GB2354371A

GB2354371A - A cable with reduced electromagnetic reflections

Info

Publication number: GB2354371A
Application number: GB9917538A
Authority: GB
Inventors: Stephen Pearce
Original assignee: ELETTRONICA
Current assignee: ELETTRONICA
Priority date: 1999-07-26
Filing date: 1999-07-26
Publication date: 2001-03-21
Also published as: GB9917538D0

Abstract

A cable that has the property of reduced reflections of electromagnetic radiation in directions approximately normal to the length of cable. The cable (4) has a plurality of coaxial cylinders (28, 29) interconnected as electromagnetic centre-fed dipoles by a radio frequency transmission line (30) and separated by sections of dielectric medium. Radiation reflected from any one such dipole (28) is largely cancelled by radiation intercepted by said dipole (28), transferred by means of the radio frequency transmission line (30), and transmitted through the adjacent dipole (29), and vice versa. Interconnected helical windings may be used instead of the coaxial cylinders. The cable has particular application to airborne towed targets or decoys.

Description

2354371 A CABLE WITH REDUCED ELECTROMAGNETIC REFLECTIONS This invention

relates to the reduction of the property of a metallic cable to reflect electromagnetic radiation in directions approximately normal to the length of the cable.

It is well known that a long metallic cable that may, for example, be deployed by an aircraft for the purposes of towing remote apparatus, gives rise to disadvantageous characteristic reflections of electromagnetic signals. The reflected electromagnetic signals may enable the detection and identification by radar of such a towed cable.

The present invention aims to provide a cable exhibiting significant reduction of radar cross section at chosen electromagnetic wavelengths.

Accordingly, in one non-limiting embodiment of the present invention, there is provided a metallic cable such as may be deployed by an aircraft. The metallic cable is modified by the incorporation of a secondary coaxially placed outer sheath of inter-connected elements distributed along the length of the said cable. The co-axial elements are of such dimension and spatial periodicity that the assembly acts cohesively to reduce the electromagnetic energy reflected in a direction normal to the length of the said cable.

2 Advantageously, an appropriate dielectric medium may be incorporated between the co-axial elements and the tow cable in order to modify the required dimensions and separation of those elements.

A non-limiting embodiment of the invention will now be described solely by way of example and with reference to the accompanying drawings in which:

Figure 1 shows an aircraft with a known tow cable; Figure 2 shows part of a modified tow cable; Figure 3 shows part of a cable of one particular construction; and Figure 4 shows another type of cable construction.

Referring to Figure 1, there is shown an aircraft 1 having a tow cable 2. Figure 1 illustrates schematically the reflection of illumination by an electromagnetic source 3. Such illumination is typically emitted by a hostile radar system.

Figure 2 shows part of a modified tow cable. A cable 4 is surrounded by a multiplicity of co-axially placed elements 5 whose lengths Li and separation L2 are determined by design in order to reduce the electromagnetic reflections, within a selected radio frequency bandwidth, in a direction normal to the length of the cable. A dielectric medium 7 incorporated between the elements may be used advantageously to influence the design.

Figure 3 shows a construction givensolely for the purpose of clarification. In the construction shown in 3 Figure 3, pairs of co-axial cylinders 28, 29 are interconnected as electromagnetic centre-fed dipoles by a radio frequency transmission line 30. Radiation reflected from any one such dipole is largely cancelled by radiation intercepted by said dipole 28, transferred by means of a radio frequency transmission line 30, and transmitted through the adjacent dipole 29, and vice versa.

Referring now to Figure 4, the co-axial cylindrical elements 5 shown in Figure 2 have been replaced by interconnected helical windings 8. Such an implementation of the present invention may confer advantages of reduced mass and enhanced flexibility, facilitating storage and deployment of the tow cable.

It is to be appreciated that the embodiments of the invention described above with reference to the accompanying drawings have been given by way of example only and that modifications may be effected. Thus, f or example, the illustrated radiative elements and their inter- connections may be altered.

4

Claims

A cable comprising means for the modification of the level of reflection of electromagnetic radiation.
2. A cable according to claim 1 in which the design favours the reduction of radar cross section.
3. A cable according to claim 2 in which the radar cross section modification means is effected by co-axially distributed cylindrical elements arranged to act as alternate dipole radiators.
4. A cable according to any one of the preceding claims in which the distributed elements are mounted on or embedded in a dielectric medium.
S. A cable according to claim 2 in which the radar cross section modifications means is effected by means of coaxially distributed helical windings.
6. A cable substantially as herein described with reference to the accompanying drawings.