Figure 10.4: Relative magnitude of far-field radiation as a function of frequency.
When the spectral envelope of the digital signal (the input into the radiator) is combined with
the frequency dependence of the far-field radiation shown in
, we arrive at the
differential radiated emission envelope shown in
. Note that the frequency F =
will not necessarily occur at a higher frequency than F = c/2
, as shown in the figure.
The frequencies that will be most likely to radiate (differential mode) are contained between
the frequencies F = 1/P
and F = 1/T
or F = c/2
(whichever is highest).
Figure 10.5: Resultant differential radiation behavior when far-field characteristics are
combined with spectral input.
RULE OF THUMB: Minimizing Differential-Mode Radiation
Since the magnitudes of the fields are proportional to the loop area, smaller loops
produce less radiated emission. During design, minimize current loops whenever
The frequencies that will be most likely to radiate (differential mode) are contained between the frequencies F = 1/P W and F = 1/T r or F = c/2 (whichever is highest).