Patent Publication Number: US-7916097-B2

Title: Enhanced band multiple polarization antenna assembly

Description:
RELATED APPLICATIONS 
     This application claims priority from pending U.S. application Ser. No. 11/279,941, filed Apr. 17, 2006 and published as U.S. Published Patent Application No. 2007/0132651 which is a divisional of patent application Ser. No. 10/786,656, filed on Feb. 25, 2004, now U.S. Pat. No. 7,030,831, issued Apr. 18, 2006, which was a continuation-in-part of patent application Ser. No. 10/294,420 filed on Nov. 14, 2002, now U.S. Pat. No. 6,806,841 which issued on Oct. 19, 2004. Each of these documents are incorporated herein by reference in their entirety. 
     Further the subject matter of each of U.S. Pat. No. 7,348,933, issued Mar. 25, 2008, U.S. Pat. No. 7,236,129, issued Jun. 26, 2007, U.S. Pat. No. 7,138,956, issued Nov. 21, 2006, and U.S. Pat. No. 6,496,152, issued Dec. 17, 2002, is incorporated herein by reference. 
     TECHNICAL FIELD 
     Certain embodiments of the present invention relate to antennas for wireless communications. More particularly, certain embodiments of the present invention relate to an apparatus and method providing a multi-band, wide-band, or broadband multi-polarized antenna exhibiting substantial spatial diversity for use in point-to-point and point-to-multipoint communication applications for the Internet, land, maritime, aviation, and space. 
     BACKGROUND OF THE INVENTION 
     For years, wireless communications have struggled with limitations of audio/video/data transport and internet connectivity in both obstructed (indoor/outdoor) and line-of-site (LOS) deployments. A focus on antenna gain as well as circuitry solutions have proven to have significant limitations. Unresolved, non-optimized (leading edge) technologies have often given way to “bleeding edge” attempted resolutions. Unfortunately, all have fallen short of desirable goals. 
     While lower frequency radio waves benefit from an ‘earth hugging’ propagation advantage, higher frequencies do inherently benefit from (multi-) reflection/penetrating characteristics. However, with topographical changes (hills &amp; valleys) and object obstructions (e.g., natural such as trees, and man-made such as buildings/walls) and with the resultant reflections, diffractions, refractions and scattering, maximum signal received may well be off-axis (non-direct path) and multi-path (partial) cancellation of signals results in null/weaker spots. Also, some antennas may benefit from having gain at one elevation angle (‘capturing’ signals of some pathways), while other antennas have greater gain at another elevation angle, each type being insufficient where the other does well. In addition, the radio wave can experience altered polarizations as they propagate, reflect, refract, diffract, and scatter. A very preferred (polarization) path may exist; however, insufficient capture of the signal can result if this preferred path is not utilized. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with an aspect of the invention, an antenna assembly is provided for receiving and transmitting radio frequency signals over an enhanced frequency band. A first radiative element has a first end, a second end, and an associated length, and is comprised of an electrically conductive material. The first end of the first radiative element is electrically connected to an antenna feed at an apex and at least a portion of the first radiative element is disposed outwardly away from the apex at an acute angle relative to, and on a first side of, an imaginary plane intersecting the apex. A second radiative element has a first end and a second end and is comprised of an electrically conductive material. The first end of the second radiative element is electrically connected to the antenna feed and the first radiative element at the apex. The second end of the second radiative element has an associated height above the imaginary plane that is less than the product of the length of the first element and the sine of the acute angle at which the first element is disposed outwardly from the apex. The assembly further comprises an electrically conductive ground reference. 
     In accordance with another aspect of the invention, an antenna assembly is provided for receiving and transmitting radio frequency signals over an enhanced frequency band. The antenna assembly comprises an electrically conductive ground reference. A first set of a plurality of curvilinear radiative elements are each electrically connected at respective first ends to an antenna feed at an apex and are comprised of an electrically conductive material. At least a portion of each of the first set of radiative elements are disposed outwardly away from the apex on a first side of the imaginary plane. Each of the first set of curvilinear elements having a length are tuned to a first characteristic frequency and curved such that respective second ends of the first set of radiative elements are located below a predetermined height above the imaginary plane. 
     In accordance with yet another aspect of the present invention, an antenna assembly is provided for receiving and transmitting radio frequency signals over an enhanced frequency band. A set of a plurality of radiative elements are each electrically connected to an antenna feed at an apex and comprised of an electrically conductive material, At least a portion of each of the set of radiative elements are disposed outwardly away from the apex at an acute angle relative to, and on a first side of the imaginary plane. Each of the set of radiative elements has a length within a first range associated with a first characteristic frequency, such that the associated lengths of the set of radiative elements are selected as to tune the antenna to the first characteristic frequency. 
     A second set of a plurality of radiative elements are each electrically connected to the antenna feed at the apex and comprised of an electrically conductive material. At least a portion of each of the second set of radiative elements is disposed outwardly away from the apex at an acute angle relative to, and on a first side of the imaginary plane. Each of the second set of radiative elements has a length within a second range that does not overlap the first range. The assembly further comprises an electrically conductive ground reference. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an enhanced band, multi-polarized antenna for transmitting and receiving radio frequency signals in accordance with various aspects of the present invention. 
         FIG. 2  illustrates a side view of a first exemplary implementation of an antenna assembly in accordance with an aspect of the present invention. 
         FIG. 3  illustrates an overhead view of a first exemplary implementation of an antenna assembly in accordance with an aspect of the present invention. 
         FIG. 4  illustrates a side view of a second exemplary implementation of an antenna assembly in accordance with an aspect of the present invention. 
         FIG. 5  illustrates an overhead view of a second exemplary implementation of an antenna assembly in accordance with an aspect of the present invention. 
         FIG. 6  illustrates a side view of a third exemplary implementation of an antenna assembly in accordance with an aspect of the present invention. 
         FIG. 7  illustrates a side view of a fourth exemplary implementation of an antenna assembly in accordance with an aspect of the present invention. 
         FIG. 8  illustrates a side view of a fifth exemplary implementation of an antenna assembly in accordance with an aspect of the present invention. 
         FIG. 9  illustrates a side view of a sixth exemplary implementation of an antenna assembly in accordance with an aspect of the present invention. 
         FIG. 10  illustrates a side view of a seventh exemplary implementation of an antenna assembly in accordance with an aspect of the present invention. 
         FIG. 11  illustrates a cross sectional view of a parabolic reflector dish for directing radiation received at and transmitted from an omni-directional enhanced band antenna to provide directionality to the antenna in accordance with an aspect of the present invention. 
         FIG. 12  illustrates a cross sectional view of a folded sheet reflector for providing directionality to an omnidirectional enhanced band antenna assembly in accordance with an aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Generally stated, a novel three-dimensionally constructed antenna with in-built spatial diversity (one part perhaps in a “null spot,” while another part of the antenna in a: “hot spot”), relatively broad signal patterning, and in-built polarization diversity serves to stabilize signal and throughput (minimizing Ethernet rejects and the like) in the real “obstructed,” often dynamic world.  FIG. 1  illustrates a first embodiment of an enhanced band, multi-polarized antenna  10  for transmitting and receiving radio frequency signals in accordance with various aspects of the present invention. It will be appreciated that the term “radio frequency,” is intended to encompass frequencies within the microwave and traditional radio bands, specifically frequencies between 3 kHz and 3 THz. Further, the term “enhanced band” is intended to refer to wideband and multiband applications. The antenna comprises a multi-polarized driven assembly  20  that includes at least a first radiative element  22  and a second radiative element  24 , each formed from a conductive material. The two radiative elements  22  and  24  of the driven element  20  have respective first ends are electrically connected to one another and an antenna feed  30  at an apex point  32  such that the radiative elements  22  and  24  each extend to respective second ends. In accordance with an aspect of the invention, at least a portion of the first radiative element extends outwardly from the apex point at an acute angle, that is an angle less than ninety degrees, relative to an imaginary plane  34  intersecting the apex point  32 . The radiative elements  22  and  24  are all located to a first side of the imaginary plane  34 . It will be appreciated that additional radiative elements (not shown) can be utilized in the driven element in accordance with various implementations of the invention. 
     Electromagnetic waves are often reflected, diffracted, refracted, and scattered by surrounding objects, both natural and man-made. As a result, electromagnetic waves that are approaching a receiving antenna can be arriving from multiple angles and have multiple polarizations and signal levels. The antenna  10  illustrated in  FIG. 1  is configured to capture or utilize the preferred approaching signal whether the preferred signal is a line-of-sight (LOS) signal or a reflected signal, and no matter how the signal is polarized. In the illustrated antenna  10 , the multiple radiative members  22  and  24  are positioned over a ground plane and properly spaced to allow signals of diverse polarizations to generated and/or received in various different directions. Therefore, such a driven element is said to be “multi-polarized” as well as providing “geometric spatial capture of signal”. If a driven element produced all polarizations in all planes (e.g., all planes in an x, y, z coordinate system) and the receiving antenna is capable of capturing all polarizations in all planes, then the significantly greatest preferred polarization path, that is the signal path allowing for maximum signal amplitude, may be utilized, as well as well as a variety of polarization diverse and spatially diverse resultant signals. 
     A conductive ground plane structure  40  can be located at the imaginary plane or on a second side of the imaginary plane  34 . The ground plane structure  40  is illustrated herein as a conical member, but it will be appreciated that the ground plane structure can be configured in any of a number of ways. For example, a planar or cylindrical ground plane can be utilized. Further, the ground plane structure  40  does not need to be a single, solid structure. For example, the ground plane can be implemented as a conductive mesh or comprise a number of discrete conductive elements evenly spaced around the apex point  32 . 
     In accordance with an embodiment of the present invention, the first radiative antenna element  22  can have a length, L, and an angle of incidence, θ, with the imaginary plane  34 . The second radiative antenna element  24  can be configured such that a second end  42  of the second radiative element is at a height, H, above the imaginary plane  34  that is less than the product of the length of the first antenna element  22  and the sine of the angle of incidence, such that:
 
 H&lt;L  sin(θ)  Eq. 1
 
     By maintaining the height of the second end  42  of the second radiative element  24  below this level, it is possible to introduce enhanced band sensitivity to the antenna assembly without significantly increasing the size and complexity of the antenna assembly. 
       FIG. 2  illustrates a side view of a first exemplary implementation of an antenna assembly  50  in accordance with an aspect of the present invention. 
       FIG. 3  illustrates an overhead view of the first exemplary implementation of the antenna assembly. The illustrated antenna assembly  50  comprises a driven antenna assembly  52  located on a first side of an imaginary plane  54 , and a ground reference  56  located at the imaginary plane or on a second side of the imaginary plane. The driven antenna assembly  52  can be driven by an antenna feed that is electrically connected to the driven antenna assembly approximately at the imaginary plane  54 . In the illustrated implementation, the ground reference  56  is illustrated as planar, but it will be appreciated that other configurations of the ground plane can be utilized within the illustrated antenna assembly. The ground reference  56  may be comprised of any appropriate electrically conductive material such as, for example, copper or stainless steel. The radius of the ground reference  56  is at least one-quarter of a wavelength of the lowest frequency of operation. 
     The surface of the ground reference  56  may be continuous or may be a crosshatched wired mesh, in accordance with various embodiments of the present invention. Also, three or more linear elements disposed in a substantially conical shape may form the ground reference, in accordance with an embodiment of the present invention. In other implementations, the ground reference  56  can include a conical assembly or a cylindrical sleeve having a closed upper base side. Alternatively, the shield of a coaxial associated with the antenna feed can serve as the ground reference, and various styles of stubs, sleeves, matching systems, baluns, transformers, etc. may also be used. The antenna feed  58  can include an SMA (or similar) coaxial connector and a transmitter/receiver circuit board (not shown). The SMA connector and board can be electrically connected together by a length of coaxial cable. The SMA connector allows a center conductor of the coaxial cable to electrically connect to the driven antenna assembly  52  and allows a ground braid of the coaxial cable to electrically connect to the ground reference  56 . A dielectric material can be used to electrically insulate the center conductor and the driven antenna assembly  52  from the ground reference  56 . 
     The driven antenna assembly  52  comprises six radiative elements  62 - 64  and  66 - 68  that radiate out from a common apex  70 . The driven antenna assembly  52  and its constituent elements  62 - 64  and  66 - 68  are formed from a conductive material. The radiative elements  62 - 64  and  66 - 68  are electrically connected to the antenna feed  58  and one another at the apex  70 . A first set of radiative elements comprise first, second, and third radiative elements  62 - 64  that are generally linear and extend away from the apex  70  at an acute angle relative to the imaginary plane  54 . Each of the first, second, and third radiative antenna elements  62 - 64  may be at a unique acute angle or at the same acute angle relative to the imaginary plane  54 . In the illustrated implementation, the first, second, and third radiative elements  62 - 64  are oriented such that the first, second, and third elements are spaced evenly, that is, at intervals of one-hundred and twenty degrees. Each of the first set of radiative elements  62 - 64  have a length within a first range of lengths associated with a first characteristic frequency. For example, a first element  62  can have a length, L 1 , tuned to be receptive to the first characteristic frequency and each of the second and third elements  63  and  64  can have a length within an approximately ten percent variance of the length of the first element. Varying the lengths of the first set of radiative elements  62 - 64  can provide an improvement in the broadband properties of the driven antenna assembly, but it will be appreciated that a common antenna length, for example, the tuned antenna length L 1 , can be utilized for the first set of radiative elements in while still maintain the wideband properties of the antenna. 
     A second set of radiative elements comprise fourth, fifth, and sixth radiative elements  66 - 68  that are generally linear and extend away from the apex  70  at an acute angle relative to the imaginary plane  54 . Each of the fourth, fifth, and sixth radiative antenna elements  66 - 68  may be at a unique acute angle or at the same acute angle relative to the imaginary plane  54  as one another or one of the first set of radiative elements  62 - 64 . In the illustrated implementation, the fourth, fifth, and sixth radiative elements  66 - 68  are oriented such that they are spaced evenly between the first set of radiative elements  62 - 64 , such that each of the second set of radiative elements is spaced at sixty degree intervals from two of the first set of radiative elements and at intervals of one-hundred and twenty degrees from one another. Each of the second set of radiative elements  66 - 68  have a length within a second range of lengths associated with a second characteristic frequency. For example, the fourth element  66  can have a length, L 2 , tuned to be receptive to the second characteristic frequency and each of the fifth and sixth elements  67  and  68  can have a length within an approximately ten percent variance of the length of the fourth element. The lengths of the radiative elements  62 - 64  and  66 - 68  can be configured such that the first range of lengths and the second range of lengths do not overlap. 
     In the illustrated implementation, the antenna assembly  50  is designed with a first characteristic frequency of 2.4 GHz and a second characteristic frequency of 5 GHz, allowing the antenna to operate at a wide band of radio frequencies ranging from approximately 2.0 GHz to approximately 11 GHz. The lengths of the first set of radiative elements  62 - 64  can be tuned to a frequency of 2.4 GHz, with the first radiative element  62  having a length of approximately 0.875 inches, the second radiative element  63  being shorter by a factor less than ten percent (e.g., ˜0.813 inches) and the third radiative element  64  can longer by a factor less than ten percent (e.g., 0.938 inches). The lengths of the second set of radiative elements  66 - 68  can be tuned to a frequency of 5 GHz, such that the fourth radiative element  66  has a length of approximately 0.563 inches, the fifth radiative element  67  can be shorter by a factor less than ten percent (e.g., ˜0.5 inches) and the sixth radiative element  68  can be longer by a factor of less than ten percent (e.g., 0.625 inches). Each of the radiative elements can have a diameter of approximately one-sixteenth of an inch. By implementing the driven antenna assembly  52  as a series of elements of varying lengths, an ultra wide band, multi-polarized antenna assembly can be realized. 
     In accordance with an aspect of the present invention, each of the first and second sets of radiative elements  62 - 64  and  66 - 68  can be generalized to only two or greater than three elements having similar length and orientation. For example, in place of the first set of radiative elements  62 - 64 , four radiative elements, circumferentially spaced at intervals of ninety degrees, or otherwise, may be used. In fact, in one implementation, the first and second sets of radiative elements  62 - 64  and  66 - 68  may be effectively replaced with a continuous surface of a cone, a pyramid, or some other continuous shape that is spatially diverse on one side (e.g., has significant spatial extent) and comes substantially to a point (e.g., an apex) on the other side. For example, in accordance with an aspect of the present invention, a linear radiative member connected at one end to a radiative loop having a certain spatial extend may be used. 
       FIG. 4  illustrates a side view of a second exemplary implementation of an antenna assembly  100  in accordance with an aspect of the present invention. 
       FIG. 5  illustrates an overhead view of the second exemplary implementation of the antenna assembly. The illustrated antenna assembly  100  comprises a driven antenna assembly  102  located on a first side of an imaginary plane  104 , and a ground reference  106  located at the imaginary plane or on a second side of the imaginary plane. The driven antenna assembly  102  can be driven by an antenna feed that is electrically connected to the driven antenna assembly approximately at the imaginary plane  104 . In the illustrated implementation, the ground reference  106  is illustrated as planar, but it will be appreciated that other configurations of the ground plane can be utilized within the illustrated antenna assembly. The ground reference  106  may be comprised of any appropriate electrically conductive material such as, for example, copper or stainless steel. The radius of the ground reference  106  is at least one-quarter of a wavelength associated with the lowest frequency of operation. 
     The surface of the ground reference  106  may be continuous or may be a crosshatched wired mesh, in accordance with various embodiments of the present invention. Also, three or more linear elements disposed in a substantially conical shape may form the ground reference, in accordance with an embodiment of the present invention. In other implementations, the ground reference  106  can include a conical assembly or a cylindrical sleeve having a closed upper base side. Alternatively, the shield of a coaxial associated with the antenna feed can serve as the ground reference, and various styles of stubs, sleeves, matching systems, baluns, transformers, etc. may also be used. The antenna feed  108  can include an SMA (or similar) coaxial connector and a transmitter/receiver circuit board (not shown). The SMA connector and board can be electrically connected together by a length of coaxial cable. The SMA connector allows a center conductor of the coaxial cable to electrically connect the driven antenna assembly  102  and allows a ground braid of the coaxial cable to electrically connect to the ground reference  106 . A dielectric material can be used to electrically insulate the center conductor and the driven antenna assembly  102  from the ground reference  106 . 
     The driven antenna assembly  102  comprises six radiative elements  112 - 114  and  116 - 118  that radiate out from a common apex  120 . The driven antenna assembly  102  and its constituent elements  112 - 114  and  116 - 118  are formed from a conductive material. The radiative elements  112 - 114  and  116 - 118  are electrically connected to the antenna feed  108  and one another at the apex  120 . A first set of radiative elements comprise first, second, and third radiative elements  112 - 114  that are generally linear and extend away from the apex  120  at an acute angle relative to the imaginary plane  104 . Each of the first, second, and third radiative antenna elements  112 - 114  may be at a unique acute angle or at the same acute angle relative to the imaginary plane  104 . In the illustrated implementation, the first, second, and third radiative elements  112 - 114  are oriented such that the first, second, and third elements are spaced evenly, that is, at intervals of one-hundred and twenty degrees. Each of the first set of radiative elements  112 - 114  have a length within a first range of lengths associated with a characteristic lower bound frequency. For example, a first element  112  can have a length, L 1 , tuned to be receptive to the characteristic lower bound frequency and each of the second and third elements  113  and  114  can have a length within an approximately ten percent variance of the length of the first element. Varying the lengths of the first set of radiative elements  112 - 114  can provide an improvement in the broadband properties of the driven antenna assembly, but it will be appreciated that a common antenna length, for example, the tuned antenna length L 1 , can be utilized for the first set of radiative elements in while still maintain the wideband properties of the antenna. 
     A second set of radiative elements comprise fourth, fifth, and sixth radiative elements  116 - 118  that are generally linear and extend away from the apex  120  at an acute angle relative to the imaginary plane  104 . Each of the fourth, fifth, and sixth radiative antenna elements  116 - 118  may be at a unique acute angle or at the same acute angle relative to the imaginary plane  104  as one another or one of the first set of radiative elements  112 - 114 . In the illustrated implementation, the fourth, fifth, and sixth radiative elements  116 - 118  are oriented such that they are spaced evenly between the first set of radiative elements  112 - 114 , such that each of the second set of radiative elements is spaced at sixty degree intervals from two of the first set of radiative elements and at intervals of one-hundred and twenty degrees from one another. Each of the second set of radiative elements  116 - 118  have a length in a second range around a length of approximately four-fifths the tuned length associated with the characteristic frequency. In one implementation, the length of each of the second set of radiative elements  116 - 118  can be equal to four-fifths the length of a corresponding one of the first set of radiative elements  112 - 114 . 
     In the illustrated implementation, the antenna assembly  100  is designed with a characteristic lower bound frequency around 700 MHz, and the lengths of the first set of radiative elements  112 - 114  selected as to tune the antenna to that frequency. In the illustrated implementation, the first radiative element  112  can have a length of approximately 3.19 inches, the second radiative element  113  can have a length of approximately 2.88 inches, and the third radiative element  114  can have a length of approximately 3.25 inches). The lengths of the second set of radiative elements  116 - 118  can be cut to approximately four-fifths the length of the first set of radiative elements  112 - 114 . Accordingly, the fourth radiative element  116  can have a length of around 2.56 inches, the fifth radiative element  117  can have a length on the order of 2.31 inches, and the sixth radiative element  118  can have a length of approximately 2.63 inches. Each element  112 - 114  can have a diameter of approximately one-sixteenth of an inch, and the planar ground reference  106  can have a diameter of eleven inches. The illustrated antenna  100  can operate at an extremely wide band of radio frequencies ranging from approximately 700 MHz to approximately 6 GHz. 
     In accordance with an aspect of the present invention, each of the first and second sets of radiative elements  112 - 114  and  116 - 118  can be generalized to only two or greater than three elements having similar length and orientation. For example, in place of the first set of radiative elements  112 - 114 , four radiative elements, circumferentially spaced at intervals of ninety degrees, or otherwise, may be used. In fact, the first and second sets of radiative elements  112 - 114  and  116 - 118  may be effectively replaced with a continuous surface of a cone, a pyramid, or some other continuous shape that is spatially diverse on one side (e.g., has significant spatial extent) and comes substantially to a point (e.g., an apex) on the other side. For example, in accordance with an aspect of the present invention, a linear radiative member connected at one end to a radiative loop having a certain spatial extend may be used. 
       FIG. 6  illustrates a side view of a third exemplary implementation of an antenna assembly  150  in accordance with an aspect of the present invention. The illustrated antenna assembly  150  comprises a driven antenna assembly  152  located on a first side of an imaginary plane  154 , and a ground reference  156  located at the imaginary plane or on a second side of the imaginary plane. The driven antenna assembly  152  can be driven by an antenna feed that is electrically connected to the driven antenna assembly approximately at the imaginary plane  154 . In the illustrated implementation, the ground reference  156  is illustrated as planar, but it will be appreciated that other configurations of the ground plane can be utilized within the illustrated antenna assembly. The ground reference  156  may be comprised of any appropriate electrically conductive material such as, for example, copper or stainless steel. The antenna feed  158  can include an SMA (or similar) coaxial connector and a transmitter/receiver circuit board (not shown). The SMA connector and board can be electrically connected together by a length of coaxial cable. The SMA connector allows a center conductor of the coaxial cable to electrically connect the driven antenna assembly  152  and allows a ground braid of the coaxial cable to electrically connect to the ground reference  156 . A dielectric material can be used to electrically insulate the center conductor and the driven antenna assembly  152  from the ground reference  156 . 
     The driven antenna assembly  152  comprises three radiative elements  162 - 164  that spiral outward from a common apex  170 . It will be appreciated, however, that one element, two elements, or more than three elements can also be utilized. The driven antenna assembly  152  and its constituent elements  162 - 164  are formed from a conductive material. The radiative elements  162 - 164  are electrically connected to the antenna feed  158  and one another at respective first ends at the apex  170 . Each of the radiative elements  162 - 164  are curvilinear and radiate away from the apex  170 . In the illustrated implementation, the first, second, and third radiative elements  162 - 164  are oriented such that the first, second, and third elements are spaced evenly as they leave the apex  170 , that is, at intervals of one-hundred and twenty degrees. 
     Each of the first set of radiative elements  162 - 164  has a length within a first range of lengths associated with a first characteristic frequency. It will be appreciated that length, as used herein, refers to the straightened length of the element, as opposed to the distance it extend from the apex  170 . For example, a first element  162  can have a length, L 1 , tuned to be receptive to the first characteristic frequency and each of the second and third elements  163  and  164  can have a length within an approximately ten percent variance of the length of the first element. Varying the lengths of the radiative elements  162 - 164  can provide an improvement in the broadband properties of the driven antenna assembly, but it will be appreciated that a common antenna length, for example, the tuned antenna length L 1 , can be utilized for the first set of radiative elements in while still maintain the enhanced band properties of the antenna. 
     In accordance with an aspect of the present invention, the radiative elements  162 - 164  can be curved such that respective second ends  172 - 174  of the radiative elements are located at a predetermined height above the ground reference  156 . This height can be selected to be approximately one-quarter of a wavelength associated with a second characteristic frequency. The rate of ascent of the curvilinear elements  162 - 164  can be relatively high until this height is approached and then significantly slowed to maximize the length of the curvilinear element at or near this height. By curving the curvilinear elements  162 - 164  in this manner, an additional degree of capacitive and inductive coupling between the elements  162 - 164  and the ground reference  156  can be established, allowing the antenna increased sensitivity around the second characteristic frequency. Accordingly, the illustrated antenna assembly  150  is sensitive to frequencies in bands around both the first characteristic frequency and the second characteristic frequency, allowing for true dual-band operation from a single driven radiative assembly. 
     In accordance with an aspect of the present invention, the polarization diversity of the antenna assembly  150  around the horizon can be greatly enhanced through the use of the curvilinear elements  162 - 164 . In the illustrated antenna assembly  150 , the radiation pattern includes alternating horizontally and vertically polarized lobes around the horizon of the pattern, allowing the antenna to be responsive to multiple polarizations even at a low elevation. This alternating horizontal and vertical polarization is particularly useful in dynamic environments and mobile applications. The use of the curvilinear elements  162 - 164  also allows for a significant reduction in the size of the ground reference  156 , such that the radius of the ground reference can be significantly smaller than one-quarter of the wavelength associated with the lowest frequency of operation. 
     In the illustrated implementation, the antenna assembly  150  is designed to operate in a first band around 800 MHz and a second band around 1.8 GHz to 1.9 GHz. To this end, the lengths of the curvilinear radiative elements  162 - 164  can be as to tune the antenna to a frequency of 800 MHz. Accordingly, the first curvilinear element  162  can have a length of approximately 4 inches, the second curvilinear element  163  can have a length of approximately 4.13 inches, and the third curvilinear element  214  can have a length of approximately 3.44 inches. The height of each of the second ends  172 - 174  of the curvilinear elements  162 - 164  above the ground reference  156  can range around one-quarter of a wavelength corresponding to a frequency of 1.8 GHz. It has been determined in implementing the illustrated antenna that a height of approximately 1.75 inches for the second ends  172 - 174  of the curvilinear elements  162 - 164  allows for operation in the 1.8 GHz-1.9 GHz band. 
       FIG. 7  illustrates a side view of a fourth exemplary implementation of an antenna assembly  200  in accordance with an aspect of the present invention. The illustrated antenna assembly  200  comprises a driven antenna assembly  202  located on a first side of an imaginary plane  204 , and a ground reference  206  located at the imaginary plane or on a second side of the imaginary plane. The driven antenna assembly  202  can be driven by an antenna feed that is electrically connected to the driven antenna assembly approximately at the imaginary plane  204 . In the illustrated implementation, the ground reference  206  is illustrated as planar, but it will be appreciated that other configurations of the ground plane can be utilized within the illustrated antenna assembly. The ground reference  206  may be comprised of any appropriate electrically conductive material such as, for example, copper or stainless steel. The antenna feed  208  can include an SMA (or similar) coaxial connector and a transmitter/receiver circuit board (not shown). The SMA connector and board can be electrically connected together by a length of coaxial cable. The SMA connector allows a center conductor of the coaxial cable to electrically connect the driven antenna assembly  202  and allows a ground braid of the coaxial cable to electrically connect to the ground reference  206 . A dielectric material can be used to electrically insulate the center conductor and the driven antenna assembly  202  from the ground reference  206 . 
     The driven antenna assembly  202  comprises a first set of three radiative elements  212 - 214  and a second set of radiative elements  216 - 218  that spiral outward from a common apex  220 . It will be appreciated, however, that one element, two elements, or more than three elements can also be utilized in each set. The driven antenna assembly  202  and its constituent elements  212 - 214  and  216 - 218  are formed from a conductive material. The radiative elements  212 - 214  and  216 - 218  are electrically connected to the antenna feed  208  and one another at respective first ends at the apex  220 . Each of the radiative elements  212 - 214  and  216 - 218  are curvilinear and radiate away from the apex  220 . In the illustrated implementation, the curvilinear elements extend away from the apex  220  near a desired horizontal radius from the apex at a first rate of ascent, and tend proceed at a second rate of ascent, greater than the first rate of ascent. In the illustrated implementation, this is accomplished without any change to the sign of the curvature; the direction of concavity of the element does not change. Accordingly, the maximum horizontal extent of the curvilinear elements, and thus, the radius of the ground reference  206 , can be limited without a significant loss of sensitivity in the lower frequency portion of the band. It will be appreciated, however, that due to the curvature of the curvilinear elements, the height of the curvilinear elements will also be limited, lowering the overall profile of the antenna assembly. 
     In the illustrated implementation, the first, second, and third radiative elements  212 - 214  are oriented such that the first, second, and third elements are spaced evenly as they leave the apex  220 , that is, at intervals of one-hundred and twenty degrees. The fourth, fifth, and sixth radiative elements  216 - 218  are oriented such that they are spaced evenly between the first set of radiative elements  212 - 214 , such that each of the second set of radiative elements is spaced at sixty degree intervals from two of the first set of radiative elements as they leave the apex and at intervals of one-hundred and twenty degrees from one another. 
     Each of the first set of radiative elements  212 - 214  has a length within a first range of lengths associated with a first characteristic frequency. It will be appreciated that by “length,” reference the actual or straightened length of the curvilinear element is intended. A first element  212  can have a length, L 1 , tuned to be receptive to the first characteristic frequency and each of the second and third elements  213  and  214  can have a length within an approximately ten percent variance of the length of the first element. Varying the lengths of the first set of radiative elements  212 - 214  can provide an improvement in the broadband properties of the driven antenna assembly, but it will be appreciated that a common antenna length, for example, the tuned antenna length L 1 , can be utilized for the first set of radiative elements in while still maintain the enhanced band properties of the antenna. Each of the second set of radiative elements  216 - 218  have a length in a second range around a length of approximately four-fifths the tuned length associated with the characteristic frequency. In one implementation, the length of each of the second set of radiative elements  216 - 218  can be equal to four-fifths the length of a corresponding one of the first set of radiative elements  212 - 214 . In the illustrated implementation, the antenna assembly  100  is designed to operate band of frequencies ranging from around 700 MHz to around 6 GHz continuously. To this end, the first curvilinear element  212  can have a length of approximately 4.25 inches, the second curvilinear element  213  can have a length of approximately 4.5 inches, and the third curvilinear element  214  can have a length of approximately 4 inches. The maximum height of each of the of the first set of curvilinear elements  212 - 214  above the ground reference  206  can be limited to approximately 2.5 inches. The lengths of the second set of radiative elements  216 - 218  can be cut to approximately four-fifths the length of the first set of radiative elements  212 - 214 . Accordingly, the fourth radiative element  216  can have a length of around 3.5 inches, the fifth radiative element  217  can have a length on the order of 3.75 inches, and the sixth radiative element  218  can have a length of approximately 3.25 inches. Each element  212 - 214  and  216 - 218  can have a diameter of approximately one-sixteenth of an inch. 
       FIG. 8  illustrates a side view of a fifth exemplary implementation of an antenna assembly  250  in accordance with an aspect of the present invention. The illustrated antenna assembly  250  comprises a driven antenna assembly  252  located on a first side of an imaginary plane  254 , and a ground reference  256 . The driven antenna assembly  252  can be driven by an antenna feed  258  that is electrically connected to the driven antenna assembly approximately at the imaginary plane  254 . The ground reference  256  may be comprised of any appropriate electrically conductive material such as, for example, copper or stainless steel. 
     In the illustrated implementation, the ground reference  256  is implemented as a series of curvilinear ground elements  262 - 264  that extend along the second side of the imaginary plane  254  to form an outline of a conical structure having a crenellated edge. Each of the curvilinear ground elements  262 - 264  can have a substantially linear portion that extends from a shield portion of the antenna feed  258  at an acute angle relative to the imaginary plane  254 . In generally, the acute angle between each of the curvilinear ground elements  262 - 264  and the imaginary plane  254  will be between forty-five degrees and seventy degrees, and in the illustrated implementation, each curvilinear ground element forms a sixty degree angle with the imaginary plane. A crenellated portion of each of the curvilinear ground elements  262 - 264  can run substantially parallel to the imaginary plane as to form at least a portion of an elliptical or circular outline in a plane parallel to the imaginary plane. 
     The antenna feed  258  can include an SMA (or similar) coaxial connector and a transmitter/receiver circuit board (not shown). The SMA connector and board can be electrically connected together by a length of coaxial cable. The SMA connector allows a center conductor of the coaxial cable to electrically connect the driven antenna assembly  252  and allows a ground braid, or shield portion, of the coaxial cable to electrically connect to each of the discrete curvilinear elements comprising the ground reference  256 . A dielectric material can be used to electrically insulate the center conductor and the driven antenna assembly  252  from the ground reference  256 . 
     The driven antenna assembly  252  comprises a set of curvilinear radiative antenna elements  266 - 268  that spiral outward from a common apex  270 . It will be appreciated, however, that one element, two elements, or more than three elements can also be utilized in each set. The driven antenna assembly  252  and its constituent elements  266 - 268  are formed from a conductive material. The radiative elements  266 - 268  are electrically connected to the antenna feed  258  and one another at respective first ends at the apex  270 . Each of the radiative elements  266 - 268  are curvilinear and radiate away from the apex  270 . In the illustrated implementation, the curvilinear elements extend away from the apex  270  near a desired horizontal radius from the apex at a first rate of ascent, and then proceed at a second rate of ascent that is less than the first rate of ascent. It will be appreciated, however, that in other implementations, the second rate of ascent can be greater than the first rate of ascent. Accordingly, the maximum vertical extent of the curvilinear elements  266 - 268 , and thus the vertical profile of the antenna assembly  250 , can be limited without a significant loss of sensitivity in the lower frequency portion of the band. The vertical profile and ground plane radius of the assembly can be further reduced through use of the discrete curvilinear ground elements  262 - 264 , greatly reducing the amount of space necessary to implement the antenna assembly. 
     In the illustrated implementation, the curvilinear ground elements  262 - 264  are oriented such that respective first, second, and third elements are spaced evenly as they leave the shield portion of the antenna feed, that is, at intervals of one-hundred and twenty degrees. The respective first, second, and third radiative elements  266 - 268  are oriented such that they are spaced evenly as they leave the apex, at intervals of one-hundred and twenty degrees. Each of the set of curvilinear ground elements  262 - 264  has a length within a first range of lengths associated with a first characteristic frequency. It will be appreciated that by “length,” reference the actual or straightened length of the curvilinear element is intended. A first curvilinear ground element  262  can have a length, L 1 , the second and third curvilinear ground elements  263  and  264  can have a length within an approximately ten percent variance of the length of the first element. Varying the lengths of the curvilinear ground elements  262 - 264  can provide an improvement in the broadband properties of the antenna assembly, but it will be appreciated that a common antenna length, for example, L 1 , can be utilized while still maintaining the enhanced band properties of the device. 
     Each of the radiative elements  266 - 268  have a length within a second range of lengths associated with a second characteristic frequency. For example, the First radiative element  266  can have a length, L 2 , tuned to be receptive to the second characteristic frequency and each of the second and third radiative elements  267  and  268  can have a length within an approximately ten percent variance of the length of the first element. In one implementation, the antenna assembly  250  is designed to operate the three ISM bands of radio frequencies, including a first frequency band around 912-928 MHz, a second frequency band around 2.4 GHz, and a third frequency band around 5-6 GHz. The three curvilinear ground elements can be cut to lengths associated with the first and lowest frequency band, such that the first curvilinear ground element  262  can have a length of approximately 5.81 inches, the second curvilinear ground element  263  can have a length of approximately 5.63 inches, and the third curvilinear ground element  264  can have a length of approximately 6 inches. The lengths of the second set of radiative elements  266 - 268  can be cut to tune the antenna to the second frequency band, such that the first radiative element  266  can have a length of approximately 0.81 inches, the second radiative element  267  can have a length of approximately 0.69 inches, and the third radiative element  268  can have a length of approximately 0.94 inches. Capacitive and inductive interaction among the various elements  262 - 264  and  266 - 268  increase the sensitivity of the antenna  250  in the third frequency band. Each of the radiative elements  266 - 268  can have a diameter of approximately one-sixteenth of an inch. 
       FIG. 9  illustrates a sixth exemplary implementation of an antenna assembly  300  in accordance with an aspect of the present invention. The illustrated antenna assembly  300  comprises a driven antenna assembly  302  located on a first side of an imaginary plane  304 , and a ground reference  306  located at the imaginary plane or on a second side of the imaginary plane. In the illustrated implementation, the ground reference  306  is illustrated as planar, but it will be appreciated that other configurations of the ground plane can be utilized within the illustrated antenna assembly. The driven antenna assembly  302  can be driven by an antenna feed that is electrically connected to the driven antenna assembly approximately at the imaginary plane  304 . 
     The antenna feed  308  can include an SMA (or similar) coaxial connector and a transmitter/receiver circuit board (not shown). The SMA connector and board can be electrically connected together by a length of coaxial cable. The SMA connector allows a center conductor of the coaxial cable to electrically connect the driven antenna assembly  302  and allows a ground braid of the coaxial cable to electrically connect to the ground reference  306 . A dielectric material can be used to electrically insulate the center conductor and the driven antenna assembly  302  from the ground reference  306 . 
     The driven antenna assembly  302  comprises three radiative elements  312 - 314  that extend outward from a common apex  320 . The driven antenna assembly  302  and its constituent elements  312 - 314  are formed from a conductive material. The radiative elements  312 - 314  are electrically connected to the antenna feed  308  and one another at respective first ends at the apex  320 . The radiative elements  312 - 314  comprise respective first linear segments  332 - 334  that extend away from the apex  320  at an acute angle relative to the imaginary plane  304 , and respective second linear elements  336 - 338  that extend in a direction substantially parallel to the imaginary plane. Each first segment  332 - 334  is connected to its associated second segment  336 - 338  at an acute angle at a vertex  346 - 348 . In accordance with an aspect of the invention, each second linear segment  342 - 344  can extend from their associated vertex  346 - 348  to the vertex of another radiative element  312 - 314 , such that each radiative element has a second end terminating on the vertex of another radiative element, forming the outline of an inverted pyramid. By bending the radiative elements  312 - 314  into the illustrated pyramidal shape in this manner, an additional degree of capacitive and inductive coupling is provided such that the pyramidal shape allows for a significant reduction in the vertical profile of the antenna  300 . 
       FIG. 10  illustrates a seventh exemplary implementation of an antenna assembly  350  in accordance with an aspect of the present invention. The illustrated antenna assembly  350  comprises a driven antenna assembly  352  and an SMA connector  356  having a center lead and a shield element that serves as a ground reference. The driven antenna assembly  352  comprises three radiative elements  362 - 364  that extend outward from a common apex  370 . The driven antenna assembly  352  and its constituent elements  362 - 364  are formed from a conductive material. The radiative elements  362 - 364  are electrically connected to the center lead  358  and one another at respective first ends at the apex  370 . The radiative elements  362 - 364  comprise elliptical loops that extend away from the apex  370  and loop back to terminate on the shield element of the SMA connector  356 . The radiative elements  362 - 364  are generally substantially circular, but can be compressed to reduce the horizontal footprint of the antenna. In accordance with an aspect of the invention, the antenna assembly  350  is designed with a characteristic lower bound frequency, and each radiative element  362 - 364  has a length approximately equal to a wavelength associated with the characteristic lower bound frequency. In the illustrated example, the characteristic lower bound frequency is around 300 MHz, and the length of each radiative element  362 - 364  is approximately 40 inches, allowing the antenna  350  to be sensitive across at least dual frequency bands of 310-325 MHz and 915-917 MHz. 
       FIG. 11  illustrates a cross sectional view of a parabolic reflector dish  400  for directing radiation received at and transmitted from an omni-directional enhanced band antenna  402  to provide directionality to the antenna in accordance with an aspect of the present invention. The parabolic reflector dish  400  is formed from a conductive material and shaped as a circular paraboloid that can be represented by the revolution of a parabola around its axis, wherein the parabola having dimensions as described herein, can be described by the formula: 
     
       
         
           
             
               
                 
                   y 
                   = 
                   
                     
                       x 
                       2 
                     
                     24 
                   
                 
               
               
                 
                   Eq 
                   . 
                   
                       
                   
                   ⁢ 
                   2 
                 
               
             
           
         
       
     
     The cross-sectional view represents a center plane in the parabolic reflector  400 , wherein the center plane is a plane that encompasses an apex  404  of the parabolic reflector and a focal point  406  of the parabolic reflector. It will be appreciated that while there are a number of planes that encompass these two points, the parabolic reflector  400  is a circular paraboloid, and thus all of these planes will produce substantially identical cross-sectional views. In the cross sectional plane, a horizontal axis represents the y variable and a vertical axis represents the x variable, with the origin at the apex  404  of the parabolic reflector  400 , 
     In accordance with an aspect of the present invention, the parabolic reflector dish  400  is configured such that the focal depth  408  of the dish is well within a volume defined by the dish. For example, the parabolic reflector dish  400  can be continued past the focal point  406  to a point where a line tangent to the edge  412  of the dish forms an angle between fifty-five and sixty degrees with an axis of dish. By configuring the dish to have a focal point within the volume of the dish, significant electromagnetic energy that might otherwise escape around the edge  412  of the dish is redirected along the axis of the dish. Accordingly, the directionality, and corresponding gain, of the enhanced band antenna  402  located at the focal point  406  of the dish  400  can be significantly increased, greatly enhancing the utility of the antenna for point-to-point communications. 
     In the illustrated implementation, the parabolic reflector  400  is configured for a wide band antenna  402  sensitive to a frequency band between 2.4 GHz and 11 GHz. The focal point  406  of the dish is located at point six inches from the apex. The parabolic reflector dish  400  has a focal point radius  416  of twelve inches. The dish has a depth  418  of thirteen and one-half inches, and a maximum radius  420  of eighteen inches. Using the illustrated parabolic reflector dish, a gain of the order of 25-35 dBi can be realized. 
       FIG. 12  illustrates a cross-sectional view of a folded sheet reflector  450  for providing directionality to an omni-directional enhanced band antenna assembly  452  in accordance with an aspect of the present invention. The folded sheet reflector  450  is folded along a vertex  454  and extends from the vertex in two substantially planar conductive members  456  and  458 . In the illustrated implementation, the folded sheet reflector  450  is folded at an angle of approximately ninety degrees at the vertex  454  and each planar is substantially rectangular, extending to a length of twelve inches with a width of seven inches. In accordance with an aspect of the present invention, the antenna assembly  452  is placed immediately adjacent to a center point  460  of the vertex, such that a ground reference  462  of the antenna is physically and electrically connected to the folded sheet reflector  450 . It will be appreciated that the planar members  456  and  458  can be slightly deformed near the vertex to accommodate the antenna assembly  452 . This electrical connection between the ground reference  462  and the folded sheet  450  substantially mitigates the effects of any mismatch in impedance at the antenna assembly, allowing for significant increase of the directionality, and corresponding gain, of the enhanced band antenna  452 , greatly enhancing the utility of the antenna for point-to-point communications. Using the illustrated folded sheet reflector  450 , a gain of the order of 10 dBi can be realized. 
     While the invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.