Teledyne LeCroy VirtualProbe - Manual (Page 14)

VirtualProbe Software
Warnings and Error Messages
If all lanes are not setup as 4 port, Channel in the VP Setup dialogs for each lane, then a message will be
displayed. For example:
Warning triangles may also be displayed in the XTalk dialog when an error situation exist. Touch the tri-
angle to call up a dialog that explains the error.
Touchstone File Format
Touchstone is a file format used for specifying S-parameters. It is a standard that is commonly adopted
by vector network analyzers (VNAs), time-domain network analyzers (TDNA) and EDA tools such as micro-
wave simulators.
Specification
VirtualProbe requires that Touchstone files meet the following specification:
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The extension must be in the form .s[N]p where [N] corresponds to the number of ports in the
device. For example, a two port S-parameter file has an extension ".s2p".
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Lines cannot be longer than 2000 characters.
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Lines beginning with ! are comment lines. Comments must be at the front of the file. No com-
ments are allowed once the frequencies and S-parameter values start.
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There should be at least one line that begins with ‘#'. This line is a line that contains tokens that
help interpret the S-parameters. Valid tokens are:
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Hz – frequencies are in Hz.
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MHz – frequencies are in MHz.
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GHz – frequencies are in GHz.
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MA – S-parameters are in magnitude/angle form where the magnitudes are true mag-
nitudes and the angle is in degrees.
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RI – S-parameters are in real/imaginary form.
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DB – S-parameters are in magnitude/angle form where the magnitude is in decibels and the
angle is in degrees.
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If the above tokens are not found, the frequencies are assumed to be in MHz, and the S-param-
eters are assumed to be in magnitude/angle form.
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The S-parameters for each frequency are assumed to be listed as:
[frequency] (S11) (S12) …(S1[N])(S21) (S22) … (S2[N]) … (S[N]1) (S[N]2) … (S[N][N])
where N is the number of ports dictated by the file extension, except for two-port S-parameters
which are assumed to be listed as [frequency] (S11) (S21) (S12) (S22) according to the standard.
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All S-parameters are assumed to be 50 Ohm. In S-parameter files, on the line beginning with ‘#',
usually there is a token pair: R [Z0] where [Z0] is the characteristic impedance. We assume Z0 is 50
and ignore these tokens.
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