Nesting wire monopole HF antenna

Abstract

Method and apparatus for an antenna (300) having first and second nested monopoles (302, 304) each having arms (306a-f, 316a-f) with bent portions (312, 318). In some embodiments, the monopoles are offset at a clocking angle. In some embodiments, the monopoles are aligned at a clocking angle. In embodiments, the bent portions of the arms may be positioned at half the height of the antenna.

Description

Background Art

[0001] As is known in the art, monopole antennas can be used for various applications. Some special monopoles, such as trapezoidal ring fractal monopoles, have a bandwidth of up to about 5:1 (2.2 - 10.8 GHz). Known monopoles may be limited by planar designs (such as microstrips), and are not practical for high-frequency (HF) applications that require monopoles with heights of dozens of feet, such as 16 - 35 feet. Some planar monopoles may require a large electrically large vertical ground plane (36 mm x 16 mm for 2.2 - 10.8 GHz), which is not suitable for HF array applications and may require an array of about 50 feet x 25 feet arranged horizontally under the vertical monopole. Some planar monopoles are limited to single-element applications because they cannot be used for array applications due to their large installation area. Furthermore, in some monopole antennas and antenna arrays, distributed lumped elements such as resistors, inductors, and PIN diodes strategically arranged along the radiator are used to achieve broadband performance, resulting in reduced radiation efficiency, a need for an external DC bias circuit, and increased costs. The load of the distributed lumped elements also limits high-power operation of 10 - 20 kW or more.

[0002] Some known broadband antennas have a so-called wide-angle aperture with an apex angle of about 85 degrees, and are usually traveling-wave antennas formed on a radial ground screen to excite transverse electromagnetic waves (TEM). Wide-angle aperture antennas have a very large installation area, which limits their ability to form linear or 2D arrays without generating grating lobes and increases mutual coupling.

Summary of the Invention

[0003] Exemplary embodiments of this disclosure provide methods and apparatus for multiple nested wire monopoles to provide ultra-wideband (UWB) RF performance to an HF antenna or HF array element. Exemplary monopole antenna embodiments may provide additional resonant paths to partially fill nulls in the monopole pattern at high frequencies. In some embodiments, the monopole antenna comprises a smaller monopole offset at a clocking angle from a larger monopole. In some embodiments, the monopole antenna comprises first and second monopoles aligned at a clocking angle and sharing a portion of the lower wire.

[0004] Embodiments of the present disclosure include an HF antenna having a nested wire monopole, which uses a ground screen to provide imagery and offers high-power (up to 20kW) UWBRF performance covering 5MHz to 45MHz (9:1 bandwidth) with a slim aperture that does not excite previously unachieved TEM modes.

[0005] In one embodiment, the antenna comprises a first monopole having a first number of arms and an upper and lower section, wherein the arms of the first monopole have bent sections, and a second monopole having a second number of arms, wherein the second monopole is at least partially nested inside the first monopole.

[0006] The antenna may further have one or more of the following features: the first monopole is offset from the second monopole by a clocking angle; the first and second monopoles are aligned by a clocking angle; the first and second have the same number of arms; the first has 3 arms; the first has 2 to 7 arms; each arm of the second monopole has a bend, each bend forms a rhombus shape around the first monopole; each bend of the arm of the first monopole is located at half the height of the antenna formed by the first and second monopoles; and the bend of the arm of the first monopole defines the width of the antenna. The antenna has a single feed section for the first and second monopoles, a portion of the arm of the first monopole is shared by a portion of the arm of the second monopole, the arm of the first monopole has a diameter in the range of approximately 0.09 to 0.1λ, where λ is the wavelength of the mid-frequency of the antenna's operating band, the antenna formed by the first and second monopoles has no lumped elements, the antenna provides ultra-wideband performance covering a bandwidth of 9:1 or greater, the antenna forms part of an over-horizon radar and / or forms low-bandwidth and high-bandwidth arrays formed from elements comprising nested first and second monopoles.

[0007] In another embodiment, the system includes means for radiating RF signals with first and second nested monopole antennas.

[0008] In a further embodiment, the method includes radiating a signal with an antenna comprising first and second nested monopoles. The method may further comprise one or more of the following features: the first monopole is offset from the second monopole by a clocking angle; the first and second monopoles are aligned by a clocking angle; the first and second have the same number of arms; the first has 3 arms; the first has 2 to 7 arms; each arm of the second monopole has a bend, each bend forms a rhombus shape around the first monopole; each bend of the arm of the first monopole is located at half the height of the antenna formed by the first and second monopoles; and the bend of the arm of the first monopole defines the width of the antenna. The antenna has a single feed section for the first and second monopoles, a portion of the arm of the first monopole is shared by a portion of the arm of the second monopole, the arm of the first monopole has a diameter in the range of about 0.09 to 0.1λ, where λ is the wavelength of the mid-frequency of the antenna's operating band, the antenna formed by the first and second monopoles has no lumped elements, the antenna provides ultra-wideband performance covering a bandwidth of 9:1 or greater, the antenna forms part of an over-horizon radar and / or forms low-band and high-band arrays formed from elements comprising nested first and second monopoles. [Brief explanation of the drawing]

[0009] The aforementioned features of the present invention, as well as the present invention itself, can be understood in more detail from the following description of the drawings. [Figure 1] This shows a conventional HF antenna array. [Figure 2] This shows a conventional duoconical monopole antenna. [Figure 3A] This is a side view of a nested multiwire monopole antenna. [Figure 3B] This is a top view of a nested multi-wire monopole antenna. [Figure 4A] This is a side view of a nested multiwire monopole antenna. [Figure 4B]This is a top view of a nested multi-wire monopole antenna. [Figure 5A] This is a side view of a nested multiwire monopole antenna. [Figure 5B] This is a top view of a nested multi-wire monopole antenna. [Figure 6A] This is a side view of a nested multiwire monopole antenna. [Figure 6B] This is a top view of a nested multi-wire monopole antenna. [Figure 7] Figures 3, 4, and 5 show exemplary performance of the monopole antenna. [Figure 8A] An example of the dimensions of an exemplary monopole antenna is shown. [Figure 8B] This shows a monopole antenna on a ground screen. [Figure 9] This is a schematic diagram of an exemplary embodiment of a two-row linear array having nested monopole antennas. [Modes for carrying out the invention]

[0010] Before describing in detail the embodiments of this disclosure, some information is provided. A monopole antenna is a radio antenna that is typically a straight conductor mounted on a conductive ground plane. Signals are transmitted and / or received along the length of the antenna. One end of the antenna feed line is connected to the lower end of the monopole, and the other end is connected to a ground plane, which is located on the Earth. A monopole antenna can operate as a resonant antenna, which acts as a resonator for radio waves and oscillates with a current wave that travels along a length corresponding to the wavelength of the transmitted wave and / or radio wave. One common type of antenna is called a quarter-wavelength monopole, which has a length of about one-quarter of the wavelength of the operating radio wave.

[0011] A monopole antenna has an omnidirectional radiation pattern, radiating power equally in all directions perpendicular to the antenna. A monopole radiates a vertically polarized signal. The radiated power varies with elevation and is nearly zero at the zenith. A monopole antenna placed on an infinitely perfect conductor (PEC) ground has maximum power very close to the horizon, while a monopole placed on a finite-sized groundscreen has maximum power at an elevation angle determined by the radius and conductivity of the groundscreen.

[0012] Figure 1 shows a conventional HF antenna array for an over-the-horizon (OTH) radar. Conventional OTH radars have two independent transmitting arrays, with a low-band array covering the lower half of the bandwidth and a high-band array covering the remaining half.

[0013] Figure 2 shows a conventional XL duoconical monopole antenna. Zhang et al: "An Optimum Design of Low-Profile Ultra-Wideband HF Skeletal Wire Duoconical Monopole Antenna with Parasitic Grounded Poles" (incorporated herein by reference).

[0014] Figure 3A is a side view of a nested multiwire monopole antenna 300 according to an exemplary embodiment of the present disclosure, and Figure 3B is a top view. The antenna 300 comprises a first monopole 302 and a second monopole 304. In the illustrated embodiment, the second monopole 304 is nested inside the first monopole 302. The first monopole 302 can be considered a large monopole, and the second monopole 304 can be considered a small monopole.

[0015] In a nested monopole configuration, it is understood that the interactions between each aperture must be analyzed to achieve broadband performance in the desired direction. Each monopole is analyzed individually, with larger monopoles designed for the low-frequency band and smaller monopoles designed for the high-frequency band. The antennas are then combined and further tuned to eliminate resonances occurring near the overlapping region of the two frequency bands. Optimization parameters include determining the appropriate wire radius, the optimal clocking angle, and smoothing sharp angles to eliminate spark gaps and corona.

[0016] In the illustrated embodiment, the first monopole 302 comprises six equally spaced arms 306a-f extending from the top 308 to the bottom 310 of the antenna. Note that, as shown in the figure, the u-space and v-space indicators are superimposed on the arms of the first monopole 302 and the second monopole 304. Each arm 306 has a bend 312 extending a predetermined radial distance from the axis 314 of the array. In the illustrated embodiment, the second monopole 304 comprises six equally spaced arms 316a-f nested within the first monopole 302. Each arm 316 is provided with a bend 318. As can be seen from the figure, the arms 316 of the second monopole 304 are offset from the arms 306 of the first monopole 302 by a clocking angle 318. The antenna is installed perpendicular to the ground.

[0017] Figure 4A is a side view of a nested multiwire monopole antenna 400 according to an exemplary embodiment of the present disclosure, and Figure 4B is a top view. In the illustrated embodiment, the antenna 400 comprises a first monopole 402 and a second monopole 404. In the illustrated embodiment, the second monopole 404 is partially nested within the first monopole 402. The first monopole 402 has six equally spaced arms 406a-f, and the second monopole 404 has six equally spaced arms 416a-f. As best shown in Figure 4B, the arms 406a-f, 416a-f are aligned at a clocking angle and overlap in a vertical view.

[0018] In an embodiment, each arm 406, 416 of the first and second monopoles 402, 404 shares a wire 407 from each respective bend 412, 418 to the bottom 410 of the antenna. As shown, it should be understood that the u - space and v - space indicators for the first monopole 402 and the second monopole 404 are shown.

[0019] FIG. 5A is a side view of a nested multi - wire monopole antenna 500 according to an exemplary embodiment of the present disclosure, and FIG. 5B is a top view. In the illustrated embodiment, the antenna 500 includes a first monopole 502, a second monopole 504, and a third monopole 505. In the illustrated embodiment, the second monopole 504 is partially nested within the first monopole 502, and the third monopole 505 is partially nested within the first and second monopoles. As can be seen from the figure, as shown in FIGS. 3A and 3B, the first monopole 502 and the second monopole 504 of the antenna 500 are offset at a clocking angle, and as shown in FIGS. 4A and 4B, the first monopole 502 and the second monopole 504 share the wires of the monopole arms 506, 516.

[0020] FIG. 6A is a side view of a nested multi - wire monopole antenna 600 according to an exemplary embodiment of the present disclosure, and FIG. 6B is a top view. In the illustrated embodiment, the antenna 600 includes a first monopole 602 and a second monopole 604 having three equally spaced arms each and symmetric clocking angles.

[0021] Figure 7 shows exemplary performance for the monopole antenna 300 in Figure 3, the monopole antenna 400 in Figure 4, the monopole antenna 500 in Figure 5, and a conventional duo-monopole antenna. As can be seen from the figure, the exemplary nested monopole antennas 300, 400, and 500 provide ultra-wideband (UWB) RF performance for HF antennas and / or HF array elements. The monopole 300 (Figure 3) offers a good balance of complexity and cost to performance. The monopole 400 (Figure 4) has a simpler structure than the monopole 300 but has lower gain and higher return loss. The monopole 500 (Figure 5) has a wider bandwidth and is more complex than the monopoles 300 and 400.

[0022] Compared to conventional monopole antennas, the exemplary monopole embodiment provides an additional resonant path to partially fill the nulls in the monopole pattern at high frequencies. The exemplary monopole embodiment provides ultra-wideband performance covering 5–45 MHz (9:1 bandwidth), which has never been achieved before.

[0023] An exemplary embodiment of the present disclosure provides a nested wire monopole ultra-broadband HF antenna having a rhomboid structure oriented perpendicular to the Earth and perpendicular to a radial ground screen. The radial ground screen is positioned between the monopole and the Earth and oriented parallel to the Earth. The radiated polarization is perpendicular electric. The ground screen provides maximum directional gain at low elevation angles for above-horizon radar.

[0024] It is understood that any practical number of nested monopole antennas can be used. In the exemplary embodiment, two nested monopoles are shown, but in other embodiments, three antennas are nested. The larger monopole antennas radiate towards the lower frequencies of the frequency band, while the smaller (nested) antennas radiate towards the higher frequencies of the frequency band. Each nested antenna is designed individually and coupled to a single aperture with a single feed point, and further optimized to eliminate unwanted resonances.

[0025] It is understood that the arms of a monopole can be constructed from any suitable conductive material of any suitable shape. For example, monopole arms can be tubular, circular, and / or square. In some embodiments, the diameter of the arms is in the range of about 0.09 to 0.1λ, based on providing structural stability without compromising performance, where λ is the wavelength corresponding to the center frequency of the operating band.

[0026] In embodiments, smaller nested antennas may have the same number of arms as a larger antenna and be symmetrically centered with a clockwise offset to fill the available space from the larger elements. In embodiments, the bends in the arms that define the width of the antenna are located at or near the midpoint of the overall height of the antenna. The points where the arms intersect are located at the top and bottom of each radiator and form joints that can be assembled into pointed tips, rounded end caps, and / or grouped and fixed onto a circular plate as a common connection platform. Electrical continuity must be maintained throughout these joints. In embodiments, the radius dimension of the disc should not exceed approximately 0.05 l, and the thickness of the disc should be greater than many skin depths.

[0027] In one embodiment, the antenna has a single feed point that feeds all the nested monopoles positioned on a base. Balanced excitation is achieved by connecting one end to the base and the other end to a radial ground screen oriented parallel to the ground. In one embodiment, the feed point may include a current balun with a 50W coaxial cable input.

[0028] As an example, as shown in Figures 8A (explanatory dimensions) and 8B (antenna on ground screen and on Earth), for HF use of approximately 3-30 MHz (6:1 bandwidth) with three arms, the maximum antenna height is approximately 11 m, the width is approximately 7 m, and the height at the bend is approximately 5.5 m. The height of the inner nested monopole is approximately 7 m, the width is approximately 2 m, and the height at the bend is approximately 3.5 m. The diameter of the monopole wire is approximately 8 inches to ensure structural stability.

[0029] In exemplary embodiments, the antenna is constructed using steel, aluminum, or a similar conductive material with an appropriate arm diameter, as described above. High power utilization up to approximately 20 kW is achieved with high efficiency based on the thin skin depth of the material. Skin depth is the thickness of the metal through which approximately 63% of the current flows. Radiation efficiency is high when the arm diameter is approximately 0.09–0.1λ, as the material thickness is orders of magnitude thicker than the skin depth. In embodiments, the antenna does not require distributed loads such as inductors, capacitors, or resistors, which would reduce radiation efficiency at high power. The effects of high-power corona are minimized by eliminating sharp bends and sharp angles.

[0030] For broadband array applications requiring high directional gain, wide-angle scanning, and low interconnection near the horizon (on the ground screen) (up to approximately 6:1), two-dimensional (2D) arrays may be necessary. Spiral arrays with mixed narrowbands, or nested wire monopole ultra-broadband elements formed with non-uniform spiral radii, exhibit low grating lobes and low interconnection. Spiral arrays arranged like the central lattice of a sunflower, with a nearly constant unit cell size, also exhibit very low grating lobes and extremely low interconnection. Rotational symmetry allows for the rotation of the antenna using non-overlapping guy wires, reducing interconnection at a fixed unit cell size.

[0031] Exemplary embodiments of nested monopoles provide antennas that offer performance characteristics not previously achieved. For example, Mayes' U.S. Patent No. 6,608,598 requires the use of strategically placed, dispersed, lumped elements (such as resistors, inductors, and pin diodes) along the radiator to achieve broadband performance, which reduces radiation efficiency and necessitates an external DC bias circuit.

[0032] In contrast, exemplary embodiments of nested monopole UWB antennas do not require lumping elements, thus achieving higher efficiency, with losses based solely on structural resistance.

[0033] Furthermore, the distributed, concentrated load of elements in conventional arrays limits high-power operation (high power refers to a maximum of 20 kW). Forming arrays of wide-angle aperture antennas to excite TEM modes is difficult because the aperture angle expands to approximately 85 degrees, resulting in excessively large unit cell sizes.

[0034] Figure 9 shows an exemplary embodiment of a two-row linear array having nested monopole antennas according to an exemplary embodiment of the present disclosure. The two-row array may be suitable for OTH radar systems.

[0035] Various embodiments of the concepts, systems, devices, structures, and technologies for which protection is sought are described herein with reference to the relevant drawings. Alternative embodiments can be considered without departing from the scope of the concepts, systems, devices, structures, and technologies described herein. Note that various connections and positional relationships between elements (e.g., above, below, adjacent, etc.) are described in the following description and drawings. These connections and / or positional relationships may be direct or indirect unless otherwise specified, and the concepts, systems, devices, structures, and technologies described herein are not intended to be limited in this respect. Thus, the connection of entities may refer to a direct or indirect connection, and the positional relationship between entities may be a direct or indirect positional relationship.

[0036] As an example of an indirect positional relationship, the reference in this description to forming layer "A" above layer "B" includes situations where one or more intermediate layers (e.g., layer "C") are located between layer "A" and layer "B," provided that the relevant properties and functions of layers "A" and "B" are not substantially altered by the intermediate layer(s). The following definitions and abbreviations should be used for the interpretation of the claims and specification. As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” “contains,” or “containing,” or any other variation thereof, are intended to extend to non-exclusive inclusion. For example, a composition, mixture, process, method, article, or apparatus containing a list of elements is not necessarily limited to these elements alone, and may include other elements not expressly enumerated, or other elements specific to such composition, mixture, process, method, article, or apparatus.

[0037] For the purposes of the following explanation, the terms “top,” “bottom,” “right,” “left,” “vertical,” “horizontal,” “top,” and “bottom,” and their derivatives, shall be those of the structures and methods described, as oriented in the drawings. The terms “overlying,” “atop,” “ontop,” “positioned on,” or “positioned atop” mean that a first element, such as a first structure, is located on a second element, such as a second structure, and that intervening elements, such as an interface structure, may be located between the first and second elements. The term “direct contact” means that a first element, such as a first structure, and a second element, such as a second structure, are connected at the interface between the two elements without any intermediate conductive, insulating, or semiconductor layer. It should be noted that the term “selective” means that the first element can be etched and the second element can act as an etching stopper, for example, “the first element is selective for the second element.”

[0038] The use of ordinal numbers such as "first," "second," and "third" in a claim to modify elements of a claim does not in itself imply priority, precedence, or order of one element of a claim relative to another, or the chronological order in which the actions of the method are performed. Rather, it is simply used as a label to distinguish one element of a claim with a particular name from another element with the same name (other than the use of ordinal numbers).

[0039] The terms “approximately,” “substantially,” and “about” mean within ±5% of a value unless otherwise defined. For example, a first direction that is “substantially” perpendicular to a second direction means a first direction that is within ±5% of the angle that makes a 90-degree angle with the second direction.

[0040] While exemplary embodiments of the present invention have been described, it will be apparent hereto those skilled in the art that other embodiments incorporating these concepts may also be used. The embodiments included herein should not be limited to those disclosed, but rather should be limited only by the spirit and scope of the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.

[0041] Elements of different embodiments described herein may be combined to form other embodiments not specifically described above. Various elements described in the context of a single embodiment may be provided separately or in any suitable subordinate combination. Other embodiments not specifically described herein are also within the scope of the following claims.

Claims

1. A first monopole having a first number of arms and an upper and lower section, wherein the arms of the first monopole have a bent portion, An antenna comprising a second monopole having a second number of arms, wherein the second monopole is at least partially nested within the first monopole.

2. The antenna according to claim 1, wherein the first monopole is offset from the second monopole by a clocking angle.

3. The antenna according to claim 1, wherein the first and second monopoles are aligned at a clocking angle.

4. The antenna according to claim 1, wherein the number of the first and second arms is the same.

5. The antenna according to claim 1, wherein the number of the first arms is three.

6. The antenna according to claim 1, wherein the number of the first arms is 2 to 7.

7. The antenna according to claim 1, wherein each of the arms of the second monopole has a bent portion.

8. The antenna according to claim 7, wherein each of the aforementioned bent portions forms the first monopole in a rhomboid shape.

9. The antenna according to claim 8, wherein each of the bent portions of the arm of the first monopole is positioned at half the height of the antenna formed by the first and second monopoles.

10. The antenna according to claim 9, wherein the bent portion of the arm of the first monopole defines the width of the antenna.

11. The antenna according to claim 1, wherein the antenna has a single feed point for the first and second monopoles.

12. The antenna according to claim 1, wherein a portion of the arm of the first monopole is shared with a portion of the arm of the second monopole.

13. The antenna according to claim 1, wherein the arm of the first monopole has a diameter in the range of about 0.09 to 0.1λ, where λ is the wavelength of the central frequency of the antenna's operating band.

14. The antenna according to claim 1, wherein the antenna formed by the first and second monopoles does not include a centrifugal element.

15. The antenna according to claim 1, wherein the antenna provides ultra-wideband performance exceeding a 9:1 bandwidth.

16. The antenna according to claim 1, wherein the antenna forms part of the over-horizon radar.

17. The antenna according to claim 16, further comprising a low-bandwidth array and a high-bandwidth array formed from elements comprising the nested first and second monopoles.

18. A system including means for radiating an RF signal using first and second nested monopole antennas.

19. A method for radiating a signal using an antenna comprising a first and a second nested monopole.

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