Reactance buffered loop antenna and method for making the same

• US 5,128,686 A
• Filed: 08/27/1990
• Issued: 07/07/1992
• Est. Priority Date: 01/23/1989
• Status: Expired due to Term

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Tan, William, Kurcbart, Robert
• Primary Examiner(s): Wimer, Michael C.
• Application Number:
  US07/572,306
• Time in Patent Office: 680 Days
• Field of Search: 343/718, 343/741, 343/743, 343/744, 343/868, 343/866, 343/870, 343/871, 343/702, 333/17.3, 333/32, 333/24 R, 333/24 C, 455/274, 455/290, 455/292, 455/344, 455/349, 455/351, 455/193
• US Class Current: 343/718
• CPC Class Codes: H01Q 1/273 Adaptation for carrying or wearing by persons or animals
• CPC Class Codes: H01Q 7/02 Collapsible antennas; Retractable antennas

Abstract

A reactance buffer maintains a substantially constant reasonant frequency for an adjustable size loop antenna having first and second antenna segments. Each segment has first and second ends, the first ends being coupled to a receiver, and the second ends providing loop size adjustment. The reactance buffer comprises a reactance buffer input coupled to the second end of the first antenna segment. A plurality of taps are linearly disposed along a longitudinal axis of the first wristband section, and has a predetermined length between the outermost taps corresponding to the loop antenna size adjustment required. The taps provide selectable reactance buffer outputs for coupling to the second end of the second antenna segment. A plurality of reactance elements are arranged non-serially and couple the reactance buffer input to each of the plurality of taps and provide a substantially constant reactance measured between the reactance buffer input and each of the plurality of taps.

Claims

1. A reactance buffer, for maintaining a substantially constant resonant frequency for a loop antenna having a plurality of selectable loop circumferences, the loop antenna formed from first and second conductor antenna segments, each antenna segment having first and second ends, the first ends of each antenna segment being coupled to a receiver input, the second ends of each antenna segment being selectably coupled for providing adjustment of the loop circumference, said buffer comprising:

a reactance buffer input coupled to the second end of the first antenna segment;

a plurality of taps, linearly disposed along a longitudinal axis of the reactance buffer, the distance between the outermost of said plurality of taps providing a predetermined length corresponding to the length of adjustment of the loop circumference, said taps providing selectable coupling positions for coupling to the second end of the second antenna segment; and

a plurality of reactance elements, arranged non-serially between said reactance buffer input and each of said plurality of taps, wherein one or more of said reactance elements are coupled between said input and a corresponding one of said taps to provide a substantially constant reactance when measured between said reactance buffer input and each of said plurality of taps,

whereby the resonant frequency of the loop antenna remains substantially constant when the loop circumference is adjusted.

2. The reactance buffer according to claim 1, wherein said reactance elements are inductive elements.

3. The reactance buffer according to claim 2, wherein the magnitude of the inductance measured between the buffer input and each tap is substantially constant.

4. The reactance buffer according to claim 2, wherein each of said inductive elements is formed from a conductor.

5. The reactance buffer according to claim 4, wherein said conductors are formed from sheet metal.

6. The reactance buffer according to claim 5, wherein said sheet metal is selected from a group of sheet metals consisting of copper, beryllium copper, and nickel silver.

7. The reactance buffer according to claim 1, wherein said reactance elements comprise a plurality of paired inductive and capacitive elements defining inductor/capacitor pairs.

8. The reactance buffer according to claim 7, wherein said inductive elements are coupled in series with said buffer input.

9. The reactance buffer according to claim 7, wherein each of said inductive elements if formed from a conductor.

10. The reactance buffer according to claim 9, wherein said conductors are formed from sheet metal.

11. The reactance buffer according to claim 10, wherein said sheet metal is selected from a group of sheet metals consisting of copper, beryllium copper, and nickel silver.

12. The reactance buffer according to claim 7, wherein said capacitive elements are fixed value capacitors.

13. The reactance buffer according to claim 12, wherein each inductor of each inductor/capacitor pair has an input and an output terminal, each of said capacitors of each inductor/capacitor pair has an input and an output terminal, each capacitor input terminal being coupled to a respective inductor output terminal, and each capacitor output terminal being coupled to a respective one of said plurality of taps.

14. The reactance buffer according to claim 13, wherein the magnitude of 2π

fL_cum +1/(2π

fC_tap) measured from said buffer input to each of said plurality of taps is substantially constant, f being the frequency of operation, L_cum being the cumulative inductance associated with each of said plurality of taps, and C_tap being the tap capacitance of each of said inductor/capacitor pairs coupled to each of said plurality of taps.

15. The reactance buffer according to claim 4, wherein the inductance of each inductive element is controlled by the conductor geometry.

16. The reactance buffer according to claim 9, wherein the inductance of each inductive element is controlled by the conductor geometry.

17. A buffered loop antenna, having a plurality of selectable loop circumferences, the loop antenna being coupled to a receiver having signal and ground inputs coupled to an antenna resonating capacitor for resonating the loop antenna to a predetermined frequency, said loop antenna comprising:

a first conductor, having a first end coupled to the receiver signal input and a second end, said first conductor forming a first portion of the loop antenna;

a second conductor, having a first end coupled to the receiver ground and a second end, said second conductor forming a second portion of the loop antenna;

reactance buffer means, comprising

a reactance buffer input coupled to said second end of said first conductor,

a plurality of taps linearly disposed along a longitudinal axis of said reactance buffer the distance between the outermost of said plurality of taps providing a predetermined length corresponding to the loop circumference adjustment, and

a plurality of reactance elements, arranged non-serially between said reactance buffer input and each of said plurality of taps, wherein one or more of said reactance elements are coupled between said input and a corresponding one of said taps to provide a substantially constant reactance when measured between said reactance buffer input and each of said plurality of taps; and

coupling means, coupled to said second end of said second conductor, for coupling said second conductor to any of said plurality of taps,

whereby the resonant frequency of the loop antenna remains substantially constant when any of said plurality of taps is selected to adjust the loop circumference.

18. The buffered loop antenna according to claim 17 wherein said first and second conductors are sheet metal.

19. The buffered loop antenna according to claim 18 wherein said sheet metal is selected from a group consisting of copper, beryllium copper, and nickel silver.

20. A wristband loop antenna for a wrist worn electronic device, the device including a receiver having signal and ground inputs coupled to an antenna resonating capacitor for resonating the loop antenna to a predetermined frequency, said wristband loop antenna comprising:

a first wristband section, including

a first conductor, having a first end for coupling to the receiver signal input and a second end, said first conductor forming a first portion of the loop antenna within said first wristband second, and

reactance buffer means, comprising

a reactance buffer input coupled to said second end of said first conductor,

a plurality of taps linearly disposed along a longitudinal axis of said reactance buffer the distance between the outermost of said plurality of taps providing a predetermined length corresponding to the loop antenna diameter adjustment, and

a plurality of reactance elements, arranged non-serially between said reactance buffer input and each of said plurality of taps, wherein one or more of said reactance elements are coupled between said input and a corresponding one of said taps to provide a substantially constant reactance when measured between said reactance buffer input and each of said plurality of taps; and

a second wristband section including

a second conductor, having a first end coupled to the receiver ground and a second end, said second conductor forming a second portion of the loop antenna within said second wristband section, and

coupling means, coupled to said second end of said second conductor, for coupling said second conductor to any of said plurality of taps, whereby when the wristband length is adjusted by selecting any of said plurality of taps, the resonant frequency of said loop antenna remains substantially unchanged.

21. The wristband antenna according to claim 20 wherein said first wristband section further includes compliant top and bottom members for enclosing said first conductor and said reactance buffer means, and said second wristband section further includes compliant top and bottom members for enclosing said second conductor.

22. The wristband antenna according to claim 21 wherein said top and bottom members are molded from a urethane rubber.

23. The wristband antenna according to claim 21 wherein said top and bottom members are die cut from leather.

24. The wristband antenna according to claim 20 wherein said first and second wristband sections further include attachment means for attaching said wristband sections to the electronic device.

25. The wristband antenna according to claim 20 wherein said first and second conductors are sheet metal.

26. The wristband antenna according to claim 25 wherein said sheet metal is selected from a group consisting of copper, beryllium copper, and nickel silver.

27. A wrist worn receiving device, comprising:

a receiver located within a housing; and

a wrist band, including first and second wrist band sections coupled to said housing, for securing the housing to a users wrist,

said first wristband section forming a first portion of a loop antenna, and including a reactance buffer having an input coupled to said receiver, and a plurality of outputs linearly disposed along a longitudinal axis of said first wristband section opposite said housing, said reactance buffer comprising a plurality of reactance elements, arranged non-serially between said reactance buffer input and each of said plurality of outputs, wherein one or more of said reactance elements are coupled between said input and a corresponding one of said outputs for providing a substantially constant reactance measured between said reactance buffer input and each of said reactance buffer outputs,

said second wristband section forming a second portion of the loop antenna, and including a coupling means, coupled to said receiver and affixed to said second wristband section opposite said housing, said coupling means providing selective coupling to said plurality of reactance buffer outputs when securing the housing to the users wrist,

whereby the length of said wristband is freely adjustable to fit the users wrist by coupling said coupling means to a corresponding one of said plurality of reactance buffer outputs, and whereby the resonant frequency of said loop antenna remains substantially unchanged when said coupling means is coupled to any of said plurality of outputs.

28. The wrist worn receiving device according to claim 27, wherein each of said reactance elements are formed from a conductor.

29. The wrist worn receiving device according to claim 28, wherein said conductors are formed from sheet metal.

30. The wrist worn receiving device according to claim 29, wherein said sheet metal is selected from a group of sheet metals consisting of copper, beryllium copper, and nickel silver.

31. The wrist worn receiving device according to claim 27 wherein said first and second wrist band sections further include attachment means for coupling said first and second wrist band sections to said housing.

32. The wrist worn receiving device according to claim 27 wherein said first wrist band section further includes a first conductor coupled between said reactance buffer input and said receiver to form the first portion of the loop antenna, and further wherein said second wrist band section further includes a second conductor coupled between said coupling means and said receiver to form the second portion of the loop antenna.

33. The wrist worn receiving device according to claim 32 wherein said first and second conductors are sheet metal.

34. The wrist worn receiving device according to claim 33 wherein said sheet metal is selected from a group consisting of copper, beryllium copper, and nickel silver.

35. The wrist worn receiving device according to claim 27 wherein said first and second wrist band sections are molded from a urethane rubber.

36. The wrist worn receiving device according to claim 27 wherein said first and second wrist band sections are die cut from leather.

37. The wrist worn receiving device according to claim 27 wherein said coupling means is a conductive clasp for providing adjustment of the wrist band length and electrical coupling of the first and second antenna portions.