Agilent Technologies 8719D, User Manual

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TRL Terminology
Notice that the letters TRL, LRL, LRM, are often interchanged, depending on the
standards used. For example, “LRL” indicates that two lines and a reflect standard are used;
“TRM” indicates that a thru, reflection and match standards are used. All of these refer to the
same basic method.
How Calibration Works
The calibration used in the HP relies on the characteristic
impedance of simple transmission lines rather than on a set of discrete impedance standards.
Since transmission lines are relatively easy to fabricate (in a microstrip, for example), the
impedance of these lines can be determined from the physical dimensions and substrate’s
dielectric constant.
Error Model
8 Error Terms
Figure 6-53.
functional block diagram for a
error-corrected measurement& system.
For an HP calibration, a total of 10 measurements are made
to quantify eight unknowns (not including the two isolation error terms). Assume the two
transmission leakage terms, and are measured using the conventional technique. The
eight error terms are represented by the error adapters shown in Figure 6-52. Although
this error model is slightly different from the traditional Full model, the
conventional error terms may be derived from it. For example, the forward reflection tracking
is represented by the product of and Also notice that the forward source match
and
reverse load match are both represented by
while the reverse source match
and forward load match are both represented by In order to solve for these
eight unknown error terms, eight linearly independent equations are required.
The step in the calibration process is the same as the transmission step for
a Full calibration. For the thru step, the test ports are connected together directly
(zero length thru) or with a short length of transmission line (non- zero length thru) and the
transmission frequency response and port match are measured in both directions by measuring
all four S-parameters.
Application and Operation Concepts