Concepts and features
R&S
®
ZNA
168
User Manual 1178.6462.02 ─ 20
unknown but must be nonzero; its phase must be roughly known (90 deg). The magni-
tude and phase of the reflection coefficient must be the same at both test ports.
TRM calibration is especially useful for DUTs in test fixtures.
4.5.1.9
TRL calibration
A TRL (Through – Reflect – Line) calibration requires the two-port standards Through
and Line, which are both assumed to be ideally matched. The Through must be loss-
less, and its length must be exactly known. The length of the Line standard must be
known approximately.
Furthermore, a reflecting one-port standard (Reflect) is needed. The magnitude of the
reflection coefficient of the Reflect standard can be unknown but must be nonzero; its
phase must be roughly known (90 deg). The magnitude and phase of the reflection
coefficient must be the same at both test ports.
TRL calibration is especially useful for DUTs in planar line technology (e.g. test fixtures,
on-wafer measurements) where it is difficult to design and connect accurately modeled
Open, Short or Match standards.
If TRL is not practicable, TNA can be an alternative.
TRL with several Lines and with TRM
The system of equations that have to be solved for the error terms exhibits singularities
whenever the length difference ΔL between the Through and the Line is an integer
multiple of half of the wave length:
2
n
L
As a rule, singularities are avoided with sufficient accuracy if the phase shift resulting
from the (electric) length difference between the Through and the Line standard is
between 20° and 160°. This corresponds to a ratio of 1:8 for the start and stop fre-
quency of the calibrated sweep range.
To shift the calibrated sweep range to smaller or larger frequencies, you can use a lon-
ger or shorter Line. To extend the calibrated range, use one of the following methods:
●
Perform TRL calibration with two or three different Line standards. With an appro-
priate length of the Lines, the ratio for the start and stop frequency of the calibrated
sweep range can increase to approx. 1:64 (for 2 lines) or 1:512 (for 3 lines).
●
In the low-frequency domain where TRL becomes inaccurate, replace TRL by TRM
calibration. See
"Low-frequency extension with TRM"
The methods can be combined or used separately. The list of measured standards in
the calibration step for TRL calibration is extended if the calibration kit in use contains
the necessary standards:
●
A 2-line (3-line) calibration requires two (three) different Lines of matching gender.
The lines must be measured between any combination of two ports.
Calibration
