Backfire axial mode antenna

Abstract

To provide an antenna system.SOLUTION: An antenna system includes a base structure, a transmission line, a ground plane, and a backfire antenna element. The transmission line extends from the base structure and is coupled to the base structure at a first end of the transmission line. The ground plane is coupled to the transmission line at a second end of the transmission line. The backfire antenna element extends between the ground plane and the base structure. The backfire antenna element is coupled to the second end of a TEM line.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The following relates generally to antennas, and more particularly to systems and methods for backfire axial mode helical antennas. [Background technology]

[0002] Helical antennas are generally signal fed from the base or bottom and can be used for a wide range of RF applications. In some applications, space and volume constraints may limit the use of helical antennas. Similarly, the application environment of the helical antenna may contain dense or otherwise conductive materials. The presence of such objects and / or materials may lead to RF signal scattering when using helical antennas in these environments. Summary of the Invention [Problem to be solved by the invention]

[0003] Therefore, there is a need for improved systems and methods for helical antennas that overcome at least some of the shortcomings of existing systems and methods. [Means for solving the problem]

[0004] An antenna system is provided that includes a base structure, a transmission line extending from the base structure, the transmission line coupled to the base structure at a first end of the transmission line, a ground plane coupled to the transmission line at a second end of the transmission line, and a backfire antenna element between the ground plane and the base structure, the backfire antenna element coupled to the second end of the transmission line.

[0005] In one aspect, the backfire antenna element is helical.

[0006] In one aspect, the system further comprises a transmission line, the transmission line being a TEM line.

[0007] In one aspect, the system further comprises a transmission line, the transmission line being a microstrip line.

[0008] In one aspect, the system further comprises a transmission line, the transmission line being a coaxial cable.

[0009] In one aspect, the system further comprises a transmission line, the transmission line being a dielectrically loaded waveguide.

[0010] In one aspect, the system further includes a dielectric support structure, the helical antenna element being coupled to the dielectric support structure.

[0011] In one aspect, the dielectric support structure is constructed from a dielectric material.

[0012] In one aspect, the backfire antenna element includes a rectangular cross section.

[0013] In one aspect, the backfire antenna element is constructed from a conductive material.

[0014] In one aspect, the transmission line includes a matching network.

[0015] In one embodiment, the matching network includes a quarter wave transformer or a stub.

[0016] In one aspect, the transmission line includes a central conductive ground stub.

[0017] In one embodiment, the base structure is constructed from a metallic material.

[0018] In one embodiment, the antenna system is configured to transmit and / or receive UHF frequency signals.

[0019] In one aspect, the system may be configured to allow for relative thermal displacement between the antenna elements and the dielectric support structure.

[0020] In one aspect, the transmission line further includes a support structure for supporting the ground plane and the antenna element.

[0021] In one aspect, the antenna system may be coupled to a spacecraft.

[0022] A method of transmitting an RF signal through an antenna system is also provided, the method including providing an RF signal as an input to the antenna system, transmitting the RF signal through a transmission line of the antenna system, the transmission line comprising an impedance matching network, transmitting the RF signal through a helical antenna element having an axis, and radiating the RF signal away from the antenna system through the helical antenna element, the transmission line being positioned at the axis of the helical antenna element.

[0023] In one embodiment, the transmission line is a TEM line.

[0024] In one embodiment, the transmission line is a microstrip line.

[0025] In one embodiment, the transmission line is a coaxial cable.

[0026] In one aspect, the transmission line is a dielectrically loaded waveguide.

[0027] In one aspect, the transmission line comprises a matching network.

[0028] In one embodiment, the matching network comprises a quarter wave transformer or a stub.

[0029] In one aspect, the antenna elements have a rectangular cross section.

[0030] In one embodiment, the antenna elements are constructed from a conductive metallic material.

[0031] In one aspect, the antenna system is configured to at least one of transmit and receive UHF frequency signals.

[0032] In one aspect, the antenna system is coupled to a spacecraft. Effect of the Invention

[0033] The systems and methods for backfire axial mode helical antennas described herein may reduce the antenna footprint and reduce scattering effects when operating at UHF frequencies.

[0034] Other aspects and features will become apparent to those of ordinary skill in the art upon review of the following description of certain exemplary embodiments.

[0035] The drawings included herein are intended to illustrate various examples of the articles, methods and apparatus herein. [Brief description of the drawings]

[0036] [Figure 1] FIG. 1 is a perspective view of a backfire helical antenna according to one embodiment. [Diagram 2] FIG. 13 is a front view of a backfire helical antenna according to another embodiment. [Diagram 3] 3 is a flow chart illustrating a method of operating the antenna system of FIGS. 1-2 according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] Various devices or processes will be described below to provide an example of each claimed embodiment. The embodiments described below do not limit any claimed embodiment, and any claimed embodiment may include processes or devices different from those described below. A claimed embodiment is not limited to a device or process having all of the features of any one device or process described below, or to features common to multiple or all of the devices described below.

[0038] Additionally, although process steps, method steps, algorithms, etc. may be described (in this disclosure and / or in the claims) in a sequential order, such processes, methods, and algorithms may be configured to function in alternative orders. In other words, any order or sequence of steps that may be described does not necessarily indicate a requirement that the steps be performed in that order. Steps of processes described herein may be performed in any order that is practical. Additionally, some steps may be performed simultaneously.

[0039] Described herein is a backfire mode helical antenna in which the antenna is fed from the opposite end of the helical element extending away from the base of the antenna, as opposed to a frontfire mode helical antenna in which the antenna is fed at the proximal end of the helical element. In contrast to a frontfire axial mode helical antenna, a backfire mode helical antenna may provide acceptable performance at a reduced physical size and may be less susceptible to signal scattering effects. By packaging the antenna components within the typically aperture volume of the antenna element helix, antenna packaging is made more efficient, further reducing the overall volume and footprint of the antenna, which may be particularly advantageous when applied to space environments. In contrast, conventional frontfire mode helical antennas require matching network components to be placed outside the antenna's aperture interior volume, which may increase the required volume of the antenna.

[0040] In a front-firing helical antenna configuration, the ground plane for the antenna element helix is ​​typically at least 0.5 wavelengths in diameter. However, as the ground plane is made smaller, the front-to-back ratio rapidly degrades to 0 dB and then transitions to dominate almost pure back-firing radiation.

[0041] In the UHF bands, the wavelengths are large enough that if the antenna footprint or real estate available (e.g., on the spacecraft to which the antenna is coupled) is insufficient to have a sufficiently large ground plane, the conditions for backfire radiation to occur become non-negligible.

[0042] To overcome this situation, the antenna system described herein is by design a backfire antenna, where the ground plane size is intentionally kept small enough to generate backfire radiation. This ground plane is located on top of the antenna system next to its feed point. Optimization of the ground plane size leads to low frontfire radiation, which in turn leads to lower RF scattering effects (e.g., from the spacecraft to which the antenna system is coupled).

[0043] Optimization of the helix diameter and pitch angle leads to the radiation of a circularly polarized electromagnetic field over a selected frequency band and coverage area.

[0044] Referring first to FIG. 1, depicted therein is a perspective view of a backfire mode helical antenna system 100 for transmitting and / or receiving radio frequency (RF) signals according to a radiation pattern. The radiation pattern associated with antenna system 100 herein generally corresponds to a typical radiation pattern of a helical antenna. Antenna system 100 is configured to transmit and / or receive ultra high frequency (UHF) band RF signals. In other embodiments, antenna system 100 may be configured to transmit and / or receive different RF bands. In such variations, the overall and relative dimensions of antenna system 100 may be altered to provide performance in other RF bands.

[0045] As seen in FIG. 1, the antenna system 100 is coupled to a base object 122 using mechanical fasteners or other coupling means. The base object 122 is close to the antenna system 100, such that the presence of the base object 122 may interfere with and / or scatter RF signals transmitted or received by the antenna system 100, thereby hindering the expected and desired radiation pattern associated with the antenna system 100 and degrading RF performance. In the embodiment of FIG. 1, the base object 122 is a satellite and is configured to communicate with other objects or systems using RF signals. In other embodiments, the base object 122 may be a space station, a spacecraft, a vehicle, a building, a radio tower, or any other object that may require or advantageously include RF communication capabilities. The antenna system 100 is specifically configured to operate in a space environment and accordingly configured to tolerate radiation and thermal cycles that may occur in a space environment. Additionally, the antenna system 100 is optimized to reduce space and volume requirements, which may be particularly advantageous in space applications where volume may be limited by launch vehicle space and / or cost.

[0046] 2, depicted therein is a detailed front view of antenna system 200, an alternative embodiment of antenna system 100 of FIG. 1. Antenna system 200 is a backfire mode helical antenna, with the feed point to the helical antenna element located at the tip of the helical element relative to the closest point of the helical element, as would be expected from a frontfire mode helical antenna. Antenna system 200 comprises a support structure 202 for mechanically supporting antenna system 200, a transverse electromagnetic (TEM) line 204 for transmitting and / or receiving RF signals to and / or from ribbon 208, a ground plane 206 for providing a ground area for antenna system 200, ribbon 208 acting as a helical antenna radiating element, a dielectric support structure 210 providing additional mechanical support to antenna system 200, and a TNC connector 212 for coupling antenna system 200 to an RF signal source and / or receiver.

[0047] The support structure 202 comprises a mechanical structure for supporting the components of the antenna system 200. The support structure 202 includes a base 214 having a generally cylindrical shape, and a central support 216 extending perpendicularly from the base 214 to provide a central, vertical support for the components of the antenna system 200, including the dielectric support structure 210, the TEM traces 204, the ground plane 206, and the ribbons 208. The support structure 202 may be constructed as a single, integral part using additive manufacturing, such as, for example, selective laser sintering. In other examples, the support structure 202 may comprise a multi-part assembly, where the base 214 and the central support 216 are separate parts that may be coupled together using, for example, mechanical fasteners such as machine screws.

[0048] The TEM line 204 comprises a transmission line and / or conductive path through which an RF signal is transmitted and / or received to the ribbon 208 and provides an RF signal at the tip of the ribbon 208 such that the system 200 operates in a backfire mode configuration. The TEM line 204 may include multiple conductors and / or conductor paths. The TEM line 204 extends from the base 214 to the ground plane 206. As used herein, backfire mode refers to a configuration in which a signal is provided at the tip of the ribbon 208 relative to the closest point of the ribbon 208 to the TNC connector 212. The TEM line 204 carries an electromagnetic signal that propagates in a transverse electromagnetic mode. The TEM line 204 is generally positioned at the axis of the helix of the ribbon 208, allowing for compact packaging of the system 200. Positioning the TEM line 204 within the axis of the ribbon 208 helix does not significantly affect RF performance and / or radiated fields relative to configurations in which the TEM line 204 is positioned outside the ribbon 208 helix.

[0049] The TEM line 204 has a first end 224 and a second end 226. The first end 224 is closest to the base 214, while the second end 226 is closest to the ground plane 206. The TEM line 204 feeds the ribbon 208 proximate the second end 226 of the TEM line 204.

[0050] Incorporated into the TEM line 204 is a matching network 218. The matching network 218 comprises a set of microwave components, such as quarter wave transformers, stubs, and / or other microwave components, for impedance matching of the antenna system 200. By incorporating the matching network 218 into the TEM line 204, the antenna system 200 may be constructed more compactly since less volume is required due to use of the typically free space within the helix of the ribbon 208.

[0051] In one embodiment, the center support 216 is integrated into the TEM line 204, such that the center support and the TEM line 204 comprise a single, integral part, with the TEM line 204 providing mechanical support to the ribbons 208, the dielectric support structure 210, and the ground plane 206. In another embodiment, the TEM line 204 may be coupled to the center support 216 by fusing the TEM line 204 to the center support 216 using an adhesive. In other examples, the TEM line 204 may be coupled to the center support 216 through other means. Such an arrangement may reduce the mass and volume requirements of the system 200.

[0052] Incorporated into the TEM line 204 (e.g., as a particular conductor within the set of conductors present in the TEM line 204) is a ground stub 220. The ground stub 220 is a conductive component and is maintained at a neutral potential. The ground stub 220 is coupled to other grounded components to maintain those components at a neutral potential. The ground stub 220 provides an electrostatic discharge discharge path for the center conductor of the TEM line 204. The ground stub 220 may ultimately be coupled to a primary ground of the vehicle, structure, spacecraft, satellite or other object to which the antenna system 200 is coupled.

[0053] In one embodiment, the TEM line 204 may be specifically configured to tolerate thermal cycling so that unequal thermal expansion of materials (e.g., flexible PCB components and metallic structural components) within the TEM line 204 may be accounted for without leading to deleterious mechanical stresses. For example, cavities or volumes may exist within the TEM line 204 near areas of expected relative thermal expansion to provide space for the expansion to occur without creating mechanical distortion and associated mechanical stresses. In alternative embodiments, other means or methods may be applied to account for thermal cycling and associated mechanical stresses.

[0054] In one embodiment, the transmission line may be a microstrip line, a coaxial cable, a dielectric loaded waveguide or other suitable transmission line instead of a TEM line.

[0055] The ground plane 206 comprises a generally planar conductive structure and is positioned at an end of the ribbon 208 proximate the second end 226 of the TEM line. The ground plane 206 is a grounded portion of the antenna system 200. The ground plane 206 is coupled to the TEM line 204 near the second end 226 of the TEM line 204.

[0056] The ground plane 206 is generally planar; however, in other embodiments, the ground plane 206 may comprise different configurations, such as a partial sphere, a parabolic dish, and / or other curved configurations.

[0057] The ribbons 208 comprise conductive antenna elements and are arranged in a helical pattern, extending from the base 214 to the ground plane 206. The ribbons 208 are elements that transmit and / or receive radio frequency signals, which are circularly polarized. In this embodiment, the ribbons 208 are specifically configured to receive and / or transmit UHF RF signals. In this embodiment, the ribbons 208 are flat ribbons and have a square cross section, however, in other embodiments, the ribbons 208 may comprise other cross sections, such as an elliptical or circular cross section. The ribbons 208 are arranged in a tapered or conical helical pattern and extend from the base 214 to the ground plane 206, however, in other embodiments, the ribbons 208 may be arranged in a cylindrical helical pattern or a tapered helical pattern with different taper angles or dimensions.

[0058] The ribbon 208 is coupled to the TEM line 204 proximate a second end 226 of the TEM line 204 for receiving and / or transmitting RF signals from / to the TEM line 204 .

[0059] The ribbon 208 comprises a conductive metallic helical ribbon. In other embodiments, other suitable conductive materials may be used to construct the ribbon 208.

[0060] The dielectric support structure 210 comprises an RF transparent support material to which the ribbons 208 are bonded. The dielectric support structure 210 provides support and mechanical stability to the antenna system 200. The dielectric support structure 210 has a generally conical shape and has dimensions such that the circumference of the ribbons 208 is equal to the wavelength and the pitch angle of the ribbons 208 is approximately 13 degrees. In other embodiments, the dimensions of the dielectric support structure 210 and the ribbons 208 may be different. For example, the dielectric support structure 210 may comprise threads or ribbons instead of conical sheets. The ribbons 208 are fused to the dielectric support structure 210 so that the ribbons 208 maintain the shape of the dielectric support structure 210.

[0061] The dielectric support structure 210 is additionally coupled to the base 214 and the ground plane 206 to provide greater mechanical stability for both the dielectric support structure 210 and the ribbons 208 .

[0062] The dielectric support structure 210 is constructed from a glass cloth material impregnated with epoxy resin. The dielectric material is RF transparent in the UHF range. The dielectric support structure 210 generally maintains its shape and dimensions under its own weight due to the structural properties of the dielectric material. In other embodiments, the dielectric support structure 210 may be constructed from other materials having similar mechanical and electrical properties.

[0063] While in this embodiment the dielectric support structure 210 has a conical form, the cone 210 may be replaced in other embodiments with a similar support structure having a different shape, such as a cylindrical support.

[0064] In some examples, the dielectric support structure 210 and the ribbons 208 may be bonded in a manner that allows for relative thermal expansion of each component while minimizing mechanical stresses associated with this thermal expansion due to the different thermal expansion coefficients between the dielectric support structure 210 and the ribbons 208. For example, the dielectric support structure 210 and the ribbons 208 may only be bonded (e.g., using an adhesive) at the base of the dielectric support structure 210, proximate the first end 224 of the TEM line 204, to allow for upward thermal expansion toward the second end 226 of the TEM line 204. In other examples, there may be other ways to account for thermal expansion.

[0065] The threaded Neale-Concelmann ("TNC") connector 212 is an electromechanical connector that may connect a signal feed line to the antenna system 200. The TNC connector 212 is coupled to the TEM line 204 such that an input signal provided to the TNC connector 212 is directed to and conducted through the TEM line 204. As previously mentioned, signals input to the TNC connector 212 (or received from the TNC connector 212 in receive mode operation) may be propagating in a transverse electromagnetic mode.

[0066] While TNC connectors are used herein, in other embodiments, other electromechanical connectors may be used, such as a Bayonet Neal-Concelmann ("BNC") connector, a Subminiature Version A ("SMA") connector, or other suitable RF connectors.

[0067] In operation, the TNC connector 212 is coupled to an input conductor to provide an RF signal to the system 200. The signal is passed up through the TEM line 204 where it is impedance matched by the matching network 218. The signal is then passed from the TEM line 204 to the ribbon 208 which then radiates or transmits the signal away from the antenna system 200 for reception by another antenna system operating in a receive mode. In one embodiment, this operation may be reversed to operate the system 200 in a receive mode instead of a transmit mode. Due to the backfire mode physical configuration of the antenna system 200, signal scattering effects are reduced improving the predictability of the performance of the antenna system 200 in instances where the antenna system 200 is positioned near potentially scattering surfaces, such as spacecraft components. Furthermore, due to the backfire mode configuration, the antenna system 200 may be constructed in a smaller volume as previously described herein.

[0068] In comparison to a front-fire axial mode helical antenna, in which the input signal to ribbon 208 is input near the base of ribbon 208, the back-fire mode helical antenna described herein provides acceptable performance and a wider radiation pattern at a smaller physical size (e.g., reduced diameter and / or length of ribbon 208) because components such as TEM line 204 can be incorporated within the aperture volume of ribbon 208. The presence of TEM line 204 and other components in this location has negligible effect on the radiation pattern and overall RF performance.

[0069] Additionally, the antenna system 200 described herein is robust to temperature cycling due to the relative placement of the dielectric support structure 210 and ribbon 208 as well as the coupling of the TEM line 204 and center support 216. Furthermore, by packaging the TEM line 204, including the matching network 218 and center support 216, within the inner diameter of the dielectric support structure 210 and ribbon 208, the system 200 can be made compact, which may be advantageous in space applications, such as coupling the system 200 to a spacecraft, as previously described herein.

[0070] While the antenna system 200 described herein is configured for use in space applications and for operation in the UHF frequency range, in other embodiments, the system 200 may be configured for other applications (e.g., terrestrial applications on buildings, vehicles, and / or radio towers) and for operation in other RF bands. In such examples, the dimensions of the system 200 may be altered to provide performance in other RF bands.

[0071] Referring now to Figure 3, depicted therein is a flow chart illustrating a method 300 of using the antenna system of Figures 1-2. The method 300 includes steps 302, 304, 306 and 308.

[0072] At 302, an RF signal is provided as an input to an antenna system.

[0073] At 304, an RF signal is transmitted through a TEM line of the antenna system, the TEM line including a matching network.

[0074] At 306, an RF signal is transmitted through a helical antenna element having an axis.

[0075] At 308, the RF signal is transmitted away from the antenna system through the helical antenna element.

[0076] While the disclosure herein is directed to a helical backfire antenna system, in other embodiments, the antenna system may comprise other forms of backfire antennas, for example, a two-wire or four-wire antenna.

[0077] While the above description provides examples of one or more devices, methods, or systems, it will be recognized that other devices, methods, or systems may be within the scope of the claims, as interpreted by one of ordinary skill in the art. [Explanation of symbols]

[0078] 100 Backfire mode helical antenna system, antenna system 122 Base Object 200 Antenna System 202 Support structure 204 Transverse Electromagnetic (TEM) Line 206 Ground plane 208 Ribbon 210 Dielectric Support Structure 212 TNC Connector, Threaded Neil-Concelmann ("TNC") Connector 214 Base 216 Center support 218 Matching Network 220 Ground stub 224 First End 226 Second End

Claims

1. 1. An antenna system, comprising: A base structure; a transmission line extending from the base structure, the transmission line being coupled to the base structure at a first end of the transmission line; a ground plane coupled to the transmission line at a second end of the transmission line; a backfire antenna element between the ground plane and the base structure; Equipped with the backfire antenna element being coupled to the second end of the transmission line.

2. 10. The antenna system of claim 1, wherein said backfire antenna element is helical.

3. 10. The antenna system of claim 1, further comprising a transmission line, the transmission line being a TEM line, a microstrip line, a coaxial cable, or a dielectric waveguide.

4. 10. The antenna system of claim 1, further comprising a dielectric support structure, the helical antenna element being coupled to the dielectric support structure.

5. The antenna system of claim 4 , wherein said dielectric support structure is constructed from a dielectric material.

6. The antenna system of claim 1 , wherein said backfire antenna element has a rectangular cross section.

7. 10. The antenna system of claim 1, wherein said backfire antenna element is constructed from a conductive metallic material.

8. The antenna system of claim 1 , wherein the transmission line comprises a matching network.

9. 9. The antenna system of claim 8, wherein the matching network comprises a quarter wave transformer or a stub.

10. 10. The antenna system of claim 1, wherein the transmission line comprises a central conductive ground stub.

11. The antenna system of claim 1 , wherein the base structure is constructed from a metallic material.

12. The antenna system of claim 1 , wherein the antenna system is configured to at least one of transmit and receive UHF frequency signals.

13. 10. The antenna system of claim 1, wherein the antenna system is configured to allow relative thermal displacement between the backfire antenna element and a dielectric support structure.

14. 10. The antenna system of claim 1, wherein the transmission line further comprises a support structure for supporting the ground plane and the antenna element.

15. 1. A method for transmitting an RF signal through an antenna system, the method comprising: providing an RF signal as an input to an antenna system; transmitting the RF signal through a transmission line of the antenna system, the transmission line comprising an impedance matching network; transmitting the RF signal through a helical antenna element having an axis; radiating the RF signal away from the antenna system through the helical antenna element; Including, The method of claim 1, wherein the transmission line is positioned at the axis of the helical antenna element.

16. The method of claim 15 , wherein the transmission line is a TEM line, a microstrip line, a coaxial cable, or a dielectrically loaded waveguide.

17. The method of claim 15 , wherein the transmission line comprises a matching network including a quarter-wave transformer or a stub.

18. The method of claim 15 , wherein the helical antenna element has a rectangular cross-section.

19. The method of claim 15 , wherein the helical antenna element is constructed from a conductive metallic material.

20. The method of claim 15 , wherein the antenna system is configured to at least one of transmit and receive UHF frequency signals.

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