US2745101A - Dielectric antenna with dielectric wave-guide feed - Google Patents

Description

May 8, 1956 Filed Dec. 13, 1954 P. G. MARIE 2,745,101

DIELECTRIC ANTENNA. WITH DIELECTRIC WAVE-GUIDE FEED 7 Sheets-Sheet l Fig. 2

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//VVEN ro ATTOR Y DIELECTRIC ANTENNA WITH DIELECTRIC WAVE-GUIDE FEED v a Pierre G. Mari, Paris, France I Application December 13, 1954, Serial No. 474,764

Claims priority, application France December 14,1953

6 Claims. (Cl. 343-785 The invention relates to a dielectric antenna provided with a circular dielectric wave guide to feed micro-wave electromagnetic energy along the walls of said Wave guide to the antenna for radiation therefrom. Further the invention relates to new and improved coupling means between a circular dielectric wave guide feed and a metallic guide either rectangular or circular in cross-section for the transmission of micro-wave energy to said metallic guide. I I

An object of the invention is to provide an antenna and wave guide feeding and/or coupling'meansconstituted substantially entirely of dielectric materials except for the micro-wave focusing elements.

In accordance with the invention, the essential electrical components of the antenna, the coupling means and the wave guide feeding means are constituted by pipe shaped dielectric members, said pipe shaped members being substantially circular in cross-section at the micro-wave feed ing portion of the tube and being ribbon-shaped or stripshaped in the radiating terminal portions as well ,as in the connecting portions where a connection is made to the metal wave guide members. The metal wave guide members are conveniently either rectangular or circular in cross-section. The tube elements constituting the wave guide feed or coupling elements are formed with intermediate transition portions between the tubular feeding sections and the terminal strip radiating sections. These transition portions are formed by notching the pipe along a generatrix to spread the tubular periphery; of the-pipe flat-wise to form the ribbon or strip at the radiating portions. The flat ribbon of dielectric formed by notching the top is branched in accordance with a predetermined scheme to provide a series of identical forked strips arranged in a particular geometric relationship to constitute cophasal primary radiators. These radiators may be arranged in a linear terminalarray, in line, to lie along the focal line of a cylindrically shaped parabolic reflector which thereby forms .an antenna which is. desig nated hereinafter as an antenna of the first type. I

In another arrangement, the ends of the strips may be connected at equidistant points and inthe samecophasal wave radiating relationship to an internal surfaceof a radiating wall of a hollow cylindrical dielectric antenna. The antenna having said radiating wall is an antenna of the second type; the ends of the strips therein 'are. no longer the primary radiators but are rather connected to the cylindrical dielectric radiator.

Micro-wave radiant energy guided by thestrip continues to be guided by the wall of said hollow cylindrical dielectric radiator if the curvature of the generatrix along said hollow cylindrical wall is greater than that which permits the radiation of the wave energy into free space. But if along the generatrix of this wall the curvature is less, the penetration of the waves into free spaceoccurs and the micro-waves emerge from the wall of the guiding dielectric to be radiated into space. 1 According to the invention, the bifurcation ofthe incident feeding ribbon or strip creates two or four ribrate of 4x27 strips per cylinder. I Y

I distance perpendicularly to the wall at the end of which;

bonsidentical to the incident ribbons which are termed the emergent strips. In an antenna of the second type possessing f our radiatingcylinders, the guiding or" incident strip may be bifurcated three times into four emergent strips,v which provide sixty-four final emergent strips, there'being sixteen strips for each cylinderconnected to the four radiating cylinders. I Generalizing, if the antenna has 2" radiating cylinders, i the guided strips are bifurcated (n+1) times intofour emergent strips, which 'give A dfinal emergentstrips connected to the 2 cylinders at the The important advantageof this antenna of the second type is that it presents a lesser; resistance {to the. wind while at the same time pro 'ngjan efficient radiating surface. I I I A micro-wave which is guide'dalong a circular tube of dielectric substance, travels partially in the wall of the tube and partially along said-wall. "In more precise terms, if the wall has a thickness a, the electrical-field a valueE on the surface of this wall and if sigma designates the the field diminishes by, a valuezof one neper," then an energy which is proportional to al) :is distributed in the wall andan energy sigma E is distributedalong.the sur face of the wall, half of said latter energy beingdistributed along the exterior surface and half along the interior surface.

In the transmission which' is preferred, the electric field is contained in the plane of the tube wall and the mode of vibration of the guided wave is the TEdi mode as in the case of the metallic circular. wave guide..=-.The elec-' trical field is perpendicular at all points to the axis of the tube; it is a maximum in the dielectric material and decreases rapidly at distances away from the internal and external surfaces of the tube. 'Propagation takes places only if the diameter of the tube is greater than 2 sigma. The propagated waves in the antenna and coupling structures which are described below are in the TEOI mode as .1

. vention.

In connection with that more detailed description, there is shown in the drawings, in

Fig. 1, a unit plate of dielectric material which oriented with respect to rectangular coordinates; in

Fig. 2, curves illustrating the variation of the guided wave-length in the'dielectric substance as a function of the thickness of the tube wall of the dielectric tube; in

Fig. 3, a perspective view of a dielectric. coupling means" in accordance with, the invention between a metallic rectangular wave guide and dielectric circular wave, guide; in N between a metallic circular 'wave guide and dielectric circular wave guide; in

Fig. 5, a perspective view of a first type of dielectric antenna and dielectric wave guide feed; in

Fig. 6, 'a perspective view-,ofqa mOdlfiCfiilOnuOflhQ wave guide. feed andof the antennaof Fig. 5; in-

Fig. 7, a face view of an antenna assemblymofzth'e I antenna of the second type;.-ii1

Fig. 8, a Perspective view illustrating 'detailsr'of thequadruple 'bifurcation 'or branching of the dielectric strips; in

Figs. 9, I'Oand 11, sectional views showing thequadruple bifurcation or branching of the dielectric strips P e edy 9 Fig. 4, a perspective view of a dielectric coupling means taken along line 9-9, -10 and 11-11 respectively of'Fig'. 8; in

Fig. 12, a schematic arrangement partly in perspective illustrating the disposition of the strips relative to the dielectric radiating cylinders in an antenna of the second type; an in Fig. 13, a cross-sectional view of the antenna of Fig. 7 taken along diagonal line 13-13 in Fig. 7.

Referring to Fig. 1, the unit plate of dielectric material is of undeterminate-lengthand width and consists of a material having dielectric constant eand the point of origin 0 of the rectangle coordinate axes is shown in the figure. The thickness of the unit plate is a. At the propagation of an electromagnetic wave in said plate, the electric field decreases exponentially from the exterior surface of the plate in the form of an evanescent wave. The phase velocity of thewaves which are propagated in the dielectric plate is a function of both the thickness of the plate and the wave length of the electromagnetic wave travelling through the dielectric.

In more precise terms:

e==th6 dielectric constant =the plate thickness 7i=wavelength of the electromagnetic wave in free space Xg=wavelengthof the guided electromagnetic wave in the dielectric of the plate v==the phase velocityof electromagnetic waves guided in said plate If the electric field oftheelectromagneticwave is parallel to the plate, the followingrelation exists:

If the electric field of the electromagnetic wave is perpendicular to the plate, thefollowing equation is obtained:

From Formulae 2 and 4 it is seen that the phase velocity v in the plate tends towards the velocity of light 0 as the thickness of the dielectric plate a falls toward 0. The phase velocity v approaches tan surface of the plate decreases exponentially and in proportion to:

k 2 w 1 (lg) may be eliminated in these formulae and in view of the relationship in Formula 5 above, we obtain 2 Z A 41r (e-1 (6) This is the case of polarization which is parallel to the plate. In the case of polarization of the field which is perpendicular to the plate, we have:

The Formulae 6 and 7 relate the thickness of the plates to the penetration of the waves into the air. When a is small, xg/k is substantially equal to 1 and sigma 0' is large (see Formula 5). The term M 0' in the Formulae 6 and 7 can be neglected in favor of the term and these formulae show that the product an is substantially'constant for a given wave length. The result therefore is that for a small thickness at, a and a are substantially inversely proportional to each other.

The Formulae 6 and 7 show that for the same value of a, the plates in which the wave is propagated with an electric field perpendicular to the plate are to be 6 times thicker than the plates in which the Wave is propagated with its electric field parallel to the plate. Since in both cases the electric field exterior to the plate is carried without power loss and the losses are localized in the dielectric, the propagation in plates in which the field is parallel to the plate thus exhibits smaller losses in the dielectric.

Fig. 3 shows a coupling means between a rectangular metallic guide and a circular dielectric guide. The metallic rectangular guide 2 forms the terminus of a pyramidal horn 3. The circular dielectric guide 4, is notched at generatrix line 5 near its extremity and is developed into a fiat strip 6.

Pyramidal horn 3 consists of two half portions joined by the'upstanding flat edges 7 and 8 which are held together by screws 9. Strip 6 is pressed between edges 7 and 8,'on opposite sides of the horn.

The Fig. 4 shows a coupling means between a circular metallic guide and a circular dielectric guide. The circular metallic guide 10, terminates at conical horn 11 which is provided with a cylindrical sleeve portion or rim 12, in the interior of which guide 10 is seated. The circular dielectric guide 13, is terminated on the other side of the metallic guide 10 at the same rim 12. Said circular dielectric guide 13 is notched by three generatrices, apart, 14, 15 and 16 respectively, to form three strips, which are tongue-shaped, 17, 18 and 19 respectively. The tongueshaped strips which are developed are substantially flat strips and these three strips are pressed between guide and rim 12 to anchor them.

-In Fig. 5 there is shown a first type of dielectric antenna fed by a circular dielectric wave guide 20. Said circular dielectric guide 20 is shown in a vertical arrangement and radiating flat strip 21 is obtained by cutting the circular guide along a generatrix as shown and by developing the cylindrical surface on a plane. This strip 21 is bifurcated into two other identical fiat strips 221 and 222, arranged in the same vertical plane as strip 21 and also proportionately inclined towards the vertical direction. In the same manner strips 221 and 222 are themselves bifurcated respectively into further fiat strips 231, 232, 233 and 234, which are identical to eachother arranged in the same plane as 21 and also proportionately inclined towards the vertical direction. Finally strips 231 to 234 are further bifurcated into two additional branches in order to obtain strips 241, 242, 243, 244, 245, 246, 247, and 248. These last strips have their ends arranged in the straight line which is the focalline of a mirror 26. Mirror 26 is a portion of a parabolic cylinder whose generatrices are horizontal, as shown.

Thefree ends of strips 241 to 248 are suspended as is convenient by means of fine strong supporting wires 27 which are fixed to support post 28.

Thus, the electromagnetic wave energy guided by dielectric wave guide 20 is divided into two paths at each bifurcation. After n bifurcation, the energy, guided by 2 strips, is proportioned or sub-divided into 2" waves (eight in the case of Fig. 5) which arrive in phase at line 25.

The-distance AB between strips 241 and 24s is large in comparison with the wave length. Under these conditions the radiating waves at the ends of strips 241 to 24s are cylindrical as a first approximation. The wave surfaces form parallel cylinders about focal line 25 and the intensity of the radiated field in a plane passing through focal line 25, diminishes quite rapidly when the plane is tipped from the vertical direction, thus it can be considered for practical purposes that substantially all of the energy is directed on to mirror 26 at focal line 25. This mirror which lies close to the plane inclined at 45 to the vertical direction, converts the cylindrical wave into a plane horizontally polarized wave which is propagated in the horizontal direction. The dielectric antenna of Fig. 6 is similar to that of Fig. 5, with the exception that the fiat strip 31 which is obtained by developing the dielectric circular guide 30 on a plane and the bifurcated strips 321 and 322, 331 to 334, 341 to 34s are located within vertical planes perpendicular to the focal line 25, whereas in Fig. 5 they were in a vertical plane passing through said focal line. Mirror 26 converts the cylindrical wave radiated by the'ends of the dielectric strips into a horizontally polarised plane wave which is propagated in the horizontal direction.

In Fig. 7 there is shown an antenna of the second type which is viewed from the rear. Cylindrical radiating members of dielectric material 35, 36, 37 and 38 are shown in a rectangular array in said figure and the crosssection of these members is a rectangle having rounded sides. The rounding of the sides of the rectangle constitutes a feature of the invention which is explained in greater detail hereinafter. Metal shields 39, 40, 41, 42, 43 and 44 are fixed to the rear of the antenna by conventional fastening means as are shown in Fig. 13.

In Fig. 13 the dielectric strips which serve as the dielectric wave guide means of the invention are shown arranged within these metal shields which are disposed with an inclination of 45 with respect to the direction of the cylindrical radiating members. The cross-section of the metal shields is rectangular, the longer sides of the rectangle being parallel to the axis of the antenna. The strips are extended within the shields with the surface of the strip being disposed parallel to the smaller side of the shields so that the strips in effect are disposed in parallel to the plane of the antenna. a

,The flat plates at the rear of the cylindrical radiating members are closed by means of metal plates 45, these metal plates being provided with openings or holes 46 in theregion where the metal shields cross the wave guide cylinders. :The metal shields are closed'at the front by means of flat plates 54 and these flat plates are likewise providedwith openings or holes which are coincident with holes 46. Rear and front plates 45 and 54 respectively are assembled and joined by means of screws 62 as shown in Fig. 13. The cylindrical radiating members are mechanically tightened in place between braces 63 and counter-plates 64 by means of screws 65..

Strip 47 which guides the wave energy is completely enclosed within shield 48. The strips which are branched into four strips are illustrated in Fig. 12, schematically which shows point 51, corresponding to strip 47 and then shows the bifurcation into strips 521 to 524 and 531- to 5316. The four emergent strips from point 51 can be taken as representative of the emergent strips from the shown inFig. 8 the opposite bars of the emergent stripsare shown on opposite faces of the incident strip, two being on one face of the incident strip and two being on the other face. The emergent strips have substantially the same size or dimensions as the incident strip. The twov emergent strips which derive from one face of the incident strip are glued to the latter at a part of their surface and then glued to each other on another part of their surface as is shown in Fig. 8. The remaining two emergent strips are glued in substantially the same manner to thereby form a flange construction 50 which is perpendicular at its middle portion to the surface of the incident strip 47.

,In order to better comprehend the details of the bifurcated structure of the incident strip and emergent strips, reference is made to Figs. 9, l0 and 11 which, respectively, are sections of Fig. 8 along lines 9-9, 10-10 and 1111.

In Fig. 13 there is shown a sectional view along line 13-13 of Fig. 7. In this sectional view through metal shield 40, the cylindrical radiating members 35 to 38 are seen as also are bifurcations 511, 52.2 and 524, 53s, 53s, 5314 and 5316. At each bifurcation, the arrangement is such that there arebut two emergent strips within the section taken and that the two other strips are perpendicular to the plane of the figure and therefore are seen on end. For example, in Figs. 12 and 13, 51 is the point of bifurcation and the four emergent strips are represented. Of the four emergent strips which are represented in Fig. 12, only three are shown in Fig. 13 that is to say 492, 493 and 494.

The walls 55 of the cylindrical radiating members are formed of a dielectric material as already mentioned. The emergent strips which are the terminated strips 56 are disposed tangentially to the interior surface of the said walls 55 and are glued or otherwise adhered to these latter at points 59. The guided wave which is propagated by strip 56 is thereafter guided by the wall 55 and is radiating from point 57. In effect, at point 57 of wall 55 of the radiating cylinder, the wall is curved in such manner to provide a surface or face in advance of the wall at 58 which is rounded. The radius of curvature at 57 is smaller than the penetration a which is given by Formula 5 so that there results therefrom the radiation of the microwave energy, which had previously followed the dielectric Wall into free space from the neighbourhood of point 57.

One, therefore, observes on the same cylindrical radiating member, 37 for example, that there are-eight points such as 59 on one of the faces 55 of the member, the lefthand side for example and additionally, eight other points on the face to the right. These eight points on the one face (left) are aligned within the rectangle 60 as is shown in Fig. 12. Similarly the eight points on the right are disposed in rectangle 61 on said cylindrical radiating member.

Although the rounded forward face 58 of the cylindrical radiating members 35 to 38 does not play too important a role in the construction shown, they are quite essential to maintain the necessary mechanical tightness of the antenna, and for this reason they are of importance to the antenna construction.

Having thus disclosed the invention, what is claimed is:

1. A dielectric antenna with dielectric feed means to be fed with microwave electromagnetic energy from a metallic wave-guide comprising a tubular dielectric waveguide, first transition means between said tubular dielectric wave-guide and said metallic wave-guide, a main flatwise wave-guide dielectric strip, second transition means between said tubular dielectric wave-guide and said main flatwise dielectric strip formed by cutting the tubular dielectric wave-guide along a generatrix to develop it flatwise, said flatwise strip being bifurcated, secondary flatwise wave-guide dielectric strips issued from said bifurcation means, and an array arrangement of a plurality of radiators located at the ends of said secondary flatwise dielectric strips at equal distances from said bifurcation means.

2. A dielectric antenna with dielectric feed means as in claim 1, wherein the radiators are the terminal crosssections of the secondary flatwise wave-guide dielectric strips.

3. A dielectric antenna with dielectric feed means to be fed with microwave electromagnetic energy from a metallic wave-guide comprising a tubular dielectric waveguide, first transition means between said tubular dielectric wave-guide and said metallic Wave-guide, a main flatwise wave-guide dielectric strip, second transition means between said tubular dielectric wave-guide and said main flatwise dielectric strip formed by cutting the tubular dielectric wave-guide along a generatrix to develop it flatwise, said flatwise strip being bifurcated, secondary fiatwise wave-guidedielectric strips issued from said bifurcation means and guiding the microwave electromagnetic energy partly inside themselves and partly within penetration zones of a given width adjacent to said secondary strips, and hollow cylindrical dielectric radiators, having in cross-section a curved portion the radius of curvature of which is smaller than the penetration zone given width, and connected to the ends of the secondary strips at equidistant points at the internal surface of the hollow cylin- 8 drical dielectric radiators, said secondary strip'ends being located at equal distancesfrom said bifurcation.

4. A dielectric antenna with dielectric .feed means to be fed with microwave electromagnetic energy from a metallic wave-guide, rectangular in cross-section, comprising a pyramidal electromagnetic horn connected with said rectangular metallic wave-guide, a tubular dielectric waveguide, a flatwise portion of the dielectric Wave-guide formed by cuttingsaid guide along a generatrix to develop it flatwise and extending into the plane of symmetry of. said horn, a main flatwise wave-guide dielectric strip,,

transition means between said tubular dielectric waveguide and said main flatwise dielectric strip formed by cuting the tubular dielectric wave-guide along a. generatrix to develop it flatwise, said flatwise strip being bifurcated,

secondary flatwise Wave-guide dielectric strips issued from said bifurcation means, and a plurality of radiators located at the ends of said secondary flatwise dielectric strips at equal distances from said bifurcation.

5. A dielectric antenna with dielectric feed means to be fed with microwave electromagnetic energy from a metallic wave-guide, circular in cross section, comprising a conical electromagnetic horn connected'with said circular metallic wave-guide, a tubular dielectric wave-guide, tongue-shaped portions of the dielectric wave-guide formed by cutting said guide along a plurality of generatrices to develop them substantially flatwise and secured to the conical surface of the horn, a main flatwise waveguide dielectric strip, transition means between said tubular dielectric wave-guide and said main flatwise dielectric strip formed by cutting the tubular dielectric wave-guide along a generatrix to develop it flatwise, said flatwise strip being bifurcated, secondary flatwise wave-guide dielectric strips issuing from the bifurcation, and a plurality of radiators located at the ends of said secondary flatwise dielectric strips at equal distances from said bifurcation.

6. In a dielectric antenna with dielectric feed means as claimed in claim 1, wherein said main flatwise wave-guide dielectric strip having a given width and four secondary flatwise wave-guide dielectric strips of the same width is secured to the main strip, both on each side of said main strip, along half their width, the second halves of the secondary strips are secured to the main one at a given side being secured to one another and forming wing portions perpendicular to the main strip.

References Cited in the file of this patent UNITED STATES PATENTS 2,595,078 Iams Apr. 29, 1952 FOREIGN PATENTS 878,830 France Nov. 2, 1942 888,619 France Sept. 13,. 1943

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