EP0435739B1 - Magic microwave source and its application in an antenna with electronic scanning - Google Patents

Description

The present invention relates to a microwave radiation source called magic, and its application to the illumination of an active lens to form an antenna with electronic scanning.

In an antenna with electronic scanning thus composed, it is known that certain parasitic phenomena of multiple reflections can appear on the interfaces, reflections which have the effect of increasing the level of the secondary lobes or of the diffuse radiation. To eliminate these multiple reflections, it is possible to absorb the energy reflected in the antenna itself, before its re-emission. To this end, it is notably known to use, to effect the power division necessary for the supply of each radiating element of the antenna, a large number of directional couplers absorbing the reflected energy. However, this type of structure has the drawback of being complex, delicate to develop and costly.

The present invention relates to a source of radiation which at least partially achieves the absorption of radiation reflected by the lens, whatever the incidence of this radiation when it is outside the main lobe of the antenna. This is what is meant in the present description by magic source, by analogy with the microwave junctions known under the name of magic Tees.

More specifically, the subject of the invention is a source of microwave radiation as defined by claim 1.

It also relates to an electronic scanning antenna using such a source, as defined by claim 6.

• la figure 1, un schéma d'une antenne à balayage électronique selon deux plans perpendiculaires, utilisant la source selon l'invention ;
• les figures 2a et 2b, différents modes de réalisation d'un élément constitutif de la source selon l'invention, et la figure 2c, un schéma explicatif de la figure 2b ;
• la figure 3, un mode de réalisation d'une antenne à balayage électronique intégrant la source selon l'invention.

Other objects, features and results of the invention will emerge from the following description, given by way of nonlimiting example and illustrated by the appended figures, which represent:

• Figure 1, a diagram of an electronic scanning antenna in two perpendicular planes, using the source according to the invention;
• Figures 2a and 2b, different embodiments of a component of the source according to the invention, and Figure 2c, an explanatory diagram of Figure 2b;
• Figure 3, an embodiment of an electronic scanning antenna incorporating the source according to the invention.

In these different figures, the same references relate to the same elements.

Furthermore, throughout the following description, the operation of the device according to the invention is described on transmission, but of course it operates, symmetrically, also on reception.

FIG. 1 therefore represents the diagram of an embodiment of a two-plane electronic scanning antenna using the source according to the invention.

The antenna includes a microwave radiation source, also called an illuminator and marked I, providing an electromagnetic wave propagating in a direction OZ and whose electric field E is directed in a direction OY, normal to the previous one. On the path of the electromagnetic wave are successively arranged a first microwave lens L₁, a grid G ensuring the rotation of the polarization of the wave and finally a second microwave lens L₂.

The illuminator I is composed in this mode of production of a stack of elementary illuminators, marked I₁, I₂ ... I _i ... I _n , the stack being produced along the axis OY.

The lens L₁ comprises, in a similar manner, a stack of channels marked C₁, C₂ ... C _i ... C _n produced along the axis OY. Each of these channels includes electronically controllable phase shifting means. It is thus possible to carry out, by variation of the phase shift values, an electronic scanning of the beam supplied by the illuminator I in the plane of the field E, ie the plane YOZ. An embodiment of such a lens is for example described in French patent No. 2,469,808. In a preferred embodiment, the illuminator can be integrated into the lens L₁ as described in French patent application No. 84 11066.

To further obtain an electronic scan in the perpendicular plane, that is to say in an XOZ plane, the OX axis being perpendicular to the OY and OZ axes, a second lens L₂, of the same type, is added according to this embodiment. type as the lens L₁ but where the stacking of the channels is crossed with the previous one, that is to say carried out along the axis OX. The polarization rotation grid G is provided so that the electric field E is always perpendicular to the stacking of the channels.

FIG. 2a represents an embodiment of an elementary illuminator, marked I _i , of the stack forming the illuminator I of the previous figure.

• d'un premier plan 1 conducteur, formant court-circuit, sensiblement parallèle au plan XOY ;
• d'un second plan 2, également disposé sensiblement selon le plan XOY, formant filtre d'incidence et repéré 2 ;
• d'un troisième plan 3, toujours sensiblement parallèle au plan XOY et portant un élément rayonnant.

This elementary illuminator is composed, arranged successively in the direction OZ:

• a first plane 1 conductor, forming a short circuit, substantially parallel to the plane XOY;
• a second plane 2, also arranged substantially along the XOY plane, forming an incidence filter and marked 2;
• of a third plane 3, always substantially parallel to the plane XOY and carrying a radiating element.

The assembly is arranged between two conducting planes P, substantially parallel to the plane XOZ.

The radiating element is for example of the snake line type; it is formed by a conductive deposit 31 on an insulating substrate 30 in the form of a pseudo-sinusoid extending substantially in the direction OX. On either side of the conductive line 31 are periodically arranged capacitive elements 32, also known by the Anglo-Saxon name of "stub", intended for the adaptation of impedance of the plane 3.

The plane 2 forming an incidence filter is, in this embodiment, constituted by an insulating substrate covered substantially over its entire surface with a resistive layer.

The plane 2 is separated from the planes 1 and 2 respectively by distances D₁₂ and D₂₃.

The distance D₁₂ is chosen to be of the order of the half-wavelength (λ _o ) of operation of the illuminator, at normal incidence (angle of incidence measured with respect to the axis OZ: ϑ = 0).

The distance D₂₃ is determined, as well as the parameters of the radiating element, so that the illuminator is adapted for the incidences corresponding to the main lobe of the radiating element. It is recalled that, in the case of a snake line, the parameters are the amplitude of the pseudo-sinusoid formed by the snake line, the half-period of the sinusoid, the position and the length of the stubs.

For a wave with normal incidence (ϑ = 0), the distance D₁₂ being equal to λ _o / 2, a short circuit is brought back into the plane of the filter 2, whatever the constitution of the latter: the latter is therefore transparent and does not introduce any loss.

For the incidences different from those corresponding to the main lobe, the snake line is transparent and the reflection coefficient of the antenna is that of the incidence filter 2.

As is known, at an angle of incidence ϑ, the wavelength becomes λ (ϑ) = λ _o / cosϑ. For ϑ = π / 3, it appears that the distance D₁₂ becomes equal to λ / 4, thus bringing an open circuit in parallel on the filter 2. For this incidence, the wave is therefore completely absorbed in the resistive plane 2, this absorption decreasing when moving away from the incidence ϑ = π / 3.

It thus appears that a wave emitted by the illuminator and subsequently reflected by one of the interfaces of the antenna, is absorbed by the illuminator, thus avoiding parasitic lobes at the antenna outlet.

FIG. 2b represents a variant of FIG. 2a, relating to the production of plane 2.

The plane 2 forming an incidence filter here consists of an insulating substrate 20 carrying resistive elements R. These are connected by connections 23 with two conductors, or tracks, 21 and 22, extending substantially parallel to the OX axis. The resistive elements R can be resistors or diodes.

FIG. 2c represents the equivalent diagram of plane 2 of FIG. 2b.

This diagram comprises, between two planes P, two capacities C₁ and C₂ in series; at the terminals of the capacitor C en are connected in series an inductance L and a resistor r.

This variant embodiment, which adds an imaginary part (inductive and capacitive) to the impedance introduced by the plane 2, makes it possible to obtain, by action on the parameters of filter 2, the adaptation of this filter, and therefore the absorption of the reflected waves, for an incidence other than ϑ = π / 3. The parameters of filter 2 are the distance between tracks 21 and 22 (capacitance C₂), the position of tracks 21 or 22 relative to the planes P (capacitance C₁), the value of the resistances R and the length of the connections 23 (inductance L and resistance r).

When the resistive elements R are constituted by diodes, the variation of the bias current of the diodes allows the previous parameters to be varied on command and therefore to obtain the absorption of the reflected waves for incidences whose value is thus adjustable electronically.

FIG. 3 represents an embodiment of an illuminator I according to the invention, integrated into the lens L₁.

In this figure, or found the three planes 1, 2 and 3 of Figure 2, extending along the plane XOY and forming the illuminator I. The device also includes the conductive planes P, parallel to the plane XOZ and defining between them channels I₁, I₂ ... I _i , ...

According to this embodiment, the conducting planes P extend to form the channels C₁, C₂ ... C _i , ... of the lens L₁. In each of the channels C are arranged planes D, parallel to the plane XOY, each carrying electronically controllable phase shifting means. These phase shifting means comprise diodes 40 connected by connections 41, substantially parallel to the axis OY, to conductors 42, substantially parallel to the axis OX; the latter connect all the diodes of the same phase-shifting plane to a controllable bias voltage. This type of phase shifting planes arranged in channels is described in the aforementioned French patent 2,462,808.

The electronic scanning obtained by controlling the phase shifting planes D takes place in the plane of the field E (YOZ), as described above.

Of course, as illustrated in FIG. 1, it is possible to have, behind the lens L₁, a grid G and a lens L₂ to obtain an electronic scan in the XOZ plane.

Claims (6)

1. Microwave radiation source, for transmitting or receiving radiation along a first direction (OZ), the electric field of which is directed substantially along a second direction (OY), normal to the preceding one, the source being characterized in that it includes a stack of channels (I₁...I_n) separated by conducting planes (C₁, C₂, ..., C_i, ...) which is produced substantially parallel to the second direction (OY) and in that each channel includes, successively in the first direction (OZ) and arranged substantially perpendicularly to the latter:

   - a first conducting plane (1) forming a short-circuit;

   - a second plane (2) forming an incidence filter, situated at a distance (D₁₂) from the first plane of the order of a half-wavelength of the radiation, the filter including resistive means;

   - a third plane (3) carrying a microwave illuminator of the snake-line type (31), the snake line extending substantially along a third direction (OX), perpendicular to the preceding ones;

   the illuminator and the filter having characteristics such that the filter is at least partially absorbing for microwave energy received at a non-zero angle of incidence in the plane YOZ.
2. Source according to Claim 1, characterized in that the second plane (2) includes a resistive layer over substantially its whole surface.
3. Source according to Claim 1, characterized in that the second plane (2) includes an insulating substrate (20) carrying two tracks (21, 22) which are substantially parallel to the third direction (OX) and resistive elements (R) connected (23) between the tracks.
4. Source according to Claim 3, characterized in that the resistive elements (R) are resistors.
5. Source according to Claim 3, characterized in that the resistive elements (R) are diodes.
6. Electronic scanning antenna, characterized in that it includes a source according to one of the preceding claims, and in that each of the channels further includes a plurality of phase-shifting planes (D), arranged after the third plane (3), each imparting an electronically controllable phase shift to the wave which passes through them.

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