CONFORMAL ANTENNA

Abstract: An antenna structure and a method of forming an antenna on a conductive carrier are claimed and disclosed. The structure includes a carrier (18) having an electricity conductive surface (18.1) and a magnetic field interacting layer (20) including an amorphous or nanocrystalline magnetic material alloy, such as VITROPERM 500 F<TM>, provided on or near the surface. In use, the antenna structure is driven with a signal source generating a frequency in the band 1 MHz to 3000 MHz.

Description: CONFORMAL ANTENNA TECHNICAL FIELD THIS invention relates to radio frequency antennas and more particularly to conformal antennas for use on a vehicle or craft, such as an aeroplane or helicopter. BACKGROUND ART A conformal antenna conforms to the shape of a carrier body, such as that of a vehicle or craft. They are used in practice to form a large enough antenna on the carrier to cover a desired frequency range and/or to reduce air resistance and/or for aesthetical reasons. For example, in the case of an aeroplane, the antenna may be formed to include at least parts of the metallic skinned fuselage and/or at least one metallic skinned wing of the aeroplane. However, a conformal antenna requires regions of high impedance in some areas of the metallic carrier surface. This may be achieved by physically interrupting or slotting the carrier body or skin in such areas. Such a construction is not desirable, because in most situations the carrier is weakened. OBJECT OF THE INVENTION Accordingly it is an object of the present invention to provide an antenna structure and a method of forming same with which the applicant believes the aforementioned disadvantages may at least be alleviated. SUMMARY OF THE INVENTION According to the invention there is provided an antenna structure including a carrier having a conductive surface and a layer of magnetic field interacting means applied on or near a region of the surface, to inhibit flow of electrical current in the surface across the region. The magnetic field interacting means serves to interact with magnetic fields associated with surface currents to suppress those currents. The magnetic field interacting means may be an amorphous or nanocrystalline magnetic material alloy, preferably an amorphous or nanocrystalline magnetic metal alloy. An example of a suitable alloy is VITROPERM 500 F ™ which is a Fe-based alloy (Fe73.5 Cu 1 Nb3 SM 5.5 B7) . The carrier may be a vehicle, such as a motor vehicle or craft, such as an aeroplane or helicopter having metallic skinned wings or fuselages. The magnetic field interacting means may be applied on the carrier to form a slot, loop or dipole antenna, for example. According to another aspect of the invention there is provided a method of forming an antenna on a conductive carrier, the method including the steps of providing a layer of magnetic field interacting means on a region of the carrier, to inhibit flow of electrical current in the carrier across the region. The magnetic field interacting means may be a suitable amorphous or nanocrystalline magnetic material alloy, preferably a magnetic metal alloy. The material may be provided in the form of a tape and the layer may thus be provided by applying the tape on the surface in a linear form or by wrapping it around a region of the carrier. BRIEF DESCRIPTION OF THE ACCOMPANYING DIAGRAMS The invention will now further be described, by way of example only, with reference to the accompanying diagrams wherein figure 1 is a plan view of an aeroplane including an antenna structure according to the invention; figure 2 is a section on line II in figure 1 ; figure 3 shows an alternative configuration for the antenna structure; figure 4 is a diagrammatic perspective view of yet another alternative antenna structure according to the invention; and figure 5 is a diagram of a dipole antenna which is equivalent to the structure in figure 4. DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION An aeroplane including a conformal antenna structure 1 0 according to the invention is generally designated by the reference numeral 1 2 in figure 1 . The aeroplane body includes a fuselage 1 4 and wings 1 6 and 1 8, each covered with an electricity conductive metallic skin. The skin 1 8.1 of wing 1 8 is shown in better detail in figure 2. The conformal antenna structure 10 conforms to the shape of the body of its carrier, namely the aeroplane wing. It is formed by applying a layer 20 of a magnetic field interacting means in the form of an amorphous or nanocrystalline metal alloy in suitable regions on the body, effectively to create on the metallic surface high impedance regions, thereby to create a suitable surface mounted antenna geometry or pattern on the body. The magnetic field interacting means may be the product VITROPERM 500 F™ which is a Fe-based alloy (Fe73.5 Cu1 Nb3 Si1 5.5 B7). The layer 20 on the conductive wing 18 is shown in more detail in figure 2. The layer 20 interacts with magnetic fields associated with electrical current to suppress the current in the skin below the layer, with the result that electronically speaking a slot is emulated in region a of the antenna, separating feed point regions 22 and 24 from one another. By the provision of such layers on the fuselage and/or wings, the flow of current in the metallic skin can be controlled. Should an RF source 26 generating a frequency in the range 1 MHz to 3000MHz be connected to the feed point regions, the result would be that a conformal antenna (which may be a large dipole antenna, a slot antenna or the like) is formed at these frequencies. The magnetic field interacting means may be provided in the form of a tape or the like to facilitate application thereof on the wing and on or around selected regions of the fuselage. In figure 3 there is shown another antenna structure according to the invention. The magnetic field interacting means 30 is applied in the form of a ring on the conductive carrier 32. When driven as shown, the structure yields a substantially omnidirectional antenna. The polarization of the antenna is perpendicular to the plane of the carrier 32. In figure 4 there is shown yet another antenna structure 40. The structure includes a hollow or solid rod 42 of an electricity conductive material. The magnetic field interacting means is provided in the form of a body 44 in a centre region of the rod. The body 44 is formed by winding a tape 46 of the magnetic field interacting material on itself. The tape is wound directly onto the rod or an air gap 47 may be provided between the rod and the body. When driven by an RF source 48 on either side of the body 44, a dipole antenna is formed. The equivalent dipole antenna 50 is shown in figure 5. It will be appreciated that there are many variations in detail on the antenna structure and method of forming same according to the invention without departing from the scope and spirit of the appended claims.

Claims: CLAIMS 1 . An antenna structure including a carrier having an electricity conductive surface; and a body of magnetic field interacting means mounted on or near a region of the surface, to inhibit flow of electrical current in the surface across the region. 2. An antenna structure as claimed in claim 1 wherein the magnetic field interacting means includes an amorphous or nanocrystalline magnetic material alloy. 3. An antenna structure as claimed in claim 2 wherein the magnetic material alloy is a magnetic metal alloy. 4. An antenna structure as claimed in claim 3 wherein the magnetic metal alloy includes VITROPERM 500 F™. 5. An antenna structure as claimed in any one of the preceding claims wherein the surface is substantially planar and wherein the body is in the form of at least one layer superimposed on the surface. 6. An antenna structure as claimed in claim 5 wherein the layer is of elongate configuration. 7. An antenna structure as claimed in any one of claims 1 to 4 wherein the surface is substantially planar and the body is of annular configuration. 8. An antenna structure as claimed in any one of claims 1 to 4 wherein the carrier is of elongate configuration, wherein the body is of annular configuration and provided co-axially with the carrier, in a centre region thereof. 9. An antenna structure as claimed in claim 8 wherein the carrier is a rod and the body includes a tape of the material coiled on itself. 10. An antenna structure as claimed in any one of the preceding claims including a signal source for generating a frequency between 1 MHz and 3000MHz connected to the carrier on opposite sides of the body. 1 1 . A method of forming an antenna on a conductive carrier including the steps of providing a layer of magnetic field interacting means on or near a region of the carrier. 12. A method as claimed in claim 1 1 wherein the magnetic field interacting means includes an amorphous or nanocrystalline magnetic material alloy. 1 3. A method as claimed in claim 1 2 wherein the magnetic material alloy includes a magnetic metal alloy. 1 4. A method as claimed in claim 1 3 wherein the magnetic metal alloy includes VITROPERM 500 F™. 1 5. A vehicle including a body at least part of which includes an electricity conductive surface; and an antenna structure at or near the surface, the antenna structure including a body of magnetic field interacting means mounted on or near a region of the surface, to inhibit flow of electrical current in the surface across the region. 6. An antenna structure substantially as herein described with reference to the accompanying diagrams. 7. A method of forming an antenna on a conductive carrier substantially as herein described with reference to the accompanying diagrams. 8. A vehicle or craft substantially as described with reference to the accompanying diagrams.

Inventors: DRESEL JUERGEN, FOURIE ANDRIES PETRUS CRONJE, DRESEL, JUERGEN, FOURIE, ANDRIES, PETRUS, CRONJE
Applicants: DRESEL JUERGEN, FOURIE ANDRIES PETRUS CRONJE, POYNTING INNOVATIONS PROPRIETA, DRESEL, JUERGEN, FOURIE, ANDRIES, PETRUS, CRONJE, POYNTING INNOVATIONS (PROPRIETARY) LIMITED
Application year: 1999
Main classification: H01Q1
IPC codes: H01Q1, H01Q9, H01Q13