SI4785 Ver la hoja de datos (PDF) - Silicon Laboratories
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SI4785 Datasheet PDF : 69 Pages
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AN383
Figure 16. Rectangular Loop (Wire) Antenna—Orthogonal View
5.1.2.3. Design Guidelines
Route the antenna as shown in Figure 16.
A > 5 mm
B + C + D + E > 13 cm
C > 3 cm
Maximize antenna length (B+C+D+E >13 cm) to provide sufficient radiating power for transmit and maximize
incident voltage for receive.
Keep the antenna as far from the ground plane and shield as possible (A > 5 mm), and make the enclosure
from non-conductive material (plastic), to minimize parasitic capacitance and maximize radiation for transmit or
maximize incident voltage for receive.
Antenna inductance for an ideal loop antenna is given by Lant = n²µ0r[ln(8r/b)].
r: loop radius (m)
n: number of turns
µ0: permeability (4 x 10–7 N/A2)
b: wire radius (m)
Number of turns greater than one usually results in a high inductance loop with which the varactor cannot resonate.
It is acceptable to place two loops in a parallel structure to reduce the effective inductance.
For a loop with a small radius used in cellular handset or mp3 applications, the loop antenna equation can be
approximately applied to a rectangular loop of the same circumference.
Radius (cm)
2
3
4
Turns
1
1
1
Total Length (cm)
12.6
18.8
25.1
Lant (nH)
111.5
182.6
257.9
Use an ideal vertical loop (wire) antenna as a reference point to measure the performance of the loop antenna.
Antenna performance will degrade in a practical application where the loop antenna is bent parallel to the GND
plane.
Rev. 0.8
29
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