In total, ten measurements are made, resulting in ten independent equations. However, the TRL error model has only eight error terms to solve for. The characteristic impedance of the line standard becomes the measurement reference and, therefore, has to be assumed ideal (or known and defined precisely).

At this point, the forward and reverse directivity (Enr and Enn), transmission tracking (Err and Em), and reflection tracking (Em and ERR) terms may be derived from the TRL error terms. This leaves the isolation (EXF and ExR), source match (Esr and Esn) and load match (ELF and ELR) terms to dkUSS.

IsoIation

Two additional measurements are required to solve for the isolation terms (EXF and ExR). Isolation is characterized in the same manner as the Full 2-port calibration. Forward and reverse isolation are measured as the leakage (or crosstalk) from port 1 to port 2 with each port terminated. The isolation part of the calibration is generally only necessary when measuring high loss devices (greater than 70 dE8).

Note

If an isolation calibration is performed, the ikture leakage must be the

 

same during the isolation calibration and the measurement.

 

 

.

 

 

 

.

 

 

 

 

 

 

.

 

 

.

 

.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

r

 

 

 

'32

 

 

 

 

 

 

El0

 

 

 

 

s21

 

 

 

 

 

 

 

 

,,Eoo

Eli,,

 

 

 

,,Sll

S22,\

 

 

 

,,&22

E33,,

 

I

 

 

EOl

 

 

 

 

%2

 

 

 

&23

*

/

.

 

 

 

 

 

 

 

 

 

 

.

 

 

 

 

 

 

 

.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I

 

 

 

 

 

 

 

 

 

 

 

EioEoi

= ERF

E23E33

= ERR

 

 

 

 

 

 

 

 

 

 

 

 

%o= EDF

E33 = EDR

 

 

 

 

 

 

 

 

 

 

 

91 = k~, ELR

E22 = &.R,ELF

 

 

 

 

 

 

 

 

 

 

 

 

'IO&32

= bF

'01'23 = %R

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

pb6121d

Figure 6-53. S-term TRL error model and generalized coefkients

644 Application and Operation Concepts

Page 375
Image 375
HP 8753E manual IsoIation, Same during the isolation calibration and the measurement