US3366965A

US3366965A - Omni-directional dielectric lens reflector and method of manufacturing same

Info

Publication number: US3366965A
Application number: US417373A
Authority: US
Inventors: Ochiai Noriomi
Original assignee: Tokyo Keiki Seizosho Co Ltd
Current assignee: Tokyo Keiki Inc
Priority date: 1963-12-13
Filing date: 1964-12-10
Publication date: 1968-01-30
Anticipated expiration: 1985-01-30
Also published as: GB1085257A

Description

LXE IRBE! //7 Jan. 30, 1968 NORIOMI OCHIAI 3, 66,965

OMNI-DIRECTIONAL DIELECTRIC LENS REFLECTOR AND METHOD OF MANUFACTURING SAME Filed Dec. 10, 1964 2 Sheets-Sheet 1 INVENTQR. A arvam/ OCA/a/ zan Jan. 30, 1968 Filed Dec. 10, 1964 9P 1101102; s90}? may: v

NORIOMI OCHIAI 3,366,965

OMNI-DIRECTIONAL DIELECTRIC LENS REFLECTOR AND METHOD OF MANUFACTURING SAME 2 Sheets-Sheet 2 0216; Theoretical vaLue 0 I20 1401601802002403102602803flfl32034036 5; Azimuth INVENTOR.

War/om Oclwa/ M! TTORNEYS United States Patent 3,366,965 OMNI-DIRE'CTIONAL DIELECTRIC LENS REFLECTOR AND METHOD OF MANU- FACTURING SAME Noriomi Ochiai, Suginami-ku, Tokyo, Japan, asa'gnor to Kabushikikaisha Tokyo Keiki Seizosho (Tokyo Keiki eizosho Co., Ltd.), Tokyo, Japan, a corporation of apan . Filed Dec. 10, 1964, Ser. No. 417,373 Claims priority, application Japan, Dec. 13, 1963, 38/67,171 7 Claims. (CL 343-911) ABSTRACT OF THE DISCLOSURE An omni-directional lens reflector consisting of a spherical core, an outer shell and an intermediate shell interposed between the spherical core and the outer shell, the respective dielectric constants K of the spherical core, the intermediate shell and the outer shell being selected in accordance with the equation where r represents a normalized radius.

This invention relates to an omni-directional dielectric lens reflector, more particularly to a highly efficient omnidirectional reflector for microwave use which could not have been obtained in the past and to a method of the manufacture of the same.

The present invention principally lies in the provision of an omni-directional dielectric lens reflector in which waves having entered it upon impingement of microwaves on a spherical lens thereof are reflected back in the direction of the incident waves along an elliptic path in accordance with dielectric constants of a dielectric material forming the lens.

An object of the present invention is to provide an omnidirectional dielectric lens reflector which could not have been put to practical use in the past and the efliciency of which is enhanced by minimizing loss in the lens.

Another object of the present invention is to provide a method of manufacturing an omni-directional dielectric lens reflector, according to which gaps between adjacent concentric spherical layers are filled up so as to remove internal loss between the layers due to the gaps, thereby enhancing the efficiency of the omni-directional dielectric lens reflector.

Another object of the present invention is to provide a method of manufacturing an omni-directional dielectric lens reflector, according to which thickness of concentric spherical layers and their dielectric constants can readily be made uniform so that the omni-directional dielectric lens reflector can show its excellent ability.

Other objects, features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a diagram, for explaining operations of an omni-directional dielectric lens reflector;

FIGURES 2A to 20 are perspective views of dielectric hemispherical shells, for explaining a prior art method of the manufacture of an omni-directional dielectric lens reflector which has been studied by some people;

FIGURE 3 is a graph illustrating variations in the specific dielectric constant of a dielectric material of an omni-directional dielectric lens reflector of this invention in response to the blending of fine materials;

FIGURE 4 is a diagram illustrating an example of a method of manufacture according to this invention;

FIGURE 5 is a perspective view of a hemispherical portion of the omni-directional dielectric lens reflector assembled according to the method of this invention;

FIGURES 6A and 6B are diagrams for illustrating another method of this invention; and

FIGURE 7 is a characteristic curve illustrating an example of measurements of the omni-directional dielectric lens reflector constructed according to this invention.

Referring to the drawing, the present invention will hereinafter be explained.

With an attachment of a radar reflector to a small target whose reflecting power is low, its detection by a radar can be made easier. For this purpose a corner reflector or a Luneberg lens reflector has heretofore been employed, but they do not act etfectively in all directions. Reflectors having an omni-directional reflection characteristic are much desired for various uses. However, there have not ever been realized such desirable reflectors which satisfy the requirement. This invention has been devised to provide a reflector which is capable of fulfiling the requirement of an excellent omni-directional reflection characteristic. This omni-directional dielectric lens reflector consists of a spherical dielectric 1 as illustrated in FIGURE 1 and its specific dielectric constant K is a function of a distance r alone from the center thereof and can be expressed as follows,

where r is a normalized radius and K is infinite at the center of the sphere and 1 at the outer periphery. It is well-known that the above formula can be derived by putting one focus to be +00 and the other one to be +00 similarly in the general solution by Luneberg. If now a plane wave 2 strikes the lens 1 as illustrated in FIGURE 1, the wave traverses an elliptic path back in the direction from which it came. The structure of the lens is symmetrical with respect to the center and hence the lens acts as an omni-directional reflector. As is seen from the foregoing equation, the specific dielectric constant of the omni-directional reflector is l at the outer periphery thereof and infinite at the center. However, a dielectric material of low loss and infinite specific dielectric constant cannot be obtained at present. Instead of such an unobtainable dielectric material, a dielectric one whose specific dielectric constant is up to about may well be employed, if some losses (about 10%) are sacrificed in practical use. The dielectric lens can be produced by hollowing out the center thereof less than about 2.5% in radius or filling up the space with the same material. It has heretofore been impossible, however, to make uniformly dielectrics of low loss and high dielectric constant as predetermined, so that no omni-directional dielectric lens reflector has been put to practical use in any countries.

It is diflicult in practice to make a dielectric lens reflector the specific dielectric constant of which varies continuously from 1 to about 100 as a function of the radius. Accordingly, a method is adopted such that the specific dielectric constant is varied in a stepwise manner by dividing a lens reflector into 10 to 50 concentric spherical shells in accordance with the dimension of its diameter.

To cite an example of such conventional method, radiuses and specific dielectric constants of respective layers in an omni-directional dielectric lens reflector 128 mm, in diameter are given in the following table.

This reflector was designed for use at frequencies lower than the X band (a region of a wavelength of 3 cm.) and the thickness of the layers must be selected less than t/4 /K ()tzwavelength). Where the thickness is more than )\/2 /K, waves having entered the lens causes a trapping phenomenon, from which loss results. A method of manufacture which has been attempted by some people is a method described later such that titanium dioxide or metallic flakes are mixed with polystyrene foam beads or polyethylene foam material and the mixture is heated to be molded by foaming into hemispherical shells t/4 /K in thickness). Their specific dielectric constants are adjusted in accordance with the compounding ratio of the materials. This method is referred to as a heat fusion method. In the conventional heat fusion method, however, it is difficult to make distribution of the specific dielectric constant uniform in the same layer. Particularly in the case of omni-directional dielectric lens reflectors requiring high specific dielectric constants, it becomes more and more difficult to produce dielectric materials of uniform specific dielectric constant distribution, since the layers are thin due to )t/4 /K and those below the fourth layer are as thin as 3 cm., as is apparent from the foregoing table.

That is, in the conventional method, for example, polystyrene beads are packed into a spherical closed mold and heated at a suitable temperature, for instance, 120 C., for several minutes to foam to be molded, into a spherical shell. A plurality of thus molded shells are assembled one on another into a spherical omni-directional dielectric lens reflector, if necessary, by means of a binder. In order to obtain a shell of high dielectric constant, a mixture of polystyrene beads and grains of titanium dioxide is employed. However, the inventor of the present invention has found that such a heat fusion method heretofore used possesses disadvantages described hereinbelow. That is, this method employs a metal mold consisting of two parts which are provided with additional equipments such as an inlet for the materials, confronting marginal edges, handles and so on. Therefore, the metal mold is not usually uniform in thickness over the entire area thereof. Beads of the aforementioned foam material are packed into such a mold and placed in a chamber. Then, the mold is heated by applying, for example, heated steam, into the chamber. However, since the thickness of the respective portions of the mold is not uniform as described above, the relatively thinner portion of the mold transmits heat to the inner part thereof more rapidly than the relatively thicker portion. The foam material at the thinner portion begins to foam more rapidly than at the thicker portion, so that the foam material at the latter portion is compressed. Accordingly, the density of the foam material at the thicker portion becomes large and its dielectric constant increases. Furthermore, when the heated steam is removed and the mold is cooled the foam material in contact with the inside of the metal mold is rapidly cooled. However, since the molding is a bad conductor of heat, the foam material remote from the inside of the mold still continues to foam to some extent and its mass tends to be less dense than that of the former. For these reasons, the dielectric constant distribution which is required to be uniform varies about :10% in the same spherical shell according to the conventional heat fusion method, and accordingly it is diflicult to obtain a highly efficient dielectric lens by assembling such spherical shells.

Furthermore, according to the conventional heat molding by foaming described above, titanium dioxide or metallic flakes, which are suitable for obtaining layers each having a desired dielectric constant, are mixed with the aforementioned foam materials and the mixture is heated to be molded by foaming into hemispherical shells corresponding to the respective layers mentioned in the foregoing. Then, the resultant shells are assembled spherical about a core. In order to make possible the assembly of the respective shells, tolerance of the radius of the molded shells is required to be $0.25 mm. Accordingly, it is naturally considered that where the shells of such tolerance are assembled gaps of 0.5 mm. at maximum are made between the adjacent layers. In presence of such gaps between the layers of high dielectric constant, internal reflections occur between the layers to cause propagation loss, since the dielectric constant of the gap is about 1. The hemispherical shells of the respective layers thus made will hereinbelow be explained more concretely with reference to FIGURE 2. Dielectric

hemispherical shells

4 and 5 of the inner diameter R and R and outer diameters R and R respectively, obtained by the heat molding as described above, are assembled one on the other to be a hemispherical shell 6 of the inner diameter R and outer diameter R Since the layers are thus assembled in a sequential order from the inner ones to be a sphere, there are gaps of, for example, 0.5 mm. at maximum between the adjecent layers as described above. Accordingly, the conventional method like this has a disadvantage that efliciency of the dielectric lens is caused to lower due to internal reflections between the adjacent layers.

This invention is to provide an omni-directional dielectric lens reflector in which distribution of a specific dielectric constant is uniform in the same layer and no gap exists between the adjacent layers thereby to eliminate loss due to the gap. In the present invention, polystyrene beads are preheated at a suitable temperature lower than 70 C. to effect partial foaming thereof, by which the beads are suitably expanded so as to obtain a predetermined dielectric constant. For adjusting the dielectric constant, the grain size of the heads is selected beforehand. That is, grains or powders of a desired grain size are chosen and, if necessary, titanium dioxide is added thereto. Then, a binder is mixed into the material thus selected. An inner layer having already hardened is surrounded by such mixed material. In this case, it is a matter of course to use a suitable mold in order that the outer layer may be concentric with the inner layer and its respective parts may be uniform in thickness. However, heating is not effected such that the beads may foam again. If heating is made, its heating temperature is held merely enough to evaporate the solvent in the binder. In some cases, it is possible to evaporate the solvent without heating. Thus, the dielectric constant distribution in the same layer can be made extremely uniform and gaps between the adjacent layers can be eliminated. The present invention will hereinafter be explained in detail.

In short, the present invention essentially resides in the provision of an omni-directional dielectric lens reflector which comprises a spherical core composed of a dielectric material, an outer shell made of a dielectric material, surrounding the spherical core substantially concentrically therewith, and an intermediate shell composed of a dielectric material and disposed between the spherical core and the outer shell. Each of the respective portions has a specific dielectric constant according to the equation of TABLE II 1st Iayer-e=83.4

Material: Mixed weight, g. 7 5 z 77.4 where r is a normalized radius and K is a specific dielec- Galione clay tric constant which is infinite at the center and 1 at the Cacoe outer periphery of the lens. The spherical core consists of li one block produced by ceramic dielectrics of high dielecz 0-45 tric constant and relatively low microwave loss containing titanium dioxide. The intermediate shell consists of a plu- 10 Bakmg temperature: 1280a -r 3 rality of concentric spherical layers and at least one inner TABLE III portion thereof is a hom ogeneous layer such that fine 2nd laye, =43.7 gram or powder of high dielectric constant is mixed with Percent b h y wer t a binder and bound thereby. The outer shell consists of Ticon M a 60 one or a plurality of foamed plastic layers. The relation- Ticon C 40 ship of the specific dielectric constants of the respective Baking temperature: 3500 C 3 hr. layers 15 such as to satisfy the foregoing equation, and I further the spherical core and almost all the layers of the M and C: mammals by TAM intermediate shell adhere closely to one another without In this example the core Consists of two y but the gaps therebetween. core can be composed of one block by using ceramic di- The method of the manufacture of an omni-directional t i sdielectric lens reflector of this invention will hereinafter be The intermediate Shell comprises third to twelfth layersexplained with reference to Table I. A material of the third and fourth layers can be of com- This is an example of the manufacture of a dielectric Position Such, for p as Shown in FIGURE lens reflector in which a spherical core is composed of 11 FIGURE the ordinates represent the dielectric two block an intermediate hell is composed of t n constantKof the mixture of granular and powdered titanispherical layers and an outer shell consists of three spherum dioxide with a binder, and the abscissa the quantity 0 ical layers. In the Table I the Column I represents the layof powdered titanium dioxide in grams per cubic inch of er number, the Column II the specific dielectric constant granular titanium dioxide, the granular material comand permissible deviation, the Column III the radius and prising grains of 0.4 mm. in diameter and of the bulk the Column IV the compound weight of grain or powder density 1.89. The values of the blending for the third and of titanium dioxide, both of which are finely divided ones fourth layers shown in the Table I are examples obtained obtained by grinding baked ceramic dielectrics. The Colfrom the curve in FIGURE 3. In order to join the third umn V shows the weight of pre-expanded polystyrene layer to the second layer, a uniform mixture of the aforefoam beads, the degree of expansion being determined by mentioned titanium dioxide grain, powder and polyvinyl the bulk density (bd) in grams per cubic centimeter. The acetate emulsion is put spherically on the core concen- Column VI shows weight of polyvinyl acetate emulsion. trically therewithand uniform in thickness over the entire TABLE I I II III IV V VI Specific Grain of Powder of Partially Ex- Polyvinyl Layer Number Dielectric Radius TlOz TIO; (gt) panded Poly- Acetate Constant (mm.) d=(()-; r)nm styretsgieads lgtnlsion Spherical Core:

eaeeassaee anese 4. 75 0 0. 23 0 0. 0.45 0 1. 30 0. 51 O 4. 9O 1. I7 3 23:5 51 333 0 35. 30 4. 34 0 57. 20 6. 54 0 78. 20 7.89

0 86.00 bd=0.48 10.50 0 84.00 bd=0.31 15.50 0 46. 00 bd=0. 12 0 Since the dielectric constant of the core designed as the first and second layers in the present example exceeds 40, the core is made of ceramic dielectrics that a mixture of various materials are baked, so as to keep the dielectric constant at a predetermined value. A formation of the core is carried out as follows. That is, materials given in the Table II are first baked to obtain a spherical core of one block and a spherical layer made of a mixture of materials stated in the Table III is put on the outside of the spherical core and then it is baked to produce a second layer. It must be noted that the first and second layers are in close contact with each other without any gaps therebetween according to the present method.

area. The second and third layers are stuck together due to the binder with practically no gap therebetween. The fourth layer is likewise stuck closely to the third layer without any gaps therebetween.

An example of materials of the fifth to tenth layers is as given in the Table I. As is apparent from the Table I, a mixture is employed which is composed of grains or titanium dioxide, and grains produced by heat foaming of polystyrene foam beads and polyvinyl acetate emulsion.

In this case, when the fifth layer is formed on the fourth layer, a uniform mixture of the aforementioned three materials is laid on the fourth layer concentrically and uniform in thickness and stuck to the fourth layer due to evaporation of the solvent in the binder with or without heating in a state that the grain of polystyrene beads does not foam again. Accordingly, the fifth layer is one stratiform block and adheres closely to the fourth layer without gaps therebetween.

A sixth layer is stuck closely to the fifth layer in the same manner as the fifth layer to the fourth one. Thus, the layers up to a twelfth one are thus assembled one after another. Therefore, it is apparent that the intermediate shell from the fifth to the twelfth layers adhere closely to adjacent layers without gaps therebetween.

In the present example, the outer shell consists of thirteenth to fifteenth layers and the thirteenth and fourteenth layers are those which foamed polystyrene beads are bound by a polyvinyl acetate emulsion. In this case, a bulk density of foamed polystyrene heads is different from those of the aforementioned inner layers and as given in the Table I. The thirteenth layer is also stuck to the twelfth layer in the same manner as the inner layers described above. The layers of the outer shell are joined to the inner layers one after another without gaps therebetween in a state that foamed polystyrene beads do not foam again. The fifteenth layer integrally encloses the aforementioned fourteenth layer with two hemispherical shells, each produced by heat molding of pre-foamed polystyrene grains packed in a predetermined hemispherical mold. In this case, this final layer has a dielectric constant approximately equal to that of air, and hence even if there is a little gap between the fourteenth and fifteenth layers, such gap can be neglected in practice.

In the foregoing example, the dielectric constants of the respective layers are determined as given in the Table I and it goes without saying that the dielectric constants satisfy the aforementioned equation.

In the above example, it is possible to obtain dielectric constants substantially equal to the aforementioned ones by suitably adding the material in the Column V of the Table I in case of changing the materials in the Column IV for the third and fourth layers. Also in the fifth layer and several layers outside of it, specific dielectric constants similar to those given in the Table I can be obtained by introducing titanium dioxide powder into the materials in the Column IV and increasing or decreasing (including zero) the amount of the grain of foamed polystyrene beads. Furthermore, it is also possible in the layers of the outer shell that even if the grain of foamed polystyrene beads of lower bulk density is used, similar specific dielectric constants can be obtained by introducing grain or powder of titanium dioxide. In this case, the layers of the outer shell can be regarded as those of the intermediate shell and further this outer shell can be formed in a single layer.

Referring now to the drawing, an embodiment of the present invention will hereinafter be explained.

FIGURE 4 illustrates an example in which after first and

second layers

9 and 10 described in the foreging example have been assembled spherically hemispherical outer layers are joined to it one after another. In the figure the spherical core composed of the first and

second layers

9 and 10 is placed in a mold 8, and the core is positioned correctly in the center of the mold with a uniform gap between its outer periphery and the mold. Materials for a third layer 11 are packed into the gap, and the third layer is formed as in the foregoing example. Thus, the third layer is formed in close contact with the second layer. As a result of this, the present method is advantageous in removal of gaps between adjacent layers inevitably experienced in the prior art method. In this process, when the aforementioned binder has hardened a resultant assembly is removed from the mold. It is then placed in a mold for the next layer to form that layer similarly. Thus, many layers are molded one after another. After all the layers have been molded, such two hemispheres are secured to each other to be spherical, obtaining an omnidirectional dielectric lens reflector. In order to prevent the material 8 from adhering to the mold, it is possible that a sheet of, for example, synthetic resin such as a vinyl sheet is spread on the inside of the mold and removed therefrom after the layer is molded and removed from the mold.

It has been found that, in the present method, distribution of a specific dielectric constant can be made extremely uniform in the same layer by well stirring mixed materials to be uniform in the mixture. Such uniform distribution of the specific dielectric constant could not have been realized by the conventional heat fusion method. In view of results obtained, it is easy in the present invention that precision of the specific dielectric constant is made as given in the Table I and it has been made possible for the first time by the present method to precisely control the precision of the specific dielectric constant in practical use.

FIGURE 5 is a sketch of the hemisphere described in connection with FIGURE 4. In an actual manufacture all the layers are not required to be stuck closely to one another. Since the ratio of permissible deviations of the specific dielectric constant in an nth layer and an n-l layer of the outer shell is relatively great, no troubles are caused in performance, even if layers according to the conventional heat fusion method are employed as the layers of the outer shell. In this case, such prior art layers are preferable from the strength standpoint. In some cases, some of the intermediate layers can be molded by the heat fusion method.

In the foregoing, two hemispherical members are assembled to be a sphere, but the members are not always required to be formed hemispherically. That is, the sphere can be assembled by four members each being a quarter of the sphere or by a member of a quarter and a member of three quarters. The sphere can also be obtained by assembling a plurality of members of such shape that the resultant assembly becomes spherical. Where a sphere is made up by assembling partially spherical members according to this method, it is necessary to consider mechanical precision so that the respective layers may not be caused to be discontinuous at their junction.

A method of the manufacture will hereinbelow be explained which does not require such consideration.

A spherical core composed of first and second layers is made in the same manner as in the foregoing example. Then, a material is prepared for other layers. That is, foamed polystyrene beads, grain of titanium dioxide (0.4 mm. in diameter), titanium dioxide powder, polyvinyl acetate emulsion, are suitably compounded in such a manner as to obtain a predetermined specific dielectric constant. Using the above materials, spherical layers are molded one after another as in the foregoing example.

In FIGURE 6, a second layer 20 is placed as a core in a mold 21, and one half of the sphere is positioned correctly in the center of the mold with a uniform gap between its outer periphery and the mold. A material for a third layer is then packed into the gap and molded. After this, a material 23 for other half of the third layer is tamped into a mold 22 and pressed on the other half of the second layer and molded. Then, the third layer is molded spherically in close contact with the second layer. Accordingly, the present method is advantageous in that there are made no gaps between the adjacent layers nor junction planes between the two hemispheres. When the binder has hardened the sphere is removed from the mold and then placed in a mold of the next layer. Thus, spherical layers are likewise molded one after another. By molding all the layers in this manner, an omni-directional dielectric lens reflector is completed. In this example when outer layers are molded on the outer periphery of the spherical core one by one, layers of a hemispherical portion are molded at first and then layers of the other hemispherical portion are molded, thereby to form spherical layers. However, it is not always necessary to form the layers hemispherically. It is also possible to complete a spherical layer by firstly molding a partially spherical 9 portion and then the other portion. Furthermore, a spherical mold can be employed. That is, a molded core is positioned in the center of the spherical mold with a predetermined uniform gap between the core and the mold, and a material for an outer layer is tamped into the gap and molded.

In order to prevent the material from adhering to the mold, it is possible in this case that a sheet of, for example, synthetic resin such as a vinyl sheet is spread on the inside of the mold and removed therefrom after the layer has been molded and removed from the mold.

Also in this method, distribution of the specific dielectric constant can be made extremely uniform by sufficiently stirring the mixed material to be uniform in the mixture prior to packing the material into the gap between the mold and the previously molded sphere. Such uniform distribution is impossible to obtain by the conventional heat fusion method. Also in the present example, precision of the specific dielectric constant may easily be made as given in the foregoing table. With this method, an excellent omni-directional dielectric lens reflected can be put to practical use for the first time.

In actual practice of this method all the layers need not be molded as in the foregoing method. Since one or two layers of the outer shell have relatively large ratios of permissible deviation of the specific dielectric constant, layers made by the conventional heat fusion method can be employed with practically no trouble in actual use. From the strength standpoint, the heat fusion method is preferred in some cases, so that layers by this conventional method can be used as one or two layers of the outer shell. In addition, a lens may also be manufactured by molding some of the layers of intermediate shell according to the heat fusion method.

It must be noted in the above described method of manufacturing the omni-directional dielectric lens reflector that the outer layer of the intermediate shell and the inner layer of the outer shell respectively adhere to the adjacent inner layer thereof including the spherical core with the mixture itself of the outer layer when the solvent of the binder is evaporated from the mixture.

FIGURE 7 illustrates an example of measured results by an X band of the omni-directional dielectric lens reflector fabricated according to this method. This refiector is 128 mm. in diameter and composed of fifteen layers, which was made on the basis of the values given in the Table I. In FIGURE 7, the ordinate expresses measured radar cross-section in db and the abscissa shows azimuth, db being atheoretical value of radar crosssection.

Two way loss of electromagnetic waves is about 5.4 db and the reflection characteristic varies only withinilA db in accordance with direction. In the conventional Luneberg lens the two way loss of electromagnetic waves is within 2.0 db and, in order to give a radar cross-section equal to a maximum radar cross-section of the Luneberg lens, an omni-directional dielectric lens reflector which is 20% larger in diameter may well be used. Thus, the reflector has a merit that an omni-directional reflection characteristic can be obtained together with a value equal to the maximum radar cross-section of the Luneberg lens reflector. In case of using the Luneberg lens as having the same efficiency as the omni-directional dielectric lens reflector, at least eight similar-shaped Luneberg lenses using specific reflecting metallic plates are required to be arranged suitably in actual use. Accordingly, it will be seen that the omni-directional dielectric lens reflector of the present invention is extremely excellent.

It will be apparent that many modifications and variations may be efl'ected without departing from the scope of the novel concept of this invention.

What is claimed is:

1. An omni-directional dielectric lens reflector comprising a spherical core composed of a dielectric material, an outer shell composed of a dielectric material and I0 surrounding said spherical core substantially concentrically therewith, and an intermediate shell composed of a dielectric material and interposed between said spherical core and said outer shell, each of said respective portions of said spherical core, outer shell and intermediate shell having a specific dielectric constant of r being a normalized radius, said spherical core consisting of a block made of ceramic dielectrics of relatively low microwave loss containing titanium dioxide, said intermediate shell consisting of a plurality of concentric spherical layers, at least one inner layer of said plurality of concentric spherical layers being homogeneous and containing high dielectric constant material, said outer shell consisting of at least one layer composed of foamed I plastics, the specific dielectric constant of said respective layers satisfying said equation, and said spherical core and almost all the layers of said intermediate shell adhering closely to one another without gaps therebetween.

2. An omni-directional dielectric lens reflector as claimed in claim 1, wherein one block of said spherical core consists of a plurality of layers.

3. An omnidirectional dielectric lens reflector as claimed in claim 1, wherein the inner portion of said intermediate shell is a solid homogeneous mixture portion of grains and powders of titanium dioxide and polyvinyl acetate and the outer portion thereof is a solid homogeneous mixture portion of grains of titanium dioxide, expanded polystyrene beads and polyvinyl acetate.

4. An omni-directional dielectric lens reflector as claimed in claim 1, wherein said intermediate shell consists of a solid homogeneous mixture of metallic particles, expanded plastic beads and polyvinyl acetate.

5. An omni-directional dielectric lens reflector as claimed in claim 1, wherein said outer shell consists of a solid homogeneous mixture portion of expanded plastic beads and polyvinyl acetate.

6. A method of manufacturing an omni-directional dielectric lens reflector which comprises a spherical core composed of a dielectric material, an outer shell composed of a dielectric material and surrounding said spherical core substantially concentrically therewith and an intermediate shell composed of a dielectric material and interposed between said spherical core and outer shell, said respective portions each having a specific dielectric constant of r being a normalized radius, comprising the steps of preparing said spherical core made of ceramic dielectrics of high dielectric constant and low microwave loss containing titanium dioxide, surrounding concentrically said spherical core with a first layer of said intermediate shell, said first layer being a homogeneous layer of a mixture of fine grains or powders of a high-dielectric-constant material with a binder, evaporating the solvent of said binder so that a homogeneous layer the dielectric constant of which satisfies said equation adheres over said spherical core with said mixture itself without any gaps therebetween, thereafter surrounding concentrically said homogeneous layer with a second layer of said intermediate shell, said second layer being of a homogeneous layer of another mixture of fine grains or powder of high-dielectricconstant material with a binder, evaporating solvent of said binder so that another homogeneous layer the dielectric constant of which satisfies said equation adheres over said first mentioned homogeneous layer with said second mentioned mixture itself without any gaps therebetween, thus forming other layers of said intermediate shell one after another in the same way, then surrounding concentrically the outermost layer of said intermediate shell with a mixture of foamed plastic grains with a binder 11 and evaporating solvent of said binder so that a homogeneous layer of said outer shell the dielectric constant of which satisfies said equation adheres over said outermost layer of said intermediate shell with said mixture itself without any gaps therebetween.

7. A method of manufacturing an omni-directional dielectric lens reflector, as claimed in claim 6, comprising the steps of forming the first layer of said intermediate shell over said spherical core hemispherically, forming the second layer over said first layer hemispherically, forming similarly other layers of said intermediate shell and layers of the outer shell of predetermined numbers over the inner layers one after another in the form of a hemisphere, preparing another hemisphere similar to the above one except said spherical core, and assembling said two hemispheres into a lens sphere.

References Cited UNITED STATES PATENTS 2,835,891 5/1958 Peeler et a1. 343-911 2,943,358 7/1960 Hutchins eta] 343-911 OTHER REFERENCES Peeler et al., Microwave Stepped-Index Luneberg Lens, April 1958, 6 pages.

ELI LIEBERMAN, Primary Examiner.