DE1238970B - Luneberg lens reflector for radar waves - Google Patents

Description

GERMAN WT ^f SLSS ^ PATENT OFFICE

EDITORIAL HOlq

German AI .: 21 a4 - 48/63

Number: 1 238 970

File number: T 21317 IX d / 21 a4

1 238 970 filing date: December 22, 1961

Open date: April 20, 1967

The invention relates to a known Luneberg lens reflector for linear, circular or elliptically polarized electromagnetic waves emitted by radar devices, which thus belongs to the so-called radar reflectors and which, on the one hand, consists of a plurality of concentrically arranged dielectric spherical shells, the outer one of which is one large to the air wavelength I of the waves Diameter, with relative dielectric constant ε _η increasing towards the center point of ε _Γ ? »1 in such a way that the parallel rays of a plane electromagnetic wave enter the lens without reflection and are approximately focused on the spherical surface opposite the entrance surface, and on the other hand from in focus in such a way arranged reflection means, for example a metal disk, is that the rays are reflected, pass through the lens on a path running mirror-inverted to the outward path and the lens again parallel to the direction of the incident rays leaving.

A directional antenna is known in which a parabolic reflector is used as a radiating element at the focal point a dipole is arranged. To the direction of polarization one by means of this radiator element to rotate transmitted or received electromagnetic wave and thus undesired feedback To avoid the reflected waves on the dipole, it is known to use this directional antenna to expand a confocal second reflector surface between the parabolic reflector and the radiator element is arranged such that the apex of the parabolic reflector and the additional reflector surface have a mutual distance of.

The additional reflector surface here consists of a direction inclined by 45 ° with respect to the dipole axis ladders running towards each other whose opposite

side distance small opposite - is and the em

Form polarization grating, which reflects vibrations, whose polarization direction is parallel to the Ladders runs while it lets through oscillations polarized perpendicular to them. With this dimensioning is the direction of polarization of the waves in the secondary directional diagram generated by means of the reflectors the directional antenna perpendicular to the direction of polarization of the waves by means of the radiator element generated primary directional pattern of the directional antenna.

This known directional antenna allows in an embodiment in which the mutual spacing of the Vertex of the additional reflector surface and the Luneberg lens reflector for radar waves

Applicant:
Telefunken

Patentverwertungsgesellschaft mb H.,
Ulm / Danube, Elisabethenstr. 3

Named as inventor:

Dipl.-Ing. Paul Münzer, Constance (Lake Constance)

Parabolic reflector

or an odd multiple of this value and in the case of the radiator element again a dipole is provided, the axis of which is 45 ° with respect to the direction of polarization of the polarization grating is inclined, even a change in the type of polarization; so hereby becomes a linearly polarized oscillation is converted into a circular oscillation, and vice versa.

It is obvious that the findings on which this known directional antenna is based in a Evaluate Luneberg lens reflector of the type specified at the outset, which is also used in conjunction with radar devices should be used as a radar reflector, the display suppression of rain echo signals work with circularly polarized oscillations without adapting to circularly polarized ones This Luneberg lens reflector waves in its retroreflective properties for linearly or elliptically polarized Waves is affected.

The invention is thus based on a Luneberg lens reflector of the type specified at the beginning

that at a distance of about η ■ (with η = 1, 2,

3 ...) - preferably at a distance of about -

in front of the reflection means in the direction of the center of the spherical shells and parallel to the spherical surface a parallel wire grid is arranged, the individual adjacent grid wires of which a mutual separation

own stand that is less than -.

The invention is based on the object of this Luneberg lens reflector with regard to the half-width and the side lobe attenuation of its retroreflective diagram versus the retroreflective diagram to improve the well-known Luneberg lens reflectors.

709 550/125

The invention consists in that that formed from the reflection means and the parallel wire grating System is shifted radially outward by an empirically determinable amount that is small compared to is the diameter of the outer spherical shell.

A particularly advantageous exemplary embodiment of the invention is given below with reference to the drawings to explain the same in detail.

In Fig. 1, 1 denotes the spherical Luneberg lens body made of dielectric spherical shells, not shown in detail. The rays incident parallel to axis 2 , for example rays 3 and 4, enter the spherical body at points 5 and 6 without reflection, since the relative dielectric constant of the lens surface is approximately the same as that of air. On the spherical surface opposite the entry plane, these rays are focused in focus 7 and reflected by the metal disk 8 acting as a reflector in the direction of the rays 9 and 10 shown. From the exit points 10 and 12 , the rays 9 and 10 are directed parallel to the incident rays 3 and 4 , so that they are reflected to the point of origin of the rays 3 and 4.

If the incident radiation symbolized by rays 3 and 4 is the radiation emitted by a radar device working with circular polarization and if the reflector is to be displayed in the radar image, i.e. if the reflector is to represent an asymmetrical target for the circularly polarized electromagnetic wave, then one of the two linear components, which are offset from one another by 90 ° in terms of time and space and which make up the circularly polarized oscillation, must be shifted by 180 ° relative to the other, in addition to the 90 °. This is done by attaching a parallel wire grid 13 at a distance of a = η - with η - 1, 2, 3 ...,

but preferably with η = 1, achieved in front of the metallic reflector plate 8 , the mutual

The spacing of the grid wires is smaller than y (2 = wavelength).

If the Luneberg lens reflector according to the invention described so far is also to be used for reflecting the radiation emitted by a radar device operating with linear polarization and for display in this radar device, the disadvantage arises that a parallel wire grating arranged at the specified distance in front of the reflector plate 8 only produces a linearly polarized wave again radiates back with the same direction of polarization when the E-vector of this wave is either exactly in the direction of the grid wires or perpendicular to it. A wave whose direction of polarization is inclined by 45 ° to the wire direction appears after reflection on this arrangement with an E-vector rotated by 90 ° and is consequently rejected by the receiving system of the linearly polarized radar device.

This disadvantage can be avoided in that the

Parallel wire grids not at a distance a - η · -, but instead at a distance a = η · --- in front of the re-

reflector surface is attached, preferably

again η - 1. A linearly polarized wave with an E-vector oscillating in or across the direction of the wire is derived from the arrangement described last (with a = 4, as before with unchanged

ΰ O

Direction of polarization reflected. A linearly polarized wave, the E-vector of which is 45 ° to the direction of the wire is inclined, has a polarization direction rotated by 45 ° after reflection.

ίο As far as described so far, the Luneberg lens reflector is correct according to FIG. 1 coincides with the known Luneberg lens reflector described at the outset and its design which has already been designated as obvious.

For generating particularly good reflection diagrams with regard to half-width and side lobe attenuation however, is the system formed from the reflector disk and the parallel wire grid according to the invention radially outwards to a minor extent, the size of which can easily be determined empirically, postponed.

The invention is of course also applicable to Luneberg lens reflectors of other known types, for example, of those with a metal reflector ring that surrounds the Luneberg lens equatorially applicable.

On the basis of the vector diagrams shown in FIG. 2, the mode of operation of the reflector is shown below described according to the invention in the reflection of circularly polarized electromagnetic waves.

Let us assume a Luneberg lens reflector according to the invention in which the parallel wire grating

ο at a distance of ^ in front of the reflector disc

finds and whose grid wires are directed vertically. If, for example, a circularly polarized wave in the direction of propagation - as indicated by the dashed directional arrows - strikes the grating, its vector 14, assumed at any angle in FIG. 2a, splits into its components 15 and 16 , of which component 15 is parallel and component 16 is perpendicular to the grid wires. The component 15 is reflected on the grating, while the component 16 passes through the grating unimpeded. The signs given in brackets next to the vectors indicate whether the amounts of the vectors have an increasing or decreasing tendency. The vector 17 symbolizes the circular

polarized wave at a distance - ^ - in front of the grating, ie mathematically positive by - offset from vector 14.

Fi g. 2b shows the corresponding vector diagram,

after the vector 16 has the distance a = - between

Has traversed the grating and reflector plate back and forth so that the vectors 14 ' and 17' in

Arrow direction by 90 ° accordingly - mathematically

have turned negative. The tendency of the vector 16 ', which represents the perpendicular to the wire direction component of the vector 14' , is - as again indicated by the sign - with respect to its amount falling, as well as that of the vector 18, which is parallel to the grid wires ver -

Claims (1)

represents the current component of the vector 17 which is reflected at the grating at the same instant. The vectorial addition of the vectors 16 and 18 results in a linearly polarized electromagnetic wave returning to the point of origin due to their mutual spatial offset by 90 °, but with phase equality (same decreasing amount tendency). Such a wave can, however, be broken down into two circularly polarized waves with opposite directions of rotation, one of which is processed in the radar receiver so that the reflector appears in the radar image. Claim: LuneberglinsenrefIektor for linear, circular or elliptically polarized electromagnetic waves emitted by radar devices, consisting on the one hand of a plurality of concentrically arranged dielectric spherical shells, the outer diameter of which is large in relation to the air wavelength A of the waves, increasing in _{this way from ε Γ «1 towards the center point} relative dielectric constant ε _η that the parallel beams of a plane electromagnetic wave enter the lens without reflection and are focused approximately on the spherical surface opposite the entrance surface, and on the other hand from those arranged in focus in this way Reflection means, for example a metal disk, that the rays are reflected, the Pass through the lens on a path that is a mirror image of the path there and the lens is parallel the direction of the incident rays leave the one where at a distance of about n- - (with η = 1, 2, 3 ...) - preferably at a distance of about ~ - in front of the reflection means in the direction direction to the center of the spherical shells and parallel to the spherical surface a parallel wire grid is arranged, the individual adjacent grid wires have a mutual distance, the λ is smaller than, characterized in that in the sense of improving the retroreflective diagram of the Luneberg lens reflector with regard to half-width and side lobe attenuation the system formed from the reflection means and the parallel wire grating radially is shifted outside by an empirically determinable amount that is small compared to the diameter the outer spherical shell is. Considered publications:
German Auslegeschrift No. 1015 869;
U.S. Patent No. 2,866,971. 1 sheet of drawings 709 550/125 4.67 © Bundesdruckerei Berlin