Coherent and Non-Coherent Power Combining - RF Cafe Forums
Post subject: Coherent and non-coherent power combining
Posted: Thu May 07, 2009 4:36 pm
Tue Sep 04, 2007 7:54 am
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?
subject: Re: Coherent and non-coherent power combiningPosted: Fri
May 08, 2009 8:30 am
Joined: Fri Jul
16, 2004 4:12 pm
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
Signal Power (each) = +10 dBm
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:
= 0 dBm
P2 = +10 dBm (in phase wrt P1)
Combiner Loss= 0.5
Output Power = (1 mW + 10 mW) / 10^(0.5/10)
= 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.
Post subject: Re: Coherent and non-coherent power combiningPosted:
Fri May 08, 2009 10:46 am
Sep 04, 2007 7:54 am
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?
Re: Coherent and non-coherent power combiningPosted: Sun May 10,
2009 11:57 am
Joined: Fri Jul 16,
2004 4:12 pm
It depends on how you are measuring
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.
Post subject: Re: Coherent and non-coherent power
combiningPosted: Mon May 11, 2009 10:38 am
Joined: Thu Sep 25, 2003 1:19 am
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.
the internal losses)