Main criteria for key antenna design

AN3394

18/29

Doc ID 018754 Rev 5

4

Main criteria for key antenna design

The following sections explain how to determine the antenna dimensions for a given value of

antenna inductance (L).

4.1

Inductance of a circular antenna

Equation 1

, where:

●

r is the radius in millimeters

●

●

N is the number of turns

●

●

4.2

Inductance of a spiral antenna

Equation 2

, where:

●

●

c is the thickness of the winding in micrometers

●

N is the number of turns

●

●

Figure 17.

Spiral antenna

L

ant

μ

0

N

1.9

r

×

r

r

0

----

⎝⎠

⎛⎞

ln

×

×

=

L

ant

31.33

μ

0

×

N

2

×

d

ant

8d

ant

11c

+

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

×

=