Slot antenna with reduced ground plane

• US 5,646,637 A
• Filed: 09/05/1996
• Issued: 07/08/1997
• Est. Priority Date: 09/10/1993
• Status: Expired due to Fees

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Motor Company
• Inventors: Miller, Alan Wayne
• Primary Examiner(s): Le, Hoanganh T.
• Application Number:
  US08/711,402
• Time in Patent Office: 306 Days
• Field of Search: 343/713, 343/715, 343/711, 343/712, 343/767, 343/768, 343/770
• US Class Current: 343/713
• CPC Class Codes: H01Q 1/1271 for mounting on windscreens
• CPC Class Codes: H01Q 13/10 Resonant slot antennas

Abstract

A slot antenna has a substantially reduced ground plane by defining the slot within a loop of a narrow conductive strip, for example a deposited metal, around a slot opening less than one half the wavelength of the intended signal frequency to be received by the antenna. A conductor such as a central conductor of a coaxial cable coupled to the conductive strip on one side of the slot, while another conductor such as the ground shield of the coaxial cable is terminaled at a position across the slot from the central conductor terminal. In addition, the gain and bandwidth of the antenna may be improved by adding a similarly constructed loop or loops of slot antenna in parallel to the first slot to form an overlapping series of loops. Such a modification forms a ground plane with an overlapping series of loop conductors. As a result, the present invention permits a convenient, window mounted antenna assembly, as well as a particularly advantageous combination of window panel of a motor vehicle, as is particularly well adapted for use with remote keyless entry systems as well as cellular telephone systems.

Claims

1. A slot antenna having a slot in a reduced ground plane for a motor vehicle insulating panel comprising:

a conductive, narrow in relation to the width of the slot, strip formed in a loop on the insulating panel, said loop forming the slot having a length corresponding to a fraction of a predetermined wavelength, said reduced ground plane consisting of said strip formed in a loop peripherally defining the slot, wherein said fraction is smaller than the half wavelength of an expanded ground plane slot antenna, and

wherein non-common conductor terminals are aligned across the slot on its length sides, and wherein said loop is rectiform.

2. The slot antenna as defined in claim 1 wherein said conductive strip comprises a conductive tape.

3. The slot antenna as defined in claim 1 wherein said strip is formed in a window glass.

4. The slot antenna as defined in claim 1 wherein said antenna is coupled to a receiver by a coaxial conductor having a central conductor secured on one side of said slot and a shield conductor secured on an opposite side of said slot.

6. The slot antenna as defined in claim 4 wherein said receiver is part of a cellular telephone.

5. The slot antenna as defined in claim 41 wherein said receiver is part of a remote keyless entry system.

7. An antenna for radio wave communication with a motor vehicle comprising:

a conductive loop formed on a window glass of the motor vehicle, said loop having a rectiform shape forming a slot with a length of less than a half wavelength of a predetermined signal frequency to be communicated, a reduced ground plane consisting of a peripheral, narrow in relation to the width of the slot, strip of conductor forming said loop, and

non-common conductor terminals aligned across the slot on its length sides.

8. The slot antenna as defined in claim 7 wherein said predetermined signal frequency is a tuned frequency of a remote keyless entry system.

9. The slot antenna as defined in claim 7 wherein said predetermined signal frequency is a tuned frequency of a cellular telephone.

10. The slot antenna as defined in claim 7 wherein said antenna is coupled to a receiver by a coaxial conductor having a central conductor secured on one side of said slot and a shield conductor secured on an opposite side of said slot.

11. In combination with a motor vehicle window imprinted with a conductive grid for electric window defrosting, the improvement comprising an antenna imprinted upon the window and forming a slot antenna having a slot in a reduced area ground plane, said ground plane consisting of a flat and narrow, in relation to the width of the slot, strip conductor formed in at least two rectiform loops, each loop being the same length forming the slot having a length less than a half wavelength of a predetermined frequency to be received by the antenna, and

non-common conductor terminals aligned across the slot on its length sides.

12. The slot antenna as defined in claim 11 wherein said predetermined frequency is a tuned frequency of a remote keyless entry system.

13. The slot antenna as defined in claim 11 wherein said predetermined frequency is a tuned frequency of a cellular telephone.

14. The slot antenna as defined in claim 11 wherein said antenna is coupled to a receiver by a coaxial conductor having a central conductor secured on one side of said slot and a shield conductor secured on an opposite side of said slot.

15. A slot antenna having a slot in a reduced ground plane for a motor vehicle insulating panel comprising:

a conductive, narrow in relation to the width of the slot, strip conductor formed in a closed loop on the insulating panel, said loop forming the slot having a length corresponding to a fraction of a predetermined wavelength, wherein said fraction is smaller than the half wavelength of an expanded ground plane slot antenna;

wherein said antenna comprises a stack of a plurality of closed loops having said length, each loop having non-common conductor terminals aligned across the slot on its length sides.

16. The slot antenna as defined in claim 15 wherein said loops overlap.

17. A slot antenna having a slot in a reduced ground plane for a motor vehicle insulating panel comprising:

a conductive, narrow in relation to the width of the slot, strip conductor formed in a loop on the insulating panel, said loop forming the slot having a length corresponding to a fraction of a predetermined wavelength, wherein said fraction is smaller than the half wavelength of an expanded ground plane slot antenna; and

wherein said antenna comprises a stack of a plurality of loops having said length, each loop having non-common conductor terminals aligned across the slot on its length sides, and wherein said loops overlap.