HP HP 8712ET, Руководство пользователя, Страница: 246 / 480

6-20 ET User’s Guide
Calibrating for Increased Measurement Accuracy
Calibration Kits
For all four standard types, the Z
0
(characteristic impedance), Delay,
and Loss must be set. For an open, C
0
, C
1
, C
2
, and C
3
, the capacitive
model parameters, must also be set.
NOTE
When creating a user-defined calibration kit, if a standard is not defined,
the currently defined values for that standard will be retained. The best
practice is to define all of your standards and characteristics when
creating a user-defined calibration kit.
Z
0
Z
0
is usually set to the system characteristic impedance
(usually either 50 or 75 ohms).
Delay Delay is equivalent to a uniform length of transmission
line between the standard being defined and the actual
measurement plane. For an open, short, and load, the
DELAY is entered as the one-way travel time from the
measurement plane to the standard in seconds. For a
through, the DELAY is entered as the one-way travel
time between the measurement planes in seconds.
Delay can be measured or determined from the precise
physical length of the standard, divided by the velocity
factor.
Loss Loss is used to specify energy loss, due to skin effect,
along a one-way length of coaxial delay. The value of
loss is entered as ohms/second at 1 GHz. For many
applications, the loss value can be set to zero without
noticeable degradation. To compute the loss of your
device, measure the delay in seconds and the loss in dB
at 1 GHz. Then, compute:
C
0
, C
1
, C
2
, C
3
At high frequencies, an open rarely has perfect
reflection characteristics because fringing capacitance
causes phase shift that varies with frequency.
Loss
Ω
s
----
 
 
dB loss Z
0
Ω ( ) ×
4.3429 delay s
( ) ×
------------------------------------------- =