Abstract:
The present invention relates to a contoured dipole antenna. The antenna is suitable for ultra wide band (UWB) radio communications, and in particular UWB applications requiring antennas of small size. Elements of the dipole antenna have a curvature designed to make the antenna UWB over a desired range. Embodiments of the antenna may take the form of balanced dipole arrangements, unbalanced half-dipole arrangements, geometric arrays, and arrays distributed over a contour. In addition, embodiments of the invention may be used with or without ground planes.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 60/614,865 filed on Sep. 30, 2004, the disclosure of which is hereby incorporated by reference herein. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     This invention was supported, in whole or in part, by a grant 5-21014 from the Department of Defense (DOD). The Government has certain rights in the invention. 
     
    
     BACKGROUND OF THE INVENTION  
       [0003]     Radio transmissions have historically been approached from a stand point of frequency content. In the frequency content context, coexistent and different radio transmissions are accomplished by assigning permissible frequencies or frequency channels to different users and radio systems. Proper operation of such a scheme requires that users operate only within their assigned allocation, especially in geographic areas having numerous users. In some instances, frequency allocations may be made based on the application of the radio signal. For example, a first group of frequencies may be assigned for person-to-person voice communications (e.g., cellular telephones, 2-way radios, etc.), a second group of frequencies may be assigned for telemetry applications (e.g., data transmission) and a third group of frequencies may be allocated for remote sensing applications (e.g., global positioning system (GPS), radio-ranging, etc.). With the advent of new communication and telemetry technologies, crowding of the frequency spectra assigned to users has become an issue. As a result, alternative means of wireless communication are beginning to become available.  
         [0004]     Ultra wide band (UWB) transmission is one such alternative means of wireless radio frequency (RF) transmission. UWB transmissions, also referred to as impulse radio, differ from conventional radio transmissions in that UWB transmissions exist over a wide range of frequencies simultaneously. UWB can employ very short duration radio pulses having tightly controlled amplitude and pulse-to-pulse intervals. Since UWB transmissions use short pulses, typically less than a nanosecond, UWB antennas must be broadband for optimal operation. Conventional RF antennas tend to perform inadequately in UWB environments, since they tend to disperse and alter the amplitude of the spectral, or frequency, components of the signal resulting in broadening of the short pulses utilized in UWB systems. Thus, there is a need for further improvements in antennas for RF transmission.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     The system and method of the present invention includes an antenna having a substantially planar surface with contoured boundaries comprising a generally near triangular shape. The shape of the antenna can generally be described as having a vertex or tip at a first end along a longitudinal axis that bisects the antenna and a base at the second end that is wider than the vertex. The planar surface also has first and second curved sides that are symmetric about the. longitudinal axis. The sides are non-linear and can be concave, convex, or a combination thereof. The shape of the antenna element serves to enhance the radiating and reception patterns of the device.  
         [0006]     A preferred embodiment uses a first antenna element paired with a second matching antenna element, preferably aligned along a common axis in a single plane and meeting at a location such as the intersection of the respective vertices of the two antennas to provide a balanced dipole antenna. This balanced antenna is symmetric about both the longitudinal axis and a lateral axis that bisects the two elements. Standard terminals and antenna connections can be used to couple the antenna to the receiver and/or transmitter electronics.  
         [0007]     In another preferred embodiment, one or more antenna elements can be positioned relative to a different surface such as a planar surface. In this embodiment, the tip or distal end of the antenna element, or antenna elements, can be oriented toward the planar surface. The longitudinal axis of each antenna element preferably extends orthogonally from the planar surface. In an embodiment employing a plurality of antennas, the antennas can be oriented parallel to each other or at different angles on one side of the planar surface. The plurality of antennas can be arranged in an evenly distributed geometric pattern or along one or more contour lines. The antenna configuration will depend on the particular transmission and/or reception pattern optimized for a particular application.  
         [0008]     The present invention is particularly well suited for UWB applications with frequencies in a range of 2.5 GHz to more than 12 GHz. Preferred embodiments of the present invention can be used for transmission and/or reception of wireless signals in a variety of applications.  
         [0009]     In addition, UWB antennas of the invention have small form factors for facilitating usage in remote sensing and telemetry applications such as equipment tracking systems, smart card and reader systems, and positioning systems. For example, UWB antennas having small form factors may be placed inside smart cards without adversely impacting the overall size of the card.  
         [0010]     A preferred embodiment of the invention involves a method of using an antenna to transmit and/or receive wireless data. Transmitter electronics can be used to send data to the antenna for RF transmission to a receiver. An antenna in accordance with the invention can be used to receive the data which is then detected and proceed to provide data output signals. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0011]     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention as illustrated in the accompanying drawings in which like reference characters refer to the same or similar parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.  
         [0012]      FIG. 1A  illustrates an exemplary embodiment of contoured dipole antenna in accordance with an aspect of the invention;  
         [0013]      FIG. 1B  illustrates a method of use of the antenna in accordance with a preferred embodiment of the invention;  
         [0014]     FIGS.  2 A-D illustrate exemplary impedance performance ( 2 A- 2 B) and exemplary voltage transfer functions ( 2 C- 2 D) graphs associated with the embodiment of  FIG. 1A ;  
         [0015]     FIGS.  3 A-K illustrate exemplary E-plane patterns for an antenna having the form of the embodiment shown in  FIG. 1A ;  
         [0016]     FIGS.  4 A-K illustrate exemplary H-plane patterns for an antenna having the form of the embodiment shown in  FIG. 1A ;  
         [0017]      FIG. 5  illustrates an exemplary embodiment of the invention utilizing a single half-dipole antenna and a ground plane;  
         [0018]      FIG. 6  illustrates an exemplary embodiment of the invention utilizing a plurality of half-dipole antennas arranged in a geometric pattern on a ground plane;  
         [0019]      FIG. 7  illustrates an exemplary embodiment of the invention utilizing a plurality of half-dipole antennas arranged along a contour on a ground plane; and  
         [0020]     FIGS.  8 A-C illustrate preferred embodiments of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     The following detailed description of the invention refers to the accompanying drawings. Reference will be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings. While exemplary embodiments are provided, other embodiments are possible in light of the specification. Therefore, unless otherwise specified, the illustrated embodiments can be understood as providing exemplary features of varying detail of certain embodiments, and therefore, unless otherwise specified, features, components, modules, and/or aspects of the illustrations can be otherwise combined, separated, interchanged and/or rearranged without departing from the disclosed systems and methods. Additionally, the shapes and sizes of components are also exemplary.  
         [0022]     Before describing the invention, it is noted that exemplary coordinate systems may be used when describing embodiments of the invention. Coordinate systems, as used herein, are merely aids for describing relationships among elements of the invention. As such, coordinate systems should not be construed as limitations or essential features of the invention.  
         [0023]      FIG. 1A  illustrates an exemplary embodiment of a dipole antenna  100  consistent with aspects of the invention. Antenna  100  comprises opposedly mounted ends which have essentially similar shapes, composition and size. In particular, antenna  100  comprises a first antenna element  102 , a second antenna element  104 , and a common junction, or vertex,  106 . The junction can also be described as the intersection of the longitudinal axis  101  and the lateral axis  109  that are orthogonal to each other and define axes of symmetry of the device. In the embodiment of  FIG. 1A , the first and second elements are generally triangular in shape. Furthermore, the first element  102  and second element  104  elements are contoured in that they have respective curvatures designed to enhance performance as a UWB radiator and/or receiver. In particular, an example of the embodiment of  FIG. 1A  may be described using a mathematical equation. Each element has sides  105 ,  107  that have a curved shape.  
         [0024]     In a coordinate system oriented such that the origin is located at the center of the antenna and the x-axis is oriented along the longitudinal axis of the dipole, the curvature of the antenna in the first quadrant of the coordinate axes may be described, or substantially described, using the piecewise definition of equations 1 and 2 where x and y are in identical units. 
 
 y=x , for 0 &lt;x≦; 4.2  (1) 
 
 y= 1.25 x   0.85 , for 4.2 &lt;x&lt; 15  (2) 
 
 The equations produce curvatures that increase with distance from the center of the antenna. 
 
         [0025]     The antenna  100  can comprise electrically conductive material such as a metal, a composite material, or a non-conductive or semi-conductive material impregnated with conductive particles. In addition, the antenna  100  may be formed to a desired shape by machining, stamping, injection molding, using pressure such as forging, or by heat.  
         [0026]      FIG. 1B  illustrates an exemplary method for facilitating communication between a transmitter and a receiver using embodiments of the invention. The method begins by energizing the transmitter electronics (per step  602 ) and the transmitting antenna Electronics (per step  604 ). The transmitting antenna may be comprised of a dipole antenna such as shown in  FIG. 1A , a half dipole antenna such as shown in  FIG. 5 , a plurality of half dipole antennas such as shown in  FIGS. 6 and 7 , or a plurality of balanced dipole antennas. A data signal is received from a source such as a computer, microphone, sensor, etc. (per step  606 ). The data signal is then converted into a transmit signal compatible with the transmitting antenna (per step  608 ). Conversion of the data signal into a signal compatible with the transmitting antenna may include modulating the data signal. The modulated data signal is then conveyed to the transmitting antenna (per step  610 ). The modulated data signal is conveyed through a transmission medium such as air, water, building structure, free space, etc. as an RF signal (per step  612 ).  
         [0027]     A receiver is energized at a time prior to receipt of the transmitted data signal (per step  614 ). In addition, the receive antenna electronics are energized (per step  616 ). In alternative embodiments, receiver electronics and receive antenna electronics may not be energized until the receive antenna senses a signal. In such an alternative embodiment, the receive antenna may employ an energy threshold that serves as a trigger when received energy exceeds a predetermined threshold either instantaneously or over some time-averaged period.  
         [0028]     The RF data signal is received at the receiver antenna (per step  618 ). In alternative embodiments, a plurality of receive antennas may be employed as a receive array. In such an embodiment, data received at the antennas may be delayed by predetermined time intervals such that a main receiving lobe is steered in a desired direction. The received signal is conveyed from the receive antenna to a signal detector (per step  620 ). The received signal is then demodulated (per step  622 ) and processed to extract the data signal received from the source (per step  624 ). The data signal is then outputted to a receiving device (per step  626 ).  
         [0029]     A graph of the calculated impedance performance of antenna  100  is illustrated in  FIGS. 2A and 2B , and the calculated voltage transfer function of a communication link comprising two antennas  100  is shown in  FIGS. 2C and 2D . Graphs showing measured radiation patterns for the E and H radiating planes of antenna  100  are shown in FIGS.  3 A 3 K (E-plane) and FIGS.  4 A-K (H-plane) for frequencies ranging from 2.5 GHz to 12 GHz.  
         [0030]     The antenna of  FIG. 1A  is designed to be balanced so that it radiates effectively in the full spherical region of space with a radiation pattern producing directive gain in the vicinity of the plane bisecting the conductors of antenna  100 . The curvature imparted to elements of antenna  100  produces performance improvements when compared to prior art bow-tie antennas. The contoured antenna of  FIG. 1A  also provides operation over a wider useful bandwidth without having to employ log-periodic or fractal geometric antennas, since both types require larger antennas. In addition, the antenna of  FIG. 1A  does not disperse the spectral components of received signals. Signal dispersion in a UWB application may cause undesirable pulse distortion. The antenna of  FIG. 1A  further operates in an omnidirectional manner making it useful in applications where the location of a transmitter/receiver is a priori unknown with respect to antenna  100 .  
         [0031]     The antenna  100  may also be fabricated making it useful for remote sensing applications such as secure-ID cards, asset tracking using flat label-like radio frequency identification (RFID) tags, keyless access cards, smart cards, and other applications requiring UWB antennas having a small foot print. For example, the antennas can have a size of 1-2 centimeters or less in both length and width.  
         [0032]     The antenna  100  is also useful in wireless fidelity (Wi-Fi) applications such as IEEE 802.116 and Bluetooth. In addition, antenna  100  can operate in the gigahertz range making it useful for high speed data communications in handheld low power devices such as wireless digital communications, for example, a wireless USB connection, and for position tracking applications.  
         [0033]      FIG. 5  illustrates an embodiment of a half dipole antenna  120  incorporating a ground plane  122  at the line of symmetry of the balanced antenna  100  of  FIG. 1A . The antenna  120  is unbalanced and radiates effectively in the hemispherical region of space above ground plane  122 . In addition, the radiation pattern of antenna  120  produces directive gain in and around the plane of ground plane  122 .  
         [0034]      FIG. 6  illustrates an embodiment of the invention incorporating a plurality of substantially flat half dipole antennas. In  FIG. 6 , four antennas  124 A, B, C, Dare disposed in a two row by two column geometric layout on a ground plane  126 . Arrays using larger numbers of rows and columns can also be used. The geometry of  FIG. 6  acts as an array of elements operating in an unbalanced configuration. This configuration effectively radiates in the upper hemispherical region of space with a radiation pattern producing directive gain in and around the plane of conducting ground plane  126 . In addition, each antenna of  FIG. 6  may be driven with a different signal so as to change the directional properties of the antennas and producing a beamformed output signal.  
         [0035]      FIG. 7  illustrates an exemplary embodiment of the invention having a plurality of antennas  128 A, B, C disposed along ground plane  132  in a manner following a predefined contour  130 . Antennas  128 A,  128 B and  128 C disposed along contour  130  may be coupled so as to operate as an array of elements or may be operated independently. The embodiment of  FIG. 7  is unbalanced and it radiates effectively in the hemispherical region above ground plane  132 . In addition, the arrangement of  FIG. 7  produces a radiation pattern producing directive gain in and around the plane of ground plane  132 .  
         [0036]     FIGS.  8 A-C illustrate alternate designs of three embodiments of a balanced antenna configuration such as that shown in  FIG. 1A . In addition, the curvatures may be designed using computer models, curve fitting analyses tools and/or by experimentation.  
         [0037]      FIG. 8A  illustrates an antenna  140  having curvatures that decrease with distance away from the origin. The sides  142 ,  144  have a convex curvature.  FIG. 8B  illustrates an antenna  150  having a curvature that varies, i.e. increases and decreases, with distance away from the origin. The sides  152 ,  154  have a curvature that has a convex portion and a concave portion.  FIG. 8C  illustrates another preferred embodiment of an antenna  160  having a first end  162  and a second end  164  which meet at an intersection  106 . The sides  108 ,  110 ,  114 ,  116  of the first and second sections or ends  162 ,  164 , respectively, are concave. Thus, the sides of the planar antenna elements are generally non-linear or curved to enhance the radiating pattern.  
         [0038]     Many changes in the details, materials and arrangements of parts, herein described and illustrated, can be made by those skilled in the art in light of teachings contained hereinabove. Accordingly, it will be understood that the following claims are not to be limited to the embodiments disclosed herein and can include practices other than those specifically described, and are to be interpreted as broadly as allowed under the law.