Concepts and Features
R&S
®
ZNC
73
User Manual 1173.9557.02 ─ 13
3.5.1.8
TRL Calibration
A TRL (Through – Reflect – Line) calibration requires the two-port standards Through
and Line, which are both assumed to be ideally matched. Beyond that, the Through must
be lossless, 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 coef-
ficient 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 may be an alternative.
TRL with several lines and with TRM
The system of equations solved to derive the error terms is such that singularities occur
whenever the length difference ΔL between the Through and the Line is an integer mul-
tiple 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 frequency
of the calibrated sweep range.
To shift the calibrated sweep range to smaller or larger frequencies, you can use a longer
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 appropri-
ate 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.
The methods can be combined or used separately. The list of measured standards in the
"Calibration" dialog 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.
●
A TRM extension at low frequencies requires either a Match or a Sliding Match
standard. The standard must be measured at each port.
The complete list of measured standards for a two-port calibration is shown below.
●
For a
TRL calibration with 1 Line
, the Reflect standard at both ports, the Through,
and one Line standard must be measured.
Calibration
