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Coherent and non-coherent power combining - RF Cafe Forums
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ljoseph
Post subject: Coherent and non-coherent power combining
Posted: Thu May 07, 2009 4:36 pm
Captain
Joined:
Tue Sep 04, 2007 7:54 am
Posts: 13
Location: Dallas
Hi
As per some of the power combiner Application notes, if two non-coherent
(Different freq) signals are combined, there will be 3dB loss (For N
way combiner 10log(1/N).
For two coherent signals, with no phase
difference there will be no loss and 180 out of phase, total loss. Is
this correct?
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Loren A.
Post subject: Re:
Coherent and non-coherent power combiningPosted: Fri May 08, 2009 8:30
am
Lieutenant
Joined: Fri Jul 16, 2004 4:12 pm
Posts: 4
Hello ljoseph.
Combining 2 identical in-phase signals
will result in a 3 dB increase at the output. There will be an overall
loss of whatever the combiner loss is.
Example:
Signal
Power (each) = +10 dBm
Combiner Loss = 0.5 dB
Output Power
= +10 + 3 - 0.5 = +12.5 dB
For 180-degree OOP signals, the two
signals would totally cancel each other out.
Suppose you had
the following:
P1 = 0 dBm
P2 = +10 dBm (in phase wrt P1)
Combiner Loss= 0.5 dB
Output Power = (1 mW + 10 mW) / 10^(0.5/10)
= 9.80 mW
= 9.91 dB
So, the resulting output will be lower
than the larger signal because of the combiner loss. But, it's not always
that way and doesn't really matter.
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ljoseph
Post subject: Re: Coherent and non-coherent power combiningPosted:
Fri May 08, 2009 10:46 am
Captain
Joined: Tue Sep
04, 2007 7:54 am
Posts: 13
Location: Dallas
Hi,
Thanks.
What happens when the two signals are at different frequencies and +10dBm
each.
The ouput should be 10dBm-0.5dB(Coupler loss)=9.5dBm. Is this
correct?
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Loren A.
Post subject: Re: Coherent
and non-coherent power combiningPosted: Sun May 10, 2009 11:57 am
Lieutenant
Joined: Fri Jul 16, 2004 4:12 pm
Posts:
4
It depends on how you are measuring the power.
If you are
looking on a spectrum analyzer that can discern the individual powers
of the two separate signals, then there will only be the loss of the
power divider for each of the signals. The two signals at different
frequencies do not add or subtract from each other.
If you are
using a wideband power meter, or even a spec-an whose bandwidth is wide
enough to totally encompass both frequencies, then the total power will
be measured as a 3 dB gain, minus the power divider loss.
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yendori
Post subject: Re: Coherent and non-coherent
power combiningPosted: Mon May 11, 2009 10:38 am
General
Joined: Thu Sep 25, 2003 1:19 am
Posts: 50
Location: texarcana
If you combine 10dBm tones at different frequencies, there will
be 3dB of loss for each tone. 7dBm each tone.
Using a broadband
power meter will measure 10dBm.
(disregarding the internal losses)
Rod
Posted
11/12/2012
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