[SI-LIST] AW: Re: Return loss measurement on differential signals

Hello Arun,

Baluns work fine, but are band limited. If your frequency of interest is in the 
GHz range, you can do a so called "round robin" method. For differential return 
loss this is a measurement at your port of interest, with all other ports 
terminated. 
With Port1@P-signal and Port2@N-signal Sdd11 can then be calculated: 

Sdd11=0.5*(S11-S12-S21+S22)

BR
Gert


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Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im 
Auftrag von steve weir
Gesendet: Montag, 13. April 2009 16:06
An: Arun kumar P N
Cc: si-list@xxxxxxxxxxxxx; anuj.singh@xxxxxxxxxxxx
Betreff: [SI-LIST] Re: Return loss measurement on differential signals

For differential signals you need to do four port measurements.  The poor man's 
solution is to use baluns.  This adds error sources that need to be corrected 
and is limited to the linear range of the baluns.

Steve.
Arun kumar P N wrote:
> Hi all,
>  
>
> I had gone through the details about return loss measurement and 
> relation between VSWR(Voltage standing wave ratio) & reflection 
> coefficient in Google.
>
>  
>
> Return loss = -20log (Vr/Vt)
>
> Where,
>
> Vr- Amplitude of reflected wave
>
> Vt- Amplitude of Transmitted wave
>
>  
>
> ñ  magnitude of   Ã 
>
> ñ = | Ã | .
>
>  
>
> Relation between VSWR(Voltage standing wave ratio) and reflection 
> coefficient.
>
> VSWR = (1 + ñ)/(1 - ñ)
>
>  
>
> Will this equations applicable for differential signals?, if I am 
> going to measure Signal P with respect to Signal N in the differential pair.
>
>  
>
> If you would have any alternate solution to measure return loss of 
> differential signal, please suggest me.
>
>  
>
> Thanks & Regards,
>
>  
>
> Arun Kumar  P N
>
>  
>
>  
>
>  
>
>
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