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16
Upper/maximum frequency
This specifies the maximum frequency at which
the standard is valid. In broadband applications, a
set of banded standards may be necessary to pro-
vide constant response. For example, coaxial offset
standards (i.e.,
1
/4 λ offset short) are generally spec-
ified over bandwidths of an octave or less.
Bandwidth specification of standards, using mini-
mum frequency and maximum frequency, enables
the 8510 to characterize only the specified band
during calibration. Further, a submenu for banded
standards is enabled which requires the user to
completely characterize the current measurement
frequency range. In waveguide, this is the upper
cutoff frequency for the waveguide class and mode
of propagation. For the fundamental mode of prop-
agation in rectangular waveguide the maximum
upper cutoff frequency is twice the lower cutoff
frequency and can be calculated as follows.
F(upper) = 2 x F(lower)
The upper frequency of a waveguide standard may
also be specified as the maximum operating fre-
quency as listed in a textbook.
The MAXIMUM FREQUENCY of the WR-62 wave-
guide cal kit is 18.974 GHz and is entered into the
standard definition table for all four standards.
Coax or waveguide
It is necessary to specify whether the standard
selected is coaxial or waveguide. Coaxial transmis-
sion line has a linear phase response as
Waveguide transmission line exhibits dispersive
phase response as follows:
where
Selection of WAVEGUIDE computes offset delay
using the dispersive response, of rectangular wave-
guide only, as a function of frequency as
This emphasizes the importance of entering “f
co
” as
the LOWER FREQUENCY.
Selection of COAXIAL assumes linear response of
offset delay.
1-(fco/f)
2
Delay (seconds)
Linear delay
=
1-(λ/λco)
2
λg
λ
=
2πᐉ
∅(radians)
λg
=
2πᐉ
2πf(delay)
∅(radians)
λ
==