GB2432963A - High frequency cable - Google Patents

Abstract

A high frequency cable has at least one twisted pair of conductors forming at least a part of a core, the core being covered by a screen, the screen covered by a sheath. The screen comprises at least a substrate having a plurality of non-continuous electro conductive pathways separated by electro insulating gapways, the length of the gapways being no greater than a wavelength in the MHz range and the pathways being less than the wavelength. The non-continuous conductive pathways may be made from aluminium or copper foil on a polyester substrate and may take the form of (a) 5m lengths separated by 12mm gaps, (b) "dots", (c) checkerboard squares or (d) diamond shaped areas of foil.

Description

<p>TBS/L1(F138049gba 1 12.05 1 High Frequency Cable This invention relates

to high frequency communications cables designed for transmitting signals between 1 and 1000MHz, hereinafter referred to as "the MHz range".</p>

<p>Communications cables are susceptible to coupled noise interference, from adjacent cables and from the environment, leading to degradation of signal along the cable. The problem of noise interference will become more pertinent with the increasing use of the next generation of Ethernet technology, 1OEASE-T, which utilises a much higher bandwidth than previous generations of Ethernet.</p>

<p>Shielded Twisted Pair (STP) cables provide reduction in noise interference by wrapping each pair of insulated conductors in a metallic foil and subsequently the entire bundle in a metallic braid or foil. However, STP cables are more expensive and more complex to install and terminate than Unshielded Twisted Pair (UTP) cables, and the metallic braid or foil must also be grounded at either end of the cable route to prevent it picking up unwanted signals in a similar manner to an antenna.</p>

<p>Therefore UTP cables, although being more susceptible to S...</p>

<p>noise interference from other cables and from the environment, are more usually used in Ethernet networks than STP cables. In addition, many buildings are already *5SSSS * wired with UTP cables, and many transmission standards * 30 are adapted to use these cables. Use of UTP cables is * therefore also influenced by the high cost of rewiring buildings with alternative cabling.</p>

<p>TI3S1LHF138O49gba 1.12.05 2 Therefore there is a need for a UTP cable with the coupled noise reduction capabilities of an STP cable.</p>

<p>Accordingly the present invention provides a high frequency cable having at least one twisted pair of conductors forming at least a part of a core, the core being covered by a screen, the screen covered by a sheath, the screen comprising at least a substrate having a plurality of non-continuous electro conductive pathways separated by electro insulating gapways, the length of the gapways being no greater than a wavelength in the MHz range and the pathways being less than the wavelength.</p>

<p>Typical pathways currently anticipated are about 100mm long with gapways of 10mm or less and/or no greater than a tenth of the wavelength. This performs well for transmission frequencies up to 800MHz.</p>

<p>Pathways may be applied by sputtering the electro conductive material onto the substrate, or by applying the material to the substrate in the form of a strip. The substrate may be a web, supplied in widths such as lm, which are subsequently slit into strips.</p>

<p>::::. 25 The screen may be formed as one or more tapes wound around the core, the tapes having a preferred width of around 20mm to 22mm. Where there are a pair of tapes forming the screen, these may be wound around the core in S.....</p>

<p>* opposing directions, which reduces the effective gapway.</p>

<p>Alternatively and preferably the tape is wrapped around the core like a cigarette paper. S...</p>

<p>I13S!LUF/38049gba 1.12.05 3 The pathways may be in the form of areas of material of different shapes applied to the substrate. The areas may be circular, rectilinear or diamond shaped.</p>

<p>The substrate may be made from a polymer such as polyester in thicknesses such as 9pm, 12pm or 23pm. The electro conductive material may be a metal such as aluminium or copper, in thicknesses such as 12pm or greater, or a sputtered metal in thicknesses such as 300A.</p>

<p>The invention provides a cable with the coupled noise immunity of an STP cable, whilst maintaining the installation, termination, and economic advantages of a UTP cable. The non-continuous electro conductive path eliminates the requirement for earthing the cable at the connection points.</p>

<p>Figure 1 shows examples of screens according to the present invention in the form of tapes.</p>

<p>Figure 2 is a graphical comparison of coupled noise characteristics of different cable types.</p>

<p>* .. 25 Figure 3 is a schematic cross section of a cable according to the invention. * **.</p>

<p>Figure 1, in option 1, shows 5m lengths of aluminium foil applied as electro conductive pathways to a polyester substrate with 12mm gaps between lengths. This is designed for use with transmission frequencies up to 500MHz as indicated in Figure 2. The resulting performance as seen in Figure 2 shows a reduction in coupled noise at 10MHz of approximately 30dB over unscreened cables. The TBS/LI IF/38049gba 1.12.05 4 reduction as measured commenced at 1 MHz. Coupling noise reduction at the upper end of the frequencies tested, that is 500MHz, shows an average reduction of a similar amount over unscreened cable.</p>

<p>The test sample performed generally as well as traditional screened cable.</p>

<p>In options 2, 3 and 4, the polyester substrate is covered by "dots", checkerboard squares or diamond shaped areas of aluminium foil.</p>

<p>The embodiments of Figure 1 provide various degrees of optical coverage of the underlying four pair core of the cable, e.g. between 30% and 99% of the four pair core is covered by electro conductive material.</p>

<p>Preferably this will be at the upper end of the range.</p>

<p>Figure 3 shows a cable with a core of four twisted conductor pairs, surrounded by a screen according to the invention, and subsequently surrounded by a sheath. e is a. . *Is. I,.. * S *5Ia i. S * S* * I. * S S. *</p>

<p>S S SS*</p>

<p>S I</p>

Claims (1)

1. <p>TflSiLHFi3049gba 1.1205 5 Claims 1. A high frequency cable having at

   least one twisted pair of conductors forming at least a part of a core, the core being covered by a screen, the screen covered by a sheath, the screen comprising at least a substrate having a plurality of non-continuous electro conductive pathways separated by electro insulating gapways, the length of the gapways being no greater than a wavelength in the MHz range and the pathways being less than the wavelength.</p>

   <p>2. A cable as claimed in claim 1 wherein the pathways are between 80 and 120mm and preferably about 100mm.</p>

   <p>3. A cable as claimed in claim 1 wherein the gapways are less than 15mm and preferably less than 10mm long.</p>

   <p>4. A cable as claimed in any one of claims 1 to 3 wherein the screen is formed as one or more tapes.</p>

   <p>5. A cable as claimed in claim 4 wherein the screen is formed of a pair of tapes so arranged that the : * 25 gapways overlap to reduce the effective length. I... ****</p>

   <p>6. A cable as claimed in any one of the preceding claims wherein the pathways are formed by sputtering a metal onto the substrate.</p>

   <p>: 7. A cable as claimed in any one of claims 1 to 5 wherein the pathways are formed by applying a metal foil to the substrate.</p>

   <p>TRS/LHF/38049gba 11205 6 8. A cable as claimed in claim 6 or 7 wherein the metal is aluminium or copper.</p>

   <p>9. A cable substantially as described and as shown in any one or more of the accompanying drawings. * ** * S * S.. * . * S.. *S I * I S * SI</p>

   <p>I</p>

   <p>S'S... * S I* I</p>

   <p>S IS. *SIS</p>

   <p>I I.e.</p>