Tunable antenna system

Abstract

An antenna system with at least one tunable dipole element with a length adjustable conductive member disposed therein that enables the antenna to be used over a wide range of frequencies. The element is made of two longitudinally aligned, hollow support arms made of non-conductive material. Disposed longitudinally inside each element is a length adjustable conductive member electrically connected at one end. In the preferred embodiment, each conductive member is stored on a spool that is selectively rotated to precisely extend the conductive member into the support arm. The support arms, which may be fixed or adjustable in length, are affixed at one end to a rigid housing. During use, the conductive members are adjusted in length to tune the element to a desired frequency. The antenna is especially advantageous when configured as a Yagi-style antenna that can be optimally tuned at a specific frequency for maximum gain, maximum front-to-back ratio, and to provide a desired feed point impedance at the driven element. The antenna can also function as a bi-directional antenna by adjusting the reflector element to function as a director. An electronic control system allows the length of the conductive members to be manually or automatically adjusted to a desired frequency.

1. A tunable antenna system, comprising:
 a. at least one driven element, said element comprising two longitudinally aligned support arms made of non-conductive material, each said support arm including a length adjustable conductive member longitudinally aligned therein;  
 b. means for adjusting the length of said conductive member in each said support arm;  
 c. a radio transmitter/receiver coupled to said driven element; and,  
 d. means to coordinate the means for adjusting the length of said conductive members to receive a desired frequency used by said radio transmitter/receiver.  
 
     
     
       2. The tunable antenna system, as recited in  claim 1 , wherein said means for adjusting the length of said conductive members is a spool upon which each said conductive member is wound, and at least one motor to selectively wind and unwind said conductive members from said spools to form a dipole element used to receive a desired frequency. 
     
     
       3. The tunable antenna system, as recited in  claim 2 , wherein said means to coordinate said means to control the length of said conductive members is a programmable electronic control unit coupled to said motor to precisely control the length of said conductive members used in each said element. 
     
     
       4. The tunable antenna system, as recited in  claim 2 , wherein said motor is two directional and includes a drive shaft with at least one sprocket that engages said conductive member, whereby when said motor is activated, said sprocket winds or unwinds said conductive member from said reel  spool. 
     
     
       5. The tunable antenna system, as recited in  claim 1 , further including at least one non-driven element comprising two longitudinally aligned support arms made of non-conductive material, each said support arm including a length adjustable conductive member and means for adjusting the length of said conductive member. 
     
     
       6. The tunable antenna system, as recited in  claim 5 , wherein said driven element and said non-driven element are attached to a boom and spaced about eight feet. 
     
     
       7. The tunable antenna system, as recited in  claim 5 , further including a second non-driven element aligned parallel to said driven element and opposite to said non-driven element. 
     
     
       8. The tunable antenna system, as recited in  claim 1 , wherein said conductive member is 0.1 to 1 inch wide and 0.004 to 0.025 inch thick. 
     
     
       9. The tunable antenna system, as recited in  claim 8 , wherein each said support arm is eighteen feet in length and said conductive member is able to extend the full length thereof. 
     
     
       10. The tunable antenna system, as recited in  claim 1 , further including a housing unit with means to mount said support arms in a longitudinally aligned position on opposite sides of said housing unit. 
     
     
       11. The tunable antenna system, as recited in  claim 10 , wherein said means to mount said support arms is a transversely aligned rigid pipe attached to said housing unit, said pipe including opposite open ends that slidingly receives said support arms. 
     
     
       12. The tunable antenna system, as recited in  claim 11 , further including said rigid pipe, including a pair of slots that receive a pair of conductive members and transmits said conductive members in opposite directions through said receiver. 
     
     
       13. The tunable antenna system, as recited in  claim 12 , further including an end cap attached to the exposed end of said conductive member enabling said end caps to slide freely inside said support arm. 
     
     
       14. The tunable antenna system, as recited in  claim 1 , wherein said support arms include a plurality of sections longitudinally aligned and telescopingly interconnected so that said support arms may be adjusted in length. 
     
     
       15. The tunable antenna system, as recited in  claim 14 , further including means to couple the length of said conductive member to the length of said support arms. 
     
     
       16. A tunable antenna system, comprising:
 a. at least one element comprising two longitudinally aligned support arms made of non-conductive material;  
 b. two conductive members, each wound on a reel, said conductive members being longitudinally aligned in opposite inside said support arms, said conductive members being adjusted in length in said support arms by selectively winding and unwinding said conductive members from said reels;  
 c. a stepper motor coupled to said reels to precisely control the rotation of said reels;  
 d. a radio transmitter/receiver coupled to at least one element; and,  
 e. means to coordinate the means for adjusting the length of said conductive members to receive a desired frequency used by said radio transmitter/receiver.  
 
     
     
       17. The tunable antenna system, as recited in  claim 16 , wherein said means to coordinate said means to control the length of said boom and means to control the length of said conductive material is a programmable electronic control unit coupled to said stepper motor which is able to precisely control the length of said conductive members used in each said element to receive or transmit as a desired frequency. 
     
     
       18. The tunable antenna system, as recited in  claim 17 , further including a housing unit with means to mount said support arms in a longitudinally aligned position on opposite sides of said housing unit. 
     
     
       19. The tunable antenna system, as recited in  claim 18 , wherein said means to mount said support arms is a transversely aligned rigid pipe open at its open ends that slidingly receives said support arms. 
     
     
       20. The tunable antenna system, as recited in  claim 17 , further including at least one non-driven element comprising two longitudinally aligned support arms made of non-conductive material, each said support arm including a length adjustable conductive member coupled to said electronic control unit. 
     
     
       21. A tunable antenna system, comprising:
   a driven element, said driven element comprising a first support arm formed from non - conductive material, said first support arm being hollow and including a first length - adjustable conductive member disposed therein, and a second support arm formed from non - conductive material, said second support arm being hollow and including a second length - adjustable conductive member disposed therein;        a length - adjuster configured to adjust the lengths of said first and second conductive members disposed, respectively, in said first and second support arms; and        a transmission - line coupler electrically coupled to said driven element.     
     
     
       22. The tunable antenna system of  claim 21 , further including a controller, coupled to said length adjuster, for causing said length adjuster to adjust the length of said conductive member in said driven element to resonate at a desired frequency. 
     
     
       23. The tunable antenna system of  claim 21 , wherein said length- adjuster is disposed in a housing that mechanically supports said first and second support arms.   
     
     
       24. The tunable antenna system of  claim 23 , wherein said first and second support arms are substantially straight and extend in opposite directions from the housing. 
     
     
       25. The tunable antenna system of  claim 23 , wherein:
   each of said first and second conductive members is wound on a spool; and        said length - adjuster includes at least one motor coupled to said first and second conductive members and driven by said controller to selectively wind and unwind said first conductive member from its spool and into and out of said first support arm and to selectively wind and unwind said second conductive member from its spool and into and out of said second support arm to form an adjustable - frequency dipole element.     
     
     
       26. The tunable antenna system of  claim 25 , wherein said transmission- line coupler disposed in said housing and in electrical contact with said first and second conductive members at a position proximate to their spools.   
     
     
       27. The tunable antenna system of  claim 25 , wherein said controller includes a programmable microprocessor or microcontroller coupled to said motor to precisely control the length of said first and second conductive members. 
     
     
       28. The tunable antenna system of  claim 25 , wherein:
   each of said first and second conductive members is formed as a flat strip including a series of spaced - apart holes formed along a lengthwise axis thereof;        said at least one motor is a bi - directional motor and is mechanically coupled to a sprocketed wheel mounted on a drive shaft, sprockets on said wheel engaging said series of spaced - apart holes, whereby when said bi - directional motor is activated, said sprocketed wheel winds and unwinds each of said first and second conductive members from its spool into and out of its support arm.     
     
     
       29. The tunable antenna system of  claim 21 , wherein each of said first and second support arms comprises a plurality of nested telescoping tube sections formed from said non- conductive material.   
     
     
       30. The tunable antenna system of  claim 22 , further including:
   at least one non - driven element spaced apart from said driven element, said at least one non - driven element comprising a third support arm formed from non - conductive material, said third support arm being hollow and including a third conductive member disposed therein, said third conductive member being length - adjustable, and a fourth support arm formed from non - conductive material, said fourth support arm being hollow and including a fourth length - adjustable conductive member disposed therein, said fourth conductive member being length - adjustable; and        a length - adjuster coupled to said controller and configured to adjust the lengths of said third and fourth conductive members.     
     
     
       31. The tunable antenna system of  claim 30 , wherein said length- adjuster in each of said driven element and said non - driven elements is disposed in a housing that mechanically supports said support arms.   
     
     
       32. The tunable antenna system of  claim 30 , wherein:
   said length - adjuster for said driven element is disposed in a first housing that mechanically supports said first and second support arms; and        said length - adjuster for said non - driven element is disposed in a second housing that mechanically supports said third and fourth support arms.     
     
     
       33. The tunable antenna system of  claim 30 , wherein:
   said first and second support arms are substantially straight and extend in opposite directions from the first housing; and        said third and fourth support arms are substantially straight and extend in opposite directions from the second housing.     
     
     
       34. The tunable antenna system of  claim 30 , wherein:
   each of said first and second conductive members is wound on a spool;        said length - adjuster for said driven element includes at least one first motor coupled to said first and second conductive members and driven by said controller to selectively wind and unwind said first conductive member from its spool and into and out of said first support arm and to selectively wind and unwind said second conductive member from its spool and into and out of said second support arm;        each of said third and fourth conductive members is wound on a spool;        said length - adjuster for said at least one non - driven element includes at least one second motor coupled to said third and fourth conductive members and driven by said controller to selectively wind and unwind said third conductive member from its spool and into and out of said third support arm and to selectively wind and unwind said fourth conductive member from its spool and into and out of said fourth support arm.     
     
     
       35. The tunable antenna system of  claim 30 , wherein said transmission- line coupler is disposed in said first housing and is in electrical contact with said first and second conductive members at a position proximate to their spools.   
     
     
       36. The tunable antenna system of  claim 34 , wherein said controller includes a programmable microprocessor or microcontroller coupled to said at least one first motor to precisely control the length of said first and second conductive members and coupled to said at least one second motor to precisely control the length of said third and fourth conductive members. 
     
     
       37. The tunable antenna system of  claim 34 , wherein:
   each of said first and second conductive members is formed as a flat strip including a series of spaced - apart holes formed along a lengthwise axis thereof;        said at least one first motor is a bi - directional motor and is mechanically coupled to a first sprocketed wheel mounted on a drive shaft, sprockets on said first sprocketed wheel engaging said series of spaced - apart holes in said first and second conductive members, whereby when said at least one first motor is activated, said first sprocketed wheel winds and unwinds each of said first and second conductive members from its spool into and out of its support arm;        each of said third and fourth conductive members is formed as a flat strip including a series of spaced - apart holes formed along a lengthwise axis thereof;        said at least one second motor is a bi - directional motor and is mechanically coupled to a second sprocketed wheel mounted on a drive shaft, sprockets on said second sprocketed wheel engaging said series of spaced - apart holes in said third and fourth conductive members, whereby when said at least one second motor is activated, said second sprocketed wheel winds and unwinds each of said third and fourth conductive members from its spool into and out of its support arm.     
     
     
       38. The tunable antenna system of  claim 30 , wherein each of said first, second, third, and fourth support arms comprises a plurality of nested telescoping tube sections formed from said non- conductive material.   
     
     
       39. The tunable antenna system of  claim 32 , wherein the first and second housings are attached to a boom. 
     
     
       40. The tunable antenna system of  claim 33 , wherein at least two length- adjustable non - driven elements are spaced apart from and aligned parallel to said driven element.   
     
     
       41. The tunable antenna system of  claim 33 , wherein:
   each of said first, and second support arms are mounted to said first housing by seating them inside an opposing pair of rigid pipes attached to said housings; and        each of said third, and fourth support arms are mounted to said second housing by seating them inside an opposing pair of rigid pipes attached to said housings.     
     
     
       42. The tunable antenna system of  claim 33 , wherein the free end of each said first, second, third, and fourth conductive members is fitted with a rounded- end tip enabling said conductive member to slide freely inside said support arm.   
     
     
       43. The tunable antenna system of  claim 22 , further including at least one fixed- length parasitic element spaced apart from said driven element, said fixed - length parasitic element having a length chosen to interact with said driven element to produce a desired azimuthal radiation pattern at a selected frequency.   
     
     
       44. The tunable antenna system of  claim 30 , further including at least one fixed- length parasitic element attached to said boom and spaced apart from said driven element and said at least one non - driven element, said fixed - length parasitic element having a length chosen to interact with said driven element and said non - driven element to produce a desired azimuthal radiation pattern at a selected frequency.   
     
     
       45. The tunable antenna system of  claim 30 , wherein said controller includes a programmable microprocessor or microcontroller and is coupled to a non- volatile memory storing length data for said driven element and said at least one non - driven element.   
     
     
       46. The tunable antenna system of  claim 45 , wherein at least a portion of said length data corresponds to a plurality of selected antenna configurations. 
     
     
       47. The tunable antenna system of  claim 30 , wherein said controller includes a programmable microprocessor or microcontroller and is programmed to operate in a mode in which the individual lengths of said driven element and said at least one non- driven elements may be manually adjusted by a user to form a user antenna configuration.   
     
     
       48. The tunable antenna system of  claim 30 , wherein:
   said controller is programmed to operate in a mode in which the individual lengths of said driven element and said at least one non - driven element may be manually adjusted by a user to form a user antenna configuration; and        said controller is programmed to operate in a mode in which a user may store said user antenna configuration in said memory.     
     
     
       49. The tunable antenna system of  claim 46 , wherein:
   at least two non - driven elements are spaced apart from and aligned parallel to said driven element; and        said controller is configured to operate in a mode in which data from said memory is used to adjust the lengths of said driven element and said at least two non - driven elements to configure them as a yagi - type antenna wherein one non - driven element acts as director element and another non - driven element acts as a reflector element.     
     
     
       50. The tunable antenna system of  claim 49 , wherein said controller is programmed to operate in a mode in which data from said memory is used to adjust the lengths of said at least two non- driven elements to reverse the identities of the director element and the reflector element.   
     
     
       51. The tunable antenna system of  claim 49 , wherein said controller is configured to operate in a mode in which data from said memory is used to adjust the lengths of said at least two non- driven elements to reverse the identities of the director element and the reflector element to form a bi - directional antenna.   
     
     
       52. The tunable antenna system of  claim 49 , wherein said controller is programmed to operate in a mode in which data from said memory is used to adjust the lengths of said driven element and said at least one non- driven element to configure a yagi - type antenna for a selected frequency band in response to a user pressing a single button.   
     
     
       53. The tunable antenna system of  claim 52 , wherein said controller is programmed to operate in a mode in which data from said memory is used to adjust the lengths of said driven element and said at least one non- driven element to scroll through said selected frequency band in fixed frequency increments in response to a user pressing a single button.   
     
     
       54. The tunable antenna system of  claim 45 , wherein said controller is programmed to operate in a mode in which data from said memory is used to adjust the lengths of said driven element and said at least one non- driven elements by a selected frequency offset in response to a user pressing a single frequency - up or frequency - down button.   
     
     
       55. The tunable antenna system of  claim 45 , wherein said controller is programmed to operate in a mode in which the individual lengths of said driven element, said director, and said reflector may be manually adjusted by a user. 
     
     
       56. The tunable antenna system of  claim 22 , further including an SWR- sensing circuit and wherein said controller includes a programmable microprocessor or microcontroller and is programmed to operate in a mode in which the length of said driven element is adjusted to achieve a minimum SWR at a selected frequency.   
     
     
       57. The tunable antenna system of  claim 22 , further including a radio coupled to said controller, said radio communicating frequency data to said controller and wherein said controller is configured to operate in a mode in which said frequency data from said radio is used to adjust the length of said driven element to resonate at a frequency represented by said frequency data. 
     
     
       58. The tunable antenna system of  claim 30 , further including an SWR- measuring circuit and wherein said controller includes a programmable microprocessor or microcontroller and is further programmed to operate in a mode that adjusts the lengths of said driven element and said at least one non - driven element to achieve a minimum SWR at a selected frequency.   
     
     
       59. The tunable antenna system of  claim 30 , further including a radio coupled to said controller, said radio communicating frequency data to said controller and wherein said controller is configured to operate in a mode in which said frequency data from said radio is used to adjust the length of said driven element and said at least one non- driven element to configure a yagi antenna resonant at a frequency represented by said frequency data.   
     
     
       60. The tunable antenna system of  claim 40 , further including an SWR- measuring circuit and wherein said controller includes a programmable microprocessor or microcontroller and is further programmed to operate in a mode that adjusts the lengths of said driven element and said at least two non - driven elements to achieve a minimum SWR at a selected frequency.   
     
     
       61. The tunable antenna system of  claim 40 , further including a radio coupled to said controller, said radio communicating frequency data to said controller and wherein said controller is configured to operate in a mode in which said frequency data from said radio is used to adjust the length of said driven element and said at least two non- driven elements to configure a yagi antenna resonant at a frequency represented by said frequency data.   
     
     
       62. The tunable antenna system of  claim 22 , wherein said transmission- line coupler is electrically coupled to said driven element through an impedance - matching network.   
     
     
       63. The tunable antenna system of  claim 62 , wherein said impedance- matching network is an L network including an inductor coupled across the first and second conductive members of said driven element.   
     
     
       64. The tunable antenna system of  claim 61 , wherein said impedance- matching network is a unun and balun coupled between said driven element and said transmission - line coupler.   
     
     
       65. The tunable antenna system of  claim 30 , further including:
   a second driven element, said second driven element comprising a fifth support arm formed from non - conductive material, said fifth support arm being hollow and including a fifth conductive member disposed therein, said fifth conductive member being length - adjustable, and a sixth support arm formed from non - conductive material, said sixth support arm being hollow and including a sixth length - adjustable conductive member disposed therein, said sixth conductive member being length - adjustable;        length - adjusting means for adjusting the length of said fifth and sixth conductive members;        a transmission - line coupler electrically coupled to said second driven element; and,        wherein said controller is coupled to said length - adjusting means of said second driven element, for causing said length - adjusting means to adjust the length of said fifth and sixth conductive members of said second driven element to resonate at a desired frequency.     
     
     
       66. The tunable antenna system of  claim 21 , wherein said conductive material is formed from a copper and beryllium alloy. 
     
     
       67. The tunable antenna system of  claim 33 , wherein said conductive material is formed from a copper and beryllium alloy. 
     
     
       68. A tunable antenna element comprising:
   a support arm formed from a non - conductive material, said support arm having a longitudinal chamber disposed therein;        a length - adjustable conductive member disposed within said longitudinal chamber;        a length - adjuster configured to adjust the length of said conductive member disposed in said longitudinal chamber; and        a transmission - line coupler electrically coupled to said antenna element.     
     
     
       69. The tunable antenna element of  claim 68 , further including a controller, coupled to said length- adjuster, for causing said length - adjuster to adjust the length of said conductive member in said longitudinal chamber to resonate at a desired frequency.   
     
     
       70. The tunable antenna element of  claim 68 , wherein said length- adjuster is disposed in a housing that mechanically supports said support arm.   
     
     
       71. The tunable antenna element of  claim 70 , wherein the support arm is substantially straight and extends from the housing. 
     
     
       72. The tunable antenna element of  claim 68 , wherein said length- adjuster includes a spool upon which said conductive member is wound, and at least one motor coupled to said conductive member to selectively wind and unwind said conductive member from said spool and into and out of said longitudinal chamber.   
     
     
       73. The tunable antenna element of  claim 68 , wherein the transmission- line coupler disposed in said housing and in electrical contact with said conductive member at a position proximate to said spool.   
     
     
       74. The tunable antenna element of  claim 69 , wherein said controller includes a programmable microprocessor or microcontroller coupled to said motor to precisely control the length of said conductive member. 
     
     
       75. The tunable antenna element of  claim 72 , wherein:
   said conductive member is formed as a flat strip including a series of spaced - apart holes formed along a lengthwise axis thereof;        said motor is bi - directional and is mechanically coupled to a sprocketed wheel mounted on a drive shaft, sprockets on said wheel engaging said series of spaced - apart holes, whereby when said motor is activated, said sprocketed wheel winds and unwinds said conductive member from said spool into and out of said support arms.     
     
     
       76. The tunable antenna element of  claim 68  wherein said support arm comprises a plurality of nested telescoping tube sections formed from said non- conductive material.   
     
     
       77. The tunable antenna element of  claim 70 , wherein said support arm is mounted to said housing by seating it inside a rigid pipe attached to said housing. 
     
     
       78. The tunable antenna element of  claim 68 , wherein the free end of said conductive member is fitted with a rounded- end tip enabling said conductive member to slide freely inside said support arm.   
     
     
       79. The tunable antenna element of  claim 69 , wherein said controller includes a programmable microprocessor or microcontroller and is coupled to a non- volatile memory storing length data for said antenna element.   
     
     
       80. The tunable antenna system of  claim 79 , wherein at least a portion of said length data corresponds to a plurality of selected antenna configurations. 
     
     
       81. The tunable antenna element of  claim 69 , wherein said controller includes a programmable microprocessor or microcontroller and is programmed to operate in a mode in which the length of said antenna element may be manually adjusted by a user. 
     
     
       82. The tunable antenna element of  claim 69 , wherein:
   said controller is programmed to operate in a mode in which the length of said antenna element may be manually adjusted by a user to form an antenna configuration; and        said controller is programmed to operate in a mode in which a user may store said user antenna configuration in said memory.     
     
     
       83. The tunable antenna system of  claim 80  wherein said controller is configured to operate in a mode in which data from said memory is used to adjust the length of said antenna element for a selected frequency band in response to a user pressing a single button. 
     
     
       84. The tunable antenna system of  claim 83 , wherein said controller is programmed to operate in a mode in which data from said memory is used to adjust the lengths of said antenna element to scroll through said selected frequency band in fixed frequency increments in response to a user pressing a single button. 
     
     
       85. The tunable antenna element of  claim 80 , wherein said controller is programmed to operate in a mode in which data from said memory is used to adjust the length of said antenna element by a selected frequency offset in response to a user pressing a single frequency- up or frequency - down button.   
     
     
       86. The tunable antenna system of  claim 69 , further including an SWR- sensing circuit and wherein said controller includes a programmable microprocessor or microcontroller and is programmed to operate in a mode in which the length of said antenna element is adjusted to achieve a minimum SWR at a selected frequency.   
     
     
       87. The tunable antenna element of  claim 68 , wherein said transmission- line coupler is electrically coupled to said antenna element through an impedance - matching network.   
     
     
       88. A tunable antenna system, comprising:
   a driven element, said driven element comprising a first support arm formed from non - conductive material, said first support arm being hollow and including a first conductive member disposed therein, said first conductive member being length - adjustable, and a second support arm formed from non - conductive material, said second support arm being hollow and including a second conductive member disposed therein, said second conductive member being length - adjustable;        length - adjusting means for adjusting the length of said first and second conductive members disposed, respectively, in said first and second support arms; and        a transmission - line coupler electrically coupled to said driven element.     
     
     
       89. The tunable antenna system of  claim 88  further including a controller, coupled to said length- adjusting means, for causing said length - adjusting means to adjust the length of said first and second conductive members in said driven element to resonate at a desired frequency.   
     
     
       90. The tunable antenna system of  claim 88 , wherein said length- adjusting means is disposed in a housing that mechanically supports said first and second support arms.   
     
     
       91. The tunable antenna system of  claim 90 , wherein said first and second support arms are substantially straight and extend in opposite directions from the housing. 
     
     
       92. The tunable antenna system of  claim 88 , wherein said length- adjusting means includes at least one motor coupled to said first and second conductive members and driven by said controller to selectively adjust the length of said first conductive member in said first support arm and to selectively adjust the length of said second conductive member in said second support arm to form an adjustable - frequency dipole element.   
     
     
       93. The tunable antenna system of  claim 89 , wherein said controller includes a programmable microprocessor or microcontroller coupled to said motor to precisely control the length of said first and second conductive members. 
     
     
       94. The tunable antenna system of  claim 91 , wherein:
   each of said first and second conductive members is formed as a flat strip including a series of spaced - apart holes formed along a lengthwise axis thereof;        said at least one motor is a bi - directional motor and is mechanically coupled to a sprocketed wheel mounted on a drive shaft, sprockets on said wheel engaging said series of spaced - apart holes, whereby when said bi - directional motor is activated, said sprocketed wheel winds and unwinds each of said first and second conductive members from its spool into and out of its support arm.     
     
     
       95. The tunable antenna system of  claim 89 , wherein said transmission- line coupler disposed in said housing and in electrical contact with said first and second conductive members at a position proximate to their spools.   
     
     
       96. The tunable antenna system of  claim 88 , wherein each of said first and second support arms comprises a plurality of nested telescoping tube sections formed from said non- conductive material.   
     
     
       97. The tunable antenna system of  claim 89 , further including:
   at least one non - driven element spaced apart from said driven element, said at least one non - driven element comprising a third support arm formed from non - conductive material, said third support arm being hollow and including a third conductive member disposed therein, said third conductive member being length - adjustable, and a fourth support arm formed from non - conductive material, said fourth support arm being hollow and including a fourth length - adjustable conductive member disposed therein, said fourth conductive member being length - adjustable; and        length - adjusting means for adjusting the length of said third and fourth conductive members and coupled to said controller.     
     
     
       98. The tunable antenna system of  claim 97 , wherein:
   said length - adjusting means for said driven element is disposed in a first housing that mechanically supports said first and second support arms; and        said length - adjusting means for said non - driven element is disposed in a second housing that mechanically supports said third and fourth support arms.     
     
     
       99. The tunable antenna system of  claim 98 , wherein:
   said first and second support arms are substantially straight and extend in opposite directions from the first housing; and        said third and fourth support arms are substantially straight and extend in opposite directions from the second housing.     
     
     
       100. The tunable antenna system of  claim 98 , wherein:
   each of said first and second conductive members is wound on a spool;        said length - adjusting means for said driven element includes at least one first motor disposed in said first housing and coupled to said first and second conductive members and driven by said controller to selectively wind and unwind said first conductive member from its spool and into and out of said first support arm and to selectively wind and unwind said second conductive member from its spool and into and out of said second support arm;        each of said third and fourth conductive members is wound on a spool;        said length - adjusting means for said at least one non - driven element includes at least one second motor disposed in said second housing and coupled to said third and fourth conductive members and driven by said controller to selectively wind and unwind said third conductive member from its spool and into and out of said third support arm and to selectively wind and unwind said fourth conductive member from its spool and into and out of said fourth support arm.     
     
     
       101. The tunable antenna system of  claim 100 , wherein said transmission- line coupler is disposed in said first housing and is in electrical contact with said first and second conductive members at a position proximate to their spools.   
     
     
       102. The tunable antenna system of  claim 97 , wherein said controller includes a programmable microprocessor or microcontroller coupled to said at least one first motor to precisely control the length of said first and second conductive members and coupled to said at least one second motor to precisely control the length of said third and fourth conductive members. 
     
     
       103. The tunable antenna system of  claim 97 , wherein:
   each of said first and second conductive members is formed as a flat strip including a series of spaced - apart holes formed along a lengthwise axis thereof;        said at least one first motor is a bi - directional motor and is mechanically coupled to a first sprocketed wheel mounted on a drive shaft, sprockets on said first sprocketed wheel engaging said series of spaced - apart holes in said first and second conductive members, whereby when said at least one first motor is activated, said first sprocketed wheel winds and unwinds each of said first and second conductive members from its spool into and out of its support arm;        each of said third and fourth conductive members is formed as a flat strip including a series of spaced - apart holes formed along a lengthwise axis thereof;        said at least one second motor is a bi - directional motor and is mechanically coupled to a second sprocketed wheel mounted on a drive shaft, sprockets on said second sprocketed wheel engaging said series of spaced - apart holes in said third and fourth conductive members, whereby when said at least one second motor is activated, said second sprocketed wheel winds and unwinds each of said third and fourth conductive members from its spool into and out of its support arm.     
     
     
       104. The tunable antenna system of  claim 98  wherein each of said first, second, third, and fourth support arms comprises a plurality of nested telescoping tube sections formed from said non- conductive material.   
     
     
       105. The tunable antenna system of  claim 98 , wherein the first and second housings are attached to a boom. 
     
     
       106. The tunable antenna system of  claim 97 , wherein at least two length- adjustable non - driven elements are spaced apart from and aligned parallel to said driven element.   
     
     
       107. The tunable antenna system of  claim 103 , wherein:
   each of said first, and second support arms are mounted to said first housing by seating them inside an opposing pair of rigid pipes attached to said housings; and        each of said third, and fourth support arms are mounted to said second housing by seating them inside an opposing pair of rigid pipes attached to said housings.     
     
     
       108. The tunable antenna system of  claim 104  wherein the free end of each said first, second, third, and fourth conductive members is fitted with a rounded- end tip enabling said conductive member to slide freely inside said support arm.   
     
     
       109. The tunable antenna system of  claim 97 , further including at least one fixed- length parasitic element attached to said boom and spaced apart from said driven element and said at least one non - driven element, said fixed - length parasitic element having a length chosen to interact with said driven element and said non - driven element to produce a desired azimuthal radiation pattern at a selected frequency.   
     
     
       110. The tunable antenna system of  claim 89 , wherein said controller includes a programmable microprocessor or microcontroller and is programmed to operate in a mode in which the length of said driven element may be manually adjusted by a user. 
     
     
       111. The tunable antenna system of  claim 89 , wherein said controller includes a programmable microprocessor or microcontroller and is coupled to a non- volatile memory storing length data for said driven element.   
     
     
       112. The tunable antenna system of  claim 111 , wherein at least a portion of said length data corresponds to a plurality of selected antenna configurations. 
     
     
       113. The tunable antenna system of  claim 112 , wherein:
   said controller is programmed to operate in a mode in which the length of said driven element may be manually adjusted by a user to form a user antenna configuration; and        said controller is programmed to operate in a mode in which a user may store said user antenna configuration in said memory.     
     
     
       114. The tunable antenna system of  claim 112 , wherein said controller is programmed to operate in a mode in which data from said memory is used to adjust the length of said driven element to adjust the length of said driven element for a selected frequency band in response to a user pressing a single button. 
     
     
       115. The tunable antenna system of  claim 114 , wherein said controller is programmed to operate in a mode in which data from said memory is used to adjust the length of said driven element to scroll through said selected frequency band in fixed frequency increments in response to a user pressing a single button. 
     
     
       116. The tunable antenna system of  claim 112 , wherein said controller is programmed to operate in a mode in which data from said memory is used to adjust the length of said driven element by a selected frequency offset in response to a user pressing a single frequency- up or frequency - down button.   
     
     
       117. The tunable antenna system of  claim 97 , wherein said controller includes a programmable microprocessor or microcontroller and is programmed to operate in a mode in which the lengths of said driven element and said at least one non- driven element may be manually adjusted by a user.   
     
     
       118. The tunable antenna system of  claim 97 , wherein said controller includes a programmable microprocessor or microcontroller and is coupled to a non- volatile memory storing length data for said driven element and said at least one non - driven element.   
     
     
       119. The tunable antenna system of  claim 118 , wherein at least a portion of said length data corresponds to a plurality of selected antenna configurations. 
     
     
       120. The tunable antenna system of  claim 119 , wherein:
   said controller is programmed to operate in a mode in which the individual lengths of said driven element and said at least one non - driven element may be manually adjusted by a user to form a user antenna configuration; and        said controller is programmed to operate in a mode in which a user may store said user antenna configuration in said memory.     
     
     
       121. The tunable antenna system of  claim 119 , wherein:
   at least two non - driven elements are spaced apart from and aligned parallel to said driven element; and        said controller is configured to operate in a mode in which data from said memory is used to adjust the lengths of said driven element and said at least two non - driven elements to configure them as a yagi - type antenna wherein one non - driven element acts as director element and another non - driven element acts as a reflector element.     
     
     
       122. The tunable antenna system of  claim 119 , wherein:
   at least two non - driven elements are spaced apart from and aligned parallel to said driven element; and        said controller is programmed to operate in a mode in which data from said memory is used to adjust the lengths of said at least two non - driven elements to reverse the identities of the director element and the reflector element.     
     
     
       123. The tunable antenna system of  claim 119 , wherein:
   at least two non - driven elements are spaced apart from and aligned parallel to said driven element; and        said controller is configured to operate in a mode in which data from said memory is used to adjust the lengths of said at least two non - driven elements to reverse the identities of the director element and the reflector element to form a bi - directional antenna.     
     
     
       124. The tunable antenna system of  claim 119 , wherein said controller is programmed to operate in a mode in which data from said memory is used to adjust the lengths of said driven element and said at least one non- driven element to configure a yagi - type antenna for a selected frequency band in response to a user pressing a single button.   
     
     
       125. The tunable antenna system of  claim 119 , wherein said controller is programmed to operate in a mode in which data from said memory is used to adjust the lengths of said driven element and said at least one non- driven element to scroll through said selected frequency band in fixed frequency increments in response to a user pressing a single button.   
     
     
       126. The tunable antenna system of  claim 119 , wherein said controller is further programmed to operate in a mode in which data from said memory is used to adjust the lengths of said driven element and said at least one non- driven elements by a selected frequency offset in response to a user pressing a single frequency - up or frequency - down button.   
     
     
       127. The tunable antenna system of  claim 89 , further including an SWR- sensing circuit and wherein said controller includes a programmable microprocessor or microcontroller and is programmed to operate in a mode in which the length of said driven element is adjusted to achieve a minimum SWR at a selected frequency.   
     
     
       128. The tunable antenna system of  claim 89 , further including a radio coupled to said controller, said radio communicating frequency data to said controller and wherein said controller is configured to operate in a mode in which said frequency data from said radio is used to adjust the length of said driven element to resonate at a frequency represented by said frequency data. 
     
     
       129. The tunable antenna system of  claim 97 , further including an SWR- measuring circuit and wherein said controller includes a programmable microprocessor or microcontroller and is further programmed to operate in a mode that adjusts the lengths of said driven element and said at least one non - driven element to achieve a minimum SWR at a selected frequency.   
     
     
       130. The tunable antenna system of  claim 97 , further including a radio coupled to said controller, said radio communicating frequency data to said controller and wherein said controller is configured to operate in a mode in which said frequency data from said radio is used to adjust the length of said driven element and said at least one non- driven element to configure an antenna resonant at a frequency represented by said frequency data.   
     
     
       131. A method for transmitting an RF signal from an antenna, the method comprising:
   using a transmission - line coupler to couple the RF signal to a driven element of the antenna; and        adjusting the length of a length - adjustable conductive member to resonate the driven element, said adjusting further including receiving a portion of the length - adjustable conductive member in a hollow support arm formed from non - conductive material and storing another portion of the length - adjustable conductive member on a spool.     
     
     
       132. The method of  claim 131 , further comprising:
   controlling said adjusting with a controller coupled to control a stepper motor coupled to the spool.     
     
     
       133. The method of  claim 132 , wherein:
   said controlling includes      selecting a desired transmission frequency and, in response thereto, adjusting the length of the length - adjustable conductive member within the hollow support arm.       
     
     
       134. The method of  claim 132 , wherein:
   said controlling includes      selecting a desired antenna pattern and, in response thereto, adjusting the length of the length - adjustable conductive member within the hollow support arm.       
     
     
       135. The method of  claim 132 , wherein:
   said controlling includes      selecting a desired frequency band and, in response thereto, adjusting the length of the length - adjustable conductive member within the hollow support arm.       
     
     
       136. The method of  claim 132 , wherein:
   said controlling includes      receiving frequency data at the controller from an attached radio and, in response thereto, adjusting the length of the length - adjustable conductive member within the hollow support arm.       
     
     
       137. The method of  claim 132 , wherein:
   said controlling includes      receiving SWR information from a SWR - sensing circuit coupled to measure SWR in the RF signal; and        adjusting the length of the length - adjustable conductive member within the hollow support arm so as to minimize the measured SWR.       
     
     
       138. The method of  claim 132 , wherein:
   said controlling includes      receiving SWR information from a SWR - sensing circuit coupled to measure SWR in the RF signal; and        adjusting the length of the length - adjustable conductive member within the hollow support arm so as to achieve a selected maximum measured SWR value.       
     
     
       139. A controller for controlling a tunable antenna, the controller comprising:
   circuitry configured to cause the tunable antenna to adjust the length of a length - adjustable conductive member within a hollow support arm of a driven element of the tunable antenna;        a SWR - sensing circuit coupled to measure SWR in an RF signal coupled to the driven element; and        a programmable processor configured to execute a program of instructions to cause said circuitry to adjust the length of the length - adjustable conductive member within the hollow support arm so as to minimize the measured SWR.     
     
     
       140. A controller for controlling a tunable antenna, the controller comprising:
   circuitry configured to cause the tunable antenna to adjust the length of a length - adjustable conductive member within a hollow support arm of a driven element of the tunable antenna;        a memory storing length data for the length - adjustable conductive member;        at least one frequency - select button; and        a programmable processor configured to execute a program of instructions to cause said circuitry to adjust the length of the length - adjustable conductive member within the hollow support arm in response to input from the at least one frequency - select button.     
     
     
       141. A controller for controlling a tunable antenna, the controller comprising:
   circuitry configured to cause the tunable antenna to adjust the length of a length - adjustable conductive member within a hollow support arm of a driven element of the tunable antenna;        a memory storing length data for the length - adjustable conductive member;        at least one frequency - input button; and        a programmable processor configured to execute a program of instructions to store length data entered by a user and to cause said circuitry to adjust the length of the length - adjustable conductive member within the hollow support arm in response to length data stored by a user.