Agilent Technologies 8753ET User Manual page 410

Operating Concepts
TRL*/LRM* Calibration (ES Models Only)
• Γ must be identical on both ports.
• If the reflect is used to set the reference plane, the phase response must
be well-known and specified.
LINE/MATCH
(LINE) • Z
0
(i.e. S
as Z
equal to 50 Ω), the SYSTEMS Z
menu is used.
• Insertion phase of the line must not be the same as the thru (zero
length or non-zero length). The difference between the thru and line
must be between (20° and 160°) ± n x 180°. Measurement uncertainty
will increase significantly when the insertion phase nears 0 or an
integer multiple of 180°.
• Optimal line length is 1/4 wavelength or 90° of insertion phase relative
to the thru at the middle of the desired frequency span.
• Usable bandwidth for a single thru/line pair is 8:1 (frequency span:start
frequency).
• Multiple thru/line pairs (Z
the bandwidth to the extent transmission lines are available.
• Attenuation of the line need not be known.
• Insertion phase must be known and specified within ± 1/4 wavelength
or ± 90°.
LINE/MATCH
(MATCH) • Z
0
measurement.
• Γ must be identical on both ports.
Fabricating and defining calibration standards for TRL/LRM
When calibrating a network analyzer, the actual calibration standards must have known
physical characteristics. For the reflect standard, these characteristics include the offset in
electrical delay (seconds) and the loss (ohms/second of delay). The characteristic
impedance,
OFFSET Z0
standard. The reflection coefficient magnitude should optimally be 1.0, but need not be
known since the same reflection coefficient magnitude must be applied to both ports.
The thru standard may be a zero-length or known length of transmission line. The value of
length must be converted to electrical delay, just like that done for the reflect standard.
The loss term must also be specified.
The line standard must meet specific frequency related criteria, in conjunction with the
length used by the thru standard. In particular, the insertion phase of the line must not be
the same as the thru. The optimal line length is 1/4 wavelength (90 degrees) relative to a
zero length thru at the center frequency of interest, and between 20 and 160 degrees of
7-72
of the line establishes the reference impedance of the measurement
= S = 0). The calibration impedance is defined to be the same
11 22
of the line. If the Z
0
of the match establishes the reference impedance of the
, is not used in the calculations in that it is determined by the line
is known but not the desired value (i.e., not
0
selection under the TRL/LRM options
0
assumed identical) can be used to extend
0