Preconditions for Auto Length and Loss, effect on measured quantities and exceptions
Auto Length and Loss is enabled if the measured quantity contains the necessary phase
information as a function of the frequency, and if the interpretation of the results is unambiguous:
A frequency sweep must be active.
The measured quantity must be an S-parameter, ratio, wave quantity, a converted
impedance or a converted admittance.
The effect of Auto Length and Loss on S-parameters, wave quantities and ratios is to eliminate a
linear phase response and account for a loss as described above. Converted admittances or
impedances are calculated from the corresponding Auto Length and Loss corrected S-parameters.
Y-parameters, Z-parameters and stability factors are not derived from a single S-parameter,
therefore Auto Length and Loss is disabled.
Calculation of loss parameters
The loss is assumed to be given in terms of the DC loss Loss
DC
, the reference frequency f
ref
, and
the loss at the reference frequency Loss(f
ref
). The formula used in the Auto Loss algorithm is similar
to the formula for manual entry of the loss parameters (see Loss parameters: Definition). The result
is calculated according to the following rules:
The reference frequency f
ref
is kept at its previously defined value (default: 1 GHz).
The DC loss c is zero except for wave quantities and for S-parameters and ratios with
maximum dB magnitude larger than –0.01 dB.
Auto Length and Loss for a wave quantity centers the corrected dB magnitude as close as
possible around 0 dBm.
Auto Length and Loss for S-parameters and ratios centers the corrected dB magnitude as
close as possible around 0 dB.
The resulting offset parameters are displayed in the Electrical Length, Mechanical Length, and
Delay dialogs.
Auto Length and Loss for logical ports
The Auto Length and Loss function can be used for balanced port configurations as well. If the
active test port is a logical port, then the same offset parameters are assigned to both physical
ports that are combined to form the logical port. If different offset parameters have been assigned
to the physical ports before, they are both corrected by the same amount.
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