CA1039843A - Aberration correcting subreflectors for toroidal reflector antennas - Google Patents
Aberration correcting subreflectors for toroidal reflector antennasInfo
- Publication number
- CA1039843A CA1039843A CA226,139A CA226139A CA1039843A CA 1039843 A CA1039843 A CA 1039843A CA 226139 A CA226139 A CA 226139A CA 1039843 A CA1039843 A CA 1039843A
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- CA
- Canada
- Prior art keywords
- subreflector
- antenna system
- feed
- axis
- main reflector
- Prior art date
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-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q19/00—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic
- H01Q19/10—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces
- H01Q19/18—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces having two or more spaced reflecting surfaces
- H01Q19/19—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces having two or more spaced reflecting surfaces comprising one main concave reflecting surface associated with an auxiliary reflecting surface
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- Aerials With Secondary Devices (AREA)
Abstract
ABERRATION CORRECTING SUBREFLECTORS
FOR TOROIDAL REFLECTOR ANTENNAS
ABSTRACT OF THE DISCLOSURE
The correction of aberration in toroidal reflector antennas by a novel type of subreflector is disclosed. The specific shape of the subreflector ultimately depends on the geometry of the toroidal reflector. However, in any case, the effect of the subreflector is to achieve a point focus in a system which, without the subreflector, does not focus at a point. Considering the antenna system from a radiation point of view, this is equivalent to turning a non-planar equiphase surface in the aperture into a plane thereby eliminating the phase error about the aperture plane perpendicular to the desired direction of propagation. This is achieved while preserving the wide field of view characteristic of the torus antenna by designing the subreflector so that all pathlengths from a reference plane are constant and equal to a desired reference pathlength.
In a practical case, the design of the subreflector is accomplished by developing a heuristic geometric optics model of the focusing properties of the toroidal reflector and using a programmable general purpose digital computer to generate the subreflector shape by numerically computing points on the surface of the subreflector for separate, individual rays intercepted by the toroidal reflector, for a bundle of rays incident from the desired direction. These points may then be used to machine the subreflector surface using well-known numerically controlled milling machines.
Of special significance is an optimum antenna configuration using what may be termed a "Cassegorian" subreflector designed according to the principles of the invention having similarities to both Cassegorian and Gregorian subreflectors.
FOR TOROIDAL REFLECTOR ANTENNAS
ABSTRACT OF THE DISCLOSURE
The correction of aberration in toroidal reflector antennas by a novel type of subreflector is disclosed. The specific shape of the subreflector ultimately depends on the geometry of the toroidal reflector. However, in any case, the effect of the subreflector is to achieve a point focus in a system which, without the subreflector, does not focus at a point. Considering the antenna system from a radiation point of view, this is equivalent to turning a non-planar equiphase surface in the aperture into a plane thereby eliminating the phase error about the aperture plane perpendicular to the desired direction of propagation. This is achieved while preserving the wide field of view characteristic of the torus antenna by designing the subreflector so that all pathlengths from a reference plane are constant and equal to a desired reference pathlength.
In a practical case, the design of the subreflector is accomplished by developing a heuristic geometric optics model of the focusing properties of the toroidal reflector and using a programmable general purpose digital computer to generate the subreflector shape by numerically computing points on the surface of the subreflector for separate, individual rays intercepted by the toroidal reflector, for a bundle of rays incident from the desired direction. These points may then be used to machine the subreflector surface using well-known numerically controlled milling machines.
Of special significance is an optimum antenna configuration using what may be termed a "Cassegorian" subreflector designed according to the principles of the invention having similarities to both Cassegorian and Gregorian subreflectors.
Description
iO39843 BAC~;G~OUND OF THE INVE:NTION
Field of the Invention:
The present invention ~enerally relates -to toroidal antenna structures and systems, and more particularly to a novel aberration correcting subreflector and deslgn technique use~ul in both rectangular and non-rectangular toroidal reflector `
antenna systems.
Descriptions of the Prior Art:~
Simple reflectors useful in a multiple beam environ~.ent will, in general, suffer from aberration. That is, a point source cannot be so located to produce a planar wavefront in the reflector aperture perpendicular to the desired beam directions, except for the single exception of the axial beam of the paraboloidal reflector. This aberration is a limitation of the antenna performance.
The problem of aberration is also present in some compound reflectors, such as toroidal reflectors, but because of the complex geometry of toroidal reflectors, a solution of the problem has not before this invention been attempted. A `~-toroidal reflector may be simply defined as a section of a surface of revolution and, typically, the generating curve ~ -is a conic section. If the axis of revolution is perpendicular to the axis of the generating curve, then the reflector is a section of a rectangular torus, otherwise it is `~
a section of the non-rectangular torus. An example of the -latter is the subject of United States Patent No. 3,852,763, issued December 3, 1974, to Kreutel and Hyde, entitled -"Torus-Type Antenna Having a Conical Scan Capability."
In order to treat the aberration problem in toroidal antennas, and particularly those having parabolas as generating curves, it is useful to first understand how the toroidal reflector focuses. One approach to this is to consider separately the focusing properties of the generating .. .
~0398~3 section and the circular arc about which the generating section is swung, and then to consider the interaction of the two.
A parabolic reflector, as mentioned previously, has perfect focusing properties for axial rays. However, ~or rays incident slightly non-parallel to the axis, the focus moves in a direction opposite to the deviation from parallel by the incident rays to describe a locus of points which define a ~best" focus arc. This arc is itself a parabola of focal length one-half that of the parabolic-section of the reflector.
As the deviation angle to parallel increases, the focus spreads in a coma-like manner. This is manifested in the far-field pattern by gain loss and by the characteristic coma-lobe on the off-side and a reduced sidelobe on the near side of the off-axis beam of incident rays.
On the other hand, a circular arc provides uniform focusing over a wide angular field, but this desirable result is achieved at the expense of what is known as sperical aberration. The resultant focal region may be characteri2ed as having the possibility that more than one ray passes through a given point. More specifically, in the multiple ray regions, i.e., the region bounded by the marginal rays, the caustic surface and the paraxial focus, more than one ray may pass through a given point. The essential points here are the presence of spherical aberration and the incident angle independence of the focal region distribution. Unlike the parabolic section, which has perfect focusing for rays parallel to the section axis and imperfect focusing for a collimated bundle of rays that are not parallel to the axis, the circular section always has aberration for all directions ''`` . ` :
11~)39~43 ~
of the ray bundle. But ~hereas thle aberrations for the parabolic section are a function of the deviation angle, _ ''`
the aberrations arising from a circular section are not a ,`
function of direction. - `
Now by combining the two sections, i.e.,'the -generating parabolic section and the circular section of revolution, a conceptual picture of how the torus focuses may be realized. In such a reflector, the optimum location o,f the focal point of the parabolic section is located inside , the location of the paraxial focus of the circular section.
In turn, the optimum feed position turns out to be located just inside the focal point of the parabolic section, with ~;~
the refocused configuration giving less pathlength variation in the aperture plane than that encountered by putting the ' feed at the focal point. ~hile this location of optimum feed position minimizes the phase error about an aperture plane , perpendicular to the desired direction of propagation, the ~ -inherent aberrations of toroidal reflectors severely limits the efficiency of the design of reflectors with electrically larger apertures, i.e., larger D/~ where D is the aperture diameter and A is the wavelength, measured in the same units.
SUMMPRY OF THE INVENTION
It is therefore an object of the present invention to provide an aberration correcting subreflector for toroidal re-flector antenna systems and thereby greatly increase the effici- ;
ency and the resulting performance of the antenna system for :.... - -. . : .
1~398~13 electrically large apertures, ~Yhile preservin~ the performance for the smaller apertures.
- It is another object of the invention to provide a new feed method for antennas with torus reflectors which corrects incident ray pathlength so that true optical focusing is obtained thereby eliminating aberrations and màking the efficiency of such antennas independent of frequency.
The foregoing and other objects of the invention are attained by providing a correcting subreflector which, when il-luminated by a feed-horn, reflects energy onto the main toroidal reflector so that a beam is formed to radiate in the desired direction. Alternatively, in reception, incoming rays incident upon the main reflector are reflected onto the subreflector and from it onto the feed-horn, focusing at a point so that the pathlength from a reference plane is equal for all rays. While the specific shape of the correcting subreflector depends on the specific geometry of the main toroidal reflector, the actual de-sign of the subreflector is achieved by numerical computation of points on the surface of the subreflector for the constraints that (1) all rays focus at a single point, and ~2) all path-lengths from a reference plane to the point of focus are constant and equal to a desired reference pathlength.
Thus, broadly, the invention contemplates a toroidal refelector antenna system which includes a main reflector having the shape of a surface section of a torus of revolution and a feed-horn assembly positioned to illuminate the main reflector and thereby form beams in the desired directions of propagation.
The improvement comprises an aberration correcting subreflector interposed between ~he main reflector and the feed-horn, and forming a feed assembly with the feed-horn. The surface of the subreflector is non-concentric with the main reflector and is so .~
designed that for the aberration correcting surface oE the subreflector only one ray i5 inc~dent on the surface at each point thereon. SubstantIally all rays focus at a single point at the feed-horn and substantially all ray pathlengths from a reference aperture plane to the single point of focus are constant and equal to a predetermined reference pathlength, whereby the system is free of aberration and the efficiency of the system is independent of frequency. The feed assembly is further movable along an arc about the axis of revolution of the main reflector to provide substantially aberration free beams in scanning.
BRIEF DESCRIPTION OF THE DRAWINGS
The specific nature of the invention, as well as other objects, aspects, uses and advantages thereof, will clearly ap-pear from the following description and the accompanying drawings in which:
FIG. 1 is a pictorial view illustrating the geometry of a torus antènna;
FIGS. 2A and 2B are graphs showing efficiency as a `-~
function of antenna diameter in wavelengths with illumination as a parameter for two choices of torus geometry;
FIGS. 3A and 3B are graphs showing parabolic torus gain as a function of antenna diameter in wavelengths with il-lumination as a parameter for the two choices of torus geometry adopted in FIGS. 2A and 2B, respectively; FIGS. 2A, 2B, 3A, and 3B clearly demonstrating the deleterious effects of aberration for electrically larger antennas (larger D/l);
FIG. 4, appearing with Fig. 1, illustrates the basic geo-metric model used to design the surface of the correcting sub-reflector according to the invention;
.: .
1~39843 FIG. 5, appearing with Fig. 1, illustrates another geo-metric model representing the vector equations which define points on the surface of the subreflector according to the invention;
FIGS. 6~, 6s and 6C are, respectively, a plan view and side views of two mutually perpendicular axes of a specific subreflector shape made in accorda~ce with the teaching of the invention;
FIGS. 7A and 7B are, respectively, a plan view and a - side view of another specific subreflector, herein referred to as a Cassegorian subreflector, made by careful choice of geo-metric parameters in accordance with the teaching of the inven-tion; and FIGS. 8A and 8B show the approximate cross-sections of the Cassegorian subreflector shown in FIGS. 7A and 7B.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, and more particularly to FIG. 1, there is illustrated the geometry of a typical front-fed toroidal reflector. The specific reflector illustrated is non-rectangular in that ~ ~ 95.5, where a is the angle the axis of revolution z' makes with the desired direction of propagation z. This geometry produces a conical scan surface which closely approximates the actual conical surface subtended by an earth station site within the continental and contiguous United States and the geostationary arc as explained in the aforementioned Patent No. 3,852,763. Other dimensions useful in defining the specific toroidal reflector illustrated are the offset ratio, d/D ~ 0.1, typically, where d is the vertical distance below the toroidal reflector of a feedhorn and D is the vertical dimension of the toroidal reflector; 3 ~ R/D < 2, where R is the - : - ~: -~f)39843 radius of revolu~ion; and Q.48 ~ f/~ ~ 0.49, where f is the focal length of the parabolic generating section. In addition, ~S i5 defined as -the field-of-view angle at the antenna. The section M through the vertex V, while typically a parabola, may be any other conic section such as a circle, ellipse or hyperbola.
The reflector is formed by xotating the section M
about the z' axis. In the specific case illustrated, it should be noted that the axis of the section M is the z axis, which is the desired direction of the beam formed in the region Ao~ The optimum projected location of the focal point F of the parabolic section M is located inside the location of the paraxial focus, P. As mentioned previously, the optimum feed position turns out -to be located just inside the focal point F, the refocused con-l; figuration giving less rms pathlength variation in the apertureplane than that encountered by putting the feed at the focal point.
Because of the circular symmetry, the reflector presents the same shape to, and hence has the same beam forming capability for identical feeds located at all points on the arc described by the rotation of the feed point of the generating curve about the axis of rotation. A single moveable feed or a plurality of selectively energizable feeds located along the feed arc, when illuminating the reflector surface, will form identical beams, the torus of whose axes of beam direction describe the surface of a right circular cone.
The result of this feed positioning is to achive the best point focus in a system which really does not focus at a .
1~39843 point. In the specific example illustrated in FIG. 1, the desired direction of propagation makes an angle a = 95.5 with the axis of rotation z' so that upon rotation it rules out a very flat right circular cone giving a symmetry to the reflector that yields identical ,beams in the field of view.
The specific purpose of the invention is to turn the equiphase surface mentioned above into a plane while preserving the field of view of the antenna system.
The crux of the problem solved by the invention is that the non-planar equiphase surface characteristic of the point-fed uncorrected torus is invariant in terms of the physical measurements of the system, while wavelength changes inversely with frequency. Thus, a fixed pathlength departure from the planar condition turns into a phase error that increases with frequency. The consequences of this are shown in FIGS. 2A and 2B and FIGS. 3A and 3B in terms of efficiency and gain, respectively, as functions of wavelength-normalized antenna diameter D/~ for two choices of R/D. For D/~< 150, there is little seen of the effects of aberration, while for D/~ > 300, it is clear that aberration dominates.
The problem of subreflector correction of pathlength may be simply stated. Given an incoming bundle of rays A, as shown in FIG. 4, and a reflector M, off which the bundle is reflected, calculate a subreflector S which intercepts the reflected bundle B and reflects it to focus at H. While easy to state, it is by no means clear what the precise limitations under which a physical solution is realizable in all cases.
If the condition is imposed that S lie in a region such that no two rays reflected from M intersect at a point in that region, it is clear that the resulting surface S will be 1 ', '''' "" . ~ ~ ~" ' 1039~143 physically realizable.
Consider an incoming plane wave characterized by a unit Poynting's vector ni, incident on a reflector M, where M - M (x, y, z) where we have chosen our coordinate system such that for a plane wave from a distant source in the desired direction ni= -k. There is no loss of generality since a jimple coordinate rotation of M is all that is required for any other direction. Then the unit normal to M(x, y, z) is given by: :
~ ~ aM ~ aM ~ aM
nm-i ~ + ~ + 1~ G ) r/T tl) i=x,y,z i=x,y,z i=x,y,z taking the sign appropriate to the normal on the side of the ~;
incident ray. And the reflected vector is given by:
nrm = ni -2nm (ni n ) (~a) ;~
The question now is what is the reflecting surface required .
to meet the following two conditions:
(i) all rays focus at a single point H (x, y, æ~, and (ii) all pathlengths from a reference plane to H
are constant and equal to the desired reference pathlength.
This problem can be solved by vector analysis:
From FIG. 4, we may note that MiSi Clnrm, where Cl = constant; (3) _g_ 1~3989~3 MiH = MiSi + SiH ; (~) Clnrm ~ C2nrs~ where C2 = constant; (4a) and finally Cl + C2 + I MiAi I
where QO is the desired reference pathlength; i.e., Cl + C2 = Qo ~ IMiAil, and (5a) nrs = nrm -2ns ~ns nrm) (6 From the foregoing, we can make the following observations. Equation (1) tells us we can find the unit normal nrm to the surface M. Equation (2) says that if we know this unit normal, and the direction of the incident ray, which is given, we can find the direction of the ray reflected from the surface M, but we do not know its length Cl. Equation (4) tells us that since we know H, the desired focal points, and Mi, the incident point, we know the plane of the two ray segments the first of which is reflected off M at Mi and incident on S at Si, i.e., MiS~
and the second segment of which is the reflection off S at Si towards H, i.e., SiHi. An implicit condition is that only one ray is incident on S at each point Si.
~or the incident rays defined by the vector ~ ~ - :
ni = -k, and the reference plane defined by z = 0, then the ith ray pierces the reference plane at Ai = Ai (Xi~ Yi~ ) and is incident on the reflector M at Mi = Mi (Xi~ Yi~ Zmi)~ -~
where Zmi is the solution of M for x = xi, y = Yi, and can therefore be found. The point H is arbitrary and must be given. For our purposes H ~ H (XH, YH~ ZH)' whence -10-- , ~ ~ .:. . .. .
- . .
- : .:. . .
9843 `~
MiH = i (xH - xi)+ ~ (YH Yi) ~ k (ZH Zmi) which can readily be determined.
Substituting Equation (6) into Equation (4a), MiH ( Cl + C2 ¦ nrm ~ 2C2ns ( ns nrm ) Forming the scalar product MiH ~ nrm, and using Equation (5), one obtains successively n MiH = Cl + C2 2C2 ( s rm)
Field of the Invention:
The present invention ~enerally relates -to toroidal antenna structures and systems, and more particularly to a novel aberration correcting subreflector and deslgn technique use~ul in both rectangular and non-rectangular toroidal reflector `
antenna systems.
Descriptions of the Prior Art:~
Simple reflectors useful in a multiple beam environ~.ent will, in general, suffer from aberration. That is, a point source cannot be so located to produce a planar wavefront in the reflector aperture perpendicular to the desired beam directions, except for the single exception of the axial beam of the paraboloidal reflector. This aberration is a limitation of the antenna performance.
The problem of aberration is also present in some compound reflectors, such as toroidal reflectors, but because of the complex geometry of toroidal reflectors, a solution of the problem has not before this invention been attempted. A `~-toroidal reflector may be simply defined as a section of a surface of revolution and, typically, the generating curve ~ -is a conic section. If the axis of revolution is perpendicular to the axis of the generating curve, then the reflector is a section of a rectangular torus, otherwise it is `~
a section of the non-rectangular torus. An example of the -latter is the subject of United States Patent No. 3,852,763, issued December 3, 1974, to Kreutel and Hyde, entitled -"Torus-Type Antenna Having a Conical Scan Capability."
In order to treat the aberration problem in toroidal antennas, and particularly those having parabolas as generating curves, it is useful to first understand how the toroidal reflector focuses. One approach to this is to consider separately the focusing properties of the generating .. .
~0398~3 section and the circular arc about which the generating section is swung, and then to consider the interaction of the two.
A parabolic reflector, as mentioned previously, has perfect focusing properties for axial rays. However, ~or rays incident slightly non-parallel to the axis, the focus moves in a direction opposite to the deviation from parallel by the incident rays to describe a locus of points which define a ~best" focus arc. This arc is itself a parabola of focal length one-half that of the parabolic-section of the reflector.
As the deviation angle to parallel increases, the focus spreads in a coma-like manner. This is manifested in the far-field pattern by gain loss and by the characteristic coma-lobe on the off-side and a reduced sidelobe on the near side of the off-axis beam of incident rays.
On the other hand, a circular arc provides uniform focusing over a wide angular field, but this desirable result is achieved at the expense of what is known as sperical aberration. The resultant focal region may be characteri2ed as having the possibility that more than one ray passes through a given point. More specifically, in the multiple ray regions, i.e., the region bounded by the marginal rays, the caustic surface and the paraxial focus, more than one ray may pass through a given point. The essential points here are the presence of spherical aberration and the incident angle independence of the focal region distribution. Unlike the parabolic section, which has perfect focusing for rays parallel to the section axis and imperfect focusing for a collimated bundle of rays that are not parallel to the axis, the circular section always has aberration for all directions ''`` . ` :
11~)39~43 ~
of the ray bundle. But ~hereas thle aberrations for the parabolic section are a function of the deviation angle, _ ''`
the aberrations arising from a circular section are not a ,`
function of direction. - `
Now by combining the two sections, i.e.,'the -generating parabolic section and the circular section of revolution, a conceptual picture of how the torus focuses may be realized. In such a reflector, the optimum location o,f the focal point of the parabolic section is located inside , the location of the paraxial focus of the circular section.
In turn, the optimum feed position turns out to be located just inside the focal point of the parabolic section, with ~;~
the refocused configuration giving less pathlength variation in the aperture plane than that encountered by putting the ' feed at the focal point. ~hile this location of optimum feed position minimizes the phase error about an aperture plane , perpendicular to the desired direction of propagation, the ~ -inherent aberrations of toroidal reflectors severely limits the efficiency of the design of reflectors with electrically larger apertures, i.e., larger D/~ where D is the aperture diameter and A is the wavelength, measured in the same units.
SUMMPRY OF THE INVENTION
It is therefore an object of the present invention to provide an aberration correcting subreflector for toroidal re-flector antenna systems and thereby greatly increase the effici- ;
ency and the resulting performance of the antenna system for :.... - -. . : .
1~398~13 electrically large apertures, ~Yhile preservin~ the performance for the smaller apertures.
- It is another object of the invention to provide a new feed method for antennas with torus reflectors which corrects incident ray pathlength so that true optical focusing is obtained thereby eliminating aberrations and màking the efficiency of such antennas independent of frequency.
The foregoing and other objects of the invention are attained by providing a correcting subreflector which, when il-luminated by a feed-horn, reflects energy onto the main toroidal reflector so that a beam is formed to radiate in the desired direction. Alternatively, in reception, incoming rays incident upon the main reflector are reflected onto the subreflector and from it onto the feed-horn, focusing at a point so that the pathlength from a reference plane is equal for all rays. While the specific shape of the correcting subreflector depends on the specific geometry of the main toroidal reflector, the actual de-sign of the subreflector is achieved by numerical computation of points on the surface of the subreflector for the constraints that (1) all rays focus at a single point, and ~2) all path-lengths from a reference plane to the point of focus are constant and equal to a desired reference pathlength.
Thus, broadly, the invention contemplates a toroidal refelector antenna system which includes a main reflector having the shape of a surface section of a torus of revolution and a feed-horn assembly positioned to illuminate the main reflector and thereby form beams in the desired directions of propagation.
The improvement comprises an aberration correcting subreflector interposed between ~he main reflector and the feed-horn, and forming a feed assembly with the feed-horn. The surface of the subreflector is non-concentric with the main reflector and is so .~
designed that for the aberration correcting surface oE the subreflector only one ray i5 inc~dent on the surface at each point thereon. SubstantIally all rays focus at a single point at the feed-horn and substantially all ray pathlengths from a reference aperture plane to the single point of focus are constant and equal to a predetermined reference pathlength, whereby the system is free of aberration and the efficiency of the system is independent of frequency. The feed assembly is further movable along an arc about the axis of revolution of the main reflector to provide substantially aberration free beams in scanning.
BRIEF DESCRIPTION OF THE DRAWINGS
The specific nature of the invention, as well as other objects, aspects, uses and advantages thereof, will clearly ap-pear from the following description and the accompanying drawings in which:
FIG. 1 is a pictorial view illustrating the geometry of a torus antènna;
FIGS. 2A and 2B are graphs showing efficiency as a `-~
function of antenna diameter in wavelengths with illumination as a parameter for two choices of torus geometry;
FIGS. 3A and 3B are graphs showing parabolic torus gain as a function of antenna diameter in wavelengths with il-lumination as a parameter for the two choices of torus geometry adopted in FIGS. 2A and 2B, respectively; FIGS. 2A, 2B, 3A, and 3B clearly demonstrating the deleterious effects of aberration for electrically larger antennas (larger D/l);
FIG. 4, appearing with Fig. 1, illustrates the basic geo-metric model used to design the surface of the correcting sub-reflector according to the invention;
.: .
1~39843 FIG. 5, appearing with Fig. 1, illustrates another geo-metric model representing the vector equations which define points on the surface of the subreflector according to the invention;
FIGS. 6~, 6s and 6C are, respectively, a plan view and side views of two mutually perpendicular axes of a specific subreflector shape made in accorda~ce with the teaching of the invention;
FIGS. 7A and 7B are, respectively, a plan view and a - side view of another specific subreflector, herein referred to as a Cassegorian subreflector, made by careful choice of geo-metric parameters in accordance with the teaching of the inven-tion; and FIGS. 8A and 8B show the approximate cross-sections of the Cassegorian subreflector shown in FIGS. 7A and 7B.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, and more particularly to FIG. 1, there is illustrated the geometry of a typical front-fed toroidal reflector. The specific reflector illustrated is non-rectangular in that ~ ~ 95.5, where a is the angle the axis of revolution z' makes with the desired direction of propagation z. This geometry produces a conical scan surface which closely approximates the actual conical surface subtended by an earth station site within the continental and contiguous United States and the geostationary arc as explained in the aforementioned Patent No. 3,852,763. Other dimensions useful in defining the specific toroidal reflector illustrated are the offset ratio, d/D ~ 0.1, typically, where d is the vertical distance below the toroidal reflector of a feedhorn and D is the vertical dimension of the toroidal reflector; 3 ~ R/D < 2, where R is the - : - ~: -~f)39843 radius of revolu~ion; and Q.48 ~ f/~ ~ 0.49, where f is the focal length of the parabolic generating section. In addition, ~S i5 defined as -the field-of-view angle at the antenna. The section M through the vertex V, while typically a parabola, may be any other conic section such as a circle, ellipse or hyperbola.
The reflector is formed by xotating the section M
about the z' axis. In the specific case illustrated, it should be noted that the axis of the section M is the z axis, which is the desired direction of the beam formed in the region Ao~ The optimum projected location of the focal point F of the parabolic section M is located inside the location of the paraxial focus, P. As mentioned previously, the optimum feed position turns out -to be located just inside the focal point F, the refocused con-l; figuration giving less rms pathlength variation in the apertureplane than that encountered by putting the feed at the focal point.
Because of the circular symmetry, the reflector presents the same shape to, and hence has the same beam forming capability for identical feeds located at all points on the arc described by the rotation of the feed point of the generating curve about the axis of rotation. A single moveable feed or a plurality of selectively energizable feeds located along the feed arc, when illuminating the reflector surface, will form identical beams, the torus of whose axes of beam direction describe the surface of a right circular cone.
The result of this feed positioning is to achive the best point focus in a system which really does not focus at a .
1~39843 point. In the specific example illustrated in FIG. 1, the desired direction of propagation makes an angle a = 95.5 with the axis of rotation z' so that upon rotation it rules out a very flat right circular cone giving a symmetry to the reflector that yields identical ,beams in the field of view.
The specific purpose of the invention is to turn the equiphase surface mentioned above into a plane while preserving the field of view of the antenna system.
The crux of the problem solved by the invention is that the non-planar equiphase surface characteristic of the point-fed uncorrected torus is invariant in terms of the physical measurements of the system, while wavelength changes inversely with frequency. Thus, a fixed pathlength departure from the planar condition turns into a phase error that increases with frequency. The consequences of this are shown in FIGS. 2A and 2B and FIGS. 3A and 3B in terms of efficiency and gain, respectively, as functions of wavelength-normalized antenna diameter D/~ for two choices of R/D. For D/~< 150, there is little seen of the effects of aberration, while for D/~ > 300, it is clear that aberration dominates.
The problem of subreflector correction of pathlength may be simply stated. Given an incoming bundle of rays A, as shown in FIG. 4, and a reflector M, off which the bundle is reflected, calculate a subreflector S which intercepts the reflected bundle B and reflects it to focus at H. While easy to state, it is by no means clear what the precise limitations under which a physical solution is realizable in all cases.
If the condition is imposed that S lie in a region such that no two rays reflected from M intersect at a point in that region, it is clear that the resulting surface S will be 1 ', '''' "" . ~ ~ ~" ' 1039~143 physically realizable.
Consider an incoming plane wave characterized by a unit Poynting's vector ni, incident on a reflector M, where M - M (x, y, z) where we have chosen our coordinate system such that for a plane wave from a distant source in the desired direction ni= -k. There is no loss of generality since a jimple coordinate rotation of M is all that is required for any other direction. Then the unit normal to M(x, y, z) is given by: :
~ ~ aM ~ aM ~ aM
nm-i ~ + ~ + 1~ G ) r/T tl) i=x,y,z i=x,y,z i=x,y,z taking the sign appropriate to the normal on the side of the ~;
incident ray. And the reflected vector is given by:
nrm = ni -2nm (ni n ) (~a) ;~
The question now is what is the reflecting surface required .
to meet the following two conditions:
(i) all rays focus at a single point H (x, y, æ~, and (ii) all pathlengths from a reference plane to H
are constant and equal to the desired reference pathlength.
This problem can be solved by vector analysis:
From FIG. 4, we may note that MiSi Clnrm, where Cl = constant; (3) _g_ 1~3989~3 MiH = MiSi + SiH ; (~) Clnrm ~ C2nrs~ where C2 = constant; (4a) and finally Cl + C2 + I MiAi I
where QO is the desired reference pathlength; i.e., Cl + C2 = Qo ~ IMiAil, and (5a) nrs = nrm -2ns ~ns nrm) (6 From the foregoing, we can make the following observations. Equation (1) tells us we can find the unit normal nrm to the surface M. Equation (2) says that if we know this unit normal, and the direction of the incident ray, which is given, we can find the direction of the ray reflected from the surface M, but we do not know its length Cl. Equation (4) tells us that since we know H, the desired focal points, and Mi, the incident point, we know the plane of the two ray segments the first of which is reflected off M at Mi and incident on S at Si, i.e., MiS~
and the second segment of which is the reflection off S at Si towards H, i.e., SiHi. An implicit condition is that only one ray is incident on S at each point Si.
~or the incident rays defined by the vector ~ ~ - :
ni = -k, and the reference plane defined by z = 0, then the ith ray pierces the reference plane at Ai = Ai (Xi~ Yi~ ) and is incident on the reflector M at Mi = Mi (Xi~ Yi~ Zmi)~ -~
where Zmi is the solution of M for x = xi, y = Yi, and can therefore be found. The point H is arbitrary and must be given. For our purposes H ~ H (XH, YH~ ZH)' whence -10-- , ~ ~ .:. . .. .
- . .
- : .:. . .
9843 `~
MiH = i (xH - xi)+ ~ (YH Yi) ~ k (ZH Zmi) which can readily be determined.
Substituting Equation (6) into Equation (4a), MiH ( Cl + C2 ¦ nrm ~ 2C2ns ( ns nrm ) Forming the scalar product MiH ~ nrm, and using Equation (5), one obtains successively n MiH = Cl + C2 2C2 ( s rm)
2~ .n )2 ~ O I mil nrm MiH] , whence (Sb) (Qo lZmil) nrm - ns(Qo -lzmil~nrm MiHJ
n5 nrm ThuS, s = ~ QO _ ¦Zmi¦) nrm MiH (73 n n O - IZmi¦ - nrm MiH
i us + vs ~ X ws ~hen, since n is a unit vector, (n .n ) 2 = (US2 + VS2 + WS2) .
( ¦Zmil- nrm~MiH) 18) ( o I mil) ¦MiH¦ 2 nrm-MiH Qo~lZmil ;
Finally, ^n - -+ (Qo IZmi¦) nrm MiH __ _ (7a) ( o I mil) ¦MiH¦ 2(nrm MiH) (QO -læ ~ /2 ~;
and all the vectors in the system can now be found.
Substituting from Equation (8) into Equation (5b), C2 can be determined. Then, noting that IMiAil= lzmil~ C1 is calculated using Equation (5a), and the point on the ;
(11) ,- ~. ~ , . ... . ...
:. - - , .- .
1~398~3 subreflector is now completely established.
Returning for a moment to Equation (7), if we examine this equation geometrically as shown in FIG. 5, the simplicity of the scheme is self-evident. If Q is the reference pathlength, then QO ~ ¦Zmil is the remainder after the ray incident in the aperture plane at Ai strikes the main reflector at Mi Then MiEi is a vector of length ~o ~ Zmi in the direction of the reflectlon.
~lla) . ..... . . . . . .
, : -.
1~39843 nrm, of the ~ncident vector, ni. Also HEi = hiEi ~ MiH. Hence, HEi = nrm (Qo lZmil) Mi~
But this is the numerator of Equation (7a), and the denominator is only a constant. Hence, HEi and nS are parallel (or anti-S parallel). This is immediately verified by the geometry of FIG.5. Ai~Si, nrm and MiEi lie in the same plane, by the laws of geo-metric optics. Similarly, ~liSi, nS and SiH lie in the same plane.Further, since ~ lzmil + IMiSil ~ ¦SiHI
= lzmil + IMiEil = ¦Zmi¦ + ¦MiSi¦ + lSiEil, then ¦SiHI = lSiEil Hence, the ~HSiEi is isoceles and the equal angles ~ are equal to the angles of incidence and reflection at Si, Whence it is seen that the line HEi i5 parallel to ns.
~5 Further cos ~ = HEi ~liEi ¦HEi¦ ¦MiE ¦ , which is calculable, and ¦SiH¦ 2 = 1/2 ¦HEi¦ 2 /(1 + COS 2E) .
What the above analysis shows is that the choice of ni' the incident wave, ~1, the main reflector, H, the feed-horn loca-tion and ~0, the reference pathlength has given us a determini 20 tic situation for which a point Si can always be found. It re-mains only to be certain that one and only one reflected ray can ~
pass through each Si. This can be accomplished by tracing rays -from A into the re~ion of S, either by hand or by computer, and - -seeing if rays cross before they reach S. Equally effective is to generate S and see if it is a single-layered surface. In prac-tice, it is this latter path ~hich has been followed. More . ~ . - .. , . ... ~
specifically, by suitably programming a general purpose digital computer -to perform the numerical computations outlined above, a - ~ufficient number of points S~ on the surface of the subreflect~r can be determined to accurately def~ne the surface. These points 5 are then used as the inputs to a numerically controlled milling machine to machine the subreflector.
Since the main reflector, ~l, is the same as that described in the aforementioned Patent No. 3,852,753, a single moveable feed assembly consisting of a horn, H, and subreflector S, or a plurality of such feed assemblies located along an arc about the axis of rotation, z', of the main reflector will form identical beams. Moreover, each such feed assembly will provide aberration free beams in scanning.
FIGS. 6A, 6s and 6C show a specific subreflector de-signed according to the invention for a non-rectangular toroidal antenna system having a ten-foot aperture and dimensional ratios of f/R -~ 0.487 and R/D ~ 2. This subreflector is hyperbolic along the x-axis (the axis of symmetry) and departs from this off the x-axis. In a test at 29.95 GHz, this subreflector improved the gain of the antenna system achieved by conventional means by 2dB, from 54dB to 56dB, and the efficiency from about 28% to about 45%
aperture efficiency.
While the improvements realized with the subreflector shown in FIGS. 6A, 6B and 6C are significant, by changing the di-mensional parameters of the main toroidal reflector, a more op-timum antenna configuration can be realized which achieves an efficiency in excess of 80%. Specifically, for a main toroidal reflector having the dimensional ratio of f/R ~ 0.54, a "Casse-gorian" subreflector results for the design procedure according to the invention. Such a subreflector is shown in FIGS. 7A and 7B. The name "Cassegorian" was coined because the subreflector has cross-sectional shapes which resemble a subreflector having a hyperbolic section as shown in FIG. 8A and used in Cassegrain , 1 1~ 9843 I
systems, and a subreflector having an elliptic section as shown in FIG. 8s and used in Gregorian systems. Its shape arises due to a careful choice of the parameters f/R, f/R > .5 (actually f/R = 0.56 for the example shown), and the subreflector vertex pathlength such that the vertex lies between ~ and P. When these parameters and the feed point H are chosen carefully, the resulting subreflector (for a circular aperture of diameter D) is reasonably close to a circle when viewed from H, which is a requirement for efficient feeding.
Because the new feed method according to the invention corrects pathlength so that true optical focusing is obtained, there is no aberration in the antenna system, and the efficiency is independent of frequency. This permits the development of antennas which have high efficiency independent of frequency.
For example, a toroidal reflector antenna system can be designed for use at 4, 6, 12, 14, 20 and 30 GHz by use of appropriate feedhorns, without changing the optics of the system.
It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construc--20 tion and arrangement within the scope of the invention as defined in the appended claims. ~
.. --,-' . . ' ' ~ - . , . . . . ~
. ; ' ''j, '
n5 nrm ThuS, s = ~ QO _ ¦Zmi¦) nrm MiH (73 n n O - IZmi¦ - nrm MiH
i us + vs ~ X ws ~hen, since n is a unit vector, (n .n ) 2 = (US2 + VS2 + WS2) .
( ¦Zmil- nrm~MiH) 18) ( o I mil) ¦MiH¦ 2 nrm-MiH Qo~lZmil ;
Finally, ^n - -+ (Qo IZmi¦) nrm MiH __ _ (7a) ( o I mil) ¦MiH¦ 2(nrm MiH) (QO -læ ~ /2 ~;
and all the vectors in the system can now be found.
Substituting from Equation (8) into Equation (5b), C2 can be determined. Then, noting that IMiAil= lzmil~ C1 is calculated using Equation (5a), and the point on the ;
(11) ,- ~. ~ , . ... . ...
:. - - , .- .
1~398~3 subreflector is now completely established.
Returning for a moment to Equation (7), if we examine this equation geometrically as shown in FIG. 5, the simplicity of the scheme is self-evident. If Q is the reference pathlength, then QO ~ ¦Zmil is the remainder after the ray incident in the aperture plane at Ai strikes the main reflector at Mi Then MiEi is a vector of length ~o ~ Zmi in the direction of the reflectlon.
~lla) . ..... . . . . . .
, : -.
1~39843 nrm, of the ~ncident vector, ni. Also HEi = hiEi ~ MiH. Hence, HEi = nrm (Qo lZmil) Mi~
But this is the numerator of Equation (7a), and the denominator is only a constant. Hence, HEi and nS are parallel (or anti-S parallel). This is immediately verified by the geometry of FIG.5. Ai~Si, nrm and MiEi lie in the same plane, by the laws of geo-metric optics. Similarly, ~liSi, nS and SiH lie in the same plane.Further, since ~ lzmil + IMiSil ~ ¦SiHI
= lzmil + IMiEil = ¦Zmi¦ + ¦MiSi¦ + lSiEil, then ¦SiHI = lSiEil Hence, the ~HSiEi is isoceles and the equal angles ~ are equal to the angles of incidence and reflection at Si, Whence it is seen that the line HEi i5 parallel to ns.
~5 Further cos ~ = HEi ~liEi ¦HEi¦ ¦MiE ¦ , which is calculable, and ¦SiH¦ 2 = 1/2 ¦HEi¦ 2 /(1 + COS 2E) .
What the above analysis shows is that the choice of ni' the incident wave, ~1, the main reflector, H, the feed-horn loca-tion and ~0, the reference pathlength has given us a determini 20 tic situation for which a point Si can always be found. It re-mains only to be certain that one and only one reflected ray can ~
pass through each Si. This can be accomplished by tracing rays -from A into the re~ion of S, either by hand or by computer, and - -seeing if rays cross before they reach S. Equally effective is to generate S and see if it is a single-layered surface. In prac-tice, it is this latter path ~hich has been followed. More . ~ . - .. , . ... ~
specifically, by suitably programming a general purpose digital computer -to perform the numerical computations outlined above, a - ~ufficient number of points S~ on the surface of the subreflect~r can be determined to accurately def~ne the surface. These points 5 are then used as the inputs to a numerically controlled milling machine to machine the subreflector.
Since the main reflector, ~l, is the same as that described in the aforementioned Patent No. 3,852,753, a single moveable feed assembly consisting of a horn, H, and subreflector S, or a plurality of such feed assemblies located along an arc about the axis of rotation, z', of the main reflector will form identical beams. Moreover, each such feed assembly will provide aberration free beams in scanning.
FIGS. 6A, 6s and 6C show a specific subreflector de-signed according to the invention for a non-rectangular toroidal antenna system having a ten-foot aperture and dimensional ratios of f/R -~ 0.487 and R/D ~ 2. This subreflector is hyperbolic along the x-axis (the axis of symmetry) and departs from this off the x-axis. In a test at 29.95 GHz, this subreflector improved the gain of the antenna system achieved by conventional means by 2dB, from 54dB to 56dB, and the efficiency from about 28% to about 45%
aperture efficiency.
While the improvements realized with the subreflector shown in FIGS. 6A, 6B and 6C are significant, by changing the di-mensional parameters of the main toroidal reflector, a more op-timum antenna configuration can be realized which achieves an efficiency in excess of 80%. Specifically, for a main toroidal reflector having the dimensional ratio of f/R ~ 0.54, a "Casse-gorian" subreflector results for the design procedure according to the invention. Such a subreflector is shown in FIGS. 7A and 7B. The name "Cassegorian" was coined because the subreflector has cross-sectional shapes which resemble a subreflector having a hyperbolic section as shown in FIG. 8A and used in Cassegrain , 1 1~ 9843 I
systems, and a subreflector having an elliptic section as shown in FIG. 8s and used in Gregorian systems. Its shape arises due to a careful choice of the parameters f/R, f/R > .5 (actually f/R = 0.56 for the example shown), and the subreflector vertex pathlength such that the vertex lies between ~ and P. When these parameters and the feed point H are chosen carefully, the resulting subreflector (for a circular aperture of diameter D) is reasonably close to a circle when viewed from H, which is a requirement for efficient feeding.
Because the new feed method according to the invention corrects pathlength so that true optical focusing is obtained, there is no aberration in the antenna system, and the efficiency is independent of frequency. This permits the development of antennas which have high efficiency independent of frequency.
For example, a toroidal reflector antenna system can be designed for use at 4, 6, 12, 14, 20 and 30 GHz by use of appropriate feedhorns, without changing the optics of the system.
It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construc--20 tion and arrangement within the scope of the invention as defined in the appended claims. ~
.. --,-' . . ' ' ~ - . , . . . . ~
. ; ' ''j, '
Claims (9)
1. In a toroidal reflector antenna system including a main reflector having the shape of a surface section of a torus of revolution and a feed-horn assembly positioned to illuminate said main reflector and thereby form beams in the desired directions of propagation, the improvement comprising an aberration correcting subreflector interposed between said main reflector and said feed-horn and forming a feed assembly with said feed-horn, the surface of said subreflector being non-concentric with said main reflector and so designed that for the aberration correcting surface of said subreflector only one ray is incident on the surface at each point thereon, sub-stantially all rays focus at a single point at said feed-horn and substantially all ray pathlengths from a reference aperture plane to said single point of focus are constant and equal to a predetermined reference pathlength, whereby said system is free of aberration and the efficiency of said system is independent of frequency, said feed assembly further being movable along an arc about the axis of revolution of said main reflector to provide substantially aberration free beams in scanning.
2. The improved antenna system as recited in Claim 1 wherein said torus of revolution has a generating curve which is a conic section.
3. The improved antenna system as recited in Claim 2 wherein said generating curve is a parabola.
4. The improved antenna system as recited in Claim 3 wherein said main reflector is a surface section of a non-rectangular torus, said antenna system having a conical scan capability to scan along the geostationary arc.
5. The improved antenna system as recited in Claim 4 wherein the angle between the axis of revolution of said torus and direction of said beam is 95.5°.
6. The improved antenna system as recited in Claim 5 wherein said main reflector has the dimensional ratios f/R ? 0.5 and R/D ? 2 where f is the focal length of the parabola generating section, R is the radius of revolution, and D is the aperture of said main reflector measured parallel to the axis of revolution and said subreflector is hyperbolic along the axis of symmetry and departs from hyperbolic of the axis of symmetry in such a manner as to preserve the two essential properties of focusing all rays at the desired focal point with the desired pathlength.
7. The improved antenna system as recited in Claim 6 wherein the dimensional ratio f/R < 0.5.
8. The improved antenna system as recited in Claim 6 wherein the dimensional ratio f/R > 0.5 and the vertex of the subreflector is chosen to lie between the projection of the paraxial focus P and the focal point F and the feed point is chosen so that the subreflector formed by a circular pencil of rays incident on the aperture D approximates a circle when viewed from the feed point.
9. The improved antenna system as recited in Claim 8 wherein said main reflector has the dimensional ratios of f/R ? 0.56 and R/D ? 2 where f is the focal length of the parabola generating section, R is the radius of revolution, and D is the length of said main reflector measured parallel to the axis of revolution, and said subreflector has a cross section which resembles an elliptic section along an axis chosen perpendicular to the axis of symmetry.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US475226A US3922682A (en) | 1974-05-31 | 1974-05-31 | Aberration correcting subreflectors for toroidal reflector antennas |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1039843A true CA1039843A (en) | 1978-10-03 |
Family
ID=23886720
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA226,139A Expired CA1039843A (en) | 1974-05-31 | 1975-05-02 | Aberration correcting subreflectors for toroidal reflector antennas |
Country Status (9)
| Country | Link |
|---|---|
| US (1) | US3922682A (en) |
| JP (1) | JPS51863A (en) |
| CA (1) | CA1039843A (en) |
| DE (1) | DE2523800A1 (en) |
| FR (1) | FR2275901A1 (en) |
| GB (1) | GB1513452A (en) |
| IT (1) | IT1036133B (en) |
| NL (1) | NL7506474A (en) |
| SE (1) | SE403855B (en) |
Families Citing this family (37)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| USD244038S (en) * | 1976-01-07 | 1977-04-12 | Mecaniplast | Easel type boomerang antenna |
| US4145695A (en) * | 1977-03-01 | 1979-03-20 | Bell Telephone Laboratories, Incorporated | Launcher reflectors for correcting for astigmatism in off-axis fed reflector antennas |
| US4201992A (en) * | 1978-04-20 | 1980-05-06 | Communications Satellite Corporation | Multibeam communications satellite |
| US4272769A (en) * | 1979-08-27 | 1981-06-09 | Young Frederick A | Microwave antenna with parabolic main reflector |
| JPS5698905A (en) * | 1980-01-11 | 1981-08-08 | Kokusai Denshin Denwa Co Ltd <Kdd> | Dual reflecting mirror antenna |
| US4343004A (en) * | 1980-11-24 | 1982-08-03 | Bell Telephone Laboratories, Incorporated | Broadband astigmatic feed arrangement for an antenna |
| US4339757A (en) * | 1980-11-24 | 1982-07-13 | Bell Telephone Laboratories, Incorporated | Broadband astigmatic feed arrangement for an antenna |
| US4355314A (en) * | 1980-11-28 | 1982-10-19 | Bell Telephone Laboratories, Incorporated | Wide-field-of-view antenna arrangement |
| JPS57178402A (en) * | 1981-04-27 | 1982-11-02 | Kokusai Denshin Denwa Co Ltd <Kdd> | Multireflex mirror antenna |
| JPS58139503A (en) * | 1982-02-15 | 1983-08-18 | Kokusai Denshin Denwa Co Ltd <Kdd> | Beam feeding device |
| US4535338A (en) * | 1982-05-10 | 1985-08-13 | At&T Bell Laboratories | Multibeam antenna arrangement |
| US4491848A (en) * | 1982-08-30 | 1985-01-01 | At&T Bell Laboratories | Substantially frequency-independent aberration correcting antenna arrangement |
| US4482898A (en) * | 1982-10-12 | 1984-11-13 | At&T Bell Laboratories | Antenna feed arrangement for correcting for astigmatism |
| US4833484A (en) * | 1984-02-09 | 1989-05-23 | The General Electric Company, P.L.C. | Earth terminal for satellite communication |
| GB2154067B (en) * | 1984-02-09 | 1988-02-17 | Gen Electric Plc | An earth terminal for satellite communication systems |
| US4638322A (en) * | 1984-02-14 | 1987-01-20 | The Boeing Company | Multiple feed antenna |
| JPS60178709A (en) * | 1984-02-24 | 1985-09-12 | Nippon Telegr & Teleph Corp <Ntt> | Offset multi-reflector antenna |
| US4631545A (en) * | 1984-11-16 | 1986-12-23 | At&T Bell Laboratories | Antenna arrangement capable of astigmatism correction |
| US4806985A (en) * | 1986-07-11 | 1989-02-21 | Xerox Corporation | Stripper fingers |
| US4786910A (en) * | 1987-11-05 | 1988-11-22 | American Telephone And Telegraph Company, At&T Bell Laboratories | Single reflector multibeam antenna arrangement with a wide field of view |
| US5175562A (en) * | 1989-06-23 | 1992-12-29 | Northeastern University | High aperture-efficient, wide-angle scanning offset reflector antenna |
| USD387773S (en) * | 1996-10-28 | 1997-12-16 | Weller Roger G | Satellite dish protective visor |
| WO2002005385A1 (en) * | 2000-07-10 | 2002-01-17 | Wavefrontier Co., Ltd | Reflector antenna |
| US6563473B2 (en) * | 2001-02-22 | 2003-05-13 | Ems Technologies Canada, Ltd. | Low sidelobe contiguous-parabolic reflector array |
| EP2025045B1 (en) * | 2006-05-23 | 2011-05-11 | Intel Corporation | Chip-lens array antenna system |
| DE602006020785D1 (en) * | 2006-05-23 | 2011-04-28 | Intel Corp | MILLIMETER WAVE COMMUNICATION SYSTEM FOR THE INTERIOR |
| US8320942B2 (en) * | 2006-06-13 | 2012-11-27 | Intel Corporation | Wireless device with directional antennas for use in millimeter-wave peer-to-peer networks and methods for adaptive beam steering |
| US20080094298A1 (en) * | 2006-10-23 | 2008-04-24 | Harris Corporation | Antenna with Shaped Asymmetric Main Reflector and Subreflector with Asymmetric Waveguide Feed |
| SG191403A1 (en) * | 2011-12-29 | 2013-08-30 | Quantrill Estate Inc | Multipurpose energy concentrator |
| CN102820544B (en) * | 2012-07-03 | 2015-08-19 | 深圳光启创新技术有限公司 | A kind of antenna reflective face phasing pad pasting and reflector antenna |
| US20140055314A1 (en) * | 2012-08-21 | 2014-02-27 | Northeastern University | Doubly shaped reflector transmitting antenna for millimeter-wave security scanning system |
| WO2015026398A1 (en) * | 2013-08-19 | 2015-02-26 | Garcia Antonio Ph D | Spectrophotometer based on optical caustics |
| USD738866S1 (en) * | 2013-09-25 | 2015-09-15 | World Products Llc | Antenna with dome form factor |
| USD814449S1 (en) * | 2016-02-19 | 2018-04-03 | Samsung Electronics Co., Ltd. | Network terminal |
| USD815075S1 (en) * | 2016-02-19 | 2018-04-10 | Samsung Electronics Co., Ltd. | Network terminal |
| RU2629906C1 (en) * | 2016-11-09 | 2017-09-04 | Самсунг Электроникс Ко., Лтд. | Mirror antenna with double polarization and wide scanning angle |
| US11101569B2 (en) * | 2020-01-08 | 2021-08-24 | Dau-Chyrh Chang | Toroidal compact antenna test range |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3852763A (en) * | 1970-06-08 | 1974-12-03 | Communications Satellite Corp | Torus-type antenna having a conical scan capability |
| US3737909A (en) * | 1970-06-18 | 1973-06-05 | Radiation Inc | Parabolic antenna system having high-illumination and spillover efficiencies |
| FR2148341B1 (en) * | 1971-08-09 | 1977-01-28 | Thomson Csf |
-
1974
- 1974-05-31 US US475226A patent/US3922682A/en not_active Expired - Lifetime
-
1975
- 1975-05-02 CA CA226,139A patent/CA1039843A/en not_active Expired
- 1975-05-06 GB GB18871/75A patent/GB1513452A/en not_active Expired
- 1975-05-06 SE SE7505209A patent/SE403855B/en unknown
- 1975-05-23 JP JP50061158A patent/JPS51863A/en active Pending
- 1975-05-28 DE DE19752523800 patent/DE2523800A1/en not_active Withdrawn
- 1975-05-30 IT IT68395/75A patent/IT1036133B/en active
- 1975-05-30 NL NL7506474A patent/NL7506474A/en not_active Application Discontinuation
- 1975-06-02 FR FR7517096A patent/FR2275901A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| JPS51863A (en) | 1976-01-07 |
| IT1036133B (en) | 1979-10-30 |
| SE403855B (en) | 1978-09-04 |
| GB1513452A (en) | 1978-06-07 |
| NL7506474A (en) | 1975-12-02 |
| US3922682A (en) | 1975-11-25 |
| FR2275901A1 (en) | 1976-01-16 |
| SE7505209L (en) | 1975-12-01 |
| DE2523800A1 (en) | 1975-12-11 |
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