Abstract:
A compact broadband antenna. The antenna includes a first mechanism for receiving input electromagnetic energy. A second mechanism provides radiated electromagnetic energy upon receipt of the input electromagnetic energy. The radiated electromagnetic energy is provided via an antenna element having one or more angled surfaces. A third mechanism directs the radiated electromagnetic energy in a specific direction. In a more specific embodiment, the third mechanism includes a reflective backstop that is selectively positioned behind the second mechanism to reflect back-radiated energy forward of the second mechanism, thereby causing reflected electromagnetic energy to combine in phase with forward-radiated energy from the second mechanism. The third mechanism further includes plural layers of dielectric material. One or more of the plural layers of dielectric material partially surround an angled radiating surface of the second mechanism, which is implemented via a substantially conical transmit element in the specific embodiment.

Description:
This invention was made with Government support under Contract No. N00024-96-C-5204 ERGM. The Government may have certain rights in this invention. 

   BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   This invention relates to antennas. Specifically, the present invention relates to systems and methods for selectively directing or receiving a beam of energy. 
   2. Description of the Related Art 
   Systems for directing beams of energy are employed in various demanding applications including microwave, radar, ladar, laser, infrared, and sonar sensing and targeting systems. Such applications demand space-efficient and cost-effective receivers and antennas with sufficient gain and bandwidth characteristics for optimal sensing. 
   Efficient and accurate systems for directing electromagnetic energy are particularly important in projected munition guidance and fusing applications, where collateral damage must be avoided. Smart munitions, such as a smart artillery shells, often incorporate electronics and accompanying fuses to time munition detonation. Such electronics may include sensors for detecting target location and selectively triggering detonation when the munition is within a predetermined range of the target. The sensors may include directional antennas, often called end-fire antennas, which aim beams of electromagnetic energy forward of the projected munitions. The directed beams may reflect from targets, yielding return beams. Sensors may detect and time target return beams to determine target range and closing rate. 
   Unfortunately, various conventional antennas, such as doorstop, patch, and monopole antennas have various shortcomings, making their use in projected munition applications problematic. Doorstop antennas are often too large to efficiently incorporate into compact munition designs. Patch antennas often insufficiently direct electromagnetic energy and exhibit undesirable bandwidth constraints. Monopole antennas often lack sufficient gain or bandwidth characteristics. 
   Hence, a need exists in the art for a compact and efficient antenna that exhibits excellent beam-directing, bandwidth, and gain characteristics and that is suitable for munitions applications. 
   SUMMARY OF THE INVENTION 
   The need in the art is addressed by the compact broadband antenna of the present invention. In the illustrative embodiment, the antenna is an end-fire antenna adapted for use in munitions applications. The antenna includes a first mechanism for receiving input electromagnetic energy. A second mechanism provides radiated electromagnetic energy upon receipt of the input electromagnetic energy. The radiated electromagnetic energy is provided via an antenna element having one or more angled surfaces. A third mechanism directs the radiated electromagnetic energy in a specific direction. 
   In a more specific embodiment, the third mechanism includes a reflective backstop that is strategically positioned behind the second mechanism to reflect back-radiated energy forward of the second mechanism, thereby causing reflected electromagnetic energy to combine in phase with forward-radiated energy from the second mechanism. The third mechanism further includes plural layers of dielectric material. One or more of the plural layers of dielectric material partially surround an angled radiating surface of the second mechanism. 
   In the specific embodiment, the second mechanism includes a conical antenna element. The longitudinal axis of the antenna element is approximately parallel to the surface of the back-reflector. The conical antenna element is supported by and partially surrounded by first a layer of dielectric material. A top portion of the conical antenna element lacks dielectric material. The first mechanism includes an antenna feed having an input stripline transmission line that is coupled to a coaxial feed transmission line or wire, which is coupled to a vertex of the conical antenna element. 
   The stripline transmission line includes a center conductor having a tapered section. A dielectric material having mode-suppression holes therethrough, is positioned between a top ground plane and a bottom ground plane, which have corresponding antenna tuning holes, of the stripline transmission line. The dielectric material accommodates a stripline center conductor. A second dielectric layer is positioned between the top ground plane and the first dielectric layer. 
   The novel design of the present invention is facilitated by the second and third mechanisms, which enable a compact, high-gain, antenna with broadband performance. An embodiment of the present invention, wherein the second mechanism includes a substantially conical transmit element, and the third mechanism includes a back-reflector, is particularly efficient for end-fire applications that must withstand significant acceleration and thermal loads. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram of a compact broadband antenna according to an embodiment of the present invention. 
       FIG. 2  is a more detailed exploded view of the compact broadband antenna of  FIG. 1 . 
       FIG. 3  is an exploded cross-sectional view of the compact broadband antenna of  FIG. 2 . 
       FIG. 4  shows the bottom stripline groundplane surface of the first layer section of the compact broadband antenna of  FIG. 2 . 
       FIG. 5  shows the top surface of the first layer section of the compact broadband antenna of  FIG. 2 . 
       FIG. 6  shows the bottom surface of the third layer section of the compact broadband antenna of  FIG. 2 . 
       FIG. 7  shows the top stripline groundplane surface of the third layer section of the compact broadband antenna of  FIG. 2 . 
       FIG. 8  is a diagram of an exemplary mounting system adapted for use with the compact broadband antenna of  FIG. 2 . 
   

   DESCRIPTION OF THE INVENTION 
   While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility. 
     FIG. 1  is a diagram of a compact broadband antenna  10  according to an embodiment of the present invention. For clarity, various features, such as power supplies, frequency generators, network analyzers, and so on, have been omitted from the figures. However, those skilled in the art with access to the present teachings will know which components and features to implement and how to implement them to meet the needs of a given application. 
   The compact broadband antenna  10  includes a input coaxial connector  12  that is connected to base layer sections  14  via connector pins  60 , which include a coaxial-to-stripline center conductor transition  16  to a stripline center conductor  18 . The base layer sections  14  accommodate a stripline transmission line having the center conductor  18 . The stripline transmission line center conductor  18  is coupled to a coaxial feed transmission line,  22 , which together form a feed network  20 . The coaxial feed transmission line  22  is coupled to a vertex  24  of a conical antenna element  26 , which is strategically positioned adjacent to a back-reflector  28 . The antenna element  26  has selectively angled sidewalls  27 , which provide an efficient radiating surface. 
   The feed network  20 , conical antenna element  26 , and back-reflector  28  are supported by various layer sections  30 , which include support layers, bond layers, and dielectric layers, including a top chamfered dielectric  32 , and the base layer sections  14 , as discussed more fully below. Those skilled in the art will appreciate that while the conical antenna element  26  is employed as a radiating element in the present embodiment, the element  26  may act as a receiving element and/or a transmitting element, depending on the application. 
   In the present specific embodiment, the conical antenna element  26  is oriented relative to the back-reflector  28  and the various layer sections  30  so that a longitudinal axis  34  of the conical antenna element  26  is approximately perpendicular to the various layer sections  30  and parallel to the surface of the back-reflector  28 . 
   The top chamfered dielectric  32  includes various facets  36 - 42  including a right facet  36 , a left facet  38 , an output facet  40 , and the top facet  42 . The various facets  36 - 42  enhance the compact form factor of the broadband antenna  10  and may facilitate beam shaping. Beam shaping, mode selection, and broadband performance are further facilitated by strategic selection of layer sections  30 , including dielectric layer sections, as discussed more fully below. Beam mode selection is also facilitated by features of the feed network  20 , including mode-suppression holes  44 , which are positioned through the layer sections  30  and strategically placed about the coaxial feed transmission line  22  that feeds the conical antenna element  26 . In the present specific embodiment, the through holes  44  are separated by approximately 30° of angular separation. The mode-suppression holes  44  may facilitate tuning the antenna  10  so that the resulting radiation pattern includes a lobe that extends forward in the direction of a beam  46 . Additional mounting holes  48  are positioned in the base layer sections  14  to facilitate mounting the antenna  10 . The mounting holes  48  are positioned to minimize their effect on the output beam  46 . 
   Those skilled in the art will appreciate that the exact dimensions and angles of the facets  36 - 42  are application-specific and may be determined by those skilled in the art to meet the needs of a given application without undue experimentation. Furthermore, the facets  36 - 42  may be vertical facets without departing from the scope of the present invention. In the present embodiment, the side facets  36 ,  38  are beveled at approximately 22.4°, while front facet is angled approximately 10.4° relative to the top surface  42 . 
   In operation, electromagnetic energy of a desired frequency is input to the stripline transmission line formed by the center conductor  18  via the input coaxial connector  12 . Input electromagnetic energy propagates along the stripline center conductor  18  between groundplanes formed via the layers  14  and then couples to the coaxial feed transmission line  22 . The energy then propagates from the coaxial feed transmission line  22  to the conical antenna element  26 . As the input electromagnetic energy propagates through the feed network  20  and to the conical antenna element  26 , various features, such as the mode-suppression holes  44 , and dielectric constants of the layer sections  30  facilitate tuning of the electromagnetic energy in preparation for transmission from the conical antenna element  26 . 
   When the electromagnetic energy reaches the conical antenna element  26 , the energy radiates from the angled surface  27 , which is angled approximately 27° relative to the longitudinal axis  34  in the present embodiment. Partially due to the back-reflector  28  and the beam-shaping effects of the layered sections  30 , including the top chamfered dielectric section  32 , most energy will radiate forward from the output facet  40 , forming a directional output beam  46 . The output beam  46  propagates in a direction that is approximately perpendicular to the longitudinal axis  34  of the conical antenna element  34 . 
   By strategically positioning the back-reflector  28  relative to conical antenna element  26  and by selecting appropriate element  26  and reflector  28  dimensions for a particular application and input frequency, additional gain is achieved. Appropriate use of the back-reflector  28  may result in gains of 5 dBi or greater, as energy propagating backward from the conical antenna element  26  is reflected forward, combining in phase with energy  46  radiating forward from the conical antenna element  26 . The peak of the resulting beam  46  is forward of the compact broadband antenna  10 . 
   In the present specific embodiment, the back-reflector  28  is formed from a flat plate of nickel and/or copper or is painted or plated with a silver layer. The back-reflector  28  is cut so that edges of the back-reflector  28  align with the right chamfered facet  36  and the left chamfered facet  38  of the top dielectric layer  32 . The back-reflector  28  may be another shape other than flat without departing from the scope of the present invention. For example, the back-reflector  28  may be curved, such as parabolic-shaped and oriented so that the parabola opens in the direction of the conical antenna element  26  to facilitate focusing electromagnetic energy forward of the antenna  10 . 
   The conical antenna element  26  is substantially hollow or solid and may be constructed via well-known lithographic techniques. For example, a conic depression may be formed in the layers  30  and then plated with nickel or painted with a silver metallic conductive paint. Alternatively, the conical antenna element  26  is solid, such as solid copper. The conical antenna element  26  may be another shape. For example, the element  26  may have parabolic or trapezoidal vertical cross-section or a multi-faceted horizontal cross-section, without departing from the scope of the present invention. Use of a cone or other appropriate antenna element that increases in diameter from the input end  24  to a top surface  42  as a primary radiation source may provide greater bandwidth than conventional antennas used to create directional beams. 
   In some implementations, the coaxial feed transmission line  22  may be omitted, and instead, the conical antenna element  26  may directly couple to the stripline center conductor  18 , without departing from the scope of the present invention. Furthermore, various features of the feed network  20 , including the stripline  18 , the input coaxial connector  12 , and mode-suppression holes  44  are application-specific and may be modified, omitted, or replaced by other types of feed networks to meet the needs of a given application without departing from the scope of the present invention. 
   Electric fields radiate radially outward from the center conductor  56  and terminate on the mode-suppression holes  44 , which occurs when current is flowing up the center conductor  56 . However, this only occurs where mode-suppression holes  44  are present in layers. As the fields reach layers  62 - 70  and  32 , the electric fields begin to expand into the dielectric regions (see layer  32 ) and are shaped by those dielectrics and by bouncing off the plated back wall  28  of the top chamfered dielectric section  32  until they collimate and exit the antenna  10  as the beam  46 . Furthermore, in the present embodiment, the mode-suppression holes  44  are spaced such that gaps between them are much smaller than 1/10 of a wavelength. 
   While transmit operations of the broadband antenna  10  are discussed with reference to  FIG. 1 , those skilled in the art will appreciate that the broadband antenna  10  may also be employed for receive functions. 
     FIG. 2  is a more detailed exploded view of the compact broadband antenna  10  of  FIG. 1 . The base layer sections  14  include a first layer section  50 , a second layer section  52 , and a third layer section  54 . The first layer section  50  accommodates the stripline transmission line center conductor  18 . The first layer section  50  includes a groundplane disposed on a bottom surface and the metallic stripline center conductor  18  disposed on a top surface  76  and supported by core dielectric material, as discussed more fully below. In the present specific embodiment, the core dielectric material is Rogers 3003 dielectric. 
   The mode-suppression holes  44  have plated walls, i.e., they are plated through-holes that extend through the first layer section  50  and are strategically placed about a center coaxial feed conductor  56 , which terminates one end of the stripline transmission line center conductor  18 . Another end of the stripline transmission line center conductor  18  terminates at coaxial connector holes  58 . The coaxial connector holes  58  are designed to accommodate the input coaxial connector  12  and accompanying pins  60  so that energy from the coaxial connector  12  will efficiently couple to the stripline transmission line formed via the center conductor  18  and accompanying ground planes, as discussed more fully below. 
   The second layer section  52  acts as a bond layer and facilitates bonding the first layer section  50  to the third layer section  54 . The second layer section  52  may be constructed from Dupont Bond Film (Part No. FEP 200 C-20). The second layer section  52  also includes the strategically placed through holes  44 , which align with the corresponding through holes  44  in the first layer section  44  and the third layer section  54 . The various base layer sections  14  ( 50 - 54 ) have coaxial connector holes  58 , some of which are plated and some of which are not plated. Those skilled in the art will know which of the coaxial connector holes  58  to plate and which holes to leave clear without undue experimentation. Furthermore, the exact dimensions of the various antenna features, including mode-suppression holes  44 , the thickness of the various layers  30 , and so on, are application-specific and may be determined by one skilled in the art to meet the needs of a given application without undue experimentation. 
   The third layer section  54  includes a metallic groundplane top surface  78  and a bottom surface  92 , which are supported by a dielectric core, as discussed more fully below. In the present specific embodiment, the dielectric core is Rogers 3003 dielectric, and the groundplane  78  is implemented via Rogers ElectroDeposited Copper (EDC) foil with nickel plating. 
   A fourth layer  62  acts as a bond layer between the third layer  54  and a fifth layer  64 . The fifth layer  64  is a strategically-place dielectric layer that facilitates antenna tuning and associated broadband antenna performance and beam shaping. In the present specific embodiment, the fifth layer  64  is implemented via Rogers 3006 unclad dielectric. The fifth layer  64  is unclad, lacking any plating on top or bottom surfaces of the layer  64 . 
   A sixth layer  66  acts as a bond layer and is positioned atop the fifth layer  64  and beneath a seventh layer  68 . The bond layer  66  may be constructed from Rogers 3001 bond film. The seventh layer  68  is a second special dielectric layer that facilitates antenna tuning and associated broadband antenna performance. The seventh layer  68  may also be constructed from unclad Rogers 3006 dielectric. 
   An eighth layer  70  acts as a bond layer and is positioned atop the seventh dielectric layer  68  and beneath the top chamfered dielectric  32 . The eighth layer  70  may be implemented via Rogers 3001 bond film. The ninth layer, corresponding to the top chamfered dielectric  32 , is implemented via Rogers TMM4 unclad dielectric in the present specific embodiment. A tenth layer  71  acts as a stiffening structure and is positioned atop the fifth layer  64  and adjacent to the seventh layer  68  and the tenth layer  71 . The stiffening tenth layer  71  may be constructed of aluminum or various materials known in the art. Additional stiffening layers may be added or removed from the antenna  10  without departing from the scope of the present invention. 
   In the present specific embodiment, an electrically conductive adhesive  72 , such as Ablebond™, is employed to secure the conic antenna element  26  in a conical hole  74  in the top chamfered dielectric  32 . The conical antenna element  26  is shown connected to the coaxial feed transmission line center conductor  56 . The coaxial feed transmission line center conductor  56  and the conical antenna element  26  may be implemented as one piece, wherein the center conductor  56  of the coaxial feed transmission line is bonded to an input end, i.e., vertex end  24  of the conical antenna element  72 . The coaxial feed transmission line center conductor  56  extends through the various layers  30  and couples to the stripline transmission line center conductor  18  at the center coaxial feed transmission line conductor  56  in the first layer  50 . The mode suppression holes  44  only extend through the base layer sections  14 . 
     FIG. 3  is an exploded cross-sectional view of the compact broadband antenna  10  of  FIG. 2 . The first layer section  50  includes a first stripline groundplane surface  90  and a top center stripline conductor surface  76 . The first stripline groundplane surface  90  is constructed from a metal, such as nickel-plated copper. The top center stripline conductor surface  76  is primarily dielectric material, but includes the conductive stripline center conductor  18  of  FIG. 2 , which may be made from copper. The stripline surfaces  76 ,  90  are supported by a dielectric core, which may be constructed from Rogers 3003 dielectric. 
   The third layer section  54  includes the conductive groundplane surface  78 , which is implemented via nickel-plated copper in the present embodiment. The ground plane surface  78  is formed on a dielectric core, which also provides the bottom surface  92  of the third layer section  54 . 
   The fifth layer  64 , seventh layer  66 , and the ninth chamfered dielectric layer  32 , which are separated by bonding layers  66 ,  70 , represent layered dielectrics that facilitate beam-shaping and antenna tuning. Layer thickness and dielectric constants may be adjusted by those skilled in the art to meet the needs of a given application without undue experimentation. 
   In the present specific embodiment, the fifth layer section  64  and the seventh layer section  68  are approximately 0.025 inches thick. The chamfered dielectric layer  32  is approximately 0.26 inches thick. The longitudinal axis  34 , which corresponds to the centerline of the radiating element  2 , is positioned approximately 0.2 inches from the metallic back-reflector  28 . 
   The conical hole  74 , which accommodates the adhesive  72  and conical antenna element  26  has sidewalls that are angled approximately 27° relative to the longitudinal axis  34  of the antenna element  26 . In the present embodiment, the groundplanes  90 ,  78  are at least 0.0015 inches thick copper with a nickel overplate that is that is approximately 150 microinches thick. 
   The various transmission line feed holes that accommodate the center conductor  56  and outer conductor  82  may include padding or dielectric to facilitate accommodating the coaxial feed transmission line (see  22  of  FIG. 1 ) formed by the outer conductor  82  and center conductor  56 . The exact type of padding or dielectric is application-specific and may be omitted without departing from the scope of the present invention. 
     FIG. 4  shows the bottom stripline groundplane surface  90  of the first layer section  50  of the compact broadband antenna  10  of  FIG. 2 . The bottom groundplane surface  90  includes the plated mode-suppression holes  44 , which are partially distributed about the center coaxial feed section  22 , which shows a cross-section of the inner coaxial feed conductor  56  that passes through the outer coaxial feed conductor, which is implemented via the groundplane  90 . The bottom groundplane surface  90  also includes coaxial connector holes  58  for accommodating a standard coaxial cable connector and accompanying pins  60 , which may be implemented via a Corning GPO RF connector, part No. A008-L35-02. The coaxial connector holes  58  include a center hole  86  that accommodates a center conductor of the input coaxial connector  12  of  FIGS. 1 and 2 . In the present embodiment, the groundplane surface  90  is implemented via 0.0015 inch thick copper that is overplated with nickel that is at least 150 microinches thick. 
     FIG. 5  shows the top surface  76  of the first layer section  50  of the compact broadband antenna  10  of  FIG. 2 . The top surface  76  includes the stripline center conductor  18  that connects to a center coaxial cable connector (see center pin of pins  60  of  FIG. 1 ) at the center coaxial connector hole  86  at the coaxial-to-stripline center conductor transition  16 . The stripline center conductor  18  connects to the center conductor  56  of the coaxial feed transmission line  22  at a stripline-to-coaxial center conductor transition  84 . 
   The stripline center conductor  18  includes a first leg  94  that connects to a telescoping leg  96  at a ninety-degree bend  98  having a forty-five degree bevel  100 . The telescoping leg  96  includes a wider section  102  that extends into a narrower section  104 . In the present specific embodiment, the first leg  94  and the wider section  102  of the telescoping leg  96  are approximately 0.026 inches wide, while the narrower section  104  is approximately 0.021 inches wide. The telescoping section  96  facilitates antenna tuning. 
     FIG. 6  shows the bottom surface  92  of the third layer section  54  of the compact broadband antenna  10  of  FIG. 2 . The bottom surface  92  includes the metal-walled mode-suppression holes  44  and the coaxial feed transmission line section  22  with the inner conductor  56 . The surface  92  also accommodates the coaxial connector  58 . 
     FIG. 7  shows the top groundplane surface  78  of the third layer section  54  of the compact broadband antenna  10  of  FIG. 2 . The coaxial connector holes  58  and the mode-suppression holes  44  terminate at the top groundplane surface  78 . The coaxial feed section  22  extends through the surface  78  to the top chamfered dielectric  32  of  FIG. 2 , where it terminates. The center conductor  56  extends partially into the conical antenna element  26  or is bonded to the vertex of the conical antenna element  26  in implementations wherein the conical antenna element  26  is solid or is substantially hollow. 
     FIG. 8  is a diagram of an exemplary mounting system  110  adapted for use with the compact broadband antenna  10  of  FIG. 2 . The antenna  10  is mounted to a surface of the mounting system  110  and oriented so that energy  46  from the antenna  10  emanates forward and approximately parallel to a system longitudinal axis  112 . The mounting system  110  may also accommodate other antennas, such as a Global Positioning System (GPS) antenna  114 . The mounting system  110  represents the front end of a projected munition with its radome cover removed. 
   In various embodiments disclosed herein, Rogers materials were selected for their ability to withstand temperature without losing thermal stability, hence alleviating concerns that the antenna would expand unduly with heat and thereby de-tune the antenna. The effects of G-forces are further alleviated with the aluminum stiffeners (see  71  of  FIG. 2 ). 
   Those skilled in the art will appreciate that the antenna  10  of  FIGS. 1 and 2  may be caused to operate at a lower or higher frequency by scaling all components in size while maintaining component aspect ratios. 
   Thus, the present invention has been described herein with reference to a particular embodiment for a particular application. Those having ordinary skill in the art and access to the present teachings will recognize additional modifications, applications, and embodiments within the scope thereof. 
   It is therefore intended by the appended claims to cover any and all such applications, modifications and embodiments within the scope of the present invention. 
   Accordingly,