AN2972

How to design an antenna on a PCB

Doc ID 15629 Rev 6

11/25

2

How to design an antenna on a PCB

Designing an inductive antenna is about impedance matching. The antenna impedance

must match the conjugated impedance of the M24LRxx in order to obtain the needed tuning

frequency.

A 13.56 MHz antenna can be designed with different shapes, depending on the application

requirements. As explained previously, the major parameter is the inductance L of the

antenna. The following paragraphs offer a way of computing the antenna dimensions for a

determined value of inductance L.

2.1

Inductance of a circular antenna

, where:

●

r is the radius in millimeters

●

●

N is the number of turns

●

●

L is measured in Henry

2.2

Inductance of a spiral antenna

, where:

●

d is the mean antenna diameter in millimeters

●

c is the thickness of the winding in microns

●

N is the number of turns

●

●

L is measured in Henry

Figure 9.

Spiral antenna

L

ant

μ

0

N

1.9

r

×

r

r

0

----





ln

×

×

=

L

ant

31.33

μ

0

×

N

2

×

d

8d

11c

+

-----------------------

×

=

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