Patent Grant
11258181
The present disclosure relates generally to communication systems. More particularly, the present disclosure relates to systems and methods for providing a high gain space deployable helix antenna.
Satellites have become essential for the many purposes of communications, navigation, and timing. Radio linking to space is, of course, practical over a wide frequency range. However, VHF and UHF frequencies offer particular advantages. For instance, higher frequencies can be limited by atmospheric absorption and rain fading. Antennas at lower frequencies provide the combination of large receive aperture/capture area and broad antenna beamwidth at the same time which can reduce or eliminate antenna aiming requirements. Further advantaging lower frequencies is the earth's distance from the sun, which provides a broad band low noise window at UHF. Above about 300 MHz frequency, solar noise becomes predominant. Galactic noise becomes predominant below 300 MHz. In tropical jungles, the tree canopies cannot be penetrated at elevated frequency. At 300 MHz, a jungle canopy in Panama has been measured to cause 4 decibels of signal attenuation towards zenith, but at 3000 MHz the attenuation increased above 20 decibels. These are some of the factors that make UHF and VHF frequency ranges preferential for satellite to earth mobile station linking.
Smaller satellites have become popular for sake of economy. As antenna size is inversely related to frequency, the lower frequency antennas can be large relative the size of small satellites. For instance, a half wave dipole antenna for 300 MHz may be about 0.5 meters long, yet a ½ ESPA size satellite measures 0.63×1.0×1.15 meters. Given the competition between battery, solar cells and electronics for satellite resources, a means of antenna stowage can be needed. The antenna must make efficient use of weight as well.
Space based communication systems often employ helical antenna structures that are deployable. The helical antenna comprises one or more conducting wires wound in the form of a helix. Directional helical antennas are mounted over a ground plane structure to avoid backlobe radiation. The feed line is connected between the bottom of the helical antenna and the ground plane structure. Directional helical antennas operate in two modes: a normal mode and an axial mode. In normal mode, the diameter and the pitch of the windings are relatively small compared with the wavelength and a standing wave current flows. In axial mode, the circumference of each turn of the windings are comparable with the wavelength and traveling wave current flows. Axial mode antennas provide a directive beam.
The present disclosure concerns implementing systems and methods for improving an efficiency and a gain of a helical antenna. The methods comprise: configuring a conductive helix element of the helical antenna to comprise a proximal segment having a helical winding that extends along an axis of the conductive helix element and has a plurality of turns with linearly progressing pitch angles; configuring the conductive helix element to comprise a distal segment having a helical winding that extends along the axis of the conductive helix element and has a constant pitch angle; and coupling the distal segment to the proximal segment in a series arrangement so that a radio wave traveling along the conductive helix element reaches a terminal velocity at a point of the coupling.
The helical windings of the proximal and distal segments may have constant diameters. The spacing between successive turns of at least the proximal segment's helical winding may be constant or varied along a line parallel to the axis. The linearly progressing pitch angles and the constant pitch angle may be selected so that a radio wave velocity matches a current velocity at any location along the length of the conductive helix element.
In some scenarios, the methods comprises an elongate support member structurally supporting the conductive helix element. The an elongate support member is disposed inside of the conductive helix element and extends along the axis. The conductive helix element is mechanically coupled to the elongate support member using a plurality of struts. The elongate support member may be axially expansive. The conductive helix element may further be structurally supported by sewn longitudinal tapes or an outer fabric sleeve.
In those or other scenarios, the methods comprise coupling the proximal segment of the conductive helix element to a ground plane structure. The ground plane structure comprises a deployable ground plane structure or a cup reflector. The deployable ground plane structure comprises a solid plate to which a webbed structure is coupled via a plurality of joints such that the webbed structure is able to move in directions towards and away from the conductive helix element. A solid disc may be suspended over the distal segment of the conductive helix element.
The present disclosure also concerns helical antennas. The helical antennas comprise a conductive helix element. The conductive helix element comprises: a proximal segment having a helical winding that extends along an axis of the conductive helix element and has a plurality of turns with linearly progressing pitch angles; and a distal segment having a helical winding that extends along the axis of the conductive helix element and has a constant pitch angle. The distal segment is coupled to the proximal segment in a series arrangement so that a radio wave traveling along the conductive helix element reaches a terminal velocity at a point of the coupling.
In some scenarios, an elongate support member is disposed inside of the conductive helix element and extends along the axis so as to provide structural support to the conductive helix element. The conductive helix element is mechanically coupled to the elongate support member using a plurality of struts. The elongate support member may be axially expansive. The conductive helix element may further be structurally supported by sewn longitudinal tapes or an outer fabric sleeve.
A ground plane structure may be provided to which the proximal segment of the conductive helix element is coupled. The ground plane structure comprises a deployable ground plane or a cup reflector. The deployable ground plane structure comprises a solid plate to which a coil structure is coupled via a plurality of joints such that the coil structure is able to move in directions towards and away from the conductive helix element. A solid disc may be suspended over the distal segment of the conductive helix element.
The present solution will be described with reference to the following drawing figures, in which like numerals represent like items throughout the figures.
It will be readily understood that the components of the embodiments as generally described herein and illustrated in the appended figures could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of various embodiments, as represented in the figures, is not intended to limit the scope of the present disclosure, but is merely representative of various embodiments. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.
The present solution may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the present solution is, therefore, indicated by the appended claims rather than by this detailed description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.
Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present solution should be or are in any single embodiment of the present solution. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present solution. Thus, discussions of the features and advantages, and similar language, throughout the specification may, but do not necessarily, refer to the same embodiment.
Furthermore, the described features, advantages and characteristics of the present solution may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize, in light of the description herein, that the present solution can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the present solution.
Reference throughout this specification to “one embodiment”, “an embodiment”, or similar language means that a particular feature, structure, or characteristic described in connection with the indicated embodiment is included in at least one embodiment of the present solution. Thus, the phrases “in one embodiment”, “in an embodiment”, and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
As used in this document, the singular form “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art. As used in this document, the term “comprising” means “including, but not limited to”.
In this document, when terms such “first” and “second” are used to modify a noun, such use is simply intended to distinguish one item from another, and is not intended to require a sequential order unless specifically stated.
The present solution is described herein in relation to space based communication applications. The present solution is not limited in this regard. The present solution may also be used in ground based communication applications.
Referring now to
The antenna element 114 comprises a deployable ground plane structure 108 cooperating with a helical antenna 106 coupled thereto. The antenna element 114 is operable at relatively low frequencies (e.g., 350 MHz-380 MHz) and has a relatively high gain (e.g., 17 dBi) at these relatively low frequencies.
As shown in
The joints 206 facilitate the movement of ribs 208 in directions towards and away from the helical antenna 106, as shown by arrow 212. In some scenarios, the joints 206 include hinges and/or ball bearings coupled between the solid plate 204 and the ribs 208. Hinges and ball bearings are well known in the art, and therefore will not be described herein. The present solution is not limited in this regard. Other joint mechanisms can be employed here. The joints allow the ground plane structure 108 to be transitioned from a stowed position in which the webbed structure 210 is closed around the helical antenna 106 to a deployed position in which the webbed structure 210 is open as shown in
The ribs 208 are formed of a rigid material, such a metal or plastic. The webbed structure 210 is coupled to the ribs 208 via any suitable coupling means (e.g., an adhesive, ties, clamps, welds, etc.). The webbed structure 210 comprises one or more wires with turns wound around the axis 120 on a flat plane when the webbed structure 210 is in its deployed position shown in
As shown in
In some scenarios, bar 124 comprises an axially expansive bar that transitions from a retracted position (not shown) to an extended position shown in
In those or other scenarios, sewn longitudinal tapes or an outer fabric sleeve is provided to further structurally support the conductive helix element 118 and constrain the expansion of the conductive helix element 118 caused by vibration. The longitudinal tapes and/or outer fabric sleeve is(are) not shown for ease of illustration. The present solution is not limited in this regard.
The conductive helix element 118 extends along the axis 120, has a helix circumference (e.g., 1.0λ to 1.2λ), an outer diameter 304 (e.g., 10.310 or 11.87 inches), and a length 400 (e.g., 275.21 inches). The conductive helix element 118 is shown as comprising a circular cross-section helix. The present solution is not limited in this regard. The conductive helix element 118 can alternatively comprise a square cross-section helix (e.g., with a 0.16″×0.16″ square helix conductor diameter), a rectangular cross-section helix, a triangular cross-section helix, or any other shaped helix. The conductive helix element 118 is formed of any conductive wire. The conductive wire may be insulated or uninsulated, and formed of any conductive material (e.g., a nickel-titanium alloy, copper or aluminum).
The conductive helix element 118 comprises a proximal segment 102 and a distal segment 104. During transmit operations, current and radio waves travel along the conductive helix element 118 from its proximal end 108 to its distal end 110. The conductive helix element 118 has a winding pitch angle at any location along its length that is tailored to optimize the exchange of energy between a free space wave and current flowing in the conductive helix element 118. The winding pitch angles are selected so that the radio wave velocity matches the current velocity at any location along the length of the conductive helix element 118. As illustrated in
Considering the antenna space deployable antenna element 114 to be transmitting speed of a radio wave increases along the length of the helical antenna 106, i.e., the radio wave has a slowest speed at the proximal end 108 of the conductive helix element 118 and a fastest speed at the distal end 110 of the conductive helix element 118. The radio wave reaches a terminal velocity at a point 122 (e.g., a midpoint) somewhere between ends 108, 110 of the conductive helix element 118. A linearly progressing winding pitch angle α is used for the proximal segment 102 of the conductive helix element 118. The proximal segment 102 extends between the ground plane structure 108 and point 122. The winding pitch angle of successive turns of the proximal segment 102 are varied in linear manner (e.g., is increased by a number between 0.1 degrees and 5.0 degrees for each turn). The smallest value of the linear progressing winding pitch angle α (e.g., 1°-8°) is at the proximal end 108 of the proximal segment 102, while the largest value of the linear progressing winding pitch angle α (e.g., 20°-30°) is at the distal end 122 of the proximal segment 102. If effect, there are more turns per inch close to the proximal end 108 and fewer turns per inch close to point 122. The linearly progressing winding pitch angle α produces reduced side lobes, more gain per length and more bandwidth. The several winding pitches regions provide several distinct functions: (1) the tighter winding pitch at the proximal end traps the wave energy within a small distance from the helix; (2) the moderate pitch in the medial regions continues to guide the developing wave with reduces sidelobes; and (3) the large pitch at the distal edge is advantaged for wave release at the end antenna.
In some scenarios, the linear progressing winding pitch angle α may have a value on the order of 0-30 degrees at a given location on the conductive helix element 118. The present solution is not limited in this regard. The linear progressive winding pitch may aid in trapping and later releasing a surface wave to provide a lens effect and directivity increase.
In some scenarios, the winding pitch angle α of the first wind (i.e., the most proximal wind) of the proximal segment 102 may be selected to facilitate impedance matching of the antenna element 114 with the communications equipment 112. In some scenarios, the winding pitch angle α of the first wind is selected to be 1°-5° such that a 50 Ohm resistance is provided by the antenna element 114. The present solution is not limited in this regard.
In other scenarios, a transformer and/or other impedance matching circuit components (e.g., an inductor or resistor) is(are) used to provide the impedance matching between the antenna element 114 with the communications equipment 112. The present solution is not limited in this regard.
The helix winding spacing of the proximal segment 102 is defined by the following
Mathematical Equation (1).
S=Xn+C (1)
where S represents the spacing between two successive turns (or z axis rate of expansion), X represents a linear coefficient (e.g., 0.0137), n represents the turn number (e.g., 25 or 27), and C represents a constant (e.g., 0.1361). As evident from this mathematical equation (1), the spacing between successive turns varies within the proximal segment 102. For example, the spacing between successive turns increases from the proximal end 108 to the point 122.
The helix antenna 106 advances both a traveling wave electrical current along the helix axis conductor and an attached surface wave surrounding the helix. It has been found that in some instances, such as high gain embodiments, the velocity of the attached surface wave transmitted by the helix antenna 106 reaches a certain maximum or constant terminal velocity along the helix axis. This is particularly the case for longer helix antennas 106. For this reason a constant winding pitch angle α is used for the distal segment 104 of the conductive helix element 118. In some scenarios, the linear progressing winding pitch angle α has a value equal to the largest pitch angle value of the proximal segment 102 (e.g., on the order of 6-30 degrees). The present solution is not limited in this regard.
The distal segment 104 extends between point 122 and distal end 110 of the helical antenna 106. The length of the distal segment (e.g., ≤3.5 meters) can be selected to provide a desired beam width (e.g., a 3 dBi beam width) and antenna gain (e.g., 19.5 dBi). Graphs showing an illustrative beam and beam width for a simulated antenna are provided in
The proximal segment 102 and the distal segment 104 of the conductive helix element 118 may comprise a single part or structure. Alternatively, the two segments 102, 104 are coupled to each other via one or more couplers 600 as shown in
In some scenarios, each of the segments 102 and 104 can be formed of two or more sub-segments. The sub-segments may be joined to teach other in the same or similar manner as that discussed above in relation to the splicing of segments 102 and 104 (e.g., via an adhesive, a weld (not shown), a crimp, a winding there around, and/or mechanical crimped ferrules).
Referring now to
The ground plane structure 912 comprises a cup reflector 912 instead of a solid plate 204. Cup reflector 912 may function as a waveguide cavity. Cup reflectors are well known in the art, and therefore will not be described further herein. The cup reflector 912 prevents any unwanted back lobe radiation. The cup reflector 912 has a diameter 906 selected in accordance with a particular application (e.g., 2λ, 1.58λ, Bessel zero circumferences, etc.).
A solid disc 908 is suspended above the distal end 916 of the conductive helix element 910. The solid disc 908 is formed of an electrically conductive material, such as metal (e.g., aluminum, graphite, or copper). The solid disc 908 has a diameter 904 selected in accordance with a given application (e.g., 0.4λ, to 0.6λ). The solid disc 908 reflects some of the energy back towards the cup reflector 912 so as to provide backwards or standing wave, and a Fabry Perot resonator effect. As a result of the Fabry Perot resonator effect, the directivity of the helical antenna 900 is increased as compared to that of a conventional helix antenna. Accordingly, the solid disc 908 is a beam narrowing feature and a gain enhancing feature of the helical antenna 900. It is also contemplated to make a conductive electrical connection between the solid disc 908 and the distal end 916 or the helix element 910 with directive gain increase, which may benefit structural implementation.
Referring now to
Referring now to
The helical windings of the proximal and distal segments may have constant diameters. The spacing between successive turns of at least the proximal segment's helical winding may be constant or varied along a line parallel to the axis. The linearly progressing pitch angles and the constant pitch angle may be selected so that a radio wave velocity matches a current velocity at any location along the length of the conductive helix element.
In 1310, the conductive helix element is structurally supported. This structural support can be achieved using an elongate support member (e.g., bar 124 of
In 1312, the proximal segment of the conductive helix element is coupled to a ground plane structure. The ground plane structure comprises a deployable ground plane structure (e.g., ground plane structure 108 of
In 1314, a solid disc (e.g., solid disc 908 of
Although the present solution has been illustrated and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In addition, while a particular feature of the present solution may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Thus, the breadth and scope of the present solution should not be limited by any of the above described embodiments. Rather, the scope of the present solution should be defined in accordance with the following claims and their equivalents.
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