PROCESS FOR THE PRODUCTION OF LENSES WITH A VARIABLE REFRACTION INDEX

Abstract: This invention presents a process for the production of a lens with a given variable refraction index by fixing together several parts, at least some of them have a variable refraction index. The realization of the desired refraction index of the parts can be achieved by compressing dielectric material of a first shape into its final shape or by a doping or a mixing process respectively. Outer parts, which extend to the outer surface of the lens to be produced, have a pyramid-like shape with a pointed or truncated apex respectively. In the first case the apexes of the outer parts meet in the symmetry point of said lens; in the latter case a center part is used which is located around said symmetry point. It is also possible that some of the outer parts used have pointed apexes and the rest of them has got truncated apexes. In this case a center part used is easy to fix near the symmetry point of the lens. If dielectric material is taken, the lens to be produced can preferably be used as part of microwave antenna system.

Description: ££2_ie_. _.f 2£_t e_P.rodu2ti.2n_ of _ eπ^^^_w ι th ι _a va r_a b I e_R e_£_2_ioπ_Iπd ex The present invention relates to a lens with a variable r fraction index, e.g. a Luπeburg-type lens, which might used as part of a microwave antenna system, and an appropr ate process for the production of said lens. It is known, e.g. from US 4 288 337, that lenses of the sa art can be used as radar ref lectors or, as is known from F. Buckley; "Stepped- Index Luneburg Lenses"; Electronic D sign, Apri l, 13, 1960, as part of an antenna sytem. As Buckley has described in said article, it is a known pr cess for the production of Luneburg lenses to use hemisperical shell construction with a given number of layer According to said US patent the layers for the fabrication Luneburg and Eaton-Li ppmaπn lenses for microwave applicatio can be produced by d electrics. In such cases the relati between the relative dielectri c constant E and the refracti index π is n = E 1 /2" (1) A mixed dielectric can be obtained by mi ing expanded parti cles selected from the group cons s ing of expande polystorols, expanded po lyet hy lenes, expanded po lyure thanes glass balloons and silica balloons, with metal-coated parti cles consisting of said expanded particles, surfaces of whic have been coated with a thin fi lm selected from the group o chromium, aluminium, copper, nickel, gold, si lver, and magne sium in proper proportions to obtain a desi red dielectri constant then forming the same to the desired shape by th se of a binder. SUBSTITUTE SHEET - 1 - As M. A. Mitchel et al. described in the article "A multip beam mult ple -frequency spherical Lens Antenna System prov ing hemispherical . Coverage"; 6. Int. Conference on Anten and Propagation C CAP), 1989, Part 1; pp. 394 -398, for dielectric material, such as polystyrene, the relation b tween its relative dielectric constant E and its density may be expressed by E = 0.4 * E 0 (d/dθ) ÷ O.ό * C1 + E Q - pCd/do.), C2) where E- is the relative dielectric constant of the unexpanded dielectric material, and do is the density of the unexpanded dielectric material. Using the relation (2), Mitchel et al. produced shells for shell-construction of a Luneburg lens. By the mentioned methods for the fabrication of lenses it i just possible to approximate the variation of the refractio i ' ndex required, which is dependent on the dielectric .con stant. No practical scheme for smoothly varying the refrac tive index has been achieved. By using shells with different dielectric constants and there by with different refraction indexes, reflect on losses oc cur, by which power is reflected from the dielectric bounda ries.. In the US patent 3 470 561, which presents a spherical Luneburg Lens, is mentioned that the variation of the refrac tion index n as a function of polystyrene density d ( in Ibs./cu.ft.) is given by n = C1 + 0.02d. 0*5 . Another method for the variation of the refraction ndex which is presented by said US patent, is achieved by means a variably loaded artificial dielectric medium. There it is also mentioned to fabricate a plurality of su stantially identical orange-slice shaped wedges which colle tively form the Luneburg lens to be produced. The fabrication of said orange-slice shaped wedges is . qu cost ly. It is an object of the invention, to present a lens with given variable refraction index, .which allows a more accurat •representation of the required profile of the refractio index by using parts, which can be produced in an easy way. This can be realized by a lens according to claim 1 or by process according to the first process clai , respectively. According to the present invention a lens to be produced having a symmetry point and a variable refraction index n, i bui lt by a number of parts, which have a given variation o the refraction index n in such a manner, that the lens to b produced has got the given variable refraction index. Th shapes of said parts collecti ely form the shape of sai lens. It is preferred that most of the parts have the sam shape, which is pyramid-li e. The kind of the symmetry point depends on the shape of th lens to be produced. If the lens is spherical, the symmetr point may be identical ith the center point of the sphere. If the lens is hemispherical, then the symmetry point may b the center point of that sphere, which can be bui lt by two of said hemispherical lenses. I.f the lens is cylindrical, the symmetry "point" may be the center line of the cylinder. SUBSTITUTE SHEET The invention has the advantage, that the aperture effici of an antenna system, including the lens to be produced, increased compare.d to the use of a shell-type lens. This achieved by avoiding or reducing power reflections f dielectric boundaries, which normally occur at shell interf es. It is another advantage of the invention, that phase colliminated rays at feed points of an antenna system is m exact, whereby aperture eff ciency can be increased. By avoiding or reducing ele romagnet c fields inside lens, which are caused to propagate tangentially to sh surfaces causing surface waves to be set up, aperture ef ciency. can also be increased. 8y using identical parts, e.g. py am -l e shaoed, whi might have a shape ex.endiπg from the symmeτry point of t respective lens to ts outer surface, the invention has t advantage, that an identical process is used to produce ea part which ' collectively constitute the lens. By using different kinds of parts, whereby one of said part which may be built of sub-parts, is located around the symm try point, and the other parts extend from the outer surfa of the first part to the outer surface of the lens to produced, a sharp angle at the apex of a pyramid-like shap can be avoi deά. The present invention will be better understood with the ai of the following description of preferred embodiments an accompanying drawings, wherein Fig, 1 shows a pyramid shaped part, which is used for th production of a lens according to a first embodi ment, SUBSTITUTE SHEET Fig. 2 shows a top view of the lens constructed of parts li e shown in fig. 1, Fig. 3 shows in .principle a production process of the par of ig. 1 , Fig. 4 shows in principle another production method for a lens according to a second embodiment. In the following description means and details with the sa function or meaning which are used in several figures ha got the same reference numbers and if they are explain once, they will only be explained in the further descripti as far as it is necessary for the understanding of t present invention. According to the first embodiment of the invention parts li the one 10 shown in fig. 1 are used. Several of them colle tively form a lens to be produced. The base 11 of the pa 10, which has five edges 12,..., 16 might be flat or rounded. Other edges 17,..., 21 run from the base 11 to the apex 22 o the pyramid shaped part 10. Its not shown height h is define by the shortest distance between the base 11 and the apex 22. Fig. 2 shows a top view of a lens 23 to be produced by number of parts 10, 10a,..., 10e, which have all the sam s ape ' and the same composition like the part 10. Although on can see in fig. 2 only six identical parts 10,..., 10e with five-edge base 11, it is necessary to take twelve of them fo the constitution of the spherical lens 23. In this embodiment the apexes 22 of the twelve parts meet i the symmetry point of the lens 23. The bases 11 of the twelv parts collectively form the outer surface of the Lens 23. In the further description a production process for the par 10 is in principle described. As all the twelve parts, which collectively form the lens 23 are identical, the same process SUBSTITUTE SHEET can be taken for the other shown parts 10a,..., 10e and the not shown parts. The material, the part 10 is bu lt of, is dielectric, such polysterene, and in such case the relation between the refr tion index n and the dielectric constant E is according f o rmu la (1 ) . The refraction index πCr ) and the relative dielectr c c stant ECr ) vary for a Luneburg lens, having not shown fo paints at its outer surface for parallel waves, wi h rad accord ng to where r is the actual radius and r_ s the radius of t spher cal lens 23. The shape of the part 10, in this embodiment pyramid- lik may be fo ed by compressing the expande dielectri mate al, such as polysterene, -a an elevated temperature. To achieve the necessary dielectric constant variation alo the night h, a greater amount of forming pressure would appl ed at the apex 22 than at the base 11 of the part 10. As th*e dependence of the relative dielectric constant E wit density may be expressed by formula C2), an uncompresse shape 25, as shown in fig. 3 may be taken to achieve th final pyramid-type shape of the part 10. The uncompresse shape 25 may be ach eved e.g. by shaping or cutting. Another preferred embodiment is in principle indicated i f g. 4. Different kinds of parts are used to bui ld the len 23. SUBSTITUTE SHEET A center part 26, which may be created of sub-parts, has spherical shape and is located around the symmetry point (see f g. 2). In this embodiment one needs twelve out parts, which have a -pyramid-li e shape as the truncated pa 27 are identical to eachother, and extend from the out surface of the center part 26 to the outer surface of t lens 23. It may be mentioned that the outer parts with the shape the truncated part 27 may have flat or rounded edges at the bases. In the first case the spherical shape of the lens is only appro i ated. In a version of this embodiment, the center part 26 may ha a homogeneous dielectric constant, e.g. n that case that t size of the center part 26 is so small, that a deviation desired ray tra ectories may be negligible. For another version of this embodiment, the center part has not a spherical shape but any other, e.g. one with fl planes whereby the number of said planes is identical wi the number of the outer parts. It is also possible that some of the outer parts used hav more or less pointed apexes and the rest of them has go truncated apexes. In this case a center part used with a appropriate shape can be fixed more easily. Versions of the preferred embodiments may contain at leas one of the following variations: - By using appropriate pyramid-li e shaped parts, like th part 10 or the truncated part 27 lenses with non-spheri cal shapes may be produced, the realization of the profile of the refraction index may be achieved by other processes, e.g. by doping mixing or thermal processes, whereby metal-coated parti cles may be used, SUBSTITUTE SHEET the boundaries of the single parts 10, 26, 27 may connected together or linked with eachother, e.g. by appropriate adhesive or melting process, by using an appropriate material, the lens to be pr duced may be able to refract other elect omagnet waves, such as visible or infrared light, the lens ' to be produced may .have any desired relation ship between the dielectric constant E or the refractio index respectively and the normalized radius r/r n ,. e.g in that way, that the focal point for parallel waves i inside or outside of the surface of the lens, by us ng a material with an appropriate refraction inde even lenses, which are able to refract any other waves e.-g. acoustic waves, may be produced, instead of the pyramid-like shaped parts 10 or 27 respec tively with a five-edge base, other pyramid-like shape parts can be used, e.g. 36 of them w th a three-edg base, to build a spherical leπse, for the construction of a needed lens, which is just part of a sperical lens Chemi pher ca I, quart ersperi ca I, or the like), a spherical lens may be cut, whereby only one assembling process is necessary for the production of two or more needed lenses, or other kinds of parts can be used, which collectively form a non-spherical lens - This invention presents a lens with a given variable refrac¬ tion index by bringing together several parts, which them¬ selves have preferably a variable refraction index, and an according process for the production of said lens. The realization of the desired refraction index of the parts can be ach eved by compressing dielectri material of a first shape into its final shape or by mixing dielectric materials, which may be metal-coated. SUBSTITUTE SHEET Outer parts, which extend to the outer surface of the lens be produced, have a pyramid-like shape with a pointed truncated apex respect vely. In the first case the apexes the outer parts meet in the symmetry point of said lens; the latter case a center part is- used which is located arou said symmetry point. It is also possible that some of the outer parts used ha pointed apexes and the rest of them has gσt truncated apexe In this case a center part used is easy to fix near the symm try point* of he lens. Compared ith lenses, produced according to known processes lenses produced by the process according to the inventio have orr one hand the advantage that the aperture eff cienc is increased by avoiding reflections from the dielectri boundaries and by avoiding elect omagnetic elds nside th lens caused to propagate tangent i ally to the shell surface caus ng surface waves to be set up. Additionally the phase of collmiπated rays at feed points i more exact, also leading to an increased apperture eff ciency On the other hand the parts that collectively form the len can be produced easi ly. If dentical parts are used, the s-ame process steps for thei manufacturing can be used. If dielectric material is taken, the lens to be produced can prefarably used .as part of a microwave antenna system. SUBSTITUTE SHEET

Claims: C A I M S Lens (23) with a symmetry point C24) and a given varia refraction index (n(r)), said lens (23) being produced parts C10, 26, 27) with respective refraction index shapes of said parts C10, 26, 27) collectively form the shape of said lens (23), character zed in that ou parts (10, 27), which extend to the outer surface of lens (23) have a variable refraction index (n) and pyramid-1ike shape. Lens (23) according to claim 1, characterized in that t outer parts (10, 27) have a shape, which extends from t symmetry point (24) of said lens (23) to its outer su face. Lens (23) according to clai 1, characterized in that center part (26) is located around the symmetry poi (24) and one or more of the outer parts (27) extend fr the outer surface of the center part (26) to the out surface of said lens (23). Lens (23) according to one of the claims 1 to characterized in that said parts (10, 26, 27) ) are form of dielectric material and the desired refraction inde Cn) of one or more of said parts (10, 26, 27) is at leas partially realized by a variation of density ( d ) o dielectric material. 5. Lens (23) according to claim 4, characterized in that th variation of density (d) is realized by compressing a uncompressed block of dielectric material with a firs given shape (25) into its final shape (10, 27 ) . SUBSTITUTESHEET 6. Lens (23) according to one of the claims 1 to 5 characterized in that said parts (10, 26, 27)) are forme of dielectric material and the desired refraction inde (n) of one or more of said parts (10, 26, 27) is at leas partially realized by doping, mixing or a thermal process 7. Lens (23) according to one of the cla ms 1 to 6 characterized in. that it is a Luneburg type lens. 8. Lens (23) according to one of the cLaims 1 to 7 characterized in that it has a spherical shape and a outer parts are taken twelve pyramid-like shaped part (10) with five-edge (pentagonal) bases or thirtysix part with three-edge (triangular) bases. 9. Lens (23) according to one of the clai s 1 to 8 characterized in that the needed lens is a part of th lens (23) which is formed by said parts (10, 26, 27) an said needed lens is obta ned of said lens (23) by cut ting, sawing, or the like. 10. Process for the production of a lens (23) having a symme try point (24) and a given variable refraction index (n(r)), with the step of - manufacturing of parts (10, 26, 27) with respective refraction indexes and shapes in such a manner that they collectively form the shape of said lens (23), character zed by follo ing steps: - outer parts (10, 27) are produced, which have a vari¬ able refraction index (n) and a pyramid-like shape - said outer parts (10, 27) are assembled in such a manner that they extend to the outer surface of the lens (23).

Inventors: FUJIMOTO MASAHIRO, HARRISON DAVID, MAIER GERHARD, FUJIMOTO, MASAHIRO, HARRISON, DAVID, MAIER, GERHARD
Applicants: THOMSON CONSUMER ELECTRONICS, THOMSON CONSUMER ELECTRONICS S.A.
Application year: 1992
Main classification: G02F
IPC codes: G02B3, H01Q15