TSIRD ID#:     	3
ISSUE TITLE:   	Clarify S-parameter Definition
REQUESTOR:     	Radek Biernacki, Agilent Technologies; Michael Mirmak, Intel
DATE SUBMITTED:	July 20, 2011
DATE REVISED:  
DATE ACCEPTED BY IBIS OPEN FORUM: October 7, 2011 

****************************************************************************
****************************************************************************

STATEMENT OF THE ISSUE:

The current Touchstone 2.0 specification only implicitly (in page 19) states that
the S-parameter format uses power waves, and not the voltage waves.  This TSIRD
adds an explicit statement that Touchstone 2.0 refers to power waves when
describing S-parameters.

****************************************************************************

STATEMENT OF THE RESOLVED SPECIFICATIONS:

Add text indicated with * below (in the Adobe PDF version, page 7):

For Version 2.0 files, the reference resistance defines the system reference 
for the S-parameter data if the [Reference] keyword is not present. Network 
data for G-, H-, Y- and Z-parameters in Version 2.0 files is not normalized. 
Therefore, the reference resistance and [Reference] keyword have no impact on 
G-, H-, Y-, or Z-parameter data in Version 2.0 files. S-parameters are, by 
definition, normalized with respect to the reference impedance(s) and in this 
respect there is no difference between the treatment of S-parameters in 
* Version 1.0 and Version 2.0 files.  However, unlike Version 1.0 files, the 
* S-parameters in Version 2.0 and higher files are additionally affected by 
* the presence of different port reference resistances. Touchstone files use 
* the power wave definitions of the incident and reflected waves [1], as
*
* incident waves:
*		ai=(Vi+Ri*Ii)/(2*sqrt(Ri))
*
* reflected waves:
*		bi=(Vi-Ri*Ii)/(2*sqrt(Ri))
*
* where i is the port index, Ri is the i-th port reference resistance, and 
* Vi and Ii are the i-th port RMS voltage and current phasors, respectively. 
* In Version 1.0 files all the reference resistances are equal and therefore 
* the square root factors cancel out for 
*
*               Sij=bj/ai 

Update text indicated with * below on the final page:

*1. Kurokawa, K, "Power waves and scattering matrix," IEEE Transactions on 
*Microwave Theory and Techniques, vol. MTT-13, no. 3, pp. 194-202, 1965.
*2. Ferrero, A. and Pirola, M., "Generalized mixed-mode S-parameters," IEEE 
 Transactions on Microwave Theory and Techniques, vol. 54, no. 1, pp. 458-463, 2006.
*3. Bockelman, D. E. and Eisenstadt, W. R., "Pure-mode network analyzer for on-wafer
 measurements of mixed-mode S-parameters of differential circuits," IEEE 
 Transactions on Microwave Theory and Techniques, vol.45, no. 7, pp. 1071-1077, 1997.


****************************************************************************

ANALYSIS PATH/DATA THAT LED TO SPECIFICATION:

****************************************************************************

ANY OTHER BACKGROUND INFORMATION:

Submitted per discussion in the July 13, 2011 IBIS Interconnect Task Group
meeting.

The formatting of the formulae and references is preserved in the PDF at the link below:

http://ibis.org/tsirds/tsird3/tsird3.pdf


****************************************************************************