Abstract
An embodiment of the invention is directed to a method for manufacturing a radiator structure for a conical helical antenna that includes: (a) processing a piece of metal so as to produce a first metal structure with conical exterior and interior surfaces, and (b) processing the first metal structure to remove material between the conical exterior and interior surfaces to yield a radiator structure with a conical helical shaped conductor that can be combined with a ground plane to produce a conical helical antenna. In one embodiment, the radiator structure includes a matching structure and a cap with the conical helical conductor, matching structure, and cap being a single piece of metal.
Claims
1. A method for making a radiator structure for a helical antenna, comprising: providing a piece of metal stock; processing the piece of metal stock to produce a processed piece of metal with a frusto-conical exterior side surface and a frusto-conical interior side surface with the frusto-conical exterior and interior side surfaces defining a frusto-conical side wall, the processed piece of metal having a radiator portion and a non-radiator portion; and removing metal located between the frusto-conical exterior side surface and the frusto-conical interior side surface and associated with the non-radiator portion to produce a self-supporting conical helix having an upper lateral edge and a lower lateral edge that is separated from the upper lateral edge; the step of removing includes first removing metal located between the frusto-conical interior side surface and the frusto-conical exterior side surface and associated with the non-radiator portion to define a portion of the upper lateral edge of the conical helix and a portion of the lower lateral edge of the conical helix; the portion of the upper lateral edge of the conical helix extending partially from one of the frusto-conical exterior side surface and the frusto-conical interior side surface to the other of the frusto-conical exterior side surface and the frusto-conical interior side surface; the portion of the lower lateral edge of the conical helix extending partially from one of the frusto-conical exterior side surface and the frusto-conical interior side surface to the other of the frusto-conical exterior side surface and the frusto-conical interior side surface; and the step of removing includes, following the step of first removing, second removing metal associated with the non-radiator portion to define a series of helical voids with one helical void separated from an immediately adjacent helical void by a helical strut that is associated with the non-radiator portion.
2. A method, as claimed in claim 1, wherein: the step of second removing includes removing metal extending from a groove base surface to one of the frusto-conical interior side surface and the frusto-conical exterior side surface.
3. A method, as claimed in claim 1, wherein: the step of second removing includes removing metal extending from the frusto-conical interior side surface to the frusto-conical exterior side surface.
4. A method, as claimed in claim 1, wherein: the step of removing includes, following the step of second removing, third removing each helical strut associated with the non-radiator portion.
5. A method, as claimed in claim 1, wherein: the frusto-conical side wall is a side wall of one of: (a) a frustum of a right circular cone, (b) a frustum of an oblique circular cone, (c) a frustum of a right elliptical cone, and (d) a frustum of an oblique elliptical cone.
6. A method, as claimed in claim 1, further comprising: removing metal from the frusto-conical exterior side surface to the frusto-conical interior side surface and associated with the non-radiator portion to produce an impedance matching structure.
7. A method, as claimed in claim 6, wherein: the conical helix and the matching structure are a single piece of metal.
8. A method for making a radiator structure for a helical antenna, comprising: providing a piece of metal stock; processing the piece of metal stock to produce a processed piece of metal with a frusto-conical exterior side surface and a frusto-conical interior side surface with the frusto-conical exterior and interior side surfaces defining a frusto-conical side wall, the processed piece of metal having a radiator portion and a non-radiator portion; and removing metal located between the frusto-conical exterior side surface and the frusto-conical interior side surface and associated with the non-radiator portion to produce a self-supporting conical helix having an upper lateral edge and a lower lateral edge that is separated from the upper lateral edge; the step of removing includes first removing metal located between the frusto-conical interior side surface and the frusto-conical exterior side surface and associated with the non-radiator portion to define a portion of the upper lateral edge of the conical helix and a portion of the lower lateral edge of the conical helix; the portion of the upper lateral edge of the conical helix extending partially from one of the frusto-conical exterior side surface and the frusto-conical interior side surface to the other of the frusto-conical exterior side surface and the frusto-conical interior side surface; the portion of the lower lateral edge of the conical helix extending partially from one of the frusto-conical exterior side surface and the frusto-conical interior side surface to the other of the frusto-conical exterior side surface and the frusto-conical interior side surface; and the step of first removing metal establishes a first helical groove in the frusto-conical side wall and a second helical groove in the frusto-conical side wall that is separated from the first helical groove; wherein the first and second helical grooves each have a first groove side surface, a second groove side surface, and a groove base surface located between the first and second groove side surfaces; the step of removing includes, following the step of first removing, second removing metal associated with the non-radiator portion to define a series of helical voids with one helical void separated from an immediately adjacent helical void by a helical strut that is associated with the non-radiator portion.
9. A method, as claimed in claim 8, wherein: the step of second removing includes removing metal extending from the groove base surface of each of the first and second grooves to one of the frusto-conical interior side surface and the frusto-conical exterior side surface.
10. A method, as claimed in claim 8, wherein: the step of second removing includes removing metal extending from the frusto-conical interior side surface to the frusto-conical exterior side surface.
11. A method, as claimed in claim 8, wherein: the step of removing includes, following the step of second removing, third removing each helical strut associated with the non-radiator portion.
12. A method for making a radiator structure for a helical antenna, comprising: providing a piece of metal having a frusto-conical interior side surface and a frusto-conical exterior side surface, the frusto-conical interior and exterior side surfaces defining a frusto-conical side wall, the piece of metal having a radiator portion and a non-radiator portion; and removing material between the frusto-conical exterior side surface and the frusto-conical interior side surface and associated with the non-radiator portion to produce a self-supporting conical helix having an upper lateral edge and a lower lateral edge that is separated from the upper lateral edge; the step of removing includes first removing metal located between the frusto-conical interior side surface and the frusto-conical exterior side surface and associated with the non-radiator portion to define a portion of the upper lateral edge of the conical helix and a portion of the lower lateral edge of the conical helix; the portion of the upper lateral edge of the conical helix extending partially from one of the frusto-conical exterior side surface and the frusto-conical interior side surface to the other of the frusto-conical exterior side surface and the frusto-conical interior side surface; the portion of the lower lateral edge of the conical helix extending partially from one of the frusto-conical exterior side surface and the frusto-conical interior side surface to the other of the frusto-conical exterior side surface and the frusto-conical interior side surface; the step of removing includes, following the step of first removing, second removing metal associated with the non-radiator portion to define a series of helical voids with one helical void separated from an immediately adjacent helical void by a helical strut that is associated with the non-radiator portion.
13. A method, as claimed in claim 12, wherein: the step of removing includes, following the step of second removing, third removing a helical strut associated with the non-radiator portion.
14. A method for making a radiator structure for a helical antenna, comprising: providing a piece of metal having a frusto-conical interior side surface and a frusto-conical exterior side surface, the frusto-conical interior and exterior side surfaces defining a frusto-conical side wall, the piece of metal having a radiator portion and a non-radiator portion; and removing material between the frusto-conical exterior side surface and the frusto-conical interior side surface and associated with the non-radiator portion to produce, in the radiator portion, a self-supporting conical helix having an upper lateral edge and a lower lateral edge that is separated from the upper lateral edge; the step of removing includes removing metal associated with the non-radiator portion to define, in the non-radiator portion, a series of helical voids with one helical void separated from an immediately adjacent helical void by a helical strut that is associated with the non-radiator portion.
15. A method, as claimed in claim 14, wherein: the step of removing includes removing a helical strut associated with the non-radiator portion.
16. A method, as claimed in claim 14, wherein: the step of providing includes providing a frusto-conical interior top surface that engages the frusto-conical interior side surface.
17. A method, as claimed in claim 16, wherein: the step of providing includes providing a stub extending away from the frusto-conical interior top surface.
18. A method for making a radiator structure for a helical antenna, comprising: providing a piece of metal having a frusto-conical interior side surface and a frusto-conical exterior side surface, the frusto-conical interior and exterior side surfaces defining a frusto-conical side wall, the piece of metal having a radiator portion and a non-radiator portion; and removing material between the frusto-conical exterior side surface and the frusto-conical interior side surface and associated with the non-radiator portion to produce a self-supporting conical helix having an upper lateral edge and a lower lateral edge that is separated from the upper lateral edge; the step of providing includes providing a frusto-conical interior top surface that engages the frusto-conical interior side surface; the step of providing includes providing a stub extending away from the frusto-conical interior top surface; removing a portion of the stub to produce a frusto-conical exterior top surface; the frusto-conical interior and exterior top surfaces defining a frusto-conical top.
19. A method, as claimed in claim 18, wherein: the conical helix and the frusto-conical top are a single piece of metal.
20. A method for making a radiator structure for a helical antenna, comprising: providing a monolithic metal structure having a frusto-conical interior side surface and a frusto-conical exterior side surface that define a frusto-conical side wall that encloses a space and defines intermittent helical voids, the monolithic metal structure having a radiator portion and a non-radiator portion, the intermittent helical voids defining a helical void path that is associated with the non-radiator portion, the intermittent helical voids also defining a portion of an upper lateral edge and a portion of a lower lateral edge of a conical helix that is associated with the radiator portion, the helical void path is located between first and second portions of the conical helix associated with the radiator portion; the intermittent helical voids comprising a first helical void and a second helical void separated from the first helical void by a helical strut that extends from the first portion of the conical helix to the second portion of the conical helix and is associated with the non-radiator portion; and removing metal associated with the helical strut to produce the conical helix.
21. A method, as claimed in claim 20, wherein: the step of providing comprises processing a piece of metal to produce the frusto-conical exterior side surface.
22. A method, as claimed in claim 20, wherein: the step of providing comprises processing a piece of metal to produce the frusto-conical interior side surface.
23. A method, as claimed in claim 20, wherein: the step of providing comprises processing a piece of metal to define the intermittent helical voids.
24. A method, as claimed in claim 20, wherein: the conical helix is a self-supporting conical helix.
25. A method, as claimed in claim 20, wherein: the step of removing includes cutting metal associated with or adjacent to the helical strut.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 illustrates an embodiment of a helical antenna that includes a conical helical conductor modeled on a right circular cone, a ground plane, and a mounting structure;
(2) FIG. 2 illustrates a right circular cone and a frustum of a right circular cone;
(3) FIGS. 3-9 illustrate an embodiment of a method for making a radiator structure for a helical antenna that includes a conical helical conductor modeled on a right circular cone;
(4) FIG. 10 illustrates a matching structure that is part of the radiator structure produced using the method illustrated in FIGS. 3-9;
(5) FIG. 11 illustrates an oblique elliptical cone and a frustum of an oblique elliptical cone;
(6) FIGS. 12-18 illustrate an embodiment of a method for making a radiator structure for a helical antenna that includes a conical helical conductor modeled on an oblique elliptical cone.
DETAILED DESCRIPTION
(7) The invention is directed to a method of manufacturing a radiator structure that includes a helically shaped conductor which is suitable for use with a helical antenna. The resulting radiator structure is self-supporting and substantially avoids the need to consider springback in the design of the manufacturing method. This method of manufacturing is capable of being employed to manufacture radiator structures with helically shaped conductors suitable for use in an array of tilted conical helical antennas as described in copending U.S. patent application Ser. No. 14/572,734, which is incorporate herein by reference and in its entirety.
(8) With reference to FIG. 1, an exemplary helical antenna 20 (hereinafter antenna 20) is described. Generally, the antenna 20 comprises a radiator structure 22, a ground plane 24, and a mounting structure 26 that supports the radiator structure 22 in a desired position relative to the ground plane 24. The radiator structure 22 comprises a helically shaped conductor 28, a matching structure 30 associated one end of the conductor 28, and a cap 32 associated with the other end of the conductor 28. The helically shaped conductor 28 is the portion of the radiator structure 22 that is primarily responsible for the transmission and/or reception of electromagnetic signals by the antenna 20. The matching structure 30 provides the antenna 20 with a desired or acceptable VSWR. The cap 32 prevents the reflection of a signal being processed by the antenna 20 from adversely affecting the polarization of the antenna.
(9) The helically shaped conductor 28 is modeled on a frustum of a right circular cone. With reference to FIG. 2, a frustum of a right circular cone 40 is illustrated. The frustum of a right circular cone 40 is defined by a planar base surface 42, a lateral or side surface 44, and a planar top surface 46 that is parallel to the planar base surface 42. The perimeter of the planar base surface 42 is an ellipse and, in this example, a circle of radius r.sub.b with a base center 48. The perimeter of the planar top surface 46 is also an ellipse and, in this example, a circle of radius r.sub.t with a top center 50. The lateral surface 44 is defined as the locus of all straight line segments connecting the perimeter of the base surface 42 to the perimeter of the top surface 46 that, if extended, would pass through an imaginary apex 52. The frustum of a cone 40 has a rotational axis of symmetry 54 (hereinafter axis 54) that passes through the imaginary apex 52, the base center 48 of the circular planar base surface 42, and the top center 50 of the circular planar top surface 46. In FIG. 2, the axis 54 is perpendicular or at a right angle to the planar base surface 42. Since the planar base surface 42 is circular and the axis 54 is disposed at a right angel to the base surface 42, the frustum of a cone 40 is characterized as a frustum of a right circular cone. The frustum of a cone has a height h that is the perpendicular distance between the planar base surface 42 and the planar top surface 46.
(10) The embodiment of the method for manufacturing a radiator structure suitable for use with a helical antenna is described with respect to the manufacture of the radiator structure 22. Generally, the method involves: (a) providing a metal structure with a frusto-conical interior side surface and a frusto-conical exterior side surface that together form a frusto-conical wall that is modeled on the lateral or side surface of a frustum of a right circular cone and (b) removing metal from between the frusto-conical interior and exterior side surfaces to produce the helically shaped conductor 28.
(11) With reference to FIG. 3, the step of providing of a metal structure with a frusto-conical side wall is accomplished in several steps. Initially, a solid, round aluminum bar 60 (e.g., 6061-T6 or 6061-T651) is obtained. The dimensions of the bar 60 are sufficient to accommodate the radiator structure 22. It should be appreciated that other metal structures with different shapes and made of different materials can be utilized, provided the metal structure is of a shape that accommodates the dimensions of the radiator structure 22.
(12) With reference to FIG. 4, the bar 60 is machined to produce a first metal structure 62 comprised of a solid frustum of a right circular cone 64 and a solid cylinder 66. This machining is accomplished with a lathe or other suitable metal machining or milling machine. The solid frustum of a cone 64 provides the material for realizing the helically shaped conductor 28, the matching structure 30, and a portion of the cap 32. Further, the solid frustum of a cone 64 defines a frusto-conical exterior side surface 68. The solid cylinder 64 provides material for realizing a portion of the cap 32. The solid cylinder 64 also provides a structure that can be engaged by a collet or chuck of a milling machine that is used in the subsequent removal of additional metal.
(13) With reference to FIG. 5, the first metal structure 62 is machined to remove material associated with the solid frustum of a cone 64 and thereby realize a frusto-conical interior side surface 70. The frusto-conical exterior side surface 68 and the frusto-conical interior side surface 70 define a frusto-conical side wall 72 that encloses a space 74. The wall 72, in the illustrated embodiment, has a nominal wall thickness of 0.060 (0.152 cm). Additionally, the removal of the material to define the frusto-conical interior side surface 70 also defines a frusto-conical interior top surface 76. The machining is accomplished with a five-axis milling machine or other suitable milling machine with a collet or chuck that engages the solid cylinder 66. At this point, the bar 60 has been transformed into a second metal structure 78 comprised of a frusto-conical cup-like structure 80 and the solid cylinder 66. It is useful to conceptualize the second metal structure 78 at this point as having a radiator portion (i.e., the metal that will be the radiator structure 22) and a non-radiator portion (i.e., the metal that needs to be removed to realize the radiator structure 22). In this regard, a substantial portion of the frusto-conical cup-like structure 80 provides the material for realizing the helically shaped conductor 28, the matching structure 30, and a portion of the cap 32 and a portion of the solid cylinder 66 provides the material for realizing a portion of the cap 32. The frusto-conical cup-like structure 80 and the solid cylinder 28 also embody, at this point, the metal that needs to be removed to realize the radiator structure 22.
(14) With reference to FIG. 6, the second metal structure 78 is machined to remove metal between the frusto-conical exterior side surface 68 and the frusto-conical interior side surface 70 to produce first and second helical grooves 90A, 90B in the frusto-conical cup-like structure 80. The first helical groove 90A partially defines a lower lateral edge 29A (see FIG. 1) of the helically shaped conductor 28. The second helical groove 90B partially defines the upper lateral edge 29B (see FIG. 1) of the helically shaped conductor 28. The helical grooves 90A, 90B only partially define the lateral edges 29A, 29B of the helically shaped conductor 28 because the grooves do not extend the entire way through the frusto-conical wall 72. The machining is accomplished with a five-axis milling machine or other suitable milling machine with a collet or chuck that engaged the solid cylinder 66. At this point, the bar 60 has been transformed into a third metal structure 92 comprised of a grooved, frusto-conical cup-like structure 94 and the solid cylinder 66. Each of the first and second helical grooves 90A, 90B has a groove base 96 that is located between first and second groove edges 98A, 98B. The first groove edge 98A of the first helical groove 90A partially defines the lower lateral edge 29A of the helically shaped conductor 28. The first groove edge 98A of the second helical groove 90B partially define the upper later edge 29B of the helically shaped conductor 28. In the illustrated embodiment, the distance between the groove base 96 of each of the first and second helical grooves 90A, 90B and the frusto-conical interior side surface 70 is 0.005 (0.013 cm). This thickness in combination with other properties of the aluminum has been found to provide sufficient integrity for additional machining of the third metal structure 92.
(15) With reference to FIG. 7, the third metal structure 92 is machined to remove metal so as to form a series of intermittent helical voids 110 with consecutive helical voids separated from one another by helical struts 112, each of which has a width of approximately 0.06-0.09 (0.15-0.23 cm). In this regard, a single helical void is established by removing metal: (1) between the groove base 96 of the first helical groove 90A and the frusto-conical interior side surface 70 over an angular extent to establish a substantial angular portion of the lower lateral edge 29A, (2) between the groove base 96 of the second helical groove 90B and the frusto-conical interior side surface 70 over the angular extent to establish a substantial angular portion of the upper lateral edge 29B, (3) between first corresponding ends of the portions of lower and upper lateral edges established in the removals (1) and (2), and (4) between second corresponding ends of the portions of the lower and upper lateral edges established in the removals (1) and (2). These removals of metal are capable of being done in a number of different sequences. The machining is accomplished with a five-axis milling machine or other suitable milling machine with a collet or chuck that engaged the solid cylinder 66. At this point, the bar 60 has been transformed into a fourth metal structure 114 comprised of a frusto-conical cup-like structure that defines a series of intermittent helical voids 116 and the solid cylinder 66. Further, the graduated or multi-step removal of material between the frusto-conical exterior side surface 68 and the frusto-conical interior side surface 70 has facilitated the use of a milling machine to remove the metal. While more material could be potentially be removed with a milling machine, the likelihood of the removal of additional material being complicated due to vibrational issues and/or irreparable/unacceptable damage being imparted to the metal forming the helically shaped conductor substantially increases. The remaining metal between the frusto-conical exterior side surface 68 and the frusto-conical interior side surface 70 provides the material for realizing the helically shaped conductor 28, the matching structure 30 and a portion of the cap 32. The remaining metal between the frusto-conical exterior side surface 68 and the frusto-conical interior side surface 70 also defines, to a lesser extent, metal that still needs to be removed to realize the helically shaped conductor 28, the matching structure 30, and a portion of the cap 32.
(16) With reference to FIG. 8, the fourth metal structure 114 is processed to remove the struts 112. Due to the first and second helical grooves 90A, 90B extending across the width of each of the struts 112 and the relatively short width of each of the struts 112, removal of the struts can be readily accomplished with a hand tool, such as an X-Acto blade. Other hand tools can be employed in the removal of the struts 112, including powered hand tools that allow the user to exercise sufficient control to avoid the noted vibrational and/or damage issues. At this point, the bar 60 has been transformed into a fifth metal structure 120 comprised of the helically shaped conductor 28 and the solid cylinder 66.
(17) It should be appreciated that the sequence of steps taken to transform the bar 60 into the fourth metal structure 114 can be altered. For example, the frusto-conical interior side surface 70 and the frusto-conical interior top surface 76 can be fabricated before the frusto-conical exterior side surface 68. Additionally, in certain cases, different steps may be used to achieve the fourth metal structure 114 or a similar structure with struts that can be readily removed in a manner that avoids the noted vibrational and/or damage issues. For example, the second metal structure 78 may be susceptible to being machined in a single step to achieve the metal structure 114 or a metal structure with intermittent helical voids that are separated from one another by helical struts that are susceptible to being removed in a manner that avoids the noted vibrational and/or damage issues.
(18) With reference to FIG. 9, the fifth metal structure 120 is processed so as to remove a substantial portion of, but not all of, the solid cylinder 66 to define a frusto-conical exterior top surface 122 that is substantially parallel to the frusto-conical interior top surface 76. The frusto-conical interior and exterior top surfaces 76, 122, in turn, substantially define the cap 32. It should be appreciate that the helically shaped conductor 28 and the cap 32 are a single piece of metal. As such, there is no need for a connecting structure extending between the helically shaped conductor 28 and the cap 32 that potentially could be a source of an undesirable passive intermode. It should be appreciated that the substantial portion of the solid cylinder 66 could be removed at any point in the method of manufacturing at which the solid cylinder 66 is no longer needed for engaging a collet or chuck of a milling machine or for any other purpose. For example, the substantial portion of the solid cylinder 66 could be removed before the struts 112 are removed. Further, while the cap 32 has a circular shape, the cap need not have such a shape to be effective in preventing an undesirable reflection that could adversely affect the polarization of the signals being processed by the helical antenna. The cap 32 need only be of sufficient shape and extent to substantially inhibit this undesired reflection. Consequently, if in removing a substantial portion of the solid cylinder 66 a non-circular cap with a substantially smaller extent than the last turn of the helically shaped conductor 28 is produced, the cap may nonetheless be sufficient for preventing the undesired reflection. Additionally, if a particular radiator structure does not require a cap or it is desirable to have a separate cap with a connective structure that extends between the cap and the helically shaped conductor, the entire solid cylinder 66 and any metal extending from the frusto-conical interior top surface 76 to the solid cylinder 66 can be removed.
(19) With reference to FIG. 10, the radiator structure 22 illustrated in FIG. 9 includes the matching structure 30 that provides the antenna 20 with a desired or acceptable VSWR. The matching structure 30 is established or the material for the later establishment of the matching structure 30 is present in the third metal structure 92. Regardless of whether the matching structure 30 is established in the third metal structure 92 or created from metal present in the third metal structure 92 at a later time, the matching structure 30 and the helically shaped conductor 28 are a single piece of metal. As such, there is no need for a connecting structure extending between the helically shaped conductor 28 and the matching structure 30 that potentially could be a source of an undesirable passive intermode. It should be appreciated that in some helical antennas a matching structure may not be needed. For such helical antennas, the manufacturing method can be modified to forego the making of the matching structure 30.
(20) It should be appreciated that the method is also adaptable to the manufacture of a radiator structures that are modeled on an oblique circular cone, a right elliptical cone, an oblique elliptical cone, and a cylinder. In this regard and with reference to FIG. 18, the manufacture of a radiator structure 200 modeled on an oblique elliptical cone is also described. The radiator structure 200 comprises a helically shaped conductor 202, a matching structure 204 associated one end of the conductor 28, and a cap 206 associated with the other end of the conductor 28. The helically shaped conductor 202 is the portion of the radiator structure 200 that is primarily responsible for the transmission and/or reception of electromagnetic signals by an antenna that utilizes the radiator structure 200. The matching structure 204 provides an antenna that incorporates the radiator structure 200 with a desired or acceptable VSWR. The cap 206 prevents the reflection of a signal being processed by an antenna that employs the radiator structure 200 from adversely affecting the polarization of the signal.
(21) The helically shaped conductor 202 is modeled on a frustum of an oblique elliptical cone. With reference to FIG. 11, a frustum of an oblique elliptical cone 220 is illustrated. The frustum of an oblique elliptical cone 220 is defined by a planar base surface 222, a lateral or side surface 224, and a planar top surface 226 that is parallel to the planar base surface 42. The perimeter of the planar base surface 222 is an ellipse with an eccentricity that is greater than zero (i.e., not a circle). The perimeter of the planar top surface 46 is also an ellipse with an eccentricity that is greater than zero. The elliptical shape associated with the planar base surface 222 has a major axis 228 and a minor axis 230. The elliptical shape associated with the planar top surface 226 has a major axis 232 and a minor axis 234. The major axes 228, 232 of the elliptical shapes of the planar base and top surfaces 222, 226 are substantially parallel to one another. Further, the minor axes 230, 234 of the elliptical shapes associated with the planar base and top surfaces 222, 226 are substantially parallel to one another. The lateral surface 224 is defined as the locus of all straight line segments connecting the perimeter of the base surface 222 to the perimeter of the top surface 226 that, if extended, would pass through an imaginary apex 236. A line 238 can be defined that passes through the imaginary apex 236, a first intersection point 240 of the major axis 232 and the minor axis 234 of the planar top surface 226, and a second intersection point 242 of the major axis 228 and minor axis 230 of the planar base surface 222. The line 238 is not perpendicular to the elliptically shaped planar base surface 222. Since the line 238 is not at a right angle to the planar base surface 222 and the planar base surface has an elliptical shape, the frustum of a cone 220 is characterized as a frustum of an oblique elliptical cone. The frustum of an oblique elliptical cone 220 has a height h that is the perpendicular distance between the planar base surface 222 and the planar top surface 226.
(22) The embodiment of the method for manufacturing a radiator structure suitable for use with a helical antenna is described with respect to the manufacture the radiator structure 200. Generally, the method involves: (a) providing a metal structure with a frusto-conical interior side surface and a frusto-conical exterior side surface that together form a frusto-conical wall that is modeled on the lateral or side surface of a frustum of a right circular cone and (b) removing metal from between the frusto-conical interior and exterior side surfaces to produce the helically shaped conductor 200.
(23) As with the method described in connection with FIGS. 3-10, the step of providing of a metal structure with a frusto-conical side wall is accomplished in several steps. In this regard, the steps of obtaining a round aluminum bar or other electrically conductive stock of sufficient dimensions to accommodate the radiator structure and machining the bar to produce the first metal structure 62 comprised of the solid frustum of a right circular cone 64 and the solid cylinder 66 are the same as described with respect to the method of producing the helically shaped conductor 28 that is modeled on a frustum of a right circular cone. This machining is accomplished with a lathe or other suitable metal machining or milling machine. The solid frustum of a right circular cone 64 provides the material for realizing the helically shaped conductor 202 that is modeled on an oblique elliptical cone, the matching structure 204, and the cap 206. Further, the solid frustum of a right circular cone 64 defines a frusto-conical exterior side surface 68. The solid cylinder 64 provides a structure that can be engaged by a collet or chuck of a milling machine that is used in the subsequent removal of additional metal.
(24) With reference to FIG. 12, the first metal structure 62 is machined to remove material associated with the solid frustum of a cone 64 and thereby realize a frusto-conical interior side surface 260. The frusto-conical exterior side surface 68 and the frusto-conical interior side surface 260 define a frusto-conical side wall 262 that encloses a space 264. The wall 262, in the illustrated embodiment, has a nominal wall thickness of 0.060 (0.152 cm). Additionally, the removal of the material to define the frusto-conical interior side surface 260 also defines a first frusto-conical interior top surface 266 (i.e., a top surface of a right circular cone). The machining is accomplished with a five-axis milling machine or other suitable milling machine with a collet or chuck that engages the solid cylinder 66. At this point, the bar 60 has been transformed into a second metal structure 270 comprised of the solid cylinder 66, a first frusto-conical cup-like structure 272, and a solid frustum of a right circular cone 274 that extends between the cup-like structure and the cylinder. The frusto-conical cup-like structure 272 provides material for realizing the helically shaped conductor 202 and the matching structure 204. The solid frustum of a right circular cone 274 provides material for producing the helically the helically shaped conductor 202 and the cap 206.
(25) With reference to FIG. 13, the second metal structure 270 is machined to produce a second frusto-conical interior top surface 280 (i.e., a top surface of an oblique elliptical cone) that supersedes the first frusto-conical interior top surface 266. In addition the machining extends the frusto-conical interior side surface 260. It should be appreciated that the second frusto-conical interior top surface 280 is elliptical. The machining is accomplished with a five-axis milling machine or other suitable milling machine with a collet or chuck that engages the solid cylinder 66. At this point, the bar 60 has been transformed into a third metal structure 282 comprised of the solid cylinder 66, a partly frusto-conical cup-like structure 284, and a solid section of a frustum of a right circular cone 286 that extends between the cup-like structure and the cylinder. A substantial portion of the partly frusto-conical cup-like structure 284 provides material for realizing the helically shaped conductor 202, the matching structure 204, and a portion of the cap 206. The solid section of a frustum of a right circular cone 286 provides material for producing a portion of the cap 206.
(26) With reference to FIG. 14, the metal structure 280 is machined to remove a portion of the frusto-conical side wall 262 to define a new base edge 290 for the frusto-conical side wall 262. The machining is accomplished with a five-axis milling machine or other suitable milling machine with a collet or chuck that engages the solid cylinder 66. The new base edge 290 lies in a plane that is substantially parallel to the frusto-conical interior top surface 280. Further, the new base edge 290 has an elliptical shape that has major and minor axes that are substantially parallel to the major and minor axes of the elliptical shape associated with the frusto-conical interior top surface 280. At this point, the bar 60 has been transformed into a fourth metal structure 294 comprised of the cylinder 66, a frusto-conical cup-like structure 296 that is modeled on an oblique elliptical cone, and the solid section of a frustum of a right circular cone 286. It is useful to conceptualize the second metal structure 294 at this point as having a radiator portion (i.e., the metal that will be the radiator structure 200) and a non-radiator portion (i.e., the metal that needs to be removed to realize the radiator structure 200). In this regard, a substantial portion of the frusto-conical cup-like structure 296 provides material for realizing the helically shaped conductor 202, the matching structure 204, and a portion of the cap 206 and a portion of the solid section of a frustum of a right circular cone 286 provides material for producing a portion of the cap 206. The frusto-conical cup-like structure 296, the solid section of a frustum of a right circular cone 286, and the solid cylinder 66 also embodies the metal that needs to be removed to realize the radiator 200.
(27) With reference to FIG. 15, the metal structure 294 is machined is to remove metal between the frusto-conical exterior side surface 68 and the frusto-conical interior side surface 260 to produce first and second helical grooves 300A, 300B in the frusto-conical cup-like structure 296. The first helical groove 300A partially defines a lower lateral edge 203A (see FIG. 18) of the helically shaped conductor 202. The second helical groove 300B partially defines the upper lateral edge 203B (see FIG. 18) of the helically shaped conductor 202. The helical grooves 300A, 300B only partially define the lateral edges 203A, 203B of the helically shaped conductor 202 because the grooves do not extend the entire way through the frusto-conical wall 262. The machining is accomplished with a five-axis milling machine or other suitable milling machine with a collet or chuck that engaged the solid cylinder 66. At this point, the bar 60 has been transformed into a fifth metal structure 302 comprised of the cylinder 66, a grooved, frusto-conical cup-like structure 304, and the solid section of a frustum of a right circular cone 286. Each of the first and second helical grooves 300A, 300B has a groove base 306 that is located between first and second groove edges 308A, 308B. The first groove edge 308A of the first helical groove 300A partially defines the lower lateral edge 203A of the helically shaped conductor 202. The first groove edge 308A of the second helical groove 300B partially define the upper later edge 203B of the helically shaped conductor 202. In the illustrated embodiment, the distance between the groove base 306 of each of the first and second helical grooves 300A, 300B and the frusto-conical interior side surface 260 is 0.005 (0.013 cm). This thickness in combination with other properties of the aluminum has been found to provide sufficient integrity for additional machining of the metal structure 302.
(28) With reference to FIG. 16, the fifth metal structure 302 is machined to remove metal so as to form a series of intermittent helical voids 320 with consecutive helical voids separated from one another by helical struts 322, each of which has a width of approximately 0.06-0.09 (0.15-0.23 cm). In this regard, a single helical void is established by removing metal: (1) between the groove base 306 of the first helical groove 300A and the frusto-conical interior side surface 260 over an angular extent to establish a substantial angular portion of the lower lateral edge 203A, (2) between the groove base 306 of the second helical groove 300B and the frusto-conical interior side surface 260 over the angular extent to establish a substantial angular portion of the upper lateral edge 203B, (3) between first corresponding ends of the portions of lower and upper lateral edges established in the removals (1) and (2), and (4) between second corresponding ends of the portions of the lower and upper lateral edges established in the removals (1) and (2). These removals of metal are capable of being done in a number of different sequences. The machining is accomplished with a five-axis milling machine or other suitable milling machine with a collet or chuck that engaged the solid cylinder 66. At this point, the bar 60 has been transformed into a sixth metal structure 330 comprised of the solid cylinder 66, a frusto-conical cup-like structure that defines a series of intermittent helical voids 332, and the solid section of a frustum of a right circular cone 286. Further, the graduated or multi-step removal of material between the frusto-conical exterior side surface 68 and the frusto-conical interior side surface 260 has facilitated the use of a milling machine to remove the metal. While more material could be potentially be removed with a milling machine, the likelihood of the removal of additional material being complicated due to vibrational issues or irreparable/unacceptable damage being imparted to the metal forming the helically shaped conductor substantially increases. The remaining metal between the frusto-conical exterior side surface 68 and the frusto-conical interior side surface 260 provides the material for realizing the helically shaped conductor 202 and the matching structure 204. The solid section of a frustum of a right circular cone 286 provides material for producing the cap 206. The remaining metal between the frusto-conical exterior side surface 68 and the frusto-conical interior side surface 260 also defines, to a lesser extent, metal that still needs to be removed to realize the helically shaped conductor 28 and the matching structure 30.
(29) With reference to FIG. 17, the metal structure 330 is processed to remove the struts 322. Due to the first and second helical grooves 300A, 300B extending across the width of each of the struts 322 and the relatively short width of each of the struts 322, removal of the struts can be readily accomplished with a hand tool, such as an X-Acto blade. Other hand tools can be employed in the removal of the struts 322, including powered hand tools that allow the user to exercise sufficient control to avoid the noted vibrational and/or damage issues. At this point, the bar 60 has been transformed into a metal structure 340 comprised of the solid cylinder 66, the helically shaped conductor 202, and the solid section of a frustum of a right circular cone 286.
(30) It should be appreciated that the sequence of steps taken to transform the bar 60 into the sixth metal structure 330 can be altered. For example, the first metal structure 62 could be processed to realize a solid with a planar elliptical base surface that, when a frusto-conical interior side surface is later created, provides the material that defines the base edge 290. Additionally, in certain cases, different steps may be used to achieve the sixth metal structure 330 or a similar structure with struts that can be readily removed in a manner that avoids the noted vibrational and/or damage issues. For example, the fourth metal structure 294 may be susceptible to being machined in a single step to achieve the metal structure 330 or a metal structure with intermittent helical voids that are separated from one another by helical struts that are susceptible to being removed in a manner that avoids the noted vibrational and/or damage issues.
(31) With reference to FIG. 18, the metal structure 340 is processed so as to remove a substantial portion of, but not all of, the solid cylinder 66 and the solid section of a frustum of a right circular cone 286 to define a frusto-conical exterior top surface 342 that is substantially parallel to the frusto-conical interior top surface 280. The frusto-conical interior and exterior top surfaces 280, 342, in turn, substantially define the cap 206. It should be appreciated that the helically shaped conductor 202 and the cap 206 are a single piece of metal. As such, there is no need for a connecting structure extending between the helically shaped conductor 202 and the cap 206 that potentially could be a source of an undesirable passive intermode. It should be appreciated that the substantial portion of the solid cylinder 66 and the solid section of a frustum of a right circular cone 286 could be removed at any point in the method of manufacturing at which the solid cylinder 66 is no longer needed for engaging a collet or chuck of a milling machine or for any other purpose. For example, the substantial portion of the solid cylinder 66 and the solid section of a frustum of a right circular cone 286 could be removed before the struts 322 are removed. Further, while the cap 206 has an elliptical shape, the cap need not have such a shape to be effective in preventing an undesirable reflection that could adversely affect the polarization signals being processed by the antenna. The cap 206 need only be of sufficient shape and extent to substantially inhibit this undesired reflection. Consequently, if in removing a substantial portion of the solid cylinder 66 and the solid section of a frustum of a right circular cone 286 a non-elliptical cap with a substantially smaller extent than the last turn of the helically shaped conductor 202 is produced, the cap may nonetheless be sufficient for preventing the undesired reflection. Additionally, if a particular radiator structure does not require a cap or it is desirable to have a separate cap with a connective structure that extends between the cap and the helically shaped conductor, the entire solid cylinder 66 and any metal extending from the frusto-conical interior top surface 280 to the solid cylinder 66 can be removed.
(32) With reference to FIG. 15, the radiator structure 200 illustrated in FIG. 18 includes the matching structure 204 that provides the helical antenna that incorporates the radiator structure 200 with a desired or acceptable VSWR. The matching structure 204 is established or the material for the later establishment of the matching structure 204 is present in the fifth metal structure 302. As such, the subsequently created helically shaped conductor 202 and the matching structure 204 are a single piece of metal. As such, there is no need for a connecting structure extending between the helically shaped conductor 200 and the matching structure 204 that potentially could be the source of an undesirable passive intermode. It should be appreciated that in some helical antennas a matching structure may not be needed. For such helical antennas, the manufacturing method can be modified to forego the making of the matching structure 204.
(33) While the helically shaped conductors 28, 202 respectively associated with the radiator structures 22 and 202 resulting from the manufacturing process described herein both have a right-handed twist, the manufacture process can be readily adapted to the production of helically shaped conductors that have a left-handed twist.
(34) The foregoing description of the invention is intended to explain the best mode known of practicing the invention and to enable others skilled in the art to utilize the invention in various embodiments and with the various modifications required by their particular applications or uses of the invention.
