Feature
Electronic Military & Defense Annual Resource, 4th Edition
33
field is quasinull will not significantly modify the field distri-
bution, and the object will not receive or absorb significant
radiation. Such an objective was obtained by associating
several basic antennas with specific amplitude and phase
feeding, just as in array antennas.
There are important differences, however, in that there is
no periodic structure, and the group of antennas can be het-
erogeneous and not necessarily locat-
ed in the same plane. Moreover, the
antennas are placed in such a way that
they can be integrated or printed on the
clothing. As a consequence, the anten-
nas are close to the body and therefore
are bent around the natural shape
of the body. As an example of this
principle, Figure 1 shows a group of
three similar antennas located and fed
in such a way that the convex region
defined by the antennas receives signif-
icantly low-level radiation. If a human
body is placed in that convex region, it
is expected that the radiated field will
not be significantly affected. Therefore,
the SAR will be low. To prove this
behavior, we performed a simulation
of two groups of antennas, each com-
posed of three single radiating dipoles
placed on the human body, as depicted
in Figure 2. You can see that the elec-
tromagnetic field is quite low, and that
the body compliance with SAR level
(here, 2W/kg) is achieved. For a total
injected power value of 1 W, the calcu-
lated SAR is 0.62 W/kg.
Example Of
WBAN Antenna Integration
The Giante WBAN device is essentially
a 3D one, but it is advantageously real-
ized as a planar circuit. The 3D behav-
ior stands
because
antennas
must be
f o l d e d
on a part
of the
h u m a n
b o d y
like the
arms, as
shown in
Figure 3.
In prac-
tice, the
design of the antenna group will depend on operating fre-
quency, the excitation circuit that needs to separately feed
the three antennas of the group, the type of antennas, and
the human body parameters. Usually, monopole antennas
allow for obtaining a very satisfactory radiation pattern —
provided that their relative orientation with respect to each
other is optimized.
Reliability
isn't an
option – it's a
requirement.
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Figure 3: An example of a military
vest equipped with the Giante WBAN
concept