Patent Publication Number: US-2019181562-A1

Title: Method of manufacturing a stacked-disk antenna element

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to methods of manufacturing radiating elements used in, for example, phased array radar systems. 
     BACKGROUND 
     Antenna arrays, such as those used in radar systems, are typically populated by a plurality of antenna elements or transducers which transduce electromagnetic energy between unguided and guided-wave forms. More particularly, the unguided form of electromagnetic energy is that propagating in “free space,” while guided electromagnetic energy follows a defined path established by a transmission line, such as a coaxial cable, waveguides, dielectric paths, and other conductors and the like. The beam characteristics of an antenna are established, in part, by the size of the radiating portions of the antenna relative to the wavelength. In general, small antennas make for broad or nondirective beams, and large antennas make for small, narrow or directive beams. When more directivity (narrower beamwidth) is desired than can be achieved from a single antenna, several antennas may be grouped together into an array and fed together in a phase-controlled manner, to generate the beam characteristics of an antenna larger than that of any single antenna element. The structures which control the phase and apportionment of power to (or from) the antenna elements are termed “beamformers”, and allow for the simultaneous generation of multiple antenna beams. 
     In order to transmit or receive electromagnetic signals, an antenna element must respond to an electromagnetic field traveling toward or from the desired direction. In order to respond to the electromagnetic signal, the antenna must have a finite physical extent or “aperture” in the desired polarization in order to interact with the field being transduced. A planar array of planar patch antenna elements, when viewed from a direction orthogonal to the plane of the array, has a physical extent which substantially equals the patch dimension for the polarization in question. Viewed from a location within the plane of the array, however, each patch antenna has substantially zero projected extent or dimension, at least in one polarization. Consequently, the ability of a planar array of planar or patch antennas to transceive in the direction of the plane may be limited, or in antenna terms, it may have relatively low “gain”. In addition to the problem of lack of projected dimension which results in low gain in the plane of the array, there is the problem that radiation to or from any one element of the array must pass by one or more adjacent antenna elements. These adjacent antenna elements tend to interact with so much field as may exist, which in turn tends to “block” the field to or from adjacent antenna elements. This interaction between mutually adjacent antenna elements of an array is termed “mutual coupling.” One manifestation of mutual coupling is a tendency of the impedance of the antenna element to be dependent on the signal transduced by the adjacent (and sometimes semi-adjacent) elements. Mutual coupling often has adverse consequences in the overall operation of the array, and may be undesired. Moreover, developing antenna elements or arrays which reduce or mitigate mutual coupling often necessitate adding features which increase the cost of the individual elements, as well as complicate the manufacturing process. As antenna arrays may be populated by large quantities of elements, these cost and manufacturing difficulties are further magnified. 
     Improved and/or alternative antenna elements, as well as improved and/or alternative methods of manufacture thereof, are desired. 
     SUMMARY 
     According to one embodiment of the present disclosure, a method of manufacturing a radiating element for a radar array antenna is provided. The method includes arranging a dielectric puck over a surface of a ground plane. A first conductive disk assembly is realized by forming a first conductive disk having a plurality of through holes, inserting a plurality of conductive posts through the plurality of through holes, and attaching the plurality of conductive posts to the first conductive disk. The method further comprises arranging the first conductive disk assembly on the dielectric puck such that at least a portion of the plurality of conductive posts extend therethrough. A conductive rod is inserted through the first conductive disk and the dielectric puck, and a second conductive disk is attached thereto. At least one wing element is attached to the ground plane. 
     According to another embodiment, a method of manufacturing a radiating element for an antenna comprises a first step of forming a stacked conductive disk assembly. The assembly is formed by attaching a plurality of conductive posts to a first conductive disk, inserting a first end of a conductive rod through an aperture formed through the first conductive disk, and attaching a second conductive disk to the conductive rod proximate a second end of the conductive rod. The method further comprises the steps of arranging the stacked conductive disk assembly on a dielectric puck such that at least a portion of the plurality of conductive posts extend therethrough, arranging the dielectric puck and stacked conductive disk assembly on a ground plane, and attaching at least one wing element to the ground plane. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view of a radiating or antenna element according to an embodiment of the present disclosure. 
         FIG. 1B  is a side view of the antenna element of  FIG. 1A . 
         FIG. 1C  is a top view of the antenna element of  FIGS. 1A and 1B . 
         FIG. 2  is a side view of a wing for use with an antenna element according to embodiments of the present disclosure. 
         FIG. 3  is a side view of a wing for use with an antenna element according to embodiments of the present disclosure. 
         FIG. 4  is a side view of a wing for use with an antenna element according to embodiments of the present disclosure. 
         FIG. 5  is a side view of a wing for use with an antenna element according to embodiments of the present disclosure. 
         FIG. 6  is a top view of a four-by-four array of antenna elements according to an embodiment of the present disclosure. 
         FIGS. 7A and 7B  illustrate axial ratio performance of an antenna element of the prior art. 
         FIGS. 8A and 8B  illustrate axial ratio performance of an antenna element according to an embodiment of the present disclosure. 
         FIGS. 9A and 9B  illustrate return loss performance associated with an antenna element of the prior art. 
         FIGS. 10A and 10B  illustrate return loss performance of an antenna element according to an embodiment of the present disclosure. 
         FIG. 11  is a cross-sectional view of a radiating or antenna element according to an embodiment of the present disclosure. 
         FIG. 12  is an exploded view of the antenna element of  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION 
     It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for purposes of clarity, many other features found in signal transmission and reception systems, such as radar systems, including radiating elements of radar systems. However, because such elements are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein. The disclosure herein is directed to all such variations and modifications known to those skilled in the art. 
     In the following detailed description, reference is made to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. It is to be understood that the various embodiments of the invention, although different, are not necessarily mutually exclusive. Furthermore, a particular feature, structure, or characteristic described herein in connection with one embodiment may be implemented within other embodiments without departing from the scope of the invention. In addition, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, appropriately interpreted, along with the full range of equivalents to which the claims are entitled. In the drawings, like numerals refer to the same or similar functionality throughout several views. 
     Antenna arrays according to embodiments of the present disclosure include a plurality of stacked upper and lower disk radiators or elements arranged in, for example, a lattice. For each radiator or antenna element, the lower disk is arranged on a dielectric disk or puck. The upper disk is supported by a central post or conductive element that runs though the lower disk and contacts a ground plane. The lower disk is fed by, for example, four feed probes spaced 90 degrees apart. Each pair of opposing probes may be fed by a 180 degree hybrid feed arrangement. These hybrid feed arrangements can be used to generate orthogonal slant linear polarizations. They can also be fed at a 0/180 degree phase for dual linear polarization operation, or at −90/+90 degree phase for dual circular polarization operation. 
     Each antenna element further comprises shaped metal (e.g. aluminum) or dielectric baffles or “wings” for controlling mutual coupling between neighboring elements and for improving the scan loss performance of the array. Wings according to the prior art have been defined by rectangular profiles. These designs have led to poor cross polarization and axial ratio of the element, and have been shown to block infringing fields of only one polarization. However, it has been unexpectedly discovered that by altering the profile of these wing elements, improvements in antenna element performance are realized. For example, in one embodiment of the present disclosure, each improved wing comprises a width that is varied over a height of the wing. In another embodiment, portions of the wing which oppose a central post or central axis of the antenna element are arranged at different distances with respect to the central axis. More specifically, in one particularly advantageous embodiment, an exposed portion of each wing may comprise two generally vertical sidewalls, a horizontal end wall on a free end thereof, and at least one radiused or rounded corner joining at least one of the vertical sidewalls and the end wall. In one embodiment, both corners of the free ends of each wing are radiused or rounded. The surface of the wing in this radiused area is arranged farther from a center of the antenna element compared to a surface defined on the vertical sidewall of the wing. These wing profiles achieve very low cross polarization levels compared to wing elements of the prior art at least by virtue of this variation in spacing. 
     Referring generally to  FIGS. 1A, 1B and 1C , a radiating or antenna element  10  according to an embodiment of the present disclosure is shown. Element  10  includes a ground plane  12  defining an upper or top surface. A first electrically conductive disk  14  of a first diameter is fixedly mounted at a distance above the top surface of ground plane  12 , and may be centered about a central axis A of element  10 . First disk  14  may be supported by dielectric material  16 , which may be provided in the form of a puck or a disk, which in turn is supported on the upper surface of ground plane  12 . The side of ground plane  12  on which first disk  14  is arranged may be referred to as the “radiating” side of element  10 , in that electromagnetic transduction occurs in the half-plane above ground plane  12 . A second conductive disk  18  having a second diameter is mounted concentrically and parallel with first disk  14 , and is spaced therefrom at a location more remote from ground plane  12 . More particularly, second disk  18  is arranged at a second distance from ground plane  12 , greater than the distance between first disk  14  and ground plane  12 . The diameter of first disk  14  may be smaller than the diameter of second disk  18 . 
     An elongated thermally and electrically conductive element or rod  30  is affixed to ground plane  12  concentric with central axis A. Rod  30  extends through dielectric material  16 , and makes thermal and electrical contact with the underside of second conductive disk  18 . Rod  30  also makes thermal and electrical contact with first conductive disk  14 , either peripherally where rod  30  passes through disk  14 , or by being separated into two parts, one of which extends from ground plane  12  to the underside of disk  14 , and another of which extends from the upper side of disk  14  to disk  18 . 
     It should be understood that element  10  may be fed so as to transduce linear-only polarization or so as to transduce circular polarization. To transduce linear polarization, a lower surface of second disk  14  is fed at two locations, diametrically opposite to each other relative to central axis A, with signals which are out of phase. Such out of phase signals may be viewed as being represented by 0° and 180° phases. Thus, the signal feed for linear polarization may be viewed as applying relative 0° and 180° signals at locations  14 A and  14 B of disk  14 . As an alternative, the 0° and 180° signals may be applied at locations  14 C and  14 D. See  FIG. 1C . The linear feed for element  10  may be implemented by a pair of coaxial transmission lines  20 A and  20 B. 
     An outer conductor of coaxial transmission line  20 A may be fixed to a periphery of an aperture extending through ground plane  12 . Likewise, an outer conductor of transmission line  20 B may also be affixed about an aperture formed through ground plane  12 . As shown, center conductors of coaxial transmission lines  20 A, 20 B extend upward from respective apertures, through dielectric material  16 , and make contact with the underside of lower disk  14  at respective feed locations  14 A, 14 B. Another linear feed for element  10  may be implemented by another set of coaxial transmission lines  20 C and  20 D. The outer conductor of coaxial transmission line  20 C is affixed to the periphery of an aperture extending through the ground plane  12 , which aperture is centered on a projection of feed location  14 C, parallel with central axis A onto ground plane  12 . Likewise, the outer conductor of coaxial transmission line  20 D is affixed to the periphery of an aperture extending through the ground plane  12 , which aperture is centered on a projection of feed location  14 D, parallel with central axis A, onto ground plane  12 . The center conductor of coaxial transmission line  20 C extends upward from an aperture, through dielectric material  16 , and makes contact with the underside of lower disk  14  at location  14 C. Similarly, the center conductor of coaxial transmission line  20 D extends upward from an aperture, through dielectric material  16 , and makes contact with the underside of lower disk  14  at location  14 D. Those skilled in the art would understand how coaxial transmission lines  20 A- 20 D may be fed with relative 0° and 180° signals so as to effectuate a desired excitation. 
     Element  10  further comprises improved baffles or wings  50  arranged on a surface of element  10 . In the illustrated embodiment, wings  50  are mounted or otherwise affixed to ground plane  12  and extend generally perpendicularly therefrom in a vertical direction. Wings according to embodiments of the present disclosure are configured to reduce mutual coupling between neighboring elements populating an array, increasing element efficiency and enabling excellent wide angle performance. Further, they are operative to reduce the flow of surface waves along an array of elements at large elevation scan angles, thereby increasing the bandwidth and scan ability of the antenna array. 
     Referring particularly to  FIG. 1B , each wing  50  comprises a base  51  and an exposed portion  52  extending therefrom. A portion of wing  50  may be inserted into ground plane  12  and secured thereto (e.g., via a press-fit). Exposed portion  52  of wing  50  is defined by a height H, a width W and a thickness T ( FIG. 1C ). It has been determined that by varying width W over height H of wing  50 , the above-described performance increases are realized. More specifically, each exemplary wing  50  includes two generally vertical sidewalls  54  and a linear, and horizontal top end wall  55  defining a free end. End wall  55  is connected to vertical sidewalls  54  via rounded corner walls  58  having an exemplary radius R 1 . Wing  50  includes a side  53  ( FIG. 1C ) generally facing or opposing central axis A or conductive element  30  of radiating element  10 . Side  53  comprises a first portion or section  56  that is oriented at a first distance D 1  from central axis A of element  10 . A second portion or section  57  of side  51  is oriented at a second distance D 2 , greater than distance D 1 , from the centerline or central axis A of element  50 . In a particularly advantageous embodiments, second portion  57  that is positioned further from central axis A is located proximate the free end of wing  50  and/or directly adjacent or proximate second conductive disk  18 . In the illustrated embodiment, second portion  57  is defined by rounded corner wall  58 . While the exemplary embodiment shows two rounded corner walls  58 , other embodiments may comprise only a single rounded corner wall on a side of wing  50  opposing central axis A of element  10 . As shown in  FIG. 1C , wings  50  define, or are arranged in, a shared plane P oriented generally orthogonally with respect to ground plane  12 . Central axis A may lie within plane P. Wings  50  are arranged diametrically opposite one another with respect to central axis A, with plane P lying equidistant from the feed elements or transmission lines  20 A, 20 B, 20 C, 20 D. 
     Referring generally to  FIGS. 2-5 , several alternative wing shapes according to embodiments of the present disclosure are shown, each having a sidewall opposing central axis A that is also non-parallel therewith. Each of these embodiments will be described as having first and second portions  56 , 57  arranged at distances D 1  and D 2  from a central axis A of radiating element  10 , as described above with respect to  FIGS. 1A, 1B and 1C .  FIG. 2  illustrates a wing  200  in the form of a polygon, and more specifically, a generally rectangle shape having a notch  201  removed therefrom or formed therein to create second portion  57  arranged at a distance D 2  that is farther from central axis A than a distance D 1  associated with a first portion  56 . Notch  201  may be defined by respective perpendicular vertical and horizontal wall segments  202 , 203  or via a single diagonal wall segment  204 .  FIG. 3  illustrates another embodiment of a wing  300  according to the present disclosure having a shape defined by two generally vertical sides  301 , 302  connected via an arcuate or arcing end wall  303 . First portion  56  is defined along sidewall  302 , while second portion  57  is defined by end wall  303 .  FIG. 4  illustrates a wing  400  defining a generally elliptical profile with first and second portions  56 , 57  defined thereby.  FIG. 5  illustrates a wing  500  having a generally triangular profile defining first and second portions  56 , 57  along a wall  501  that generally opposes central axis A. 
       FIG. 6  illustrates a “tile” or subarray  600  consisting of a plurality of antenna elements  601 , each similar to element  10  of  FIGS. 1A-1C , arranged in a staggered fashion. Exemplary subarray  600  comprises a four-by-four arrangement, with each of the sixteen antenna elements  601  thereof generally taking on a “diamond” shape (see also  FIG. 1C ). Antenna elements  601  share a common ground plane  603 . As illustrated, each elemental antenna element  601  has its wings  602  oriented in-line with wings of adjacent antenna elements on horizontal lines or planes crossing subarray  600 , and all such lines on which the wings lie are mutually parallel. Moreover, each wing  602  of each antenna element  601  lies partially between adjacent antenna elements in the vertical direction in the illustrated orientation. That is, each wing  602  does not lie directly between adjacent ones of the antenna elements, but each wing  602  lies partially between adjacent ones of the elemental antennas of subarray  600 . A plurality of subarrays  600  may be interconnected in order to create antenna areas of any desired scale. 
     As described above, the shaped wings according to embodiments of the present disclosure have been shown to offer performance improvements over those utilized by the prior art. Referring to  FIGS. 7A and 7B , the axial ratio performance (AR) vs. normalized frequency of an antenna element according to the prior art at a 0 degree scan angle (Theta,  FIG. 7A ) and at a 75 degree scan angle ( FIG. 7B ) are shown. Axial ratio is considered herein as the ratio between the major and minor axes of the polarization ellipse. At broadside, axial ratios  71  of over 2 dB are present, while at the high scan angles illustrated in  FIG. 7B , axial ratios  72  of over 6 dB are present. Utilizing the improved wing element described above, and referring generally to  FIGS. 8A and 8B , axial ratios  81  near 0 dB are realized at broadside, while at high scan angles, axial ratios  82  of under 4 dB are achieved.  FIGS. 9A and 9B  illustrate return losses  91 , 92  associated with the broadside and 75 degree scan angles, respectively, of the prior art antenna element. As shown in  FIGS. 10A and 10B , improved broadside mismatch or return loss  101  and return loss  102  performance is realized via the shaped wing elements according to embodiments of the present disclosure. Broadside mismatch or return loss is a measure of the reflected power at each element while the array is steered to broadside, or perpendicular to the ground. 
     Embodiments of the present disclosure further include improved methods of manufacturing antenna elements, such as those set forth above with respect to  FIGS. 1A-10B . Traditional antenna element manufacturing methods often include several steps that require specialized equipment and/or skilled labor, including etching of copper, hand soldering, precision machining, and the like. Embodiments of the present disclosure provide an improved method of manufacturing antenna elements which reduces the need for specialized equipment and the amount of required manual and/or skilled labor. 
     These improvements are realized, in part, by implementing the use of bulk metals into the antenna element, avoiding the thin, printed metal (e.g. copper) layers that are typically used in antenna element construction. More specifically, referring to  FIGS. 1A-1C, 11 and 12 , an exemplary method of manufacturing antenna element  10  includes forming a stacked conductive disk assembly. The assembly includes first or lower disk  14  formed by a stamping operation performed on generally planar metal stock. Apertures may be formed in lower disk  14  (e.g., via stamping or drilling) at each feed location  14 A, 14 B, 24 C, 24 D for accepting four corresponding conductive posts or pins  124 A, 124 B, 124 C, 124 D, with each post  124  having a radially protruding nail-like head  134  and defining a portion of the transmission line conductors described above with respect to  FIGS. 1A-1C . During manufacturing, each post  124  may comprise a solder ring  126  added around an end thereof proximate head  134 . Posts  124  are inserted through corresponding apertures in lower disk  14  until their respective heads  134  abut disk  14 , and are attached thereto via a single heating operation (e.g., placed in a furnace), wherein a soldered connection secures each post  124  to lower disk  14 . This operation greatly reduces the assembly complexity of this unit in terms of reduction of specialized equipment and manual labor. 
     The stacked conductive disk assembly further includes second or upper disk  18  connected to disk  14  via a conductive element or rod  30 . In one embodiment, disk  18  is also formed from a stamping and/or machining operation performed on bulk material stock. Similarly, rod  30  may be manufactured from casting and/or machining operations. Rod  30  may be attached to disk  18  via, for example, soldering, press-fit, or other techniques. In one particularly advantageous embodiment, rod  30  defines two annular shoulders  30 ′, 30 ″ and comprises at least one hollow first end  30 ′″ configured to be inserted through an aperture formed (e.g., stamped or drilled) into disk  18 . Once inserted and disk  18  abuts shoulder  30 ′, end  30 ′″ of rod  30  may be flared or swaged, securing disk  18  thereto. This arrangement further reduces manufacturing complexity and costs. 
     The stacked disk assembly is completed by inserting a second end of rod  30  through an aperture formed (e.g., stamped or drilled) in disk  14  until making contact with shoulder  30 ″. In other embodiments, rod  30  may be formed in two segments, as described above, with one segment arranged between disk  14  and disk  18 , and another segment extending from an opposite side of disk  14 , through dielectric material  16 , to a ground plane or base plate  12 , for example. In this way, disk  18 , rod  30 , disk  14  and posts  124  may comprise a conductive assembly of as many as eight individually manufactured components. 
     Dielectric material  16  (e.g., a dielectric disk or puck) may also be formed from machining operations performed on bulk dielectric stock. Ground plane or base plate  12  may be formed from material stock that has been machined to create apertures  17  therethrough. During assembly of element  10 , each post  124  of the stacked disk conductive assembly is inserted through a corresponding aperture formed in dielectric material  16 , as well as apertures  17  formed in ground plane  16 . Posts  124  may be attached or electrically connected to a printed wire board (PWB)  128  of the antenna element via connectors, embodied herein as leaf pins  127  soldered to PWB  128 . Leaf pins  127  define elastic conductive elements and are configured to permit a degree of axial and radial misalignment of posts  124 , while still ensuring a reliable electrical connection and maintaining RF performance. These connectors also limit stresses placed on the solder joints over a large thermal range, as well as insure proper electrical connection of posts  124  throughout a range of tolerances of all of the components. More specifically, leaf pins  127  each define a metal surface mount component which may be soldered directly to PWB  128 . Each leaf pin  127  consists of a wide base for added solder surface area as well as stability, and a hollow post that protrudes from the center away from PWB  128 . The hollow post may be slotted, and subsequently compressed from its perimeter in order to reduce the inside diameter of the post. This reduced inside diameter generates an interference fit with each post  124  over a wide range of tolerances. The slot allows leaf pin  127  to act as a spring around post  124  so that post  124  may be easily be inserted or removed. The combination of the slots and the compressed portion allow leaf pin  127  to take up axial misalignment due to tolerance stackups and temperature deltas as well as minor radial misalignments. Teflon sleeves  125  may be provided within apertures  17  and arranged about leaf pins  127  for maintaining correct impedance through ground plane  16 . Sleeves  125  define respective openings configured to receive each post  124 . 
     As described above with respect to  FIG. 1B , each wing  50  of an antenna element  10  may be secured to ground plane or base plate  16  via a press-fit connection. In one embodiment, in addition to base or flange  51 , each wing  50  may further comprise two post-like protrusions  59  extending therefrom. Protrusions  59  are configured to be inserted (e.g. press-fit) into two corresponding apertures formed in ground plane  16 , ensuring accurate location of the wings as well as simplifying assembly operations without the need for additional materials (adhesives, solder, etc.) or process steps. This configuration further improves positional tolerance of the wing location and the wing&#39;s angular orientation. 
     While the foregoing invention has been described with reference to the above-described embodiment, various modifications and changes can be made without departing from the spirit of the invention. Accordingly, all such modifications and changes are considered to be within the scope of the appended claims. Accordingly, the specification and the 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 not of limitation, specific embodiments in which the subject matter may be practiced. The embodiments illustrated are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments may be utilized and derived therefrom, such that structural and logical substitutions and changes may be 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. 
     Such embodiments of the inventive subject matter may be referred to herein, individually and/or collectively, by the term “invention” merely for convenience and without intending to voluntarily limit the scope of this application to any single invention or inventive concept if more than one is in fact disclosed. 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 of 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.