A SOLID DIELECTRIC LENS AERIAL

Abstract: An aerial for electromagnetic radiation comprises a lens (65) of dielectric material transparent to the radiation and having a dielectric constant substantially equal to 3.414. A convex surface portion is provided with a metallic layer (65) for reflecting the radiation and an electrical connection (64) is provided to the reflecting surface for carrying the aerial signal. The lens material may be silica glass beads or silica flour bound together by an adhesive, preferably a polyester resin binder with the reflective layer coated on the outside of the lens. The lens may be spherical or alternatively it may have a plane of symmetry (32) and formed such that the lens is axially symmetric with the lens surface having a radius of curvature that increases as the distance from the axis increases. The lens may comprise a polycarbonate shell (36) formed of two halves and filled with particulate silica flour. The reflecting layer is provided on the inner surface of the lens shell.

Description: A Soli Dielectric LeosAerial The invention relates to aerials for the transmission or reception of electromagnetic wave energy with application to a wide range of frequency covering CB radio, radio and television. Television aerials for example commonly fall into two types: directional aerials, generally suitable for outdoor or loft use and having a number of directorstoiπprσvethedirectional gainoftheaerialandloopaerialswhich are siirple, cheapand suitable or indoor use. Indooraerialshave lowgain and are highly susceptible to shadowing and atmospheric influance on signal transmission The object of the invention is toprovide an improved aerial capable ofwide angle response and particularly suited to indoor use. Ihe invention provides an aerial for electromagnetic radiation comprising: a lens of material transparent to the radiation and having a dielectric constant suitable to refract the radiation and at least a surface portion which is convex; a material layer covering the surface portion and selected to reflect the radiation; and anelectrical connectionprovided tothe reflecting surface for carrying the aerial signal. GB Patent application No 8615317 discloses a radar reflector comprising a mirrored dielectric lens. Such reflectors are used, for example, to provide GBPboatswitharadarreflectingcapabilitytofacilitateradarsearch. The inventor has made the surprising discovery that these passive radar reflectors can be used as aerials for transmission and reception of electromagnetic signals by suitable connection of signal wires to the radar reflector. The aerial has been found to effective over a wide range of frequencies for a single size of lens. Preferably the dielectric constant of the lens material is substantially equal to 3.414. In one arrangement an electrically conducting member may be formed on a surface of the lens remote rom the reflecting layer and an electrical connection provided to the conducting me-iber whereby signal wires are connectable to the conducting member and-the reflecting-layer. - Hie lens may be a simple lens or a complex lens involving more * than one component. Inonearrangement thelensmaterialmaybesilicaglassbeadsor ' silica flour bound together by an adhesive, preferably a polyester resin binder. In thecaseofasinglelensthereflectivelayerandtheconducting member may then be coated on the outside of the lens. The lens may be sphericaloralternativelyitmayhaveaplaneofsymmetrydefiningidentical forward and rearwardhalveswiththeconductivememberbeingattachedtothe forward half and the reflective layer being attached to the rearwardhalf. Advantageouslythislens is axially-symmetricwith thelens surfacehavinga radius of curvature that increasesas thedistancefromthe axis increases. Inanalternativearrangement thelensmaycoπprisea shell, advantageously madeofpolycarbonate, and filledwithparticulatesilica flour, Sheshell maybe formedof twohalveswith the reflectinglayerandconductivemember, when present, located on the surface of respective halves. Advantageously the dielectric lens is located above an earthed plate, a coaxial cablebeingconnectedsuchthatthecentreconnectionisconnectedto the reflective layer and the screen wire is connected tothe earthedplate. Preferably a solder tag is attached toapartially copper platedportion of the reflective layer for attachment of the signal wire. In an advantageous arrangement particularly suited for transmission an electricallyisolatedconductingbackplateisprovidedperpendiculartothe earthed plate. The inventionwill nowbedescribedbywayofexampleonlywith referenceto the accoopanying Drawings of which: Figures 1 and2 showa spherical lensaerial inend elevation and side cross section; Figure 3 shows a sectional view of an alternative non-spherical lens arrangement; Figure 4 shows in section a further modification of the invention; Figure 5 shows a modification to the Figure 3 aerial; and Figure6isaschematicdiagramofanadditionalarrangementoftheinvention. The invention makes use of a dielectric lens/reflector arrangements as described intheGBPatentApplicationNo8615317. BywayofexampleFigures 1 and2 show a solid spherical lens 10 formed bymoulding amixtureof silica flour and a polyester resin binder. Spray coated over one hemisphere is a reflecting layer 11 of zinc. Bie lens material was selected such that the dielectricconstantwasapproximatelyequal to3.414 andthedielectricloss in the material was lew. Such lenses can be designed for high efficiency radar reflection over a wide range of incidence angles 12. In a first arrangement of the invention a cruciform copper electrode 13 is located axially (14) on the front face15 of thelens10. Acoaxial cable16 is connected to the aerial such that the signal wire 17 is connected to the electrode 13 and the screen is connected to the reflecting layer 11. As an alternativetothespherical lensarrangement shown inFigures 1 and2, ray tracingmethodshavebeen used to improve thelensperformancewhile, at the same time, reducing the overall weight. Figure 3 shows an alternative moulded lens 30 which is symmetrical about the optical axis 31 and the perpendicular plane 32. Ihe radius of curvature is smallest (33) on the opticalaxisandincreasestowardstheplaneofεyπmetry32. As intheFigure 1 arrangement, acruciformelectrode35 isprovidedonthefronthalf36 ofthe lens and a reflecting zinc coating 37 covers the rearwardhalf of the lens. The dielectric lens aerial arrangements havebeen shown tobe effective for receivingTVand radiosignalsindoorswhereconventional aerialshaveprσv-ed inadequate. InadditiontheinventionhasbeenappliedtoCitizensBand (CB) cαmunications and again the results have been surprisingly good. Lens diameters of 13.5 cm and 7.5 cm have been used. A further arrangement is shown in Figure 4 applied to a spherical lens although this could also be applied to the non-spherical Figure 3 lens. A polycarbonatespherical shell 40 formedoftwohemisphericalhalves41 and42 hasacruciformcopperelectrode43 formedinsideonehalf41andtheinsideof the second half 42 is coated with a reflective zinc coating 44. After assembling the two hemispheres 41 and 42 the hollow interior of the lens is filledwith silica flour through a hole (not shown) provided therefor in the polycarbonate shell 40. After filling, the shell is sealed and electrical connections to the electrode 43 and reflector 44 areπade through the shell wall. As with the other arrangements the dielectric constant of the lens material is substantially 3.414. The aerials described above areshewnwiththeir axis ofsynir-etryhorizontal . and they are able to receive both horizontally and vertically polarised signals. A further arrangement shown in Figure 5 has been found to give . improvedreceptionforFMradioaswell asTVsignals. In additionthislens . arrangement is simplertomanufacture, ϊhelens50 issimilar tothatshown in Figure 3 with a thin, electromagnetically transparent, polycarbonate . shellfilledwithsilicaflourandwhereinlike referencenumerals represent like integers. In this arrangement the axis of symmetry 51 is vertical, giving reception performance independent of azimuth angle. Unlike the foregoing examples, there is no conducting electrode provided on the uppermost, non-reflecting, half36 oftheaerial. Acoaxial signal cable52 is arranged such that the centreconductor 53 isconnectedtotheconducting zinc layer 37. An -impedance matching capacitor 54, adjusted for rr_3x_jτurn signal strength, is connectedbetween the centreconductor 53 and the cable screen 55. Yet a further modification of the dielectric lens aerial used for satellite cαnrunications is .shewn in Figure 6. This arrangement is similar to that shown in Figure 5. The arrangement has been shown to be equally effective when using a solid moulded lens or when using a silica flour filled shell. Surprisingly it has been found that impedancematching arrangements are not necessaryfor efficientoperationof theinventioninthereceiveortransmit mode. T e dielectric lens 61 is pointed in the general direction 62 of the earth satellite and is mounted above an earthed plate 63. A solder tag connection64 ismade to apartiallycopper coatedportionofthereflective layer 65 of the lens. A coaxial signal cable is provided with the centre conductor64' connectedtothelensreflectivelayerviathesoldertag64and theconducting screenwire66 connectedtotheearthedplate63. Theaerial has been used successfully for both transmission and reception. Othermaterialsandlensarrangements asdisclosedintheearlier referenced patent application may beapplied in the aerial according to the invention. Alternative configurations may be employed for the conducting layer 13. Aerials according to the invention have been found to work in a range of frequencies making them suitable for applications covering radio and TV frequencies. In addition the aerials also have wide angles of reception making them suitable for reception of signals from widely different directions of origin. When used for reception, solid moulded lenses andpowder filled lenses have been found to work equally well. For transmission, however, the powder filled lens has been foundtobesuperior. The inventor has discovered that the addition of an electrically isolatedmetallicbackplate 67 at 90 o to the groundedplate63 improves thetransmission fromthesolid lens aerial. Two or more similar aerials may be electrically coupled and arranged egui- angularly about a point in the horizontal plane so as to provide a response thatisuniformwithinarangeofzenithanglesforanyazimuthor anglewithin the horizontal plane.

Claims: Claims 1. An aerial for electromagnetic radiation comprisingr a lens 61 of material transparent to the radiation andhaving a dielectric^ constant suitable to refract the radiation and at least a surface portion- which is convex; amaterial layer 65 covering the surfaceportion andselectedtoreflectthe radiation; the arrangement being such that electromagnetic radiation is focussed towards the reflecting layer; and anelectricalconnection 64 provided tothereflectingsurface forcarrying the aerial signal. 2. An aerial as claimed in claim 1 characterised in that the dielectric constant of the lens material is substantially equal to 3.414. 3. An aerial as claimed in claim1 or 2 characterised in that the lens is a simple lens. 4. Anaerialasclaimedinclaim3characterisedinthatthereflectivelayer 65 is coated on the outside of the lens. 5. Anaerial asclaimedinanyoneofclaims1 to4 characterisedinthat the lens material comprises silica glass beads bound together by an adhesive. 6. Anaerialasclaimed inanyoneofclaims1 to4 characterised inthat the lens material comprises silica flour bound together by an adhesive. 7. Anaerial asclaimedinclaim5 or6 characterisedinthattheadhesiveis a polyester resin binder. 8. Anaerial asclaimed inanyoneprecedingclaimcharacterised inthatthe lens is spherical. 9. Anaerial asclaimedinanyoneofclaims1 to7 characterisedinthatthe lens has a planeof symmetrydefiningidentical forward and rearward halves with the reflective layer being attached to the rearward half. 10. An aerial as claimed in claim 9 characterised in that the lens 30 is axially-symmetricwiththelenssurfacehavingaradiusofcurvature (32, 33) that increases as the distance front the axis increases. 11. Anaerial asclaimed inanyone ofclaims1-3, 8,9 or10 characterised in thatthelenscomprises ashell 40 and filledwithparticipatesilicaflour. 12. AnaerialasclaimedinclaimUcharacterisedinthattheshell40 ismade of polycarbonate. 13. Anaerial asclaimed in claim11 or12 characterisedinthattheshell is formedof twohalves41, 42 withthe reflecting layer 44 locatedontheinside of one half 42 of the shell. 14. An aerial asclaimed inanyoneprecedingclaimcharacterised in that the dielectriclens 61 islocatedaboveanearthedplate63providedwithasecond electrical connectionsuch thatinuseacoaxial signal cable canbearranged with its centre conductor 64' connected to the lens reflector 65 and its screen wire 66 to the earthed plate 63. 15. An aerial as claimed inanyoneofclaims1 to13 characterised in that an electrically conducting layer 13 is provided on the face of the dielectric lensopposedtothe reflectinglayer11 andinuseacoaxial signal cable16 is connected with the centre conductor 17 connected to the conducting layer 13 and the screen wire connected to the reflecting layer 11. 16. An aerial as claimed in claim 14 or 15 characterised in that there is provided a ccnducting back plate 67 perpendicular to but electrically isolatedfromtheearthedplate63, thebackplate67beinglocatedbehindthe reflecting layer 65. 17. Anaerialasclaimedinclaim15 or16 characterisedinthatthereflecting layer is a cruciform. 18. An aerial asclaimed inanyoneprecedingclaimcharacterised inthat the reflecting layer is a zinc spray layer. 19. An aerial as claimed in any one precediong claim characterised in that a portion of the reflecting layer iscopper coated and asolder tag is attached for making an electrical connection to the reflecting layer.

Inventors: RIX CLIFFORD, RIX, CLIFFORD
Applicants: SECR DEFENCE BRIT, THE SECRETARY OF STATE FOR DEFENCE IN HER BRITANNI
Application year: 1989
Main classification: H01Q19
IPC codes: H01Q9, H01Q15, H01Q19