so) the pattern will tend to break
into more than one lobe in each (general) direction. This assumes of
course that the antennas are also being fed in phase, probably from the
same transmitter.

This pattern is a result of the addition and cancellation of the
voltages due to the phase differences. If your antennas dont run from
the same TX and the freq/phase is changing the pattern will be changing
at the rate of the freq difference.

Calculate the power in theoretical terms of an AC voltage either
perfectly in phase (ie twice) or if some phase difference occurs, being
somewhat less.

I am sure that you know about the squishable rubber ball analogy of
antanna radaition patterns.

Modeling your setup through 4NEC2, EZNEC etc will give you a far better
appreciation of the outcome. I'll admit I dont know how to input an
isotropic in these pgms though.

As a general rule of thumb when one combines two antennas (usually ones
with gain) at the correct spacing you get inbetween a 2dB and (just
under) 3dB power gain increase in the desired direction. As you get
close to the maximum gain possible though you also see "extra" sidelobes
that depending on your use may be undesirable.

Hope you find this of some use and not too confusing!

Cheers Bob VK2YQA in W5


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?