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Circulair patch behaves linear



Hi AMSATs,

Some time ago I posted some message where I discribed my discovery that I 
using a RHCP in front of my dish for long times without any problems 
recieving AO40. This made me suggest that my patch was not that circulair as 
many amateurs believe it is. Later when I made a LHCP version, that is even 
more accurate than the previous RHCP one I could not hear very much 
difference.

On that message I recieved some emails from other amateurs who also tested 
patches with results that showed that the so called circulair patch in not 
realy circulair. With this information I wanted to know if this circularity 
belongs more to the fairy-tale world or more to the reality.

Today it was a very nice and sunny day, so I decided to make some test setup 
and test the patch.
I made some 13cm linear metal can antenna out of an fruit can :o) which has 
the right diameter...
At some 150m distance in the garden I put the metal can with a 13cm test 
signal on it and see what my patch was recieving.

While I was rotating the (so called circulair) patch I measured a 9dB 
difference !!!!
The best signal I got when the feed-point of the patch was on top, with a 
vertical polarisation recieved.
Below the situation in a picture. (The picture shows the radiating plate, 
the reflector is not shown)

  ***********
  *                 \
  *        +        *     + = 50E feed point (BNC connector)
  *                  *
  *                  *     <-- Along this x-axis the signal strenght is 9dB 
lower than
  *                  *          along the y-axis.
   \                 *
    ***********

        ^-- Along this y-axis the polarisation is the best (9dB better than 
along x-axis!!!)

I don't say that a patch can not be made circulair, but after checking all 
the sizes that are well within
1mm I am suprised to find even a 9dB difference with these minor size 
differences !!!! The sizes I have taken out of the publication in AMSAT-DL 
magazine MAI 2003. The patch plate is from coper with a aluminium reflector 
plate and 100% air spacing between them. (There are no distance keepers that 
could cause any problems)

In my opinion the so called "simple to make circulair patch", doesn't 
dignify its glory.
The combination of "simple to make" and "circulair" belong for me to the 
fairy-tales.
I believe that patches can be made near to 100% circulair, but this is only 
for those who can measure it and have the equipment to make all sizes very 
accurate.

For all those patch freaks, don't worry... even with this 9dB difference you 
have 5% more signal reception than with a linear patch :o)

We just go on and have fun in satellite radio,
73 de PE1RAH, William
---

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