JPS5821850B2 - antenna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an antenna, and in particular includes a main reflector and a sub-reflector, the sub-reflector arranged to reflect radiation incident thereon towards the main reflector. the two reflectors are arranged to form a Cassegrain antenna, and a primary feeding means is located at an axial focal point of the Cassegrain antenna for feeding energy towards the secondary reflector. The present invention relates to an antenna in which radiation is emitted from the main reflector to form a main beam that passes through the antenna aperture.

: The Cassegrain shape is a conveniently used antenna that is compact and has an inherently large focal length relative to its aperture ratio.

It includes a main reflector, a subreflector much smaller than the main reflector, and a feeder.

The feeder is directed to the secondary reflector which in turn causes a reflection towards the primary reflector.

This reflector radiates energy through the antenna aperture.

Both the secondary reflector and the main reflector are typically oriented symmetrically with respect to the antenna axis, and the feeder is typically oriented on-axis near the vertex 1 of the main reflector, or its intersection with the axis, at a point here referred to as the on-axis focal point. positioned.

Peter W., Hannan, IRE Transactions on Antenna and Production, 1961 3
Geometrical configurations of Cassegrain systems are described in documents such as ``Microwave Antenna Derived from Cassegrainian Telescope'' on page 140.

The on-axis focus (which is the point at which a point source must be placed to produce a plane wave output) is called the true focus of the system.

The beam from the feeder is symmetrical about the feed axis, and the feeder and antenna axis are aligned.

Furthermore, the phase center of the feeder coincides with the focal point on the axis.

Earth stations for satellite communication systems, particularly those using spatially closely spaced satellites, may use multiple beam antennas to communicate with multiple satellites simultaneously.

Similarly, satellite antennas are multi-beam antennas with each beam directed to one of a number of separate earth stations.

The properties of Cassegrain antennas make them the preferred antenna type for satellite systems, and multiple feeders used in conjunction with reflective surfaces can create a multi-beam antenna.

However, when a large number of point source feeders are used in a conventional Cassegrain antenna, some of the feeders are shifted from the on-axis focus, and due to the obstruction by the sub-reflector and the shift of the feeder from the on-axis focus, the optimum It stops working.

Inefficiency due to obstruction is caused by the position of the sub-reflector within the antenna aperture, while inefficiency due to feeder misalignment is caused by two leakage effects.

First, energy from a feeder that is laterally offset from the focus will leak into the sub-reflector, which is optimized for a perfect Cassegrain antenna.

Second, if the leakage is minimized by reaiming the center of the beam to strike the center of the secondary reflector, some of the energy reflected from the secondary reflector will leak into the primary reflector. It will be.

These problems are solved by the present invention.

There, a secondary reflector and a primary feeding means are located outside the antenna aperture, and the antenna further comprises at least one secondary feeding means located outside the antenna aperture, away from the axial focal point, The sub-feed means is oriented towards the sub-reflector such that the center of its beam impinges on the main reflector at a common center point.

In accordance with the present invention, a Cassegrain antenna is designed to produce efficient multi-beam operation.

Aperture obstacles common to Cassegrain antennas are avoided by using an ``offset Cassegrain'' design that includes portions of a conventional reflective surface placed symmetrically about the antenna axis.

The main reflector in an offset design forms only part of a conventional paraboloid and is located exclusively on one of the off-axis and parallel planes.

The feeder and the hyperbolic sub-reflector are arranged exclusively on the other side of the offset plane.

The surface thus provides a conceptual line of boundaries, the aperture of the antenna on one side and the sub-reflector on the other.

Therefore, the beam directed towards or radiating from the main reflector passes through the aperture unobstructed by the feeder or the sub-reflector on the other side of the conceptual boundary.

To operate with isolated multiplexing of the beams, a group of feeders is placed around an on-axis focal point.

The surface area of the sub-reflector is enlarged with offset dimensions to accommodate the beam emanating from the off-axis feeder.

This enlargement creates a rectangular sub-reflector that is laterally extended to form a bulletin board shape when the feeder is laterally offset.

This increased sub-reflector size increases either the beam that is directed beyond the edge of the sub-reflector (secondary reflector leakage) or the reflected beam that is directed beyond the edge of the main reflector (main reflector leakage). ) is avoided.

In a conventional Cassegrain antenna, the enlarged sub-reflector would in turn increase the beam disturbance which increases the level of side lobes and reduces the separation between the beams.

However, there is no drawback created by the enlarged sub-reflector since the sub-reflector does not cause any problems in the offset Cassegrain.

Illumination efficiency is increased by carefully combing multiple feeders.

A feeder placed at the axial focus is appropriately oriented if it centers the beam so that it impinges on the effective center of the main reflector.

This produces a beam with the lowest side lobes for a given illumination efficiency with good circular symmetry.

However, if other feeds centered around the on-axis focal point are not directed to the secondary reflector, their beam center will cause points on the main reflector that are offset from this effective center to cause beam degradation. It will block you.

Each feeder is thus individually precisely directed so that the center of its beam strikes the same effective center of the main reflector.

All feeders are thus angularly offset from each other by the offset of each feeder from the on-axis focal point, producing beams that are concentrated at the same point on the main reflector.

A conventional Cassegrain antenna, as shown in FIG. 1, is generally donut-shaped because the secondary reflector 13 blocks the reflection from the main reflector 12 in a cylindrical region 18 centered around the antenna's geometric axis 15. Generate an open Ico.

A feeder 11, which may be a wave-shaped feed horn, is located on the axis 15 at an axial focal point and radiates energy towards a secondary reflector 13 which is later directed towards a main reflector 12.

Of course, antennas can either radiate or receive, but for convenience all antenna structures are described here as radiators.

On the other hand, it should be clearly understood that the present invention is not limited to radiating antennas as long as they have the same structure and can also receive at the same time.

FIG. 2 is a diagrammatic cross-section taken through the axis 15 of the antenna of FIG.

Since the antenna is symmetrical about axis 15, FIG. 2 shows all such cross-sections.

As can be clearly seen from the figure, the energy radiating from the feeder 11 hits the hyperboloid of the secondary reflector 13 and is directed towards the paraboloid of the main reflector 12 where it is reflected again through the antenna aperture. re-radiated.

As a result of the focusing properties of the reflective surface, the waves emanating from the surface 12 exhibit a parallel phase front perpendicular to the direction of radiation.

The radiation leaving the surface 12 will fill the entire aperture of the antenna, but the sub-reflector 13 will cause the effective energy leaving the antenna to form a toroidal shape represented by the area 19 producing the amplitude distribution shown on the right side of FIG. It obstructs the cylinder 18 which exists only in a portion.

A cone emanating from an on-axis focus 20 at the phase center of the feeder 110 and expanding at an angle θ is attached to the main reflector 12 by −C
This determines the portion of the energy emitted from the feeder 11 that is intercepted by the sub-reflector 13 after being reflected.

If the feeder in the Cassegrain antenna of FIG. 1 is offset from the antenna axis, 15, the radiation from the offset feeder will create leakage similar to an aperture obstruction.

This is illustrated in FIGS. 3 and 4, which are cross-sectional views taken through the antenna axis 15 of a Cassegrain antenna with a feeder 21 offset from the axis 15.

This feeder emits radiation from an effective point source at 30 in the direction of the sub-reflector 13, which in turn directs it to the main reflector 1.
Turn towards 2 again.

The subreflector 13 and main reflector 12 in FIG. 3 are the same as those shown in FIG. , thereby resulting in energy loss and potential interference.

That is, the center of the beam 24 is at the main reflector 1 on the axis 15.
When the feeder 21 is directed at the apex of the main reflector 13 so as to intercept the antenna 2, a portion of the radiation from the feeder 21 is directed over the outer periphery of the subreflector 13 so that the antenna emits a narrow polarized beam. irradiate the area.

This beam is angularly offset from the main toroidal beam of region 29, which is generally undesirable.

Shifting the feeder to position 30 will also eliminate illumination to portion 22 of main reflector 12.

Furthermore, the lateral offset of the feeder causes an angular misalignment of the beam 24 from the axis 15 resulting in a related change in the orientation of the region 290 wavefront.

A graph showing the amplitude distribution of the in-phase antenna pattern created in the cross section of FIG. 3 is shown on the right side of FIG.

As can be seen, the peak amplitude along the beam center 24 is lost due to the disturbance, and the average energy is shifted in the direction of the offset of the beam center 24 (upward in the figure); this asymmetric pattern is worse than the symmetric pattern. This will uniquely create side lobes.

To avoid leakage of the secondary reflector of FIG. 3, the feeder 21 is arranged as shown in FIG.
If the radiation beam is directed to intercept the surface 1, the leakage shown as 25 in FIG.
2, leakage of the main reflector results in a biased beam 25.

This is also misdirected from the main aperture radiation, which is of course not desirable.

Part 23 of the main reflector 12 is also missing.

Beam center 26 is parallel to beam center 24 since feeder 21 is at 30, but it is offset from antenna axis 15 than is the case with beam center 24, resulting in the amplitude of the in-phase antenna radiation shown on the right side of FIG. It is known that the distribution is more twisted (in the upper direction in the figure) than in the case of leakage from the sub-reflector in FIG.

However, the peak amplitude is blocked in both cases.

The amplitude distribution in a plane orthogonal to that of FIGS. 3 and 4 is essentially the same as that shown in FIG. 2, with the peak amplitudes also occluded.

Therefore, opening obstruction and feeder misalignment create energy loss.

However, a large focal length to aperture ratio (F/D)
An antenna with can have many multiple beams,
It is well known that the unique characteristics of Cassegrain antennas require a large F/D ratio.

Therefore, taking advantage of this property and creating a multi-beam system, the problem of leakage and open Ll failure must be overcome.

The antenna design shown in FIG. 5 provides multi-beam operation in accordance with the present invention.

Asymmetric partial modifications of the Cassegrain antenna are used to avoid aperture disturbances.

This essentially uses only those portions of the reflective surfaces used in the complete Cassegrain antenna design of FIG.

The main reflector 52 is that portion of a complete paraboloid located parallel to and offset from the main geometrical axis 50 of the parabola of the reflector 52 .

For clarity, the connections to the feeders 54-58 have been omitted and the support 61, including conventional azimuth and elevation control mechanisms, is shown only in block form.

FIG. 6 shows the offset arrangement of the Cassegrain antenna in a top cross-sectional view taken through the beam axis 66 of the on-axis beam, and FIGS. 7 and 8 are side and front views of the antenna, respectively. It is.

The main reflector 52 is confined to the space above the plane 59 and the secondary reflector 53 is confined to the space above the axis 50 and below the plane 59.

It is noted that axis 50 is a geometric axis defined with respect to the axis of development of the paraboloid and hyperboloid.

Surface 52 is a part of a line emanating from the center of the parabola, which does not obstruct surface 52.

The feeding horns 54 to 58 radiate toward the sub-reflector 53.

The generated beam is reflected towards the main reflector 52 and radiates outward through an antenna aperture 64 located exclusively on one side of the interface 59.

A simple measure of the asymmetric organization of a partial Cassegrain surface is as long as the secondary reflector 53 is located outside the aperture 64, i.e. the space through which the radiation reflected from the main reflector 52 passes, i.e. the aperture 64 is in the same plane as the main reflector 52. 59 side is removed, and the sub-reflector 53 and the power feeders 54 to 58 are
Elements located on opposite sides of the plane do not block the radiation, so the resulting radiation pattern does not have a donut shape, and the dimensions of a particular antenna can be designed without cutting unnecessary holes in the radiation pattern. I can do it.

Furthermore, support materials such as support rods 65 need not be designed with their influence on radiation in mind, as essentially no radiation falls on them.

However, if this offset configuration is to be used effectively for multiple beams, the leakage problem must be overcome.

A plurality of feeders 54, 55, 57 and 58 clustered around the on-axis focal position of feeder 56 tends to create secondary or primary reflector leakage due to their off-axis deviations.

To avoid sub-reflector leakage, the sub-reflector' 530 surface area is widened laterally from the boundary 53' to accommodate multiple horizontally offset feeders.

The collected feeders 54, 55, 57 and 58 are on an essentially straight line passing through the axial focal point, and since this line is horizontal, if the feeders are laterally displaced, sub-reflections will occur. The horizontal dimension of the vessel is made substantially larger than the vertical dimension.

This horizontally extended pattern of sub-reflectors 53 is referred to as a bulletin board, and the locations of it and the off-axis feeders 54, 55, 57 and 58 are shown in FIGS. 6 and 8.

That simply increasing the surface of the sub-reflector may not give optimal operation and therefore the surface of the sub-reflector may be reshaped to deflect particularly in regions extending from the true hyperboloid. is to be written down.

The main reflector would also need to be reshaped to improve property 1.

Although preventing leakage in the secondary reflector, enlarging the secondary reflector does not simultaneously eliminate the leakage problem in the primary reflector, nor does it cure defects caused by misaligned beams.

Each of the multiple beams is directed to a unique point, such as a particular earth station, if the antenna is used on a satellite, or to a particular satellite, if used at an earth station.

Of course, offsets of the feeders from each other will cause the required broadening of the resulting beam, but if the center of the incident beam to be reflected is deflected from the effective center 60 of the surface 52, then the paraboloid The symmetry of the amplitude distributed through the main reflector aperture of is lost.

This effective center point is the main reflector of the beam emitted from the feeder on the axis like 56! When focused at this effective center 60 of 52, the generated beam radiated from the antenna is chosen to be optimally focused to pass through the aperture 64 with a phase front perpendicular to the main beam axis 66.

Any deviation from this center point 60 will cause the generated beam to have an asymmetric distribution as it emanates from the anti-1 beam.

Therefore, each of the multiple feeders has a common effective center point 6
individually oriented to hit surface 52 at 0.

This essentially creates an amplitude distribution for each beacom as shown in FIG.

The offset of the feeder therefore determines the beam angle, but for all beams the radiation is distributed symmetrically without disturbance or leakage around the beam center.

Although only the radiation pattern of two representative beams emanating from offset feeder 54 is shown for clarity,
All feeders are oriented such that their beam centers pass through a common effective center 60.

Typical feeder 54 produces a beam centered on straight line 67.

This beam axis is reflected by the surface 52 at point 60, but the main beam axis 66 radiates from the on-axis feeder 56.
and at different angles (see Figure 6).

It is therefore an axis 6 angularly offset from the beam axis 66.
It appears as a beam centered on 7.

Of course, the front face of this offset beam will be perpendicular to the desired axis 67.

Beams originating from such other feeders at 58 will then be centered on other axes such as 68 originating from point 60 but angularly offset from all other axes.

Although the lateral displacement of the feeder causes angular displacement in one plane, as shown as the horizontal plane in Figure 6, all beam centers lie in a common orthogonal plane as seen in Figure 7. be.

Since beam offset in orthogonal planes is desired, the feeder would have to be offset in a direction perpendicular to that shown in FIG.

This would require a corresponding expansion of the sub-reflector 53 in the longitudinal direction to avoid sub-reflector leakage.

Of course, it is possible to shift the power supply both horizontally and vertically.

That is, each of the collected feeders could be offset from the on-axis focus in a separate direction.

Of course, such an arrangement may be required for special applications where multiple beams are directed in divergent directions.

The present invention will be summarized as follows.

(2) An antenna consisting of a main reflector positioned to direct radiation through an antenna aperture, the aperture being centered about the main beam axis emanating from the effective center point of the main reflector;
a secondary reflector is smaller than the primary reflector and is positioned opposite the primary reflector to direct the beam incident thereon toward the primary reflector, the antenna having an axial focus on the antenna axis; The axis is shifted from the main beam, and the main reflector and the sub-reflector are placed outside the antenna aperture. antenna arranged so that the beam is focused on the effective center point of the main reflector, and a plurality of feeders are placed around and offset from the axial focal point, with each feeder individually and an antenna oriented toward the secondary reflector such that the center of the beam associated with each feeder commonly falls on the effective center point of the primary reflector.

2. A multi-beam antenna consisting of a main reflector, a smaller sub-reflector, and a plurality of feeders that feed energy towards the sub-reflector, where the main reflector is the central beam. The feeder and the secondary reflector are positioned to redirect the radiation from the feeder towards the main reflector to form a beam with an axis such that the feeder and the secondary reflector are located outside the main reflector. An antenna positioned such that each of the plurality of feeders is oriented toward the secondary reflector such that the centers of their beams pass through a common effective center point of the primary reflector.

3. The antenna claimed in claim 2, in which the reflectors are arranged to form a Cassegrain antenna, and a plurality of feeders are concentrated around the axial focal point of the Cassegrain antenna.

[4. The antenna claimed in claim 3 further including a focal feeder at the on-axis focal point for feeding energy towards the sub-reflector.

5. The antenna claimed in claim 3, wherein the surface of the main reflector is essentially a paraboloid, the surface of the sub-reflector is essentially a hyperboloid, and the feeder is a feed horn.

6. An antenna as claimed in claim 3, wherein the plurality of feeders are offset from the on-axis focus along an essentially straight line passing through the on-axis focus, and the sub-reflector is offset in the straight direction. An antenna with an essentially oblate boundary with a long axis.

7. The antenna claimed in claim 3, in which for each of the plurality of feeders offset from the axial focus, the surface area of the sub-reflector extends in the same direction to avoid leakage.

8. An antenna consisting of a main reflector and a smaller sub-reflector, the sub-reflector being placed to direct the radiation incident thereon towards the main reflector, the reflectors being arranged to form a Cassegrain antenna. , an antenna in which the primary feeding means is located at the axial focal point of the Cassegrain antenna for feeding energy towards the secondary reflector and from which radiation is emanated by the primary reflector to form a main beam passing through the antenna aperture. , the subreflector and the secondary feeder are located outside the antenna aperture, and the antenna further comprises at least one secondary feeder located outside the antenna aperture at a location away from the on-axis focal point. , the secondary feeder is oriented towards the secondary reflector such that the center of its beam hits the main reflector at a central point common to the center of the beam generated by the secondary feeder. .

9. In the antenna claimed in claim 8, the surface of the main reflector is essentially a paraboloid, the surface of the sub-reflector is essentially a hyperboloid, and the means for feeding primary and secondary energy is a feeding horn. antenna.

10. In the antenna claimed in claim 8, the surface of the sub-reflector is essentially a hyperboloid, the boundary of the sub-reflector is essentially flat, and the secondary means for feeding energy is located from an axial focal point. An antenna with its long axis in a misaligned direction.

11. An antenna as claimed in claim 8, wherein the antenna comprises a plurality of secondary feeders centered around the axial focal point, each of the plurality individually having its beam centered on the main reflector. However, due to the deviation from the axial focus, the sub-reflector is directed to emit a beam through an aperture with a path emanating from the main beam axis and from each of the others. antenna.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a conventional Cassegrain antenna, and FIG. 2 is a cross-sectional view of FIG. 1 showing its radiation pattern.
3 and 4 are cross-sectional views of a conventional Cassegrain antenna with offset feeders showing two forms of leakage, and FIG. 5 is a perspective view of a multi-beam Cassegrain antenna designed in accordance with the present invention. 6 and 7 are top and side cross-sectional views, respectively, of the antenna of FIG. 5 showing the radiation pattern of one of its beams, and FIG. 8 is a front view of the antenna of FIG. 5. It is. Explanation of symbols of main parts Main reflector...52, Sub-reflector...53, Primary beam feeding means...
・56, Antenna axial focus 60, Secondary beam feeding means 54, 55, 57, 58, Common effective point 60, Secondary feeding Center of beam of means...67°68°

Claims (1)

[Scope of Claims] 1. A main reflector from which radiation is emitted to form a main beam passing through the antenna opening; a primary beam feeding means located at an axial focal point of the antenna; A Cassegrain antenna including a sub-reflector that reflects radiation incident from the feeding means toward the main reflector,
The secondary beam feeding means and the secondary reflector are arranged outside the antenna aperture, and at least one secondary beam feeding means is located outside the antenna aperture, and the secondary beam feeding means and the secondary beam feeding means are arranged outside the antenna aperture. And the secondary feeding means means the antenna open [
said secondary feeding means are arranged on the same side with respect to said secondary feeding means such that the center of said beam falls on said main reflector at a center point common to the center of the beam generated by said secondary feeding means. offset from the antenna axis and the axial focal point and directed toward the secondary reflector, the secondary reflector avoiding leakage corresponding to the displacement of each of the secondary feeding means from the axial focal point; Cassegrain antenna characterized in that it has a surface area that is elongated. 2. The antenna of claim 1, wherein the antenna includes a plurality of secondary feeds passing through the on-axis focus and offset from the on-axis focus along essentially straight lines. and wherein the sub-reflector has an essentially oblate spheroidal boundary with its long axis in the direction of said straight line.