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Application note
COMPANY PUBLIC
Rev. 1.1 — 19 June 2018
345311
The maximum coupling coefficient versus the operating distance can be estimated as
shown in Fig 13. This maximum coupling is related to the optimum antenna size.
(1) The absolute scale of k might not be correct due to simplifications.
Fig 13. Maximum coupling vs antenna size
Theoretical example:
The Fig 14 shows the field strength versus operating distance of two different antenna
sizes. For both antennas the antenna current is tuned to deliver the maximum allowed
field strength of 7.5 A/m at the minimum operating distance of 2mm.
The small antenna with 4cm diameter achieves an operating distance of almost 3cm, the
large antenna with 10cm diameter achieves an operating distance of almost 7cm.
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