EP1234356B1 - Active electronic scan microwave reflector - Google Patents

Abstract

An active electronic scan microwave reflector, capable of being illuminated by a microwave source to form an antenna. The reflector includes a set of elementary cells arranged side by side on a surface, each cell including a phase-shifting microwave circuit and a conductor plate arranged substantially parallel to the microwave circuit, the phase-shifting circuit including at least two half-phase-shifters. One half-phase-shifter includes at least a dielectric support, at least two electrically conductive wires substantially parallel to a given direction, arranged on the support and bearing at least a two-state semiconductor element, the conductors being substantially normal to the wires, and two conductor zones arranged towards the periphery of the cell, substantially parallel to the control conductors. The control conductors can be at least three in number in each half-phase-shifter and can be electrically insulated from one half-phase-shifter to the next to control the state of all the semiconductor elements independently from one another. The geometrical and electrical characteristics of the half-phase-shifters are such that each of the states of the semiconductor elements corresponds to a given phase-shifting value of the electromagnetic wave reflected by the cell. The reflector further includes an electronic circuit controlling the state of the semiconductor elements.

Description

The present invention relates to an electron-beam active microwave reflector capable of being illuminated by a microwave source to form an antenna.

It is known to produce antennas comprising an active microwave reflector. The latter, also called "reflect array" in the Anglo-Saxon literature, is a network of electronically controllable phase shifters. This network extends in a plane and comprises an array of phase-controlled elements, or phased array, disposed in front of reflector means, constituted for example by a ground plane forming a ground plane. The reflector network comprises in particular elementary cells each performing the electronically variable reflection and phase shift, of the microwave wave it receives. Such an antenna provides great beam agility. A primary source, for example a horn, arranged in front of the reflector network emits microwave waves towards the latter.

The phase shifts applied by the elementary cells vary in a discrete manner. Since the phase shifts are evenly distributed, they are digitally controlled as a function of a number of bits. If we write N this number, the phase shift pitch is then 2π / 2 ^N. The accuracy of a phase shift is therefore at best equal to a phase shift step. The lack of precision entails certain disadvantages, in particular it causes the existence of relatively high side lobes and poor pointing accuracy of the antenna.

Patent applications FR-A-2 708 808 and FR-A-2 747 842 describe active phase shift networks.

An object of the invention is in particular to overcome the aforementioned drawbacks. For this purpose, the subject of the invention is an active microwave reflector, capable of receiving a linearly polarized electromagnetic wave in a given first direction Oy. The reflector according to the invention comprises a set of elementary cells arranged one beside the other. another on a surface, each cell comprising a phase-shifting microwave circuit and a conductive plane disposed substantially parallel to the microwave circuit, the phase-shifting circuit comprising at least two half-phase-shifters. A half-phase-shifter comprises at least one support dielectric, at least two electrically conductive wires substantially parallel to the given direction Oy, arranged on the support and at least each carrying a semiconductor element with two states, each wire being connected to control conductors of the semiconductor elements, these conductors being substantially normal to the son, and two conductive zones disposed towards the periphery of the cell, substantially parallel to the control conductors. The control conductors are at least three in each half-phase-shifter and are electrically isolated from one half-phase-shifter to the other to control the state of all the semiconductor elements independently of each other . The geometric and electrical characteristics of the half-phase-shifters are such that at each of the states of the semiconductor elements corresponds a given phase shift value (dφ ₁ , ... dφ ₈ ) of the electromagnetic wave which is reflected by the cell. The reflector further comprising an electronic control circuit (36) of the state of the semiconductor elements.

The invention also relates to an antenna provided with such a reflector.

The main advantages of the invention are that it makes it possible to produce a low-profile and low-weight reflector, that it adapts to many types of antennas, that it improves the heat exchange between the reflector and the reflector circuits. outside, that it allows a great reliability and that it is economic.

• la figure 1, un exemple d'antenne à balayage électronique à réflecteur hyperfréquence actif en regard d'un système d'axes orthogonaux Ox,y,z;
• la figure 2, une vue partielle de la face avant d'un exemple de réseau réflecteur actif selon l'invention;
• la figure 3, une vue partielle en coupe d'un exemple d'un réflecteur selon l'invention;
• la figure 4, un premier exemple de réalisation d'une cellule élémentaire d'un réflecteur selon l'invention ;
• la figure 5, un schéma électrique équivalent d'un demi-déphaseur compris dans la cellule précitée ;
• la figure 6, un schéma électrique équivalent de la cellule;
• la figure 7, un deuxième exemple de réalisation possible d'un réflecteur selon l'invention ;
• la figure 8, un autre exemple de réalisation d'un réflecteur selon l'invention comportant une grille disposée sur sa face avant.

Other characteristics and advantages of the invention will become apparent with the aid of the following description made with reference to appended drawings which represent:

• FIG. 1, an example of a scanning electron microscope with active microwave reflector facing a system of orthogonal axes Ox, y, z;
• FIG. 2 is a partial view of the front face of an example of an active reflector grating according to the invention;
• Figure 3 is a partial sectional view of an example of a reflector according to the invention;
• FIG. 4, a first exemplary embodiment of an elementary cell of a reflector according to the invention;
• FIG. 5, an equivalent electrical diagram of a half-phase-shifter included in the aforementioned cell;
• Figure 6, an equivalent electrical diagram of the cell;
• FIG. 7, a second possible embodiment of a reflector according to the invention;
• Figure 8, another embodiment of a reflector according to the invention having a gate disposed on its front face.

FIG. 1 schematically illustrates an exemplary embodiment of an active reflective grating electronic scanning antenna where the microwave distribution is for example of the so-called optical type, that is to say, for example, provided by means of FIG. a primary source illuminating the reflector network. For this purpose, the antenna comprises a primary source 1, for example a horn. The primary source 1 transmits microwave waves 3 to the active reflector network 4 disposed in the Oxy plane. This reflector network 4 comprises a set of elementary cells performing the reflection and phase shift of the waves they receive. Thus, by controlling the phase shifts printed on the wave received by each cell, it is possible, as is known, to form a microwave beam in the desired direction. Optionally, the reflector may be illuminated by more than one source. It can in particular be illuminated by two elementary sources, having for example inverse circular polarizations.

FIG. 2 schematically shows a reflector network portion 4 in the Oxy plane, in a view from above, according to F. The reflector comprises a set of elementary cells 10 arranged side by side and separated by zones 20, used for the microwave decoupling cells. These cells 10 perform the reflection and the phase shift of the waves they receive. An elementary cell 10 comprises a phase-shifting microwave circuit disposed in front of a conductive plane. More precisely, as will appear later, the microwave circuit has two transverse phase shifters, each dedicated to a linear polarization.

FIG. 3 is a diagrammatic sectional view, in the Oxz plane, of an exemplary embodiment of the active reflector 4. The reflector 4 consists of a microwave circuit 31 distributed in the elementary cells 10 and a conductive plane 32 , disposed substantially parallel to the microwave circuit 31, at a distance d predefined. This microwave circuit receives the incident waves emitted by the primary source 1.

The conductive plane 32 has the particular function of reflecting the microwave waves. It can be constituted by any known means, for example parallel wires or a grid, sufficiently tight, or a continuous plane. The microwave circuit 31 and the conductive plane 32 are preferably made on two sides of a dielectric support 33, for example of the printed circuit type. The reflector 4 further comprises, preferably on the same printed circuit 33, which is then a multilayer circuit, the electronic circuit necessary for the control of the phase values. FIG. 3 shows a multilayer circuit whose front face 34 carries the microwave circuit 31, the rear face 35 carries components 36 of the aforementioned electronic control circuit, and the intermediate layers form the conductive plane 32 and for example two plans 37 interconnections of the components 36 to the microwave circuit 31.

FIG. 4 shows in a view from above an example of possible embodiment of the microwave circuit 31 of a reflector according to the invention. More particularly, FIG. 4 illustrates an elementary phase shifter 31 of the microwave circuit. Each phase-shifter is separated from another phase-shifter by a decoupling zone 20 comprising for example a conductive strip 48 parallel to the direction Oy and a conductive strip 49 parallel to the direction Ox. It therefore has for example at its periphery two conductive strips 48 in the direction Oy and two conductive strips in the direction Ox. Each elementary phase shifter 31, associated with the corresponding portion of the conductive plane 32 forms an elementary cell 10 of FIG.

The microwave circuit of a phase-shifter 31 comprises a plurality of conducting wires 42 substantially parallel to the direction Oy and each carrying a semiconductor element with two states D1, D2, for example a diode. The phase shifter circuit also comprises conductive zones connecting the diodes to reference potentials and control circuits. More particularly, an elementary phase shifter 31 consists of two circuits 50, hereinafter called half-phase shifter. We first describe a half-phase shifter.

A half-phase-shifter 50 comprises a dielectric support 33, two wires 42 each carrying a diode D1, D2. The two wires are connected to the ground potential, or to any other reference potential, via a conductive line 43. This line 43 is for example of the microstrip type made by metal deposition on the front face of the dielectric support 33 for example by a screen printing technique. The diodes D1 and D2 are thus wired in opposition so that, for example, their anodes are connected to the ground potential via this line 43. For this purpose, the latter is for example connected to a conductive strip 48 of the decoupling means 20. Diode supply voltage D1 and D2 is supplied by control conductors 44. The anode of the diodes being connected to the ground potential, the control conductors are then connected to the cathode of the diodes. The supply voltage supplied by these conductors is for example of the order of -15 volts. The control leads are controlled to have at least two voltage states. In a first state, their voltage is for example at the supply voltage, which makes the diode pass, or in other words polarized live. In a second state, their voltage is such that the diode is blocked, or in other words polarized in reverse. The controls of the two control conductors 44, 45 are independent of one another so as to control the diodes independently of one another. The control conductors 44, 45 and the connected ground conductor 43 are substantially parallel to the Ox direction and therefore perpendicular to the wires 42. In FIG. 4, the ground conductor is common to the two wires, in particular for space and power savings. material, it could however provide a specific driver for each wire. We could also plan to not directly connect these conductors directly to a reference potential but through a control circuit.

The control conductors 44, 45 are connected to the electronic control circuit carried by the reflector, via metallized holes 46 made for example at the decoupling zone 20, in particular for reasons of space, but also for do not disturb the functioning of the elementary cells. The metallized holes 46 are of course electrically isolated from the conductive strips of the decoupling zone. For this purpose, there is provided an interruption of the strip 20 around the ends of the control conductors directly connected to the metallized holes 46.

To describe the operation of a half-phase-shifter 50, it is necessary to consider its equivalent circuit as represented by FIG. 5. The equivalent circuit relates to the conducting wires 42 and the two diodes D1, D2, in fact what corresponds to a half-phase-shifter, associated with a given polarization and therefore a given frequency band. The incident microwave, of linear polarization and parallel to Oy and son 42 is received on terminals B ₁ and B ₂ and meets three capacitors C _O , C _I1 , C _I2 in series, connected in parallel to terminals B ₁ and B ₂ . The capacitance C _O represents the linear capacitance of decoupling between the control conductors 44 and the conductive strip of the decoupling zone 20. The capacitance C _I1 is the linear capacitance between the control conductor 44 connected to the first diode D1 and the conductor The capacitance C _I2 is the linear capacitance between the control conductor 45 connected to the second diode D2 and the central conductor 43.

• soit une capacité C_i1 (capacité de jonction de la diode) en série avec une résistance R_i1 (résistance inverse),
• soit une résistance R_d1 (résistance directe de la diode), selon que la diode D1 est en sens inverse ou direct, ce qui est symbolisé par un interrupteur 2₁.

At the terminals of the capacitor C _I1 is connected the first diode D1, also represented by its equivalent diagram. The latter consists of an inductor L ₁ , inductance of the diode D1 given its connection wire 42, in series with:

• a capacitance C _i1 (junction capacitance of the diode) in series with a resistor R _i1 (inverse resistance),
• or a resistor R _d1 (direct resistance of the diode), depending on whether the diode D1 is in the opposite or direct direction, which is symbolized by a switch 2 ₁ .

In the same way, across the capacitor C _I2 is connected the second diode D2 represented by its equivalent diagram. The latter is similar to that of the first diode D1, its components bearing an index 2.

The microwave output voltage is taken between terminals B ₃ and B _4, terminals of the capacitors C _0, C _I1, and _I2 C.

The operation of the half-phase-shifter 50 is explained below by considering, in a first step, the behavior of such a circuit in the absence of the second diode D2, which returns to the equivalent diagram of FIG. the D2 as well as the capacity C _I2 .

où Z est l'impédance de l'onde incidente et ω est la pulsation correspondant à la fréquence centrale d'une des deux bandes de fonctionnement de l'antenne.When the first diode D1 is forward biased, the susceptance B _d1 of the circuit of FIG. 5 (modified) is written: $${\mathrm{B}}_{\mathrm{di}}\mathrm{=}\mathrm{Z}\mathrm{.}{\mathrm{<figure-callout\; id="0"\; label="VS"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">VS</figure-callout>}}_{\mathrm{0}}\mathrm{.}\mathrm{\omega }\mathrm{.}\frac{\mathrm{1}\mathrm{-}{\mathrm{The}}_{\mathrm{1}}{\mathrm{VS}}_{\mathrm{11}}{\mathrm{<figure-callout\; id="2"\; label="\omega "\; filenames="imgf0001.png,imgf0004.png"\; state="\{\{state\}\}">\omega </figure-callout>}}^{\mathrm{2}}}{{\mathrm{The}}_{\mathrm{1}}{\mathrm{VS}}_{\mathrm{not}}{\mathrm{<figure-callout\; id="2"\; label="\omega "\; filenames="imgf0001.png,imgf0004.png"\; state="\{\{state\}\}">\omega </figure-callout>}}^{\mathrm{2}}\mathrm{+}{\mathrm{The}}_{\mathrm{1}}{\mathrm{<figure-callout\; id="0"\; label="VS"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">VS</figure-callout>}}_{\mathrm{0}}{\mathrm{\omega }}^{\mathrm{2}}\mathrm{-}\mathrm{1}}$$

where Z is the impedance of the incident wave and ω is the pulse corresponding to the center frequency of one of the two operating bands of the antenna.

ce qui conduit à B_d1 ≅ 0, quelle que soit notamment la valeur de la capacité C_i1.For example, the parameters of the circuit are chosen to have B _d1 ≅ 0, that is to say that, neglecting its conductance, the circuit is adapted or, in other words, that it is transparent to the wave. microwave incident, introducing neither parasitic reflection nor phase shift (dφ _d1 = 0). More precisely, we choose: $${\mathrm{The}}_{\mathrm{1}}{\mathrm{VS}}_{\mathrm{11}}{\mathrm{<figure-callout\; id="2"\; label="\omega "\; filenames="imgf0001.png,imgf0004.png"\; state="\{\{state\}\}">\omega </figure-callout>}}^{\mathrm{2}}=1$$

which leads to B _d1 ≅ 0, whatever the value of the capacity C _i1 .

When the first diode D1 is reverse biased, the susceptance B _r1 of the circuit is written: $${\mathrm{B}}_{\mathrm{Services}}\mathrm{=}\mathrm{Z}\mathrm{.}{\mathrm{<figure-callout\; id="0"\; label="VS"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">VS</figure-callout>}}_{\mathrm{0}}\mathrm{.}\mathrm{\omega }\mathrm{.}\frac{\mathrm{1}\mathrm{-}{\mathrm{The}}_{\mathrm{1}}{\mathrm{VS}}_{\mathrm{11}}{\mathrm{<figure-callout\; id="2"\; label="\omega "\; filenames="imgf0001.png,imgf0004.png"\; state="\{\{state\}\}">\omega </figure-callout>}}^{\mathrm{2}}+\left({\mathrm{VS}}_{11}/\mathrm{<figure-callout\; id="1"\; label="This\; The"\; filenames="imgf0004.png"\; state="\{\{state\}\}">This\; </figure-callout>}\right)}{{\mathrm{The}}_{}}$$

Since the capacitance C _I1 is fixed above, it appears that the value of the susceptance B _r1 can be adjusted by action on the value of the capacitance C _i , that is to say the choice of the diode D1.

If now, in a second step, we take into account the existence of the second diode D2, we see that, by analogous reasoning, we obtain two other distinct values for susceptance, depending on whether the diode D2 is forward biased or in reverse.

It thus appears that a half-phase-shifter may have four different values for its susceptance B _D , these values being denoted B _D1 , B _D2 , B _D3 and B _D4 , according to the command (direct or inverse biasing) applied to each of the diodes. D1, D2. The susceptance values B _D1 , B _D2 , B _D3 and B _D4 are a function of the parameters of the circuit of FIG. 5, that is to say the values chosen for the geometrical parameters, in particular with respect to relates to the dimensions, shapes and spacings of the various conductive surfaces 43, 44, 45, and electrical phase shifter, particularly with respect to the electrical characteristics of the diodes. In particular, it is necessary to take into account the definition constraint of the conductive strip of the decoupling zone 20 mentioned above during the determination of the different parameters for fixing phase shifts dφ ₁ - dφ ₄ .

où λ est la longueur d'onde correspondant à la pulsation ω précédente.
La susceptance B_C de la cellule est alors donnée par : $${\mathrm{B}}_{\mathrm{C}}\mathrm{=}{\mathrm{B}}_{\mathrm{D}}\mathrm{+}{\mathrm{B}}_{\mathrm{CC}}$$

If, now, we study the behavior of the entire half-phase-shifter 50 in association with the conductive plane 32, we must take into account the susceptance due to this plane 32, brought into the plane of the half-phase shifter and denoted B _CC , which is written: $${\mathrm{B}}_{\mathrm{CC}}\mathrm{=}\mathrm{-}\mathrm{cotg}\frac{\mathrm{2}\mathrm{\pi d}}{\mathrm{\lambda }}$$

where λ is the wavelength corresponding to the preceding puls pulse.
The susceptance B _C of the cell is then given by: $${\mathrm{B}}_{\mathrm{VS}}\mathrm{=}{\mathrm{B}}_{\mathrm{D}}\mathrm{+}{\mathrm{B}}_{\mathrm{CC}}$$

It follows that the susceptance B _C can take four distinct values (denoted B _C1 , B _C2 , B _C3 , and B _C4 ) respectively corresponding to the four values of B _D , the distance d representing an additional parameter for determining the values B _C1 - B _C4 .

It is also known that the phase shift dφ printed by an admittance Y to a microwave wave is of the form: $$\mathrm{d\phi }=2\mathrm{arctg\; Y}$$

et qu'on obtient quatre valeurs possibles dϕ₁ - dϕ₄ de déphasage par demi-déphaseur 50, selon la commande appliquée à chacune des diodes D₁ et D₂. Les différents paramètres sont choisis pour que les quatre valeurs dϕ₁ - dϕ₄ soient équiréparties, par exemple mais non obligatoirement : 0, 90°, 180°, 270°. Ces quatre états correspondent à une commande numérique codée sur deux bits.It thus appears that, neglecting the real part of the admittance of a cell, we have: $$\mathrm{d\phi }\cong 2{\mathrm{arctg\; B}}_{\mathrm{VS}}$$

and that four possible values dφ ₁ - dφ ₄ of phase shift per half-phase-shifter 50 are obtained, according to the command applied to each of the diodes D ₁ and D ₂ . The different parameters are chosen so that the four values dφ ₁ - dφ ₄ are equidistributed, for example but not necessarily: 0, 90 °, 180 °, 270 °. These four states correspond to a two-bit digital control.

It should be noted that the case in which the parameters of the circuit have been chosen is described above so that the null susceptances (or substantially zero) are such that they correspond to the diodes polarized in the forward direction, but that can of course choose a symmetrical operation in which the parameters are determined to substantially cancel susceptances B _r ; more generally, it is not necessary for one of the susceptances B _d or B _{r to} be zero, these values being determined so that the equidistribution condition of the phase shifts dφ ₁ -dφ ₄ is fulfilled.

To show how an elementary cell 10 allows eight possible phase shifts, that is to say a control of three-bit phase shifts, we now consider the set of two half-phase-shifters 50. By operating the two half-phase shifters 50 independently from each other, one can obtain twice as many states, that is to say phase shifts, than in the case of a single half-phase-shifter. Nevertheless, it is necessary to provide electrical insulation between the two half-phase shifters. These last two being for example juxtaposed, the control drivers 44, 45 are isolated for example by a line 47 of dielectric, corresponding in fact to a breaking line in the metallization of the conductors 44, 45. This first insulation allows in fact an isolation of the electrical controls of the diodes.

FIG. 6 shows an equivalent diagram of the entire phase shifter constituted by the two half-phase-shifters as previously described. It can be considered that the equivalent diagrams of the two half-phase-shifters 50 as shown in FIG. 5 operate in parallel. Indeed, the capacitive links between the control conductors 44 of the diodes D1 and between the control conductors 45 of the diodes D2 can be likened to microwave short circuits. One can play on the length and width of the isolation line 47 to obtain a capacitance value between the conductors that allows to assimilate the capacitive connection to a short circuit. For circuits in parallel, susceptances are added. Therefore, at the four susceptance values B _D1 , B _D2 , B _D3 , B _D4 obtained by the influence of a half-phase-shifter, four new values B ' _D1 , B' _D2 , B ' _D3 , B are thus obtained. _D4 obtained by the influence of the second phase shifter.

The geometric and electrical parameters of the phase shifter are for example defined to obtain eight phase shifts equidistant between 0 ° and 360 °.

The geometrical parameters which concern in particular the dimensions, the shapes and the spacings of the various conductive surfaces 44, 45, 33 play on the values of the capacitances and inductances of the equivalent diagram of FIGS. 5 and 6, taken again in relations (1) and (2). ). As a function of the desired phase shifts, susceptance values B _C and hence susceptance values B _D are defined according to the relations (3) and (4), the distance d being known. The susceptances values B _D being imposed, we then deduce the values of the parameters of the relations (1) and (2). The geometric and electrical parameters of the phase-shifter can then be obtained by conventional simulation means. Figure 4 shows that conductive surfaces 44, 45, 43 have particular shapes. The control conductors 44, 45 have in particular crenellated surfaces. These surfaces correspond to previously defined phase shift values.

A phase shifter as shown in FIG. 4 is simple to implement, it makes it possible to obtain eight phase shifts by simply playing on geometric parameters of conductors and on the choice of diodes. The printed circuit supporting the microwave circuits and the electronic control circuits is also thin. Such a circuit can be obtained economically and the reflector can be extremely flat, and therefore low weight.

As indicated above, an active reflector according to the invention comprises decoupling means 20 between the cells 10. The microwave wave received by the cells is polarized linearly, parallel to the direction Oy. It is desirable that this wave not does not propagate from one cell to another, in the Ox direction. To avoid such propagation, the decoupling means comprise at least the conductive zone 48. It is therefore expected to provide this substantially strip-shaped conductive zone 48, made by metal deposition on the surface 34, for example, between the cells, parallel to the direction Oy. This strip 48 forms, with the reflective plane 32 which is below, a waveguide-like space whose width is the distance d. The distance d is chosen to be less than λ / 2, λ being the length of the microwave wave, knowing that a wave whose polarization is parallel to the bands can not propagate in such a space. In practice, the reflector according to the invention operates in a certain frequency band and d is chosen so that it is smaller than the smallest of the wavelengths of the band. Of course, it is necessary to take this constraint into account when determining the various parameters for fixing phase shifts dφ ₁ ,... Dφ ₈ . In addition, the band 48 must have a width, in the direction Ox, sufficient for the effect described above is sensitive. In practice, the width may be of the order of λ / 5.

Moreover, it may be parasitically created in a cell, a wave whose polarization is directed in the direction Oz, perpendicular to the plane formed by the directions Ox and Oy. It is also desirable to avoid its propagation to neighboring cells .

With regard to neighboring cells in the direction Ox, it is possible to use, as shown in FIG. 4, the metallized holes 46 for connection from control conductors to electronic circuits. Indeed, these being parallel to the polarization of the parasitic wave, they are equivalent to a shielding conductive plane if they are sufficiently close together (at a distance from each other much less than the length of the operating wave of the reflector), so many, for the operating wavelengths of the reflector. If this condition is not fulfilled, additional metallized holes can be formed, having no connection function. It should be noted that the metallized connection holes 46 are preferably made at the level of the strips 48 so as not to disturb the operation of the cells. This provision also provides a saving of space.

Finally, with regard to neighboring cells in the Oy direction, it is possible to use metallized holes 40 similar to the connection holes 46 but aligned in the Ox direction opening into the conductive strip 49. These metallized holes 40 as the metallized connection holes 46 are made in a direction Oz substantially perpendicular to the plane Oxy. For example, it is still possible to provide a continuous conductive surface in the xOz plane.

FIG. 7 illustrates a phase-shifter according to the invention making it possible to control the phase-shifts on 4 bits, thus on an additional bit with respect to the phase-shifter illustrated by FIG. 4. The phase-shifter always comprises two half-phase-shifters 50 made as previously described. However, the two half-phase-shifters are no longer separated by a line 47 isolating the controls of the diodes, but by two conductive zones 71, 72 connected by a diode D3, or any other semiconductor with two states. These two zones 71, 72 are for example made by metal deposition on the front face 34 of the dielectric. These zones form control conductors of the diode D3. For this purpose, a conductive zone 71 is for example connected to the electronic control circuits by a metallized hole 46. Depending on the state of the electronic control, this zone 71 is at a supply potential, for example -15 volts or to another potential, for example the mass potential. The other conductive zone 72 is for example connected to the ground potential. For this purpose, it is for example connected to the conductive strip 48 parallel to the direction Oy of the decoupling means 20.

When the conductive zone 71 is controlled to be at the ground potential, or more generally to make the diode D3 blocked, that is to say in reverse bias, the phase shifter is similar to that of FIG. state eight possible phase shifts. It is of course necessary to redefine its geometrical and electrical parameters because of the introduction of the additional zones 71, 72. When the conductive zone 71 has a potential which makes the diode D3 conducting, that is to say in direct polarization , the electrical parameters of the phase-shifter are modified with respect to the previous state. In particular, the capacity formed of the space between the two conductive zones 71, 72 becomes short-circuited by the diodes D3. The eight susceptances possible of the previous state, controlled on three bits, are then modified by the conduction of the diode D3. The eight new susceptances thus obtained make it possible to obtain eight additional phase shifts. A total of sixteen phase shifts are possible. The geometric and electrical characteristics of the two half-phase-shifters 50 but also the additional conductive zones 71, 72 and their diode D3 must be defined so as to obtain the sixteen desired phase-shifts for each of the states of the diodes.

FIG. 8 illustrates a possible variant embodiment of a reflector according to the invention, the elementary cells 10 being for example of the type shown in FIG. 4 or 7. In this embodiment, a metal gate is placed on the front face of the reflector, that is to say the face which is opposite the microwave source 1. This grid is formed of meshes 81 each having the surface of an elementary cell, more particularly the base of a mesh surrounds a cell. The grid also has a thickness e _G.

To illustrate the arrangement of this grid with respect to the elementary cells 10 of the reflector, FIG. 8 presents in perspective a single elementary cell. The grid is formed of meshes whose walls 82 extend in the direction Oz, substantially opposite the conductive strips 48, 49 of the decoupling means 20. In particular the base of the grid is in contact with these bands 48, 49 and in particular with the metallized holes 40, 46 that they comprise. The thickness eG of the grid, which corresponds in fact to the length of the walls 82 is for example of the order of one centimeter, preferably of the order of half a centimeter. The relative small thickness of the grid thus allows to keep a very flat reflector, and therefore of low weight.

This metal gate makes it possible to decouple the phase shift function from the radiation function, and makes it possible to control the active coupling coefficients by making them independent of the antenna pointing law and thus makes it possible to cancel the parasitic radiation lobes such as as the image lobe and the lobes of magicity.

Furthermore, the metal grid, which is in particular in contact with the metallized holes, allows a better heat exchange between the reflector circuits and the outside through a larger exchange surface. The reliability of the reflector is thus increased.

An active reflector array according to the invention can be used for many types of antennas. It can in particular be used for space communication antennas thanks to its low weight or be used for meteorological radar antennas thanks to its low cost. Finally, it can be used for all types of application reflector antennas requiring good pointing accuracy and a low level of sidelobes.

Claims (10)

1. Active microwave reflector, capable of receiving an electromagnetic wave (3) which is linearly polarized in a first given direction (Oy), comprising a set of elementary cells (10) placed side by side over a surface,
   each cell comprising a phase-shift microwave circuit (31) and a conducting plane (32) placed substantially parallel to the microwave circuit, characterized in that the phase-shift circuit (31) comprises at least two half-phase shifters (50)
   a half-phase shifter (50) comprising at least one dielectric support (33), at least two electrically conducting wires (42), substantially parallel to the given direction (Oy), both placed on the support and each one bearing at least one semiconducting element (D1, D2) with two states, each wire being connected to conductors (43, 44, 45) controlling the semiconducting elements, these conductors being substantially normal to the wires, and two conducting zones (49) placed toward the periphery of the cell, substantially parallel to the control conductors,
   the control conductors being electrically isolated from one half-phase shifter to another in order to control the state of all the semiconducting elements independently of each other,
   the shapes and the spacings of the surfaces of the control conductors (43, 44, 45) and the electrical characteristics of the semiconductors being such that a given phase-shift value (dϕ₁, ... dϕ₈) of the electromagnetic wave which is reflected by the cell, the reflector comprising a metal grid formed by gridcells (81), the walls (82) of which lie in the direction (Oz) perpendicular to the plane of the reflector, the base of one gridcell surrounding a cell (10).
2. Reflector according to Claim 1, characterized in that a conducting strip (48) placed between each cell, parallel to the given direction (Oy), forms with the conducting plane a guided space where the wave cannot be propagated, the base of the grid being in contact with this strip (48).
3. Reflector according to either of the preceding claims, characterized in that the two phase shifters are separated by two conducting zones (71, 72) connected by a semiconducting element (D3) with two states, at least one of the zones (71) being connected to an electronic control circuit (36) in order to control the state of the semiconductor, the geometrical and electrical properties of the half-phase shifters and of the conducting zones (71, 72) and of their semiconducting elements being such that a given phase-shift value (dϕ₁, ...dϕ₁₆) of the electromagnetic wave which is reflected by the cell corresponds to each of the states of the semiconducting elements.
4. Reflector according to any one of the preceding claims, characterized in that the dielectric support (33) is of the multilayer printed circuit type, a first face (34) of which bears the microwave circuit, a first intermediate layer of which bears the conducting plane (32) and the second face (35) of which bears the components of the control circuit.
5. Reflector according to Claim 4, characterized in that the dielectric support (33) further comprises at least a second intermediate layer (37) bearing interconnects of the control circuit.
6. Reflector according to any one of the preceding claims, characterized in that it comprises plated-through holes (40, 46) made in the dielectric support (33), in the direction (Oz) perpendicular to the plane (Oxy) of the reflector, at a distance one from the other which is very much less than the electromagnetic wavelength, at least some of these plated-through holes providing the link between the control circuit and the control conductors.
7. Reflector according to Claim 6, characterized in that the plated-through holes (40, 46) emerge on the conducting strips (48, 49) placed at the periphery of a cell.
8. Reflector according to any one of the preceding claims, characterized in that the semiconducting elements are diodes.
9. Reflector according to any one of the preceding claims, characterized in that there are at least three control conductors in each half-phase shifter.
10. Microwave antenna with electronic scanning, characterized in that it comprises a reflector (4) according to any one of the preceding claims and a microwave source (1) illuminating the reflector.

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