Micro-helix antenna and methods for making same

[0001] This application claims the benefit of provisional application Ser. No. 60/576,378, filed Jun. 2, 2004 entitled Micro-Helix Antenna, the contents of which are hereby incorporated by reference.

[0002] The present invention relates generally to helical antennas and methods for making helical antennas.

[0003] There is a growing need in many technical fields to form smaller antenna elements. One technique often employed in antenna design is to embed an inductor within the antenna to add electrical length to an otherwise size-reduced antenna, making the antenna behave as if it were longer. This technique is often employed in standard CB-type antennas to provide length reduction and impedance matching. Conventional helical antennas typically utilize helix diameters that are a significant fraction of a wavelength. However, such antennas generally are too large in diameter to allow further compression. Thus, there is a need for an antenna comprising a helically formed slow-wave conductor element that can be further compressed into a selected pattern, such as a stochastic or spiral motif.

[0004] In one embodiment, the antenna of the present invention comprises an elongate dielectric core, and at least a first helically-shaped conductor disposed about the core. The diameter of the helix formed by the conductor is less than about 1/100 of the wavelength of the antenna.

[0005] In another aspect, the antenna of this invention comprises an elongate dielectric core with at least a first helically-shaped conductive element disposed on the core, wherein the core with the helically-shaped conductor thereon is compressed.

[0006] Still further, the present invention is directed to a method for making an antenna. The method for making an antenna comprises providing a helically-shaped conductive element on a dielectric core so that the diameter of the helix formed by the conductor is less than about 1/100 of the wavelength of the antenna.

[0007] Further still, the present invention contemplates a method for making an antenna comprising providing a helically-shaped conductive element on a dielectric core and compressing the core with the helically-shaped conductor thereon.

[0018] The present invention is directed to the fabrication of antennas that are significantly smaller than their established solid-conductor counterparts, such as the half-wave linear dipole. By using a “micro-helix” conductor element, significant size reductions may be achieved. Micro-helix conductors of the present invention may be used in straight-wire antennas (linear dipoles), stochastic or other meandering line antennas, spiral antennas, and other compression schemes.

[0019] Turning now to the drawings in general and to FIG. 1 in particular, there is shown therein an antenna constructed in accordance with the present invention and designated generally by the reference numeral 10. The antenna 10 preferably comprises an elongate dielectric core 12 and at least a first helically-shaped conductor 14 disposed about the core.

[0020] The dielectric core 12 preferably is flexible but relatively nonelastic to allow further compression as described in more detail below. In the embodiment of FIG. 1, the core 12 is formed of fishing line made of nylon-based copolymers. The diameter of the core 12 is about 250 μm.

[0021] The conductor 14 preferably is a flexible but relatively nonelastic material. Preferably, the conductor is metal, such as copper or silver. For example, in the embodiment of FIG. 1, the conductor is a very fine copper wire, such as 50 AWG copper wire. This fine copper wire can be wrapped around the core 12, so that the conductor is formed into a helix with uniform pitch.

[0022] As indicated in broken lines in FIG. 1, a second helically-shaped conductor 14′ may be included, thus providing a double helix. The direction of the second conductor 14′ may be the same as or opposite of the first conductor 14. Although in the embodiment shown, the second conductor 14′ is adjacent to the first conductor 14, this position may vary. For example, the second conductor 14′ may be rotated 180 degrees from the first conductor 14.

[0023] The direction (handedness), pitch and diameter of the helix of the antenna may vary. However, in accordance with the present invention, the diameter of the helix is relatively small as compared to the wavelength of the antenna. Preferably, the diameter is less than about 1/100th of the wavelength. More preferably, the diameter is less than about 1/500th of the wavelength. Most preferably, the diameter is less than about 1/1000th of the wavelength.

[0024] In the embodiment of FIG. 1, the conductor 14 is wrapped about the core 12 at about 8 turns per mm forming a helix having a diameter “D,” as shown in FIG. 2. The diameter of this helix is about the same as the core, that is, about 250 μm. The length of the core, and therefore the length of the assembled antenna may vary. In the embodiment of FIG. 1, which is fragmented and not drawn to scale, the core 12 is about 1½ inch long. This provides a 1300 MHz antenna about 67% shorter than a comparable standard half-wave dipole antenna.

[0025] As shown in FIG. 2, because the core 12 is circular in cross section, the cross-sectional shape of the helix formed by the conductor 14 is also circular, as illustrated diagrammatically in FIG. 3A. It will be understood that the cross-sectional shape of the helix may vary widely. For example, other suitable shapes include ovoid, seen in FIG. 3B, and polygonal (having multiple straight sides), such as a square, seen in FIG. 3B. Preferably, when the cross-sectional shape is polygonal, all sides of the polygon will be of equal length. Thus, as used herein, “helix” is not limited to a helix with a circular cross-sectional shape.

[0026] FIG. 4 contains a graph illustrating test data of a 1300 MHz linear dipole antenna made by wrapping 50AWG copper wire around a 250 μm wide fishing line about 1.5 inches long. The wire was wrapped at about 8 turns per millimeter.

[0027] Although the above described method of wrapping a fine wire around a fishing line or other elongate core is suitable in many applications, other methods for forming the helical conductor may be used. For example, a strip or bead of silver may be applied to a core, such as a glass fiber, in a helical pattern by using a direct-write process. An enlarged view of a portion of an antenna formed by this method is shown in the photograph of FIG. 5. In this example, the helix formed had about 3 turns per millimeter, and the glass fiber was about 125 μm in diameter.

[0028] In yet another embodiment of the present invention, the antenna 10 is formed from a silver-coated glass fiber core. A laser is used to ablate a helical pattern on the core, leaving a helically shaped strip of silver. As used herein, “ablate” means to remove by etching, erosion, melting, evaporation, vaporization or other suitable techniques. An enlarged view of a portion of an antenna formed by this method is shown in the photograph of FIG. 6.

[0029] The pitch of the of the turns in the micro-helix antenna 10 may be uniform, that is, the pitch of all the turns may be the same, as shown in FIG. 1. However, as shown in the antenna 10A of FIG. 7, the pitch may vary along the length of the antenna, that is, the pitch may be non-uniform In such a case, the varying pitch measurements are selected to modify the performance characteristics of the antenna. For example, the turns can be arranged in groups having different pitches. As shown in FIG. 7, the first group G₁ has 8 turns per millimeter and the second group G₂ has five turns per millimeter.

[0030] The very small relative diameter of the antennas of this invention permits the assembled antennas to be compressed, that is, the antennas assume the mechanical and formative properties of the core on which they are formed. Where the core is flexible, the antenna can be manipulated as if it were simply a solid wire. Accordingly, various antenna compression techniques can be applied to this micro-helical antenna.

[0031] The antenna of the present invention can be formed into three-dimensional shapes, such as the helical antenna 10B shown in FIG. 8. Alternately, the antenna can take the form of a two-dimensional double spiral 10C, as seen in FIG. 9, or the stochastically shaped planar antenna illustrated in FIG. 10. The shapes illustrated herein are exemplary only. It will be understood that the mico-helix antenna may be shaped in virtually any two- and three-dimensional configuration as any other straight line antenna may be, including discone and double-helix.

[0032] Now it will be appreciated that the present invention provides a slow-wave micro-helix antenna in which a very small diameter helix is used to incorporate and distribute an inductance along the entire length of the antenna as opposed to a few lumped-element inductances. This allows for the design of antennas with very significant size reductions while at the same time maintaining good radiation performance and VSWR (voltage standing wave ratio). The wire-like behavior of the micro helix antenna of this invention allows the helical assembly to be treated as if it were a simple wire conductor, which can be fashioned into other size-reducing antenna shapes, such as stochastic, helical and spiral antennas.

[0033] Changes can be made in the combination and arrangement of the various parts and elements described herein without departing from the spirit and scope of the invention as defined in the following claims.