Planar inverted-F antenna including a matching network having transmission line stubs and capacitor/inductor tank circuits

• US 6,819,287 B2
• Filed: 11/12/2002
• Issued: 11/16/2004
• Est. Priority Date: 03/15/2002
• Status: Expired due to Fees

• Current Assignee: Laird Technologies Incorporated (DuPont de Nemours, Inc.)
• Original Assignee: Centurion Wireless Technologies Inc (Laird Limited)
• Inventors: Sullivan, Jonathan Lee, Rosener, Douglas Kenneth
• Primary Examiner(s): Nguyen, Hoang V.
• Assistant Examiner(s): Tran, Chuc
• Application Number:
  US10/292,841
• Publication Number:
  US 20030174092A1
• Time in Patent Office: 735 Days
• Field of Search: 343/700.MS, 343/702, 343/795, 343/850, 343/846, 343/848, 343/806, 343/852, 343/793, 343/860
• US Class Current: 343/700.0MS
• CPC Class Codes: H01Q 1/243 with built-in antennas
• CPC Class Codes: H01Q 5/335 at the feed, e.g. for impedance matching
• CPC Class Codes: H01Q 5/371 Branching current paths
• CPC Class Codes: H01Q 9/0421 with a shorting wall or a shorting pin at one end of the element H01Q9/0414 takes precedence

Abstract

A small multi-band planar inverted-F antenna (PIFA) includes a metal radiating element that is physically located above a metal ground plane element, and the space therebetween includes a frequency matching network having a microstrip transmission line that connects an antenna feed to a wireless communications device (WCD) feed. The impedance matching network may include a microstrip impedance transformer whose output provides a 50 ohm connection to the WCD. A number of microstrip stubs are connected to the microstrip transmission line. At least some of the microstrip stubs connect to the microstrip transmission line by way of a LC tank circuit. The LC tanks circuits are responsive to different ones of the multiple frequencies to which the PIFA is responsive, and in this manner the impedance matching network is dynamically reconfigured in accordance with the frequency band currently traversing the microstrip transmission line. The LC tanks circuits include discrete capacitors and inductors. A two-shot molding process is used to make a unitary plastic antenna assembly whose second-shot plastic surfaces are metallized in order to provide the antenna'"'"'s metal elements, including the microstrip circuit pattern of the impedance matching network.

Claims

1. An antenna responsive to a plurality of frequency bands, comprising:

a radiating element geometrically configured to be responsive to said plurality of frequency bands;

a ground plane element positioned away from said radiating element to thereby define a space between said ground plane element and said radiating element;

an antenna-feed connected to said radiating element;

a device-feed for connection to a radio device;

a transmission line connected between said antenna-feed and said device-feed;

a plurality of transmission line stubs associated with said transmission line;

at least one frequency responsive high impedance circuit responsive to at least one frequency within said plurality of frequency bands; and

at least one transmission line stub connected to said transmission line by way of said at least one frequency responsive high impedance circuit such that said radiating element is matched to said radio feed within each of said plurality of frequency bands, as said at least one frequency responsive high impedance circuit operates to dynamically reconfigured said transmission line in accordance with a frequency band currently traversing said transmission line.

2. The antenna of claim 1 wherein said transmission line, said at least one transmission line stub and said at least one frequency responsive high impedance circuit comprise an impedance matching network that is physically located within said space between said ground plane element and said radiating element.

3. The antenna of claim 1 wherein said at least one frequency responsive high impedance circuit comprises at least one LC tank circuit having a discrete capacitor element and a discrete inductor element.

4. The antenna of claim 3 wherein said transmission line, said at least one transmission line stub and said at least one LC tank circuit comprise an impedance matching network that is physically located in said space between said ground plane element and said radiating element.

5. The antenna of claim 1 wherein the radio device is a wireless communications device, wherein said antenna is a planar inverted-F antenna having a metal planar radiating element and a metal planar ground plane element that is shorted to said radiating element.

6. The antenna of claim 5 wherein a two-shot molding process is used to make a plastic assembly whose outer surface is selectively metallized to provide said radiating element on one surface of said plastic assembly, and to provide metal patterns on an opposite surface of said plastic assembly that define said transmission line and said at least one transmission line stub.

7. The antenna of claim 6 wherein said metal patterns cooperated with said ground plane element to form a microstrip transmission line and at least one microstrip stub.

8. The antenna of claim 7 wherein said microstrip transmission line, said at least one microstrip stub and said at least one frequency responsive high impedance circuit comprise an impedance matching network that is physically located in said space between said ground plane element and said radiating element.

9. The antenna of claim 8 wherein said at least one frequency responsive high impedance circuit comprises at least one LC tank circuit having a discrete capacitor element and a discrete inductor element.

10. The antenna of claim 9 wherein the radio device is a wireless communications device.

11. The antenna of claim 10 wherein a two-shot molding process is used to make a plastic assembly whose outer surface is selectively metallized to provide said radiating element on one surface of said plastic assembly, and to provide metal patterns on an opposite surface of said plastic assembly that define said microstrip transmission line and said at least one microstrip stub.

12. A method of making a unitary mechanical assembly that includes a multi-band antenna and an impedance matching network, comprising the steps of:

providing a dielectric substrate having a top surface and a bottom surface;

providing a metal ground plane element on said bottom surface of said dielectric substrate;

providing a metal radiating element;

configuring said radiating element to be responsive a plurality of frequency bands;

spacing said radiating element from said top surface of said ground plane element;

providing a radio feed for connection to a multi-band radio device;

providing at least one metal microstrip transmission line on said top surface of said dielectric substrate and in an area thereof that is under said radiating element;

connecting said at least one microstrip transmission line between said radiating element and said radio feed;

providing a plurality of metal microstrip stubs on said top surface of said dielectric substrate and in said area under said radiating element;

providing a plurality of frequency-responsive LC tank circuits;

using said LC tank circuits to connect at least some of said microstrip stubs to said at least one microstrip transmission line, to thereby provide an impedance-matching-network that is responsive to a frequency currently traversing between said radiating element and said radio feed, to thereby dynamically reconfigure said impedance-matching-network to provide an impedance match between said radiating element and said radio feed as a function of said current-frequency.

13. The method of claim 12 wherein said plurality of frequency-responsive LC tank circuits include discrete capacitor and inductor elements that are located in a space under said radiating element.

14. The method of claim 13 including the steps of:

providing a box-like dielectric member in said space under said radiating element; and

forming said dielectric member using a two shot molding process having top portions metallized to form said radiating element and having bottom portions metallized to form said at least one microstrip transmission line and said plurality of microstrip stubs.

15. The method of claim 14 wherein said bottom portions of said dielectric member include recesses for holding said discrete capacitor and inductor elements.

16. The method of claim 15 including the step of:

electrically connecting a portion of said radiating element to said ground plane element so as to form a PIFA.

17. An impedance-matched, multi-frequency-band, antenna having a device-feed for connection to a multi-frequency-band wireless communications device, comprising:

a generally planar and dielectric substrate member having an upper surface and a lower surface that includes a generally planar and metal ground plane element;

a generally planar and metal radiating element located above a portion of said upper surface of said dielectric substrate member, said radiating element being geometrically configured to be responsive to said multi-frequency-band;

a metal microstrip transmission line on said portion of said upper surface of said dielectric substrate member, said microstrip transmission line connecting said radiating element to said device-feed;

a plurality of LC tank circuits responsive to frequencies within said multi-frequency-band; and

a plurality of metal microstrip stubs formed on said portion of said upper surface of said dielectric substrate, at least some of said microstrip stubs being directly connected to said microstrip transmission line, and at least others of said microstrip stubs being connected to said microstrip transmission line through at least one of said LC tank circuits.

18. The antenna of claim 17 wherein said plurality of LC tank circuits are located in a space between said radiating element and said portion of said upper surface of said dielectric substrate member.

19. The antenna of claim 18 wherein said radiating element is generally parallel to said ground plane element, and wherein a portion of said radiating element is electrically connected to said ground plane element.

20. The antenna of claim 19 wherein said multi-frequency-band wireless communications device is a cellular telephone.

21. An impedance-matched and multi-frequency-band antenna having a device-feed for connection to a multi-frequency-band wireless device, comprising:

a box-like dielectric carriage having a generally planar upper surface and a generally planar lower surface that extends generally parallel to said upper surface;

a generally planar and metal ground plane element having at least a portion thereof associated with said bottom surface of said dielectric carriage;

a generally planar and metal radiating element formed on said upper surface of said dielectric carriage, said radiating element being geometrically configured to be responsive to said multi-frequency-band;

a metal microstrip transmission line formed on said bottom surface of said dielectric carriage, said microstrip transmission line inter-connecting said radiating element and said device-feed;

a plurality of metal microstrip stubs formed on said bottom surface of said dielectric carriage;

a plurality of LC tank circuits responsive to frequencies within said multi-frequency-band; and

at least some of said microstrip stubs directly connected to said microstrip transmission line, and at least others of said microstrip stubs indirectly connected to said microstrip transmission line through one or more of said LC tank circuits.

22. The antenna of claim 21 wherein said dielectric carriage is formed by a two-shot molding process, followed by a metallization process that produces said metal radiating element, said microstrip transmission line, and said plurality of microstrip stubs on said dielectric carriage.

23. The antenna of claim 22 wherein a portion of said radiating element is electrically connected to said ground plane element.

24. The antenna of claim 23 wherein said multi-frequency-band wireless device is a cellular telephone.

25. An impedance-matched and multi-frequency-band antenna having a device-feed for connection to a multi-frequency-band wireless device, comprising:

a box-like dielectric carriage having a generally planar upper surface and a generally planar bottom surface that extends generally parallel to said upper surface;

a metal radiating element formed on said upper surface of said dielectric carriage, said radiating element being geometrically configured to be responsive to said multi-frequency-band;

a generally planar and metal ground plane element;

an generally planar impedance matching board located intermediate said bottom surface of said dielectric carriage and said ground plane element;

a metal microstrip transmission line formed on said impedance matching board and electrically interconnecting said device-feed and said radiating element;

a plurality of metal microstrip stubs formed on said impedance matching board;

a plurality of LC tank circuits responsive to frequencies within said multi-frequency-band; and

at least some of said microstrip stubs directly connected to said microstrip transmission line, and at least others of said microstrip stubs indirectly connected to said microstrip transmission line through one or more of said LC tank circuits.

26. The antenna of claim 25 wherein said dielectric carriage and said impedance matching board are formed by two-shot molding processes, followed by metallization processes that produces said metal radiating element on said dielectric carriage, and produces said microstrip transmission line and said plurality of microstrip stubs on said impedance matching board.

27. The antenna of claim 26 wherein a portion of said radiating element is electrically connected to said ground plane element.

28. The antenna of claim 27 wherein said multi-frequency-band wireless device is a cellular telephone.

29. An antenna for use with a radio-device, comprising:

a rigid dielectric member in the shape of a box having a generally planar exterior top-surface, having a generally planar exterior bottom-surface that is generally parallel to said top-surface, having sidewalls that extend between said top and bottom surfaces, and having an open sidewall that exposes an internal cavity and an inner-surface that lies adjacent and generally parallel to said bottom surface;

a metal radiating element on said top-surface;

a metal ground plane on said bottom-surface;

a metal microstrip impedance matching network on said internal-surface;

first electrical connection means on a first portion of said impedance matching network for connection to said radio-device; and

second electrical connection means connecting a second portion of said impedance matching network to a first portion of said radiating element.

30. The antenna of claim 29 wherein said dielectric member is formed by a two-shot molding process that produces said dielectric member including a first-shot plastic material having no affinity for metallizing, and a second-second shot plastic material having an affinity for metallization;

said a metal radiating element, said metal ground plane and said metal impedance matching network being formed by metallizing said second-shot plastic.

31. The antenna of claim 29 including:

at least one open microstrip stub in said impedance matching network; and

at least one shorted microstrip stub in said impedance matching network pattern having a portion thereof shorted to said ground plane.

32. The antenna of claim 31 wherein said dielectric member is formed of a first-shot plastic material having no affinity for metallizing and of a second-second shot plastic material having an affinity for metallization, and wherein said a metal radiating element, said metal ground plane, and said metal impedance matching network are formed by metallizing said second-shot plastic.

33. The antenna of claim 29 including:

at least one metal reactive loading plate on one of said sidewalls connected to said radiating element and isolated from said ground plane.

34. The antenna of claim 33 including:

at least one open microstrip stub in said impedance matching network; and

at least one shorted microstrip stub in said impedance matching network pattern having a portion thereof shorted to said ground plane.

35. The antenna of claim 29 including:

a metal shorting strip on one of said sidewalls connecting a second portion of said radiating element.

36. The antenna of claim 35 including:

at least one metal reactive loading plate on one of said sidewalls connected to said radiating element and isolated from said ground plane.

37. The antenna of claim 36 including:

at least one open microstrip stub in said impedance matching network; and

at least one shorted microstrip stub in said impedance matching network pattern having a portion thereof shorted to said ground plane.