Atek HP 8753D, User Manual, Page: 345 / 677

Each standard must be identied as one of ve \types": open, short, load, delay/thru, or
arbitrary impedance .
After a standard number is entered, selection of the standard type will present one of ve
menus for entering the electrical characteristics (model coecients) corresponding to that
standard type , such as
NNNNNNNNNNNNNN
OPEN . These menus are tailored to the current type , so that only
characteristics applicable to the standard type can be modied.
The following is a description of the softkeys located within the dene standard menu:
NNNNNNNNNNNNNN
OPEN denes the standard type as an open, used for calibrating reection measurements .
Opens are assigned a terminal impedance of innite ohms , but delay and loss osets may
still be added. Pressing this key also brings up a menu for dening the open, including its
capacitance .
As a reection standard, an open termination oers the advantage of broadband frequency
coverage . At microwave frequencies , however , an open rarely has perfect reection
characteristics because fringing capacitance eects 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 eects 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 coecients
are user-denable . The capacitance model equation is:
C = (C0) + (C1 2 F) + (C2 2 F
2
) + (C3 2 F
3
)
where F is the measurement frequency .
The terms in the equation are dened with the specify open menu as follows:
NNNNNNNN
C0 allows you to enter the C0 term, which is the constant term of the cubic polynomial
and is scaled by 10
015
F arads .
NNNNNNNN
C1 allows you to enter the C1 term, expressed in F/Hz (F arads/Hz) and scaled by 10
027
.
NNNNNNNN
C2 allows you to enter the C2 term, expressed in F/Hz
2
and scaled by 10
036
.
N NNNNNNN
C3 allows you to enter the C3 term, expressed in F/Hz
3
and scaled by 10
045
.
NNNNNNNNNNNNNNNNN
SHORT denes the standard type as a short, for calibrating reection measurements . Shorts
are assigned a terminal impedance of 0 ohms , but delay and loss osets may still be added.
N NNNNNNNNNNNNN
LOAD denes the standard type as a load (termination). Loads are assigned a terminal
impedance equal to the system characteristic impedance Z0, but delay and loss osets
may still be added. If the load impedance is not Z0, use the arbitrary impedance standard
denition.
NNNNNNNNNNNNNNNNN
FIXED denes the load as a xed (not sliding) load.
NNNNNNNNNNNNNNNNNNNNNNN
SLIDING denes 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.
NNNNNNNNNNNNNNNNNNNN
OFFSET denes the load as being oset.
N NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN
DELAY/THRU denes the standard type as a transmission line of specied length, for
calibrating transmission measurements .
Application and Operation Concepts 6-79