7- 60
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.
• defines the standard type as a transmission line of specified length, for calibrating
transmission measurements.
• defines the standard type to be a load, but with an arbitrary
impedance (different from system Z0).
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