FreeLists / si-list / [SI-LIST] VNA Question

[JP <edpc108@xxxxxxxxx>]

Hello SIers,

 This is a basic VNA question, yet I don't have 
clarity. 

   In theory, S parameters are obtained by perfectly
matching the relavant port impedances. 

For instance,  considering a 2 port system, 

 b1 = S11*a1 + S12*a2
 b2 = S21*a1 + S22*a2

 bi - reflected voltage
 ai - incident voltage

 S21 is obtained by ensuring a2 = 0, which implies
perfect match at port 2. 

   => S21 = b2/a1

 In reality, however DUT impedances need not be 50ohms
and is often not known. How does VNA ensure
a2(reflected component at port2) equals zero ?

 Does VNAs have the mechanism to measure mismatch 
 and account automatically?

 Thanks in advance,
 Jayaprakash. 



   



=====
Balachandran Jayaprakash                             
Celestijnenlaan,                                                   
3/61, 3001, Heverlee,                                           
Leuven, Belgium.                                                  
Mobile: +32-472-630120

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