How does link budget imrpoves for antenna arrays - RF Cafe Forums

 Post subject: How does link budget imrpoves for antenna arrays

Posted: Thu Apr 23, 2009 9:38 am 

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

 Post subject: Re: How does link budget imrpoves for antenna arrays

Posted: Tue Apr 28, 2009 1:46 pm 

Hi Michael

The answer isn't a simple one since it depends on the configuration of the antennas on both ends, and what your objective is. Theoretically, a system like 802.11n that uses three antennas, depends on orthogonality to realize maximum efficiency. In an ideal environment (no reflections, equal path lengths, equal antenna performance, equal TX/RX circuitry) the three orthogonal antennas independently transmit/receive energy from the same signal in all three planes, without any interaction. The receive system would add the signals.

In the real world you know that the antenna configurations have to be adjusted for best average performance in the operational environment. Same goes for two antennas or even one antenna.

For any system of antennas, the net performance depends on spacing between antennas and how the receiver handles the signals. Again, for and ideal scenario where all antennas are far apart enough to be considered independent and all signals arrive at the same phase (or can be adjusted for addition), the total received power is the sum, in watts (not dB), of the individual signals.

To get a meaningful feel for how your intended configuration will perform, a computer simulation will be needed.

Have fun.

 Post subject: Re: How does link budget imrpoves for antenna arrays

Posted: Fri May 01, 2009 12:23 pm 

And what would be the answer if make assumptions that will make it easiest to answer:

-Line of sight between Tx and Rx.

-No reflections

-The single transmitter is identical to each of the N transmitters.

-The single receiver is identical to the each of the M receivers.

-The direction for the single antenna maxGain is the direction of the array maxGain

-The question is asked regarding that max gain direction

What is igain link mprovement compared to single antenna link?

10LogN +10LogM ?

20LogN +10LogM ?

20LogN +20LogM ?

Why?

Thanks