Patent Publication Number: US-9905936-B2

Title: Ultra-broadband antenna array with constant beamwidth throughout operating frequency band

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part application of U.S. application Ser. No. 14/474,414, filed Sep. 2, 2014, which claims the benefit of U.S. Provisional Application No. 61/874,035, filed Sep. 5, 2013, the disclosures of which are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     Field 
     Embodiments disclosed herein generally relate to antennas and, more particularly, relate to circular, spherical, conformal ultra-broadband antenna arrays having a substantially constant beamwidth throughout a band of operation. 
     SUMMARY 
     In accordance with one embodiment, an antenna array is provided, which includes a plurality of antenna elements configured in a flare such that each of the plurality of antenna elements is uniformly spaced apart from at least one adjacent antenna element. Each of the plurality of antenna elements is coupled in a common area, and each of the plurality of antenna elements extends radially outward from the common area. 
     The plurality of antenna elements may be configured in at least one of a circle, half circle, sphere, and plane. At least one of the plurality of antenna elements may include at least one of a bow tie antenna, log-periodic antenna, and Vivaldi antenna. The antenna array may include an axis of symmetry extending through the common area, and at least one of the plurality of antenna elements may include a planar area, which includes an edge that is disposed non-parallel to the axis of symmetry when viewed normal to the axis of symmetry. The antenna array may include an axis of symmetry, and at least one of the plurality of antenna elements may be disposed at a tilt with respect to the axis of symmetry. The feed may be disposed in the common area and operatively coupled to at least one of the plurality of antenna elements. 
     In accordance with another embodiment, a method of arranging antenna elements in an antenna array includes configuring a plurality of antenna elements in a flare such that each antenna element is uniformly spaced apart from at least one adjacent antenna element, and each of the plurality of antenna elements extends radially outward from a common area; and coupling each of the plurality of antenna elements in the common area. 
     The method may include configuring the plurality of antenna elements in at least one of a circle, half circle, sphere, and plane. At least one of the plurality of antenna elements may include at least one of a bow tie antenna, log-periodic antenna, and Vivaldi antenna. The antenna array may include an axis of symmetry extending through the common area, and at least one of the plurality of antenna elements may include a planar area. The planar area may include an edge, and the method may include disposing the edge non-parallel to the axis of symmetry when viewed normal to the axis of symmetry. The antenna array may include an axis of symmetry, and the method may include disposing at least one of the plurality of antenna elements at a tilt with respect to the axis of symmetry. The antenna array may include a feed, and the method may include disposing the feed in the common area, and operatively coupling the feed to at least one of the plurality of antenna elements. 
     In accordance with another embodiment, an antenna array is provided, which includes a plurality of antenna elements. The plurality of antenna elements is coupled in a common area and extends radially outward from the common area. At least one of the plurality of antenna elements includes a first antenna portion and a second antenna portion. The first antenna portion and the second antenna portion are arranged in a configuration such that a gap is formed between the first antenna portion and the second antenna portion. The gap includes a first spacing and a second spacing. The first spacing is associated with a first operating frequency and a first operating wavelength, and the second spacing is associated with a second operating frequency and a second operating wavelength. A proportion of the first spacing to the first wavelength is substantially equal to a proportion of the second spacing to the second wavelength, thereby providing a constant beamwidth over an operating frequency band. 
     The plurality of antenna elements may be configured in at least one of a circle, half circle, sphere, and/or plane. At least one of the plurality of antenna elements may include at least one of a bow tie antenna, log periodic antenna, and/or Vivaldi antenna. An axis of symmetry may extend through the common area, at least one of the plurality of antenna elements may include a planar area, and the planar area may include an edge disposed non-parallel to the axis of symmetry when viewed in a direction that is normal to the axis of symmetry and coplanar with the planar area. At least one of the plurality of antenna elements may be disposed at a tilt with respect to the axis of symmetry when viewed in a direction that is normal to the axis of symmetry and coplanar with the planar area. The antenna array may include a feed disposed in the common area, which is operatively coupled to at least one of the plurality of antenna elements. The gap may include a serpentine configuration. 
     In accordance with another embodiment, a method of arranging a plurality of antenna elements in an antenna array is provided, which includes coupling a plurality of antenna elements in a common area, and configuring at least one of the plurality of antenna elements to comprise a first antenna portion and a second antenna portion. The plurality of antenna elements extend radially outward from the common area, and the first antenna portion and the second antenna portion are arranged in a configuration such that a gap is formed between the first antenna portion and the second antenna portion. The gap includes a first spacing and a second spacing. The first spacing is associated with a first operating frequency and a first operating wavelength, and the second spacing is associated with a second operating frequency and a second operating wavelength. A proportion of the first spacing to the first wavelength is substantially equal to a proportion of the second spacing to the second wavelength, thereby providing a constant beamwidth over an operating frequency band. 
     The method may include configuring the plurality of antenna elements in at least one of a circle, half circle, sphere, and/or plane. The method may include configuring the at least one of the plurality of antenna elements to comprise at least one of a bow tie antenna, log periodic antenna, and/or Vivaldi antenna. The method may include configuring the antenna array to include an axis of symmetry extending through the common area, and configuring at least one of the plurality of antenna elements to comprise a planar area. The planar area may include an edge disposed non-parallel to the axis of symmetry when viewed in a direction that is normal to the axis of symmetry and coplanar with the planar area. The method may include disposing at least one of the plurality of antenna elements at a tilt with respect to the axis of symmetry when viewed in a direction that is normal to the axis of symmetry and coplanar with the planar area. The method may include configuring the antenna array to comprise a feed, disposing the feed in the common area, and coupling the feed being operatively to at least one of the plurality of antenna elements. The method may include configuring the gap to include a serpentine configuration. 
     Other embodiments will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of any disclosed embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following drawings are provided by way of example only and without limitation, wherein like reference numerals (when used) indicate corresponding elements throughout the several views, and wherein: 
         FIG. 1  shows a circular array of antenna elements; 
         FIGS. 2A and 2B  show isometric views of a flare of a circular and conformal array of antenna elements; 
         FIGS. 2C and 2D  show isometric and top views, respectively, of a flare of a half circular and conformal array of antenna elements; 
         FIGS. 3A and 3B  show side views of cross-polarized antenna elements at a 45 degree tilt in a planar antenna array and a circular antenna array, respectively; 
         FIGS. 4A-C  show isometric, side, and top views, respectively, of cross-polarized antenna elements at a 45 degree tilt in a circular antenna array; 
         FIG. 5  shows a top view of a circular antenna array, in which opposing elements have been identified; 
         FIG. 6  shows a flare of antenna elements; 
         FIGS. 7A and 7B  show a flare of antenna elements arranged in a semi-sphere; 
         FIGS. 8A and 8B  show a flare of antenna elements arranged in a sphere; and 
         FIG. 9  shows a tapered slot antenna element having antenna portions arranged in a serpentine configuration; 
         FIGS. 10A-B  show an embodiment of a serpentine antenna element including first and second antenna portions that are configured to have different spacings therebetween; 
         FIGS. 11A-B  show another embodiment of a serpentine antenna element including first and second antenna portions that are configured to have different spacings therebetween; and 
         FIGS. 12A-D  show different configurations of tapered slot antennas for use in the disclosed embodiments. 
     
    
    
     It is to be appreciated that elements in the figures are illustrated for simplicity and clarity. Common but well-understood elements that are useful or necessary in a commercially feasible embodiment are not shown in order to facilitate a less hindered view of the illustrated embodiments. 
     DETAILED DESCRIPTION 
     A circular antenna array is an antenna, which includes antenna elements arranged in a circle. A conformal antenna array is an antenna that is designed to conform or follow a predetermined shape. In accordance with embodiments disclosed herein, elements on the circular and/or conformal array are spaced at a certain distance in relation to an operating wavelength λ or operating band of wavelengths. This spacing remains constant from element to element at all frequencies of operation. 
       FIG. 1  shows a circular antenna array  10  with bow tie antenna elements  12  arranged in a vertical polarization. Although bow tie antenna elements  12  are shown in the circular antenna array  10 , any type of antenna element may be used in the illustrated configuration. Embodiments disclosed herein include ultra-broadband antenna arrays, in connection with which large frequency bands are used that can result in large fluctuations in beamwidth. 
     A wavelength λ of the operating signal is given by the following equation: 
                     λ   =     V   f       ,           (   1   )               
where V represents the phase speed or magnitude of the phase velocity of light (3×10 8  meters/second), and f represents the wave frequency. Equation (1) provides a basis for explaining a flare in the embodiments disclosed herein. For every frequency f, there is a different wavelength λ since the phase velocity V is a constant. Thus, as the wavelength λ changes, so too must the frequency f change. The spacing of antenna elements in the flare in relation to the wavelength λ is maintained to provide a constant beamwidth. Thus, the flare is used to maintain the correct proportion of frequency f with respect to the wavelength λ.
 
     Since ultra-broadband operation includes a wide band of frequencies, the corresponding frequency f changes substantially, which causes the wavelength λ to change significantly as the frequency f changes. Because broadband antenna arrays in accordance with embodiments disclosed herein operate over such a wide range of frequencies, the antenna elements in the broadband antenna array are flared to maintain adequate spacing in relation to the wavelength λ throughout the frequency range of operation. Since the minimum and maximum operating frequencies of the broadband antenna array are known, the distance between each element at the minimum and maximum operating frequency can be calculated using equation (1). For example, assuming an antenna that operates from 300 MHz to 3 GHz, the wavelengths are as follows:
 
wavelength λ at 300 MHZ=3×10 8 /300×10 6 ˜1 meter; and
 
wavelength λ at 3 GHZ=3×10 8 /3×10 9 ˜0.1 meter.
 
Thus, the flare between antenna elements for this example is as shown in  FIG. 6 , in which antenna elements  11  are separated at one end by dimension  13 , which is approximately 1 meter, and separated at another end by dimension  15 , which is approximately 0.1 meter. The view of the antenna elements  11  shown in  FIG. 6  is essentially a top view, which is similar to the view of the antenna elements  16  shown in  FIG. 2D  and the view of the antenna elements  26 ,  28  shown in  FIG. 4C .
 
     To provide adequate distance between antenna elements, flares  14 ,  15  of antenna elements  16  are used as shown in  FIGS. 2A-D . These flares  14 ,  15  maintain inter-element distance between the antenna elements  16  with respect to the wavelength λ of the operating signal, which results in a constant beamwidth over the operating frequency range.  FIGS. 2A and 2B  show a flare  14  of antenna elements configured as a circular and conformal antenna array.  FIGS. 2C and 2D  show a flare  15  of antenna elements configured as a half circular and conformal antenna array. The antenna elements  16  are configured in the flare  14 ,  15  such that each of the plurality of antenna elements  16  is uniformly spaced apart from at least one adjacent antenna element  16 , each of the plurality of antenna elements  16  is coupled in a common area  46 , and each of the plurality of antenna elements extends radially outward from a common area  46 . As discussed above, the antenna elements in the flare are spaced apart from each other based on the high and low frequencies in the operational frequency bandwidth. The quantity of antenna elements can be increased or decreased to form a circle, which can be result in a semi-sphere  52  shown in  FIGS. 7A and 7B , a sphere  54 , as shown in  FIGS. 8A and 8B , and/or a conformal shape to provide azimuth and/or elevation coverage up to 360 degrees. 
     The disclosed embodiments utilize one or more broadband antenna elements. The flare, as used herein, refers to an antenna array in which the antenna elements are configured such that each antenna element is uniformly spaced apart from at least one adjacent antenna element, and each antenna element extends radially outward from a common central area. The antenna elements can be separately fed, which results in lower gain than when using a beam forming network. The beam forming network can be used to provide 360 degree coverage. Multiple beams can be generated using the beam forming network at, for example 0, 45, 90, 135, 180 degrees, each of which has substantially the same beamwidth due to the flare. 
     The antenna elements are fed from the common central area, from which the antenna elements radiate outward. However, log periodic antennas are fed in the opposite direction since the antenna elements radiate in the opposite direction, that is, towards the common central area. However, if the antenna elements are flared at 45 degrees, an opposing antenna element will be at −45 degrees, and since the antenna elements are spaced 90 degrees apart, the antenna elements will be orthogonal, and thus will not be blocked by radiation from opposing elements in such a configuration. 
     Embodiments disclosed herein also provide for a planar antenna array  18  shown in  FIG. 3A , or a circular antenna array  19  shown in  FIG. 3B  using antenna elements  20  that are cross-polarized. Cross-polarization refers to the antenna elements  18  not being disposed in a straight-up configuration, as shown in  FIG. 1 , but instead being disposed at a 45° or −45° tilt from a vertical straight line or axis of symmetry  22 ,  23 .  FIGS. 3A and 3B  illustrate this 45° tilt concept. Although a 45° tilt is shown, alternative angles may be used to define the degree of tilt including, but not limited to, 15°, 30°, 60°, and 75° while remaining within the intended scope of the embodiments disclosed herein. 
       FIGS. 4A-C  show isometric, side, and top views, respectively, of a flare  24  of antenna elements configured as a circular antenna array. In this flare  24 , opposing front and rear antenna elements  26 ,  28  are disposed at a 90° difference in orientation, thereby making the antenna elements  26 ,  28  orthogonal with respect to each other, as shown in  FIGS. 4A-C . An axis of symmetry  42  is shown in  FIGS. 4A-C , which extends through a common area  47 . The tilt concept is also illustrated by at least one of the plurality of antenna elements including a planar area, which has an edge  50  that is disposed non-parallel to the axis of symmetry  42  when viewed normal to the axis of symmetry  42 . 
     When either the front antenna element  26  or the rear antenna element  28  is propagating, neither of the elements  26 ,  28  sees the opposing element since the elements  26 ,  28  are perpendicular to each other. That is, there is no coupling or reflection between the front and rear opposing elements  26 ,  28 . Stated differently, an antenna element cannot see the antenna element on the other side of the circular antenna array, and thus there is no interaction between opposing antenna elements. 
       FIG. 5  identifies pairs of opposing antenna elements ( 26 ,  28 ), ( 30 ,  32 ), ( 34 ,  36 ), and ( 38 ,  40 ). By configuring these antenna elements at a 45 degree tilt in a circle, an inward antenna element propagates through the corresponding opposing antenna element disposed on the opposing side of the circle. As indicated above, log periodic antennas are fed in the opposite direction because the antenna elements radiate in the opposite direction. That is, the antenna elements will radiate inward towards the center of the circle. However, if the antenna elements are flared at a 45 degree angle, the opposing antenna element disposed on the opposite side of the circle, will be flared at a −45 degree angle, and since the antenna elements are 90 degrees apart, the opposing antenna elements will be orthogonal to each other, and thus opposing antenna elements will not block their respective radiations. 
     In accordance with another embodiment, an antenna array includes a plurality of tapered slot antenna elements. Each of the tapered slot antenna elements  16  includes a first antenna portion  56  and a second antenna portion  58 , which are arranged in a serpentine configuration such that a gap  60  is formed therebetween, as shown in  FIG. 9 . The serpentine configuration provides for a plurality of different distances between the first and second antenna portions  56 ,  58 , which enables the beamwidths of the antenna element to remain constant at all frequencies of operation. 
     For example,  FIGS. 10A-B  show an embodiment of a serpentine antenna element including a first antenna portion  62  and a second antenna portion  64 , which is configured to have, for example, four (4) different spacings  66 ,  68 ,  70 ,  72  therebetween, Each of the spacings  66 ,  68 ,  70 ,  72  corresponds to one of four (4) different operating frequencies F 1 - 4  with one of four (4) different wavelengths. The different spacings  66 ,  68 ,  70 ,  72  between antenna portions  62 ,  64  are configured to have a value that is in constant proportion to the wavelength at the corresponding operating frequency. 
     Thus, using the example provided above, and assuming that F 1 =300 MHz, F 2 =3 GHz, the corresponding wavelengths would be W1=1 meter, W2=0.1 meter. Accordingly, the corresponding spacing  72  for the operating frequency F 1  could be 1 meter, and the corresponding spacing  74  for the operating frequency F 2  could be 0.1. meter, which would maintain a constant 1:1 proportion or ratio between the spacing and the corresponding operating wavelength or and/or frequency. 
     Similarly,  FIGS. 11A-B  show an embodiment of a serpentine antenna element including a first antenna portion  74  and a second antenna portion  76 , which is configured to have, for example, five (5) different spacings  78 ,  80 ,  82 ,  86 ,  88  therebetween, Each of the spacings  78 ,  80 ,  82 ,  86 ,  88  corresponds to one of five (5) different operating frequencies F 1 - 5  with one of five (5) different wavelengths. 
     Thus, using the example provided above, and assuming that F 1 =300 MHz, F 2 =3 GHz, the corresponding wavelengths would be W1=1 meter, W2=0.1 meter. Accordingly, the corresponding spacing  86  for the operating frequency F 1  could be 1 meter, and the corresponding spacing  82  for the operating frequency F 2  could be 0.1. meter, which would maintain a constant 1:1 proportion or ratio between the spacing and the corresponding operating wavelength and/or frequency. 
     The plurality of tapered slot antenna elements  16  may be configured in, for example, at least one of a circle, half circle, sphere, cylinder, plane, and/or the like. At least one of the plurality of tapered slot antenna elements  16  may include at least one of a log-periodic antenna and/or Vivaldi antenna. 
       FIGS. 12A-D  show different configurations of tapered slot antennas for use in the disclosed embodiments. Specifically,  FIG. 12A  shows an exponentially tapered slot antenna  88 ,  FIG. 12B  shows a linear tapered slot antenna  90 ,  FIG. 12C  shows a continuous width slot antenna  92 , and  FIG. 12D  shows a dual exponentially tapered slot antenna  94 . 
     Broadband antenna elements, such as, but not limited to, log-periodic and Vivaldi antenna elements can be used in the embodiments disclosed above. 
     Although the specification describes components and functions implemented in the embodiments with reference to particular standards and protocols, the embodiment are not limited to such standards and protocols. 
     The illustrations of embodiments described herein are intended to provide a general understanding of the structure of various embodiments, and are not intended to serve as a complete description of all the elements and features of apparatuses and systems that may make use of the structures described herein. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. Other embodiments are utilized and derived therefrom, such that structural and logical substitutions and changes are made without departing from the scope of this disclosure. Figures are also merely representational and are not drawn to scale. Certain proportions thereof are exaggerated, while others are decreased. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. 
     Such embodiments of the inventive subject matter are referred to herein, individually and/or collectively, by the term “embodiment” merely for convenience and without intending to limit the scope of this application to any single embodiment or inventive concept. Thus, although specific embodiments have been illustrated and described herein, it should be appreciated that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description. 
     In the foregoing description of the embodiments, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting that the claimed embodiments have more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single embodiment. Thus, the following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate example embodiment. 
     The abstract is provided to comply with 37 C.F.R. §1.72(b), which requires an abstract that will allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as separately claimed subject matter. 
     Although specific example embodiments have been described, it will be evident that various modifications and changes are made to these embodiments without departing from the broader scope of the inventive subject matter described herein. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. The accompanying drawings that form a part hereof, show by way of illustration, and without limitation, specific embodiments in which the subject matter are practiced. The embodiments illustrated are described in sufficient detail to enable those skilled in the art to practice the teachings herein. Other embodiments are utilized and derived therefrom, such that structural and logical substitutions and changes are made without departing from the scope of this disclosure. This Detailed Description, therefore, is not to be taken in a limiting sense, and the scope of various embodiments is defined only by the appended claims, along with the full range of equivalents to which such claims are entitled. 
     Given the teachings of the embodiments disclosed herein, one of ordinary skill in the art will be able to contemplate other implementations and applications of the techniques disclosed herein. Although illustrative embodiments have been described herein with reference to the accompanying drawings, it is to be understood that these embodiments are not limited to those precise embodiments disclosed, and that various other changes and modifications are made therein by one skilled in the art without departing from the scope of the appended claims.