Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS3562753 A
Publication typeGrant
Publication dateFeb 9, 1971
Filing dateFeb 19, 1969
Priority dateFeb 23, 1968
Also published asDE1908793A1
Publication numberUS 3562753 A, US 3562753A, US-A-3562753, US3562753 A, US3562753A
InventorsKamimura Masao, Tanaka Mitsuo
Original AssigneeHitachi Ltd
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Casseyrain antenna system with rotatable main reflector for scanning
US 3562753 A
Images(4)
Previous page
Next page
Description  (OCR text may contain errors)

Feb. 9, 1971 Filed Feb. 19, 1969 MITSUO TANAKA EI'AL 3,562,753 CASSEYRAIN ANTENNA SYSTEM WITH ROTATABLE MAIN v A REFLECTOR FOR SCANNING TRANSMITTER-Y-RECHVER CHAMBH? INVENTOR 5 MITa/o TIA/HA! 4410 11 4; am/mull BY @4 am/ M ATTURNLYS FGb. 9,1971 rrsuo TANAKA ETAL 3,562,753

CASSEYRAIN ANTENNA SYSTEM WITH RQTATABLE MAIN REFLECTOR FOR SCANNING All I I l I a I I 7'7 ///////r///////4/////' I 20 (ZEN/7H) INVENTORS m/naa TAM/W9 amp/1745120 him/mun BY 7" M14 ATTORNKKS Feb. 9,-1971 n-suo TANAKA EI'AL 3,562,753

CASSEYRAIN ANTENNA SYSTEM WITH ROTATABLE MAIN REFLECTOR FOR SCANNING v 4 Sheets-Sheet 3 Filed Feb. 19, 1969 INVENTURS MITsun 7/9017! 0ND ////I:J//0 MAM/null.

BY g y ATTURNI1Y5 Feb..9, 1971 v n' TANAKA EI'AL 3,562,753

CASSEYRAIN ANTENNA SYSTEM WITH ROTATABLE MAIN REFLECTOR FOR SCANNING Filed Feb. 19, 1969' 4 Sheets-Sheet 4 777l 77777l7l7\ TRANSMITTER- CHAMBER FIG. 7

v RECEIVE/7 62 CHAMBER INVENTO/(b MIT5U0 Tuna my Illa-, WW

TRANS/WER- u N Y ATTORNEYS United States Patent 3,562 753 CASSEYRAIN ANTENNA SYSTEM WITH ROTAT- ABLE MAIN REFLECTOR FOR SCANNING Mitsuo Tanaka, Kokubunji-shi, and Masao Kamimura, Kodaira-shi, Japan, assignors to Hitachi, Ltd., Tokyo, Japan, a corporation of Japan Filed Feb. 19, 1969, Ser. No. 800,636 Claims priority, application Japan, Feb. 23, 1968, 43/11,125; June 17, 1968, 43/41,354 Int. Cl. H01g 1/28, 19/10 US. Cl. 343-705 6 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to antenna systems and more particularly it pertains to antenna systems of the type having an antenna section and a transmitting and receiving section which are arranged to rotate relatively with respect to each other.

In antenna systems such as an antenna having a large caliber for space communications and being capable of scanning space wholly and a high gain transmitting and receiving antenna for a spin stabilized stationary satellite, it is necessary for the transmission and reception of an electromagnetic wave to rotate the antenna section of the system or to turn it in a particular direction.

Generally, in an antenna system capable of scanning space wholly, such as a Cassegrain antenna, a horn reflector antenna, a Gregorian antenna or the like, it is impossible to fix a transmitter-receiver chamber to the ground. This is because for the reception of a weak signal such as experienced in space communications it is one of the essential factors to make a wave-guide for interconnecting a radiator (used for either transmission or reception of electromagnetic waves) and a transmitter-receiver chamber as short as possible so that any attenuation of an electromagnetic wave may be prevented. To this end, it is necessary to locate a transmitter-receiver chamber near to a radiator and to form a wave guide as linear as possible for interconnecting the radiator and the transmitter-receiver chamber because otherwise the characteristics of the antenna system will be deteriorated. Furthermore, if the transmitter-receiver chamber is fixed to the ground so that only the antenna of large caliber may be movable, the interconnection of the chamber and the antenna is complicated with the mechanical strength thereof possibly decreased. Accordingly, in an antenna system of the above-mentioned type, the antenna section and the transmitter-receiver chamber are constructed integrally with each other so that the radiator and the transmitter-re ceiver means are in a fixed relation to each other. As a result, the transmitter-receiver chamber can not but be arranged so as to be movable along with the antenna associated therewith. Thus, the antenna system of such a construction is not only large-sized but also complicated to such an extent that steering, maintenance and inspection of the system are troublesome, and that too much complicated interconnection is needed for data-processing information to be transmitted or received by the system,

ice

e.g., several tens to several hundreds of interconnection wires are needed for data processing.

Meanwhile, those antenna systems which have a main reflector turned to the ground in the horizontal direction at a low elevation angle scanning necessarily suffer from noise coming from the ground, which interferes with normal reception of electromagnetic waves from an artificial satellite. In those antenna systems which have a subreflector positioned in the center of the caliber of a main reflector, the field intensity of the main beam is lowered, the side lobe level in the vicinity of the main beam is contrariwise increased, which causes the system to be more susceptible to noise from the ground and at the same time causes the antenna gain to be lowered.

As for antenna systems capable of being mounted on a spin stabilized stationary satellite such as a despun antenna, since an antenna section must be adapted so as to be always turned in a particular direction, the antenna section has to be rotated inversely with respect to the satellite itself by a rotatory mechanism. For this purpose, a despun antenna has been conventionally provided with a rotary joint for interconnecting a wave guide coupled to the output (or input) of a transmitter (or receiver) fixed to the body of the satellite and a feeder line leading to an antenna section (or receiving line from the antenna section). Therefore, from an electrical point of view, the antenna characteristics are deteriorated while, from a mechanical point of view, the durability is questionable since the satellite itself rotates at a speed near r.p.m. for a long time. Furthermore, in such system, as a feeder line (or receiving line) is situated in the center of the electromagnetic wave radiating face of the antenna section the field intensity of the main beam is lowered, which is a large obstacle to far distance communications such as space communication.

One object of the present invention is to provide an antenna system of the type having an antenna section and a transmitting and receiving section either one of which is movable relative to the other, yet dispensing with any rotary joint to be provided in a wave transmission path between the antenna section and the transmitting and receiving section.

Another object of the present invention is to provide an improved antenna system having an increased antenna. gain.

Still another object of the present invention is to provide an antenna system in which the amount of an electromagnetic wave reflected to a radiator is extremely reduced so that the voltage standing wave ratio (VSWR) may be improved.

In order to achieve the abovementioned objects and other objects which will become apparent from the description on some embodiments of the present invention, a typical antenna system of the present invention comprises a radiator fixed to a base (the ground or an artificial satellite) and adapted for radiating an electromognetic wave, a sub-reflector shaped substantially in the form of a part of a quadric face and aligned on a main radiation axis of the radiator, a main reflector shaped substantially in the form of a part of a quadric face and adapted for converting an electromagnetic wave from the sub-reflector into a plane wave and emitting the converted wave into the air or space, a rotary mechanism for rotating a structure including the sub-reflector and the main reflector about the main radiation axis of the radiator, and another rotatory mechanism for rotating the main reflector about a reflection axis of the sub-reflector.

For a complete understanding of the above-mentioned and other objects, features and advantages of the present invention, description will be made of some preferred embodiments in conjunction with the accompanying drawings, in which:

FIG. 1A is a front view showing the outline of a structure in accordance with an embodiment of the present invention;

FIG. 1B is a sectional view taken along line 1B1B in FIG. 1A;

FIG. 2 is a diagram showing various loci of scanning by the system shown in FIGS. 1A and 1B; and

FIGS. 3-7 are diagrams each illustrating the major part of a structure in accordance with an embodiment of the present invention.

Referring to FIGS. 1A and 1B, numeral 1 denotes a radiator (to be used for either transmission or reception of electromagnetic waves) fixed onto a base, for example, onto the ground and having a main radiation axis 8 passing through the zenith, and 2 denotes a sub-reflector aligned on the main radiation axis 8 and shaped substantially in the form of a part of the concave face of an ellipsoid which has its focal points at points 3 and 4, the point 3 being concurrent with the phase center of an electromagnetic wave radiated by the radiator 1. Numeral 5 denotes a main reflector for reflecting electromagnetic waves and shaped substantially in the form of a part of a paraboloid which has its focal point at point 4 and the axis of which is a vertical axis 10 passing through the point 4. Numeral 6 denotes supporting poles for the subreflector, and 7 are horizontal rotation rails arranged so as to be rotatable about the main radiation axis 8 at the time when the antenna system operates to scan space wholly (i.e., at the time of the whole space scanning operation of the antenna system). A rotatory mechanism associated with the rails is not shown. Numeral 9 denotes an axis of rotation of the main reflector 5, i.e., an axis of elevational rotation inclined by an angle of with respect to the main radiation axis 8. 11 is a rotary bearing of the main reflector 5, and 12 denotes a transmitter-receiver chamber fixed to the ground and interconnected with the radiator 1 by a wave guide 13.

In the above-mentioned structure, as radiator 1 may be used an antenna capable of radiating a spherical wave such as a conical antenna, pyramidal antenna or linear antenna. The electromagnetic wave radiated from such an antenna is not necessarily an exact spherical wave. A spherical wave radiated from the radiator 1 and having its phase center concurrent with the point 3 which is one of the focal points of an ellipsoid a part of which constitutes the sub-reflector 2 "as described above, is converted into a spherical Wave having its phase center concurrent with the point 4 which is the other one of the focal points of the ellipsoid by the sub-reflector 2 positioned on the line of the main radiation axis 8 and above the radiator 1. The spherical wave reflected by the sub-reflector 2 is then converted into a plane wave by the main reflector shaped, as mentioned above, substantially in the form of a part of the concave portion of such a paraboloid that has its focal point concurrent with the point 4, which therefore corresponds to the phase center of the electromagnetic wave from the sub-reflector 2, and the electromagnetic wave is emitted in the direction of the main axis of the paraboloid (the main reflector) 5. It is needless to say that upon emission of the plane wave from the main reflector the suporting poles 6, the sub-reflector 2 and the radiator 1 are so arranged as not to obstruct the optical path for such emission of the plane wave. In this embodiment, though the sub-reflector 2 and the main reflector 5 are explained as being shaped (substantially) in the form of a part of a quadric face for the sake of simplicity in theoretical consideration in geometrical optics, since practically, the reflectors are part of paths for an electromagnetic wave which has not exactly the same characteristics as those of light, it is necessary to correct the shapes of the quadric faces of the reflectors defined from the viewpoint of geometrical optics so that the reflectors may have the most suitable curved faces for paths for an electromagnetic wave. Hereinafter throughout the present specification, such corrected surface is called quasi-quadric face.

Next, explanation will be given of various loci during the space scanning operation of the antenna system described above referring to FIG. 2. The antenna system is rotatable about the main radiation axis (the rotation axis for horizontal scanning) 8, and at the same time, the main reflector is rotatable about the axis 9 of elevational rotation. Thus, the scanning area of the system can be varied depending upon the angle 0 formed between the main radiation axis 8 and the axis 9 of elevational rotation. In FIG. 2, numerals 20 and 21 indicate a direction to the zenith and a horizontal direction respectively. Suppose that elevational rotation is to be effected. If the angle 0 formed between the axes 8 and 9 is 45 the scanning locus draws a circle 22 partly in contact with a circle 21 representative of a horizon and with the point 20 representative of the zenith in the drawing. If angle is smaller than 45, the scanning locus draws a circle 23, so that areas in the vicinity of the horizon can not be scanned. If the angle 0 is larger than 45 and smaller than the scanning locus draws a curve 24, and if the 0 reaches 90, the resulting scanning locus is a straight line as indicated by 25. It is therefore clear that by effecting rotation about the rotation axis 8 for horizontal scanning with an angle of 0 fixed to a value between 45 and 90, the whole space can be scanned by the antenna system. Since during a low elevation angle scanning there is some possibility of interruption of the optical path for the plane wave by the sub-reflector 2 and the supporting poles 6, it is desirable that the positioning of the main reflector 5 and the subreflector 2 and selection of the angle 0 should be such that interruption of the optical path can be prevented.

Although the above-described embodiment is an application to an antenna system having a large caliber and fixed to the ground for use in space communications, the present invention can be also used as a high gain transmitting and receiving antenna for a spin stabilized stationary satellite, i.e., as a despun antenna by merely miniaturizing the construction described. In such a case, the antenna system is mounted on the body of the satellite. Then, the radiator is fixed in a manner that the radiation axis of an electromagnetic wave is concurrent with the axis of spin of the satellite while the main reflector is so arranged as to be rotatable inversely relative to the spin of the satellite by means of a rotatory mechanism. By this arrangement the mounted antenna system is operable so as to be always turned in a particular direction, so that irrespective of the spin of the satellite, intercommunication between the satellite and a particular station, for example, a particular area on the earth is possible. Thus, the antenna system of the present invention can be used either as an antenna system for space communication or as a despun antenna to be mounted on a artificial satellite, and the construction and the operation are same in both uses. The only difference is whether the system is fixed to the ground or mounted on an artificial satellite. Accordingly, the following description of embodiments refers to both cases, i.e., in one case the system is fixed on the ground and in the other case the system is mounted on a satellite. Only major parts of the system will be described and illustrated as to the following embodiments.

In FIG. 3, the sub-reflector is constituted by a part of the concave portion of a quasi-hyperboloid. In the figure, numeral 30 denotes a radiator fixed to a base (the ground or a satellite) and adapted for radiating a spherical Wave, 31 denotes a sub-rebector constituted by a part of a quasi-hyperboloid having its focal points at points 32 and 33, the point 32 being concurrent with the phase center of an electromagnetic wave radiated from the radiator 30. Numeral 34 denotes a main reflector constituted by a part of a quasi-paraboloid which has its focal point concurrent with the point 33 and has a main axis passing through the point 33. Numerals 36 and 37 are an axis for horizontal rotation scanning and an axis for elecational rotation scanning, respectively.

A spherical wave having the phase center at the point 32 radiated from the raditor is converted into a spherical wave having the phase center at the point 33 by the sub-reflector 31, and the latter spherical wave is converted into a plane Wave and emitted into the air or space by the main reflector 34.

In FIG. 4, the sub-reflector is constituted by a plane mirror. In the figure, numeral denotes a radiator fixed to a base (the ground or a satellite) and adapted for radiating a sperical wave, 41 a sub reflector constituted by a plane mirror, 42 a phase center of a spherical wave radiated from the radiator 40, 43 a point which is in point-symmetry relation to the point 42 with respect to the sub-reflector 41, 44 a main reflector constituted by a part of a quasi-paraboloid which has its focal point at the point 43 and has a main axis concurrent with a vertical axis 45 passing through the point 43, 46 an axis for horizontal rotation scanning, and 47 an axis for elevational rotation scanning.

It should be noted that through in FIGS. 3 and 4 the axis for horizontal rotation scanning is perpendicular to the axis tfOI elevational rotation scanning, these axes may be transverse to each other at a suitable angle other than at a right angle.

In FIG. 5, the sub-reflector is constituted by a part of the convex portion of a quasi-hyperboloid. In the figure, numeral 50 denotes a radiator fixed to a base (the ground or a satellite) and adapted for radiating a spherical wave, and 51 is sub-reflector constituted by a part of the convex portion of a quasi-hyperboloid which has its focal points at points '52 and 53. The sub-reflector 51 converts a spherical wave radiated by the radiator 50 and having its phase center at point 52 into a spherical Wave having its phase center at point 5 3, the latter spherical wave is then converted into a plane wave by a main reflector 54 constituted by a part of a quasi-paraboloid which has its focal point concurrent with the point 53 and has a main axis passing through the point 53, and the plane wave is emitted into the air or space from the main reflector 54. Numerals 55 and 56 are an axis for horizontal rotation scanning and an axis for elevational rotation scanning, respectively.

In each of the foregoing embodiments, as radiator is used an antenna which radiates a spherical wave, or an other antenna that radiates a plane wave such as a horn reflector antenna or a parabola antenna may be used. And, the electromagnetic wave to be radiated from such radiator need not be an exact plane wave.

Referring to FIG. 6 showing another embodiment, numeral 60 denotes a transmitter-receiver chamber fixed to a base (the ground or a satellite), and 61 denotes a radiator fixed to the base and adapted for radiating a plane wave such as for example, a horn reflector antenna, point 62 being a phase center of a radiated electromagnetic wave from the radiator 61. Numeral 63 denotes a sub-reflector constituted by a part of the concave portion of a qu-asi-paraboloid which has its focal point concurrent with the point 64 and has a main axis concurrent with a vertical axis passing through the point 64, the sub-reflector 63 being aligned on a main radiation axis 66 of the radiator '61 and above the radiator 61. Numeral 65 denotes a main reflector constituted by a part of a quasi-paraboloid Which has its focal point concurrent with the point 64 and has a main axis concurrent with a vertical axis passing through the point 64. Numerals 66 and 67 are an axis for horizontal rotation scanning and an axis for elevational rotation scanning, respectively. A plane Wave radiated by the radiator 61 having its phase center at the point 62 is converted into spherical wave having its phase center at the point 64 by the subreflector 63, and the spherical wave is then converted into a plane wave by and emitted into the air or space from the main reflector 65.

Referring to FIG. 7 in which the sub-refletcor is constituted by a part of the convex portion of a quasi-paraboloid, numeral 70 denotes a sub-reflector constituted by a part of the convex portion of a quasi-paraboloid which has its focal point at a point 71. The sub-reflector 70 converts a plane wave radiated from a radiator 71 into a spherical Wave having its phase center concurent with the point 71. Numeral 72 denotes a main reflector constituted by a part of a quasi-paraboloid having its focal point concurrent with the point 71. The main reflector 72 converts the spherical wave reflected from the subreflector into a plane Wave and emits the plane wave into the air or space. Numerals 73 and 74 are an axis for horizontal rotation scanning and an axis for elevational rotation scanning, respectively.

In each of the embodiments the antenna system is explained as being a transmitting antenna, but it is clear that the system can also serve satisfactorily as a receiving antenna such as an antenna for receiving an electromagnetic wave from an artificial satellite in space communications, and description thereon is here omitted since the operation of the system is the same as in the foregoing embodiments.

As can be understood from the above description the antenna system constructed in accordance with the present invention provides the following various functional effects and advantages:

when used as an antenna system having a large caliber for use in space communicaitons:

(1) Since structurally, in the present invention, signal transmitting and receiving means and a radiator are fixed to the ground, many kinds of restrictions and complication in the system as have been experienced in conventional systems in which transmitting means and a radiator are rotatable can be removed, thus facilitating the steering, maintenance and inspection of the system;

(2) A radiator is always directed to the zenith, so that signal transmission and reception at low elevation angles is scarcely subjected to deterioration of the characteristics against noise;

(3) A sub-reflector and supporting poles therefor are arranged so as not to interrupt optical paths for an electromagnetic wave, so that undesirable scattering of an electromagnetic wave due to the existence of such reflector and supporting poles and any increase of side lobe levels do not take place, thus improving the antenna gain and characteristics against noise when scanning at low elevation angles;

(4) A sub-reflector is not situated in the optical path for an electromagnetic wave, so that the dimensions of the sub-reflector can be relatively large to decrease power dissipated from a radiator through the vicinity of the sub-reflector thereby increasing the antenna gain;

(5) The amount of an electromagnetic wave reflected from a sub-reflector to a radiator is extremely small, so that the characteristics defined by the VSWR is excellent;

(6) A main reflector can be provided at a low position, so that it is less susceptible to the Wind power than the conventional system; and

(7) Supporting poles for a sub-reflector are so arranged as to be mounted on a rotary plate or rails horizontally provided on the ground, so that the supporting poles are always free from torque stemming from the weight of the sub-reflector in rotating operation, and therefore impression of undesirable stress which causes distortions in the sub-reflector as in the conventional Cassegrain antennas can be avoided. Accordingly, deterioration of characteristics due to deviation of the main beam which may be caused by deviation of the position of the subreflector and by distortion at the surface of a main reflector is small.

When used as a despun antenna:

(1) No movable joint is provided for interconnecting a satellite and an antenna system, so that generation of noise from and loss of gain due to such movable joint no longer exist. Mechanical breakage does not occur, either;

(2) There exists nothing that may be an obstacle to the main beam, so that the electrical characteristics are improved, and thus the system of the present invention is very suitable for transmitting and receiving a weak electromagnetic wave; and

(3) There is no restriction to be put on the manner of rotation of the main reflector, so that control of the antenna section to turn it in any particular direction is facilitated.

The above-described embodiments are only for explanatory purpose and various other modifications are possible without departing from the spirit of the invention, so that the scope of the present invention is not limited by such embodiments.

What is claimed is:

1. An antenna system having a radiator with a main radiation axis adapted for radiating an electromagnetic wave and reflector means characterized in that said radiator is fixed to a base and said reflector means consists of a sub-reflector having a reflection axis and aligned on said main radiation axis so as to reflect the electromagnetic wave received from said radiator in the form of a spherical wave and a main reflector constituted by a quasiquadric face and adapted for converting the spherical wave from said sub-reflector into a plane Wave so that the plane wave is emitted into the air or space from said main reflector, and that the system is further provided with a first rotatory mechanism for rotating said main reflector about the reflection axis of said sub-reflector and with a second rotatory mechanism for rotating a structure which includes said sub-reflector and said main reflector about said main radiation axis of said radiator.

2. An antenna system according to claim 1, characterized in that said sub-reflector is constituted by a part of a quasi-quadric face.

3. An antenna system according to claim 1, characterized in that said sub-reflector is constituted by a plane mirror.

4. An antenna system according to claim 1, characterized in that the angle between said main radiation axis of said radiator and said reflection axis of said subreflector is selected so as to be within a range from to 5. An antenna system according to claim 1, characterized in that said base is the ground and a transmitterreceiver chamber including a transmitter-receiver means connected with said radiator is fixed to the ground.

6. An antenna system according to claim 1, characterized in that said base is an artificial satellite and said main radiation axis is made concurrent with the axis of spin of said satellite.

References Cited UNITED STATES PATENTS 3,407,404 10/1968 Cook et a1. 343-765 ELI LIEBERMAN, Primary Examiner M. NUSSBAUM, Assistant Examiner US. Cl. X.R.

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3953858 *May 30, 1975Apr 27, 1976Bell Telephone Laboratories, IncorporatedMultiple beam microwave apparatus
US4223316 *Mar 23, 1978Sep 16, 1980Thomson-CsfAntenna structure with relatively offset reflectors for electromagnetic detection and space telecommunication equipment
US4574287 *Mar 4, 1983Mar 4, 1986The United States Of America As Represented By The Secretary Of The NavyFixed aperture, rotating feed, beam scanning antenna system
US4692771 *Mar 28, 1985Sep 8, 1987Satellite Technology Services, Inc.For receiving satellite broadcast data
US4716416 *Mar 28, 1985Dec 29, 1987Satellite Technology Services, Inc.Antenna dish reflector with integral declination adjustment
US4743887 *Nov 7, 1983May 10, 1988Sanders Associates, Inc.Fault locating system and method
US5796370 *Jul 16, 1996Aug 18, 1998Alcatel EspaceOrientable antenna with conservation of polarization axes
US5844527 *Sep 26, 1997Dec 1, 1998Furuno Electric Company, LimitedFor transmitting/receiving directed radar signals
DE3631735A1 *Sep 18, 1986Apr 7, 1988Messerschmitt Boelkow BlohmNachrichtenuebertragungseinrichtung fuer raumfahrzeuge
EP0260442A2 *Aug 13, 1987Mar 23, 1988ERNO Raumfahrttechnik Gesellschaft mit beschränkter HaftungSatellite transmission device
EP0284883A1 *Mar 15, 1988Oct 5, 1988Siemens AktiengesellschaftDual reflector microwave directional antenna
EP0656671A1 *Nov 30, 1994Jun 7, 1995Alcatel EspaceOrientable antenna with maintenance of the polarisations axes
Classifications
U.S. Classification343/705, 343/837, 343/781.00R, 343/761
International ClassificationH01Q19/10, H01Q19/19
Cooperative ClassificationH01Q19/192
European ClassificationH01Q19/19D