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µ
r
= relative permeability constant of the medium
(equal to 1.0 in air)
ε
r
= relative permittivity constant of the medium
(equal to 1.000649 in air)
D = inside diameter of outer conductor
d = outside diameter of inner conductor
The 8510 requires that the characteristic imped-
ance of waveguide transmission line is assigned to
be equal to the SET Z
0
.
The characteristic impedance of other transmis-
sion media is not as easily determined through
mechanical dimensions. Waveguide impedance, for
example, varies as a function of frequency. In such
cases, normalized impedance measurements are
typically made. When calibrating in waveguide, the
impedance of a “matched” load is used as the
impedance reference. The impedance of this load is
matched that of the waveguide across frequency.
Normalized impedance is achieved by entering SET
Z
0
and OFFSET Z
0
to 1 ohm for each standard.
Offset Z
0
equal to system Z
0
(SET Z
0
) is the
assigned convention in the 8510 for matched wave-
guide impedance.
Offset loss
Offset loss is used to model the magnitude loss due
to skin effect of offset coaxial type standards only.
The value of loss is entered into the standard defi-
nition table as gigohms/second or ohms/nanosec-
ond at 1 GHz.
The offset loss in gigohms/second can be calculat-
ed from the measured loss at 1 GHz and the physi-
cal length of the particular standard by the
following equation.
where:
dB
lOSS
|1 GHz =measured insertion loss at 1 GHz
Z
0
= offset Z
0
ᐉ = physical length of the offset
The 8510 calculates the skin loss as a function of
frequency as follows:
Note: For additional information refer to
Appendix C.
For all offset standards, including shorts or opens,
enter the one way skin loss. The offset loss in
waveguide should always be assigned zero ohms by
the 8510.
Z0 = = 59.9585
µ
ε
In
1
2π
D
d
µr
εr
()
In
D
d
()
Offset loss =
GΩ
s 10 log
10
(e)
1GHz
dB
loss
1GHz c Z
0
()
ε
r
ᐉ
Offset loss
X
GΩ
s
1GHz
f(GHz)
Offset loss
GΩ
s
=
() ()