Re: Two antennas and two power amps
- From: "Steve Nosko" <suteuve.nosukowicuz@xxxxxxxxxxxxxxx>
- Date: Fri, 21 Oct 2005 13:38:38 -0500
Debate all you want, here's the scoop.
The answer to your first question (add?) is Yes. That is how multi-element
antennas work, regardless of the element shapes.
For your second & third question (how to calc &pattern, beamwidth, gain):
With the described "one transmitter feeding two antenna" system you have
nothing more than a phased array. Using two amplifiers is not important as
long as you use good techniques connecting everything and match impedances
_when both amps are transmitting_. That is if, in the first approximation,
you have all the power from each amp going into the respective antenna. I
suspect this is a valid assumption for the original poster. I'll speculate
that this will be harder with only a splitter (no amps) due to the mutual
coupling in the antennas and the impedance change therefrom, but matching
things removes this complication.
Gee... do isotropic antennas have any mutual coupling / impedance??
Seems there could be for voltage only. anyway...
The relative phase of the two antenna currents will create the pattern
(by summation in the farfield) [[regardless of the shape of the "iron in the
sky" as I call it]] I believe (and Lew can corroborate or dispel) you can
use EZNEC to get an idea what will happen by looking only at the horizontal
plane, or vertical view of two verticals; 1/4 wave should do. This is the
"plan view" or the view from above, where the verticals look like two dots.
This should represent the view of the two iso's that looks the same (two
dots).
With equal power and in phase current, you'll have a figure eight with
the nulls broad-side and the depth of the nulls will depend on the
frequency... starting from lower freq, at a frequency where the spacing is
1/2 wave, the nulls are deepest and as frequency increases, the pattern will
develop more and more lobes/nulls.
IF the two antenna currents/powers are not the same, you should also be
able to model this in EZNEC as described and the nulls will not go to zero
as expected (well, by me at least).
Looking at the two iso's from the endfire direction (the two iso's look like
one dot)..lemme think here...
Oh yea, you'll see a round pattern ( perfect circle) of varying diameter as
you vary the relative phase/amplitude. This will be equivalent to looking
at it at only one angle from the plane equidistant from the two dots. Hard
to describe, easy to imagine. As you change the angle of this cone (similar
to viewing pattern at differing radiation angles), the circle also changes
diameter.
SO... The "gain" will vary depending on Frequency, relative phase of the
two feeds and relative power of the two feeds. I don't thing path loss is
considered in pattern calculations since it is the same for all components
in the field by the time you get to any distance.
Post some pix.
OK, dispute away, I'm done.
Any comments Lew?
Regards, Steve, K,9.D;C'I
"CD" <mr.whatever@xxxxxxxxx> wrote in message
news:1129815895.553583.77090@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> 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!
>
.
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- From: CD
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