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What is the impact of antenna array on link budget - RF Cafe Forums

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Michael
 Post subject: What is the impact of antenna array on link budget
Posted: Thu Apr 23, 2009 9:35 am 
 
Lieutenant

Joined: Thu Apr 23, 2009 9:17 am
Posts: 2
I have
N antenna elements Tx array
communicating with
M antenna elements Rx array.

By how much will the link improve ?
by 20LogN + 10LogM or by 20LogN + 20LogM ?
Why?

(Compared to same link with just single identical antenna and same power, NF, distance etc)

Thanks
Michael


 
   
 
nubbage
 Post subject: Re: What is the impact of antenna array on link budget
Posted: Mon Apr 27, 2009 7:49 am 
 
General
User avatar

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 236
Location: London UK
My vote is 10*LOG(M+N) plus a fudge-factor, and assuming the antennas are still in the Far Field region.

_________________
At bottom, life is all about
Sucking in and blowing out.


 
   
 
Michael
 Post subject: Re: What is the impact of antenna array on link budget
Posted: Wed Apr 29, 2009 4:16 pm 
 
Lieutenant

Joined: Thu Apr 23, 2009 9:17 am
Posts: 2
Thank you nubbage, Could you reconsider please (I think differently at least on Tx - why do you thin I am wrong? )

Given the assumption of the original single antenna link has the same parameters to the NTx/ MRx case - same output power per antenna, NF per antenna, etc + no reflections, line of sight, ideal spatial summing at the max gain direction, array max gain direction same as the single antenna max gain direction, and any other assumption that minimizes the problem to the simple one.

For the Tx antenna side, for sure fields of the N antenna sum perfectly. So if at point P in the single antenna case field was for example E it will become now N*E. (The E vectors are all in the same size and direction according to the assumptions above).
Therefore the transmitted power which is proportional to E^2 willl follow the 20*LogN at point P.
So, the antenna gain in the link budget will increase by 20*LogN compared to the N=1 case.
i.e. at point P

What happens on the Rx side?





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