NXP Semiconductors
AN11740
PN5180 Antenna design
AN11740
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Application note
COMPANY PUBLIC
Rev. 1.1 — 19 June 2018
345311
18 of 62
(1) Minimum required field strength Hmin = 1.5A/m
(2) Both antennas scaled to deliver Hmax = 7.5 A/m at maximum
Fig 14. Operating distance x versus antenna size
Note:
The large antenna is driven with a current I
largeantenna
≈
4x I
smallantenna
.
Note:
This graph does not include the detuning and loading effect of the reader
antenna.
The Fig 15 shows the simulation result of three different square antennas. The
magnitude of the field strength is shown versus the distance from the center of the
antenna area in either X or Y direction. The curves indicate the zero points, which are
areas around the antenna slightly outside the antenna area, where no field can be
measured (i.e. where the coupling is zero).
At a zero point no tag device can be operated, even if the required field strength is very
low. This needs to be considered, if there is a requirement to read tags within a certain
given operating volume, which might touch the zero points, especially if the antenna is
too small.
