Antenna system

1. An antenna system, comprising:

an NFC (Near Field Communication) antenna, comprising a metal coil and a first dielectric substrate, wherein the metal coil is disposed on the first dielectric substrate;

a coupling metal element, disposed adjacent to the metal coil, wherein the coupling metal element does not directly touch the metal coil; and

a second dielectric substrate, wherein the coupling metal element is disposed on the second dielectric substrate;

wherein the coupling metal element is configured to adjust an operational frequency of the NFC antenna.

2. The antenna system as claimed in claim 1 , wherein the coupling metal element is floating.

3. The antenna system as claimed in claim 1 , wherein the coupling metal element has a vertical projection on the NFC antenna, and the vertical projection at least partially overlaps the metal coil.

4. The antenna system as claimed in claim 1 , wherein if a width of the coupling metal element decreases, the operational frequency of the NFC antenna becomes lower.

5. The antenna system as claimed in claim 1 , wherein if a width of the coupling metal element increases, the operational frequency of the NFC antenna becomes higher.

6. The antenna system as claimed in claim 1 , wherein the coupling metal element substantially has a spiral shape.

7. The antenna system as claimed in claim 1 , wherein the coupling metal element substantially has a meandering shape.

8. The antenna system as claimed in claim 1 , wherein a length of the metal coil is shorter than or equal to 0.25 wavelength of the operational frequency of the NFC antenna.

9. The antenna system as claimed in claim 1 , wherein a length of the coupling metal element is shorter than or equal to 0.5 wavelength of the operational frequency of the NFC antenna.

10. The antenna system as claimed in claim 1 , wherein a width of the metal coil is from 0.2 mm to 2 mm.

11. The antenna system as claimed in claim 1 , wherein a width of the coupling metal element is from 0.1 mm to 4 mm.

12. The antenna system as claimed in claim 1 , wherein a distance between the metal coil and the coupling metal element is from 0.01 mm to 1.6 mm.

13. The antenna system as claimed in claim 1 , further comprising:

a ferrite sheet, disposed adjacent to the first dielectric substrate.

14. The antenna system as claimed in claim 1 , further comprising:

an isolation layer, configured to separate the metal coil from the coupling metal element.

15. The antenna system as claimed in claim 1 , further comprising:

one or more inductors, coupled in series with the coupling metal element.

16. The antenna system as claimed in claim 1 , further comprising:

one or more capacitors, coupled in series with the coupling metal element.

17. The antenna system as claimed in claim 1 , wherein the first dielectric substrate has a first surface and a second surface opposite to each other, and a thickness of the first dielectric substrate is from 0.1 mm to 0.8 mm.

18. The antenna system as claimed in claim 17 , further comprising:

one or more first conductive via elements, penetrating the first dielectric substrate, wherein the metal coil is distributed over the first surface and the second surface of the first dielectric substrate by using the first conductive via elements.

19. The antenna system as claimed in claim 1 , wherein the second dielectric substrate has a third surface and a fourth surface opposite to each other, and a thickness of the second dielectric substrate is from 0.1 mm to 0.8 mm.

20. The antenna system as claimed in claim 19 , further comprising:

a second conductive via element, penetrating the second dielectric substrate, wherein the coupling metal element is distributed over the third surface and the fourth surface of the second dielectric substrate by using the second conductive via element.