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How does a tracking antenna work? - RF Cafe Forums

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Mr.Whatever
 Post subject: How does a tracking antenna work?
Posted: Tue Mar 20, 2007 3:45 pm 
 
Captain
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Joined: Fri Apr 07, 2006 6:10 pm
Posts: 18
Good day everyone!

I am curious about the inner-workings of a tracking antenna. How exactly does it track a signal and what issues does it have? I've read somewhere that they may have some polarization issues and such.

Thanks!


 
   
 
nubbage
 Post subject:
Posted: Wed Mar 21, 2007 11:12 am 
 
General
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Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK
Hi Mr Whatever. It is me again.
The antenna is usually configured as an array of a minimum of 4 elements. The signals are fed into a matrix of hybrids in such a way that there is a sum of the element patterns for the horizontal plane, and for the vertical plane, and there is a difference port for each. The difference port produces a deep null along the array boresight for each plane. To one side of boresight the phase is positive, but when the source is to the other side of antenna boresight the phase reverses, the sum ports providing the phase reference. Detectors on the difference ports can be connected to a servo mechanism that drives the antenna so that it oscillates very slightly either side of boresight in each plane ie azimuth and elevation.
I have the hybrid coupler configuration I could upload if anyone is interested.
Polarization purity is important only to the extent that if severe cross-polarization occurs, the null in the difference channel is not so deep. At least I seem to recall that was the argument when I was involved in tracking radars.


 
   
 
Mr.Whatever
 Post subject:
Posted: Fri Mar 23, 2007 2:55 pm 
 
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Joined: Fri Apr 07, 2006 6:10 pm
Posts: 18
Thanks again, nubbage! Hopefully, that propagation stuff has been taken care of already.


 
   
 
nubbage
 Post subject:
Posted: Mon Mar 26, 2007 5:19 am 
 
General
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Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK
Hi Mr Whatever
My pleasure. Do you need the coupler configuration up-load?
Ref the OTH propagation issue: thanks for your help. I sorted out the typos and other inconsistencies in the article, and derived a value for Over The Horizon Loss. It differs again from all the others, which all differ from each other.
I realize now what the problem is: it is statistics, not science.
"There are estimates, rough estimates and statistics".


 
   
 
Mr.Whatever
 Post subject:
Posted: Mon Mar 26, 2007 8:52 pm 
 
Captain
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Joined: Fri Apr 07, 2006 6:10 pm
Posts: 18
Hi nubbage,

Yeah, if you can upload it or send me a quick email.

Thanks!






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