WO2003067706A1

WO2003067706A1 - Antenna

Info

Publication number: WO2003067706A1
Application number: PCT/GB2003/000278
Authority: WO
Inventors: Alan Gilbert Patrick Boswell
Original assignee: Bae Systems Plc.
Priority date: 2002-02-08
Filing date: 2003-01-24
Publication date: 2003-08-14
Also published as: AU2003202682A1; GB0203525D0

Abstract

The invention relates to an antenna (10) for receiving vertically-polarised high frequency (HF) band radio signals. It is suitable for use as a low-profile antenna for applications where compactness is a key requirement. The antenna (10) comprises a conductor plate (12), an elongate conductor member (22) and an amplifier (20), wherein the conductor member (22) extends substantially orthogonally from the conductor plate (12) and provides an electrical path between the conductor plate (12) and the amplifier (20).

Description

ANTENNA

This invention relates to an antenna for receiving vertically-polarised high frequency (HF) band radio signals.

In particular, the present invention is suited to use in receiving vertically polarised radio signals in the HF radio band, i.e. in the range of 3 to 30 MHz, and is particularly suitable for use as a low-profile antenna for applications where compactness is a key requirement.

The range of typical wavelengths in the HF radio band is from 10 m to 100 m and, conventionally, antennas are a tenth to a quarter of these wavelengths in height. Much effort has been invested in reducing the dimensions of antennas whilst retaining effective performance. An overriding objective is to achieve antenna sensitivity adequate to detect signals at a level equal to the world-wide minimum observed level of external noise.

One application of such antennas is on naval ships where they are used to monitor ground-wave emissions: ground waves travel for great distances over sea and are characterised by their vertical polarisation. Accordingly, upright antennas are used to receive these ground-wave signals. One such receiving antenna in current use comprises a 1.6 m high monopole mounted on a box containing a wideband amplifier. Connecting the monopole directly to the amplifier allows a monopole of shorter length than typical to be used by reducing signal-power losses whilst retaining wide band performance.

A second relevant antenna can be found in US Patent No. 5,790,080 to Lockheed Sanders, Inc. This patent describes an antenna loop comprising three separated antenna elements forming three sides of a rectangular arch, extending from a ground plane. The three separated antenna elements are linked by a slow-wave meander line in the form of a folded transmission line.

The present invention offers an alternative solution to provide an antenna that is compact and is particularly suited to receiving vertically polarised HF band radio signals.

According to a first aspect, the present invention resides in an antenna for receiving vertically-polarised HF band radio signals comprising a conductor plate, an elongate conductor member and an amplifier, wherein the conductor member extends substantially orthogonally from the conductor plate and provides an electrical path between the conductor plate and the amplifier.

By connecting a conductor plate to the elongate conductor member, the overall length of the conductor member can be much reduced. In contrast to the 1.6 m monopole antenna discussed herein above, the present antenna can be realised with a total height of only 0.5 m. This present antenna arrangement will be referred to hereinafter as a loaded monopole antenna.

Preferably, the antenna further comprises an earth plate to which the amplifier is grounded. Optionally, the conductor plate or ground plate is constructed of honeycomb material, aluminium honeycomb material being particularly preferred. This allows a lightweight yet strong structure to be fabricated.

Optionally, the antenna further comprises wall members, wherein the wall members, the conductor plate and the earth plate meet along their edges to define a box. In this way, the wall members may be used to support the conductor plate, whilst the box may define a weatherproof housing for the amplifier and any other associated electronics. In addition, this configuration provides a robust structure that may be strong enough, for example, to tolerate one or more people standing on the antenna or other heavy objects being placed on the antenna.

Advantageously, the wall members are constructed of a dielectric such that they isolate the conductor plate from the earth plate. Optionally, the wall members comprise a dielectric honeycomb material. This choice of material provides a strong yet lightweight construction.

Preferably, any honeycomb material has an associated weatherproofing element so as to provide a barrier to mitigate or stop entirely water ingress through the honeycomb material. The weatherproofing element may be a waterproof film, membrane, panel or plate. This configuration is particularly beneficial where the wall members, the conductor plate and the earth plate meet along their edges to define a box, as the box can be weatherproof where all honeycomb materials have associated weatherproofing members. Optionally, a pair of weatherproofing elements may be attached to opposed sides of at least one of the honeycomb materials.

Optionally, the conductor member is a wire braid.

In addition, the present invention also resides in an antenna array comprising a plurality of antennas as described herein above. The compact size of the present invention means that the array may be located on a ship or the like without taking up excessive space where space is usually at a premium. Providing an array of antennas is beneficial as it gives directional properties not obtained from a single antenna.

The present invention also resides in a vehicle comprising one or more antennas as described herein above. Preferably, the earth plate is grounded to a metallic body of the vehicle.

Moreover, present invention also resides in a ship or boat comprising one or more antennas as described herein above. Preferably, the earth plate of an antenna is mounted on and electrically connected to the deck of the ship or boat. Optionally, the ship or boat may comprise a plurality of antennas positioned around the deck edges.

In order that the invention can be more readily understood, reference will now be made, by way of example only, to the accompanying drawings in which;

Figure 1 is a perspective view of an antenna according to the present invention;

Figure 2 is a section along line ll-ll of the antenna of Figure 1 ; and

Figure 3 is a perspective view of a naval ship comprising an array of the antenna of Figures 1 and 2.

Figures 1 and 2 show an antenna 10 according to the present invention comprising a top plate 12, a base plate 14 and four side walls 16 that together define a hollow box. The box is 0.5 m high, 0.5 m wide and 1.5 m long. The top plate 12, base plate 14 and side walls 16 may fasten together or be joined in any conventional manner. The base plate 14 is also attached to a supporting structure, in this case to the deck 18 of a ship 19. The top plate 12 and the base plate 14 are both constructed from an aluminium honeycomb material and, therefore, conduct electricity. The side walls 16 are insulating and are constructed from honeycomb dielectric material. The base plate 14 is attached to the deck 18 such that good electrical contact is established therebetween, such that the base plate 14 acts as an adequate ground plane.

To prevent water ingress into the interior of the box defined by top plate 12, base plate 14 and side walls 16, the honeycomb top plate 12 and honeycomb side walls 16 are backed with a water-proofed material 17. The material 17 may be in the form of a film or a rigid panel or plate and may be bonded to the top plate 12 and side walls 16 around their peripheries to ensure complete waterproof sealing.

Housed within the box defined by the top plate 12, base plate 14 and side walls 16 are an amplifier 20 and a wire braid 22. The wire braid 22 extends vertically from the centre of the top plate 12 to the amplifier 20, the amplifier 20 being mounted centrally on the base plate 14. The wire braid 22 establishes direct electrical contact between the top plate 12 and the amplifier 20. The amplifier 20 is mounted on the base plate 14 such that electrical contact is established therebetween, thereby providing a ground plane for the amplifier 20. The amplifier 20 has an output connected to an output lead 24 that extends to one of the side walls 16 in which a coaxial connector socket 26 is provided. Accordingly, the coaxial connector socket 26 provides a means for relaying signals out from the antenna 10 and for connecting a power supply unit (not shown) to the amplifier 20. As will be appreciated, the top plate 12 and the wire braid 22 form a loaded monopole antenna that serves to receive vertically polarised HF band radio signals. The antenna 10 results in a height of 0.5 m high, much less than the theoretical ideal of a quarter-wavelength of the HF signals, but directly connecting the loaded monopole to the amplifier 20 allows a better impedance match to be made, thereby improving the quality of the signal fed from the amplifier 20 to the coaxial connector socket 26.

Those skilled in the art will readily appreciate that there are many types of commonly available amplifiers that could be used in this application. In this example, a MOSFET amplifier is used as it provides adequate power gain whilst being relatively cheap and easy to replace. This is advantageous as it may then play a role as a sacrificial component in the event of a lightning strike.

Figure 3 shows an array of the antennas 10 shown in Figures 1 and 2 positioned around the edge of a deck 18 of a naval ship 19. As will be appreciated, the compact design of the antennas 10 allows many to be used around the deck edge without being too intrusive in an environment where space is at a premium. Such an array of antennas 10 provides directionality that is lacking in a single antenna 10 because they can be operated with control of the phase of the signals they emit or receive relative to one another.

Of course, there are many variations to the above embodiment that are possible without departing from the scope of the invention.

For example, whilst a cuboid box has been shown in Figure 1 , different shapes of box may be used. Where stealth is particularly important, the side walls may be sloping rather than upright to define a more stealthy shape. The square top plate 12 may be preserved in this arrangement.

Water-proofed material 17 may be bonded to either side of the top plate

12, the base plate 14 and side walls 16 rather than merely using it to back the top plate 12, the base plate 14 and side walls 16. This is advantageous as it prevents water and dirt accumulating in the voids defined by the honeycomb material.

It will be clear that the application of this antenna is wider than merely to a naval ship 19. The antenna 10 may be employed on any vehicle, whether it be a land, sea or air vehicle. In addition, the antenna may be used advantageously on a fixed structure, such as a building, particularly where compactness is desired.

Claims

1. An antenna for receiving vertically-polarised HF band radio signals comprising a conductor plate, an elongate conductor member and an amplifier, wherein the conductor member extends substantially orthogonally from the conductor plate and provides an electrical path between the conductor plate and the amplifier.

2. An antenna according to claim 1 , further comprising an earth plate to which the amplifier is grounded.

3. An antenna according to any preceding claim, wherein the conductor plate or ground plate is constructed of honeycomb material.

4. An antenna according to claim 3, wherein the honeycomb material comprises aluminium.

5. An antenna according to any of claims 2 to 4 further comprising wall members, wherein the wall members, the conductor plate and the earth plate meet along their edges to define a box.

6. An antenna according to claim 5, wherein the wall members are constructed of a dielectric such that they isolate the conductor plate from the earth plate.

7. An antenna according to claim 6, wherein the wall members comprise a dielectric honeycomb material.

8. An antenna according to any of claims 3 to 7, wherein any honeycomb material has an associated weatherproofing element.

9. An antenna according to any preceding claim, wherein the conductor member is a wire braid.

10. An antenna array comprising a plurality of antennas according to any preceding claim.

11. A vehicle comprising one or more antennas according to any claims 1 to 9 mounted thereon.

12. A vehicle according to claim 11 wherein the earth plate is grounded to a metallic body of the vehicle.

13. A ship or boat comprising of one or more antennas according to claims 1 to 9.

14. A ship or boat according to claim 13, wherein the earth plate of an antenna is mounted on and electrically connected to a deck of the ship or boat.

15. A ship or boat according to claim 14, comprising a plurality of antennas according to any of the claims 1 to 9 positioned around the deck edges.

16. An antenna substantially as hereinbefore described with reference to Figures 1 to 2.

17. A ship or boat substantially as hereinbefore described with reference to any of Figures 1 to 2.