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Operating Concepts
Modifying Calibration Kits
After a standard number is entered, selection of the standard type will present one of five
menus for entering the electrical characteristics (model coefficients) corresponding to that
standard type, such as . These menus are tailored to the current type, so that only
characteristics applicable to the standard type can be modified.
The following is a description of the softkeys located within the define standard menu:
• defines the standard type as an open, used for calibrating reflection
measurements. Opens are assigned a terminal impedance of infinite ohms, but delay
and loss offsets may still be added. Pressing this key also brings up a menu for defining
the open, including its capacitance.
As a reflection standard, an open termination offers the advantage of broadband
frequency coverage. At RF and microwave frequencies, however, an open rarely has
perfect reflection characteristics because fringing capacitance effects cause phase shift
that varies with frequency. This can be observed in measuring an open termination
after calibration, when an arc in the lower right circumference of the Smith chart
indicates capacitive reactance. These effects are impossible to eliminate, but the
calibration kit models include the open termination capacitance at all frequencies for
compatible calibration kits. The capacitance model is a cubic polynomial, as a function
of frequency, where the polynomial coefficients are user-definable. The capacitance
model equation is:
C = (C0) + (C1 × F) + (C2 × F
2
) + (C3 × F
3
)
where F is the measurement frequency.
The terms in the equation are defined with the specify open menu as follows:
— allows you to enter the C0 term, which is the constant term of the cubic
polynomial and is scaled by 10
−
15
Farads.
— allows you to enter the C1 term, expressed in F/Hz (Farads/Hz) and scaled by
10
−
27
.
— allows you to enter the C2 term, expressed in F/Hz
2
and scaled by 10
−
36
.
— allows you to enter the C3 term, expressed in F/Hz
3
and scaled by 10
−
45
.
• defines the standard type as a short, for calibrating reflection measurements.
Shorts are assigned a terminal impedance of 0 ohms, but delay and loss offsets may still
be added.
• defines the standard type as a load (termination). Loads are assigned a
terminal impedance equal to the system characteristic impedance Z0, but delay and loss
offsets may still be added. If the load impedance is not Z0, use the arbitrary impedance
standard definition.
— defines the load as a fixed (not sliding) load.
— defines the load as a sliding load. When such a load is measured during
calibration, the analyzer will prompt for several load positions, and calculate the
ideal load value from it.
— defines the load as being offset.
OPEN
OPEN
C0
C1
C2
C3
SHORT
LOAD
FIXED
SLIDING
OFFSET