5 CALIBRATION AND CALIBRATION KIT
102
Full 2-port calibration is a highly accurate method of calibration for 2-port DUT
measurements.
5.1.6.7 Sliding Load Calibration
In full one-port and full two-port calibrations it is possible to employ a SLIDING
LOAD calibration standard instead of a fixed one. The use of the SLIDING LOAD
standard allows for significant increase in calibration accuracy at high frequencies
compared to the FIXED LOAD standard.
The sliding load calibration involves a series of measurements in different positions of
the sliding element to compensate for reflection from the dissipation component.
To activate the sliding load calibration algorithm, the selected calibration kit should
contain the calibration standard of sliding load type, and it should be assigned "load"
class of the corresponding port. Calibration standard editing and class assignment are
further described in detail.
The sliding load calibration is not applied at lower frequencies. To eliminate this
limitation, use a FIXED LOAD standard in the lower part of the frequency range. For
combined calibration with SLIDING and FIXED LOADS, use the procedure of
standard subclasses assigning. This procedure is described in detail below.
5.1.6.8 Unknown Thru Calibration
An UNKNOWN THRU calibration standard is used only in full two-port calibration,
which is also known as SOLT (Short, Open, Load, Thru) calibration.
This calibration method involves connecting the test ports to each other, what is called
THRU. If the connectors’ gender or type prevent direct connection, a DEFINED THRU
is used. But it is not always possible to know the exact parameters of the THRU, in this
case UNKNOWN THRU calibration is used.
An arbitrary two-port device with unknown parameters can be used as an UNKNOWN
THRU. An UNKNOWN THRU should satisfy only two requirements.
The first requirement applies to the transmission coefficient of the THRU. It should
satisfy the reciprocity condition (S
21 = S
12), which holds for almost any passive
network. Besides, it is not recommended to use a THRU with the loss higher than 20 dB
as it can reduce the calibration accuracy.
The second requirement is to know the approximate electrical length of the
UNKNOWN THRU within the accuracy of 1/4 of the wavelength at the maximum
calibration frequency. This requirement, however, can be omitted if the following
frequency increment is selected:
0
4
1
t
×
<DF , where τ0– delay of a two-port device.
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