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Re: Antenna Questions




> >Are there any studies or data that show the effects (attenuation)
> >when one of 2 circular polarized antennas with compatible sense
> >are off-pointed at various angles ?
> 
> I'm not sure of studies, but what you are asking about is well known to
> experienced AO-10 and AO-13 operators.

As an experienced AO-10 and AO-13 user I understand from an
operations point of view what happens as a practical end result.
I guess what I am looking for are some gain measurement figures 
at various angles.  Perhaps, some other effects like what hapens 
to the incidental energy that may be produced from the sides of the 
CP antenna with respect to the reflecting surface (not the main lobe).


> >This would produce what I believe to be an elliptical pattern, but
> >is  there any data to support the perceived attenuation at the
> >receiving station provided it is pointed at the off-pointed CP
> >antenna.
> 
> You are correct, and not only that. For increasing squint angles
> polarization sense will become linear and then reverse as seen by the
> observer.  The answer is to use a CP antenna with polarization switching.
> That way you never experience more than -3 dB fades due to this effect.
> Squint angle polarization effects are addressed in chapter 7 of the
> Satellite Experimenters Handbook.

Thanks Ed, I have read the Antenna Basics Chapter in the Satellite 
Experimenter's Handbook many times. It is a highly recommended
section to read.  Although, I am ready to see some real measured 
data resulting from 0-90 degrees of off-pointing.  Surely there has 
to be some incidental radiation taking place from the side of the 
CP antenna say at 0-40 degrees off the reflector as well.  Does this 
incidental energy have a CP sense or a linear sense?  What I am 
now trying to visualize is the response of a CP antenna at very 
steep angles.  Let's say at 80 degrees of off-pointing the main lobe 
is no longer the consideration and the side lobes become the 
energy that may be more prevalent.  What sense does it produce?

The Satellite Experimenter's Handbook does a great job explaining
the effects of the squint angle using a dual boom CP antenna 
approach.  However, it does not address the squint effect when using
a single boom CP antenna.  Although, there will still be some squint 
effect at the satellite end due to its array of linear polarized antennas 
in relation to off-axis performance.  This will change the elipse as
well as the sense at various angles and has been observed on AO-13.

To requalify what I am seeking, I am specifically interested in the 
performance of single boom to single boom CP antennas or
helix to helix CP antennas where one is off-pointed. 






73's,

Tim - N8DEU
Huntsville, Alabama


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