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
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
∅(radians) = 2π = 2πf(delay)
λ
Waveguide transmission line exhibits dispersive phase response as follows:
∅2π (radians) = λg
where
λg = λ
1-( / co)2
Selection of WAVEGUIDE computes offset delay using the dispersive response, of rectangular wave- guide only, as a function of frequency as
Delay (seconds) = Linear delay
This emphasizes the importance of entering “fco” as the LOWER FREQUENCY.
Selection of COAXIAL assumes linear response of offset delay.
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