Agilent Technologies 8753ET User Manual page 376

Operating Concepts
Processing
necessarily synchronized with the sweep, and are performed by the main processor.) When full 2-port error
correction is on, the raw arrays contain all four S-parameter measurements required for accuracy
enhancement. When the channels are uncoupled ( ), there may be as many as eight
COUPLED CH OFF
raw arrays. These arrays are directly accessible via GPIB. Notice that the numbers here are still complex
pairs.
Raw Arrays
Raw arrays contain the pre-raw data which has sampler and attenuator offset applied.
Vector Error-correction (Accuracy Enhancement)
Error-correction is performed next, if a measurement calibration has been performed and correction is
activated. Error-correction removes repeatable systematic errors (stored in the error coefficient arrays) from
the raw arrays. This can vary from simple vector normalization to full 12-term error-correction.
The results of error-correction are stored in the data arrays as complex number pairs. These are
subsequently used whenever correction is on, and are accessible via GPIB.
If the data-to-memory operation is performed, the data arrays are copied into the memory arrays.
Trace Math Operation
This operation selects either the data array, memory array, or both to continue flowing through the data
processing path. In addition, the complex ratio of the two (data/memory) or the difference (datamemory)
can also be selected. If memory is displayed, the data from the memory arrays goes through exactly the
same processing flow path as the data from the data arrays.
Gating (Option 010 Only)
This digital filtering operation is associated with time domain transformation. Its purpose is to
mathematically remove unwanted responses isolated in time. In the time domain, this can be viewed as a
time-selective bandpass or bandstop filter. (If both data and memory are displayed, gating is applied to the
memory trace only if gating was on when data was stored into memory.)
The Electrical Delay Block
This block involves adding or subtracting phase in proportion to frequency. This is equivalent to
"line-stretching" or artificially moving the measurement reference plane. This block also includes the
effects of port extensions as well as electrical delay.
Conversion
This converts the measured S-parameter data to the equivalent complex impedance (Z) or admittance (Y)
values, or to inverse S-parameters (1/S).
Transform (Option 010 Only)
This transform converts frequency domain information into the time domain when it is activated. The results
resemble time domain reflectometry (TDR) or impulse-response measurements. The transform uses the
chirp-Z inverse fast Fourier transform (FFT) algorithm to accomplish the conversion. The windowing
operation, if enabled, is performed on the frequency domain data just before the transform. (A special
transform mode is available to "demodulate" CW sweep data, with time as the stimulus parameter, and
display spectral information with frequency as the stimulus parameter.)
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