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Antenna dish for satellite - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.


 Post subject: Antenna dish for satellite
Posted: Tue Jul 15, 2008 12:47 am 
 
Lieutenant

Joined: Tue Jul 15, 2008 12:42 am
Posts: 1
Hi guys,

I am quite new for the satellite staffs. Could anyone give me some explanation about the size of antenna dish? Why the dish for Ku band is smaller than C band?


 
   
 
 Post subject:
Posted: Tue Jul 15, 2008 3:45 am 
 
General
User avatar

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK
Hi pawinll
The gain formula is approximately Gain = 17.5 + 20 * LOG( F * D)
where F is the frequency in GHz and D is the diameter in metres.
Therefore as F increases for a given dish diameter, the gain increases. You might think then that if you choose a 4 feet (1.2m) dish size, you just get more gain at Ku gain, and that's good right?
Well, no, because the consequence of greater gain is narrower beamwidth. At some point the dish pointing accuracy requirements are too severe, in other words the antenna beamwidth is too narrow. Slight pointing errors will result in flutter of the signal, for example due to wind vibration.
Each satellite service has a given almost constant gain requirement, because the link parameters are stable with time, varying only by a few dB due to rain or due to sun noise. You therefore need just enough gain to satisfy the link loss budget, and having more gain achieves nothing terms of system performance. It just costs more bucks, and gives more alignment headaches.




Posted  11/12/2012
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