EP3195407A1

EP3195407A1 - Radio with a deployable antenna

Info

Publication number: EP3195407A1
Application number: EP15757543.2A
Authority: EP
Inventors: David James NETHERCOTT; Robin Granger; Aidan Tout
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 2014-08-29
Filing date: 2015-08-28
Publication date: 2017-07-26
Also published as: GB2529689A8; WO2016030655A8; GB2529689A; WO2016030655A1; GB201415303D0; GB2529689B

Abstract

A Radio comprising a radio electronics module and an antenna comprising at least one active component that is elongate in a deployed configuration to convert radio signals to or from electrical signals, the active component is substantially comprised of an electrically conductive Storable Tubular Extendible Member (STEM) structure that is spiral in a stowed configuration, and elongate with an arcuate cross section in the deployed configuration, characterized in that the STEM structure is substantially comprised of a carbon fibre material electrically coupled to the electronics module so as to perform the function of the active component. A method of deploying a radio antenna is also claimed.

Description

with a deployable antenna

This invention relates to space saving deployable radio antennas, for example for spacecraft or portable radios.

in the past, satellites have sometimes included a rollable antenna made of metal (e.g. spring steel). These structures are known as Storable Tubular Extendible Member (STEM) structures. On release from a rolled up spiral configuration they unroll as a spring to achieve their natural state - a linear element having a generally arcuate cross section.

A standard metal retractable tape measure is a good example of a STEM structure, and it is known that a cubesat antenna can be constructed of a sectiori of measuring tape deployed to unfurl from a rolled up configuration. The metal tape measure naturally unrolls in the absence of other forces, and once unrolled it adopts its natural form which is generally linear and is generally arcuate in cross section (with respect to the linear direction). This arcuate structure lends rigidity to the linear antenna which is maintained unless a force is applied that is great enough to cause the arcuate structure to flatten at any point along the antenna. In the case of a portable radio antenna or a spacecraft such forces (the weight of the antenna, any wind resistance or centripetal forces) will be small or near zero.

Particularly for spacecraft deployment, the roll of material is released to unfurl in an unconstrained fashion into space and the spirally outer end remains connected to the spacecraft. This is in contrast with a traditional tape measure where the roll of material rotates inside a housing, and the outer end extends linearly from the housing.

It is an object of the present invention to further reduce the complexity, weight and/or rolled size of a STEM antenna, or increase its unfurled length for a given rolled size.

According to a first aspect of the present invention there is provided a Radio comprising a radio electronics module and an antenna comprising at least one active component that is elongate in a deployed configuration to convert radio signals to or from electrical signals, the active component is substantially comprised of an electrically conductive Storable Tubular Extendible Member (STEM) structure that is spiral in a stowed configuration, and elongate with an arcuate cross section in the deployed configuration, characterized in that the STEM structure is substantially comprised of a carbon fibre material electrically coupled to the electronics module so as to perform the function of the active component.

This has the benefit of enabling a long antenna to be unfurled from a limited storage space, especially in environments where the forces that the antenna must withstand are low.

The inventors have investigated alternatives to spring steel and discovered that carbon fibre is suitable to further reduce the size or weight of the antenna (or provide a longer antenna). Carbon fibre has never been used to contribute to the conductivity of an antenna along its length, however the inventors have discovered that:

the material offers an improvement over the use of spring steel in the storage space required for an antenna of a given length, the problems of the material permanently tangling or kinking that would be expected of a carbon fibre ribbon released freely from a coiled state (even into a vacuum where the energy is not absorbed by air resistance) are not so likely as to prevent the device being commercially feasible,

the problem of the carbon fibre being degraded by UV light from the sun in use (even in space) does not require a layer of protective coating so thick as to undermine the space-saving benefits of the use of carbon fibre, and

- most interestingly and surprisingly, the material itself can be used to at least contribute to the conductivity of the antenna, along the length of the antenna.

The suitability of carbon fibre to contribute to the conductivity of the antenna along it length is very unexpected, because carbon fibre has a very low conductivity compared to materials normally used for radio antennae (steel). To achieve the benefit of the invention (space saving vs spring steel) the carbon fibre will inevitably be a thin ribbon structure, which therefore will have a very small cross section making the conductivity of the carbon fibre structure even lower than even a rod of carbon fibre, and thus it is even more surprising that it can usefully contribute to the conductivity of the antenna.

Previous uses of carbon fibre include:

1) Devices that are described in relevant marketing literature as 'carbon fibre antennas', and which are antenna stubs marketed for retrofit use by car enthusiasts. However these products work only because they contain a core of metal (with a sheath of carbon fibre around the metal providing only a cosmetic benefit).

2) It is possible, but unconfirmed, that some of these retrofit car antenna stubs may actually be purely carbon fibre (without a metal core). Although car enthusiasts may assume that their car has benefited from a carbon fibre antenna stub, in reality the carbon fibre is merely a cosmetic stub which does not contribute significantly to the performance of the car radio. Modern car radios can pick up reasonably strong FM radio signals without the addition of an antenna outboard of the car body (because there is a cable from the radio module which passes to where the antenna will be connected, and this cable acts as an antenna by itself whether or not a carbon fibre stub has been fixed onto the end). So the car radio works despite the addition of a carbon fibre stub, rather than because of it.

3) Reflector dishes for radio antennae. In such devices, the dish is of carbon fibre, but the antenna's active element (the part electrically connected to the radio electronics module and which converts the radio waves to electrical signals or vice versa) will be metal as usual.

In none of these examples is the carbon fibre provided as a STEM structure, and in none of these examples does the carbon fibre provide both the physical structure of the antenna, and also contribute to the conductivity of the antenna along its length.

According to a second aspect of the present invention there is provided a method of deploying a radio antenna having the steps of: providing the radio of claim 1 with an active component arranged as a spiral in the stowed configuration, and retaining an outermost end of the spiral active component in electrical connection to the electronics module, while releasing the remainder of the spiral active component so that it unravels to adopt a deployed configuration having an elongate arrangement with arcuate cross section. Preferably the release of the remainder of the spiral active component is achieved by means of an electrically activated release mechanism (of any of the various types known in the art). Preferably the electrically activated release mechanism includes a sprung pivot arranged such that the release by the release mechanism repositions the active spiral component to a position where it can unravel. This may include repositioning it outboard of a housing, such that the spiral is then free to unravel. Preferably in the stowed configuration the spiral is fully contained within the housing to protect the spiral during transport.

The term "a radio" means a device adapted to modulate and transmit or receive and demodulate radio wave signals.

The term "radio electronics module" covers any electronics able to modulate and produce electrical signals for transmission by a radio antenna, or to receive and demodulate such signals from an antenna.

The term "active component" means the conductive element electrically coupled to the radio electronics module for converting electrical signals to radio waves or converting radio waves into electrical signals. The term excludes electrical shielding that may be used to surround a cable between the antenna and radio electronics module, and it excludes a reflective ground plate or antenna dish or other collector such as a log periodic or yaggi collector array. For example in the case of a dipole antenna there may be more than one active component (in that case two).

The term "elongate" covers variations that need not be strictly linear, but should include a conductive path with two ends spaced apart from one another.

The term "substantially comprised of means that it typically has solely or mostly just the elements stated, but may have limited additional elements. In the case of the active component, this means the active component may include an unshielded cable or other unshielded conductive path between the STEM structure and the electronics module, provided that this unshielded cable or path contributes comparatively little to the radio reception/transmission capability of the active element as compared to the STEM structure in deployed configuration. In the case of the STEM structure, this means the STEM structure may include a UV (or other) protective coating around the carbon fibre material, and may include a conductive painted line, coating, foil layer or similar element provided that this is not the main source of rigidity of the STEM structure in the deployed configuration (i.e. the carbon fibre material must be the main source of this rigidity).

If any additional element in the STEM structure is conductive along the length of the STEM structure this additional element needs to be conductively coupled to the carbon fibre, either along its length (in the deployed configuration) or at least at or near the radio electronics module end of the STEM structure.

The term "so as to perform the function of the active element" means that the carbon fibre material at least jointly performs the function of the active element in conjunction with any additional conductive element arranged in parallel, if any.

Preferably, the carbon fibre material is at least the main source of electrical conductivity of the active element along substantially the length of the active element, in the deployed configuration.

This covers the use of a conductive coating or other conductive element provided that it contributes less to the conductivity of the active element along the length of it, than the carbon fibre material does. For example there may be a metal conduction path between the radio electronics module and the carbon fibre STEM structure, but this path should be short (measured in a straight line) as compared to the deployed length of the STEM structure, and preferably less than 5% thereof. Similarly the UV protective coating could have some conductivity as measured along a length of the STEM structure, but not as much as that of the carbon fibre material.

This has the benefit that additional conductive components need not be included which might add to the cost or manufacturing complexity, or which may increase the thickness of the antenna and thus reduce the length of antenna that can be unfurled from a given storage space. The inventors have discovered, to their further surprise, that it is not necessary to include a metal wire or equivalent (E.g. painted metal surface) to compensate for the comparatively low electrical conductivity of carbon fibre combined with the (in practice) low cross sectional area of such a carbon fibre antenna. This was highly unexpected.

Thus therefore for simplicity, preferably, the carbon fibre material is the sole source of electrical conductivity of the active element along substantially the length of the active element, in the deployed configuration.

Preferably the STEM carbon fibre structure is arranged such that in a deployed configuration it has a an arcuate, circular or spiral form in cross section of at least 270 degrees to provide a rigid structure for a given weight and length. In cross section the form may be substantially circular, so as to form a substantially closed tube. The form preferably extends at least 90 degrees (around a notional circle), more preferably at least 180 degrees, more preferably at least 270 degrees, optionally may be substantially 360 degrees, and optionally may exceed 360 degrees (thus forming a spiral in cross section). Arcuate, spiral and circular include substantially oval, polygonal or other variations provided that the result is an antenna having a part or whole tubular form.

Preferably there are at least two carbon fibre STEM antennae that cooperate to provide a directional antenna. Optionally the antenna is provided on a spacecraft, such as a satellite. The design may be of particular value for small satellites (less than 100kg), and particularly for a cubesat. A cubesat is a type of miniaturized satellite for space research that has a volume of around one liter or less (typically exactly one liter), has a mass of around 1 or 2 kilograms or less (typically no more than 1.33 kilograms), and typically uses commercial off-the-shelf components for its electronics.

According to one embodiment the antenna includes two active elements arranged that in a deployed configuration they form a dipole antenna. According to another embodiment there is provided a spacecraft comprising the radio as described above.

The invention will now be described by way of example only and with reference to the drawings in which:

Figure 1 is a top schematic view of a dipole antenna according to one embodiment of the invention. Figure 2 is a perspective view of the embodiment of figure 1.

As shown in figure 1 a radio 1 includes an antenna including an active element 3 made of a carbon fibre material, in this case specifically a polymer reinforced woven carbon fibre ribbon formed to have an arcuate cross section unless physically biased otherwise, arid covered with a UV protecting coating.

In a stowed configuration 4, the active element is a roll of carbon fibre ribbon. In a deployed configuration the active element is a linear strut having an arcuate form in cross section. This is achieved with a storable tubular extendible member (STEM) structure shown unfurling 5 via path 10 (dotted line circles and arrow).

A release mechanism 6 is sprung (not shown) to release the roll of carbon fibre material from a housing 7. On being released 8 the roll unfurls, and acquires it's deployed configuration, although especially if unfurled in a vacuum it may do so violently and may go through a series of semi-tangled configurations in an agitated and chaotic manner, before settling to its final linear state.

The design shown has two STEM active components to form a dipole antenna. Other variations are possible such as a monopole or multiple antenna formation.

Figure 2 shows a perspective view of the radio 1 with two STEM active components 3 in its deployed configuration (only part of the STEM structures are shown), mounted above a radio electronics module 2. As can be seen, the active STEM elements have an arcuate form in cross section, which gives them rigidity once in the deployed configuration. The arcuate form may extend around a greater angle than that shown (120 degrees), and rather than 90-180 degrees it might extend more than 180 degrees (and optionally more than 360 degrees, although there is diminishing benefit beyond 360 degrees).

The carbon fibre is typically woven before the reinforcing polymer is hardened, and is preferably arranged to be less flexible along the length (in a deployed configuration) as across the arcuate ribbon form. This can be achieved by aligning some of the carbon fibres parallel to the direction of the length of the ribbon, and either arranging fewer carbon fibres across the ribbon and/or arranging them to have an indirect route across the ribbon (e.g. zigzag) or by arranging the fibres as a sandwich including outer layers aligned along the direction of the ribbon, and a middle layer aligned across the ribbon. The carbon fibre is generally provided with a polymer reinforcement resin or plastic. This may optionally be a thermoplastic for faster setting e.g. in a continuous forming process. However if the carbon fibre ribbon is equally stiff in all directions then it can still be used however typically with a flatter arc (smaller angle and larger radius of curvature) in the deployed configuration than would otherwise be the case. The properties of the ribbon can be further optimized by those skilled in the art of carbon fibre structural design.

The STEM component 3 may have a conductive coating or foil or paint applied to it 9 either as a narrow strip (as shown) or perhaps encompassing the STEM structure. The conductive element 9 is in electrical contact with the carbon fibre at least via a conduction path to the electronics module 2, but preferably at least at the proximal end (the end of the STEM structure nearest the electronics module) and preferably along the length of the STEM member.

The conductive material might be copper foil or a polymer embedded with carbon nanotubes, or a plating of copper or silver or any other conductive material. Alternatively an additional conductive element may be included in the carbon fibre ribbon (E.g. strands of fine copper wire woven along with the carbon fibre strands) or an additional conductive element included in the reinforcement polymer of the carbon fibre material such as dispersed carbon nanotubes. Where these elements make up a substantial fraction of the carbon fibre material and contribute a substantial fraction of the conductivity of the STEM structure they are considered extrinsic to the carbon fibre material.

Preferably however there are no more than minimal such additional conductive elements, and for simplicity, preferably none. In a deployed state, multiple STEM structures can be combined to form any antenna structure that is formed through combination of linear, electrically conductive components. The simplest antenna arrangement is a monopole (or "whip") antenna, comprising a single electrically conductive element that is a deployed STEM component.

In conjunction with a monopole antenna, the use of a Ground Plane enhances the antenna performance. A true Ground Plane is large, flat plane of electrically conductive material, the plane of which is perpendicular to the monopole antenna axis and meets the monopole at one end. In practical terms, an effective Ground Plane can be emulated by using multiple STEM elements, connected in a radial spoke configuration. Optionally therefore, the antenna is provided with a ground plane arranged perpendicular to it, being formed of at least three carbon fibre STEM elements arranged radially with respect to the antenna.

An additional STEM structure configuration is formed with two STEM structures deployed collinearly, in opposite directions, to form a linear dipole antenna. This form of antenna has improved electrical performance characteristics over a monopole but typically requires twice the dimensions of the monopole to achieve this. A more general antenna design is where the two antenna elements are not collinear. The angle between the elements can be adjusted to define the receiving characteristics and performance.

When deployed in monopole or dipole configurations, the antennas could be electrically short in size. This refers to a configuration where the conductive antenna elements are shorter than is required for optimal antenna functionality, but where the limited electrical performance is an acceptable trade-off against size. An example of an electrically short antenna is a mobile phone or mobile handheld radio.

Four STEM elements, when arranged in a cross configuration, where the STEM elements meet at their ends, with 90° angle between each, and all elements lying in the same flat plane, forms an antenna configuration suitable for receiving or transmitting Electromagnetic waves that are either circularly polarized or polarized at an unknown angle, that is not ideally matched to a dipole or monopole antenna orientation for optimum reception. This is a common antenna configuration known as a crossed dipole and the benefits of using a STEM as the antenna elements apply as for the monopole and dipole antennas described above.

STEM elements can also be configured to form a directional antenna known as a Yagi-Uda antenna. This antenna form comprises a dipole receiving element as described above, with specifically sized conductive element s placed forward and behind the receiving element, in the direction of the propagation of the transmitted or received electromagnetic waves. These additional elements could be formed from STEM elements in the same manner as the receiving dipole element.

A UV coating (if required) can be applied as a painted or sprayed layer, or even incorporated into the resins used to manufacture the carbon fibre material. The need for this depends on the intended use and required duration of service.

Claims

CLAIMS:

1. A Radio comprising a radio electronics module and an antenna comprising at least one active component that is elongate in a deployed configuration to convert radio signals to or from electrical signals,

the active component is substantially comprised of an electrically conductive Storable Tubular Extendible Member (STEM) structure that is spiral in a stowed configuration, and elongate with an arcuate cross section in the deployed configuration, .

characterized in that

the STEM structure is substantially comprised of a carbon fibre material electrically coupled to the electronics module so as to perform the function of the active component.

2. The radio of claim 1 where the carbon fibre material is at least the main source of electrical conductivity of the active element along substantially the length of the active element, in the deployed configuration.

3. The radio of claim 2 where the carbon fibre material is the sole source of electrical conductivity of the active element along substantially the length of the active element, in the deployed configuration.

4. The radio of any one of the preceding claims comprising a second antenna substantially similar to the said antenna, such that in the deployed configuration they jointly form a dipole antenna.

5. The radio of any one of claims 1 to 3 further comprising a ground plane arranged perpendicular to the said antenna, formed of at least three carbon fibre STEM elements arranged radially with respect to the antenna.

6. A spacecraft comprising the radio of any one of the preceding claims.

7. A method of deploying a radio antenna having the steps of:

Providing the radio of claim 1 with an active component arranged as a spiral in the stowed configuration, and

Retaining an outermost end of the spiral active component in electrical connection to the electronics module, while releasing the remainder of the spiral active component so that it unravels to adopt a deployed configuration having an elongate arrangement with arcuate cross section.