EP1133000B1 - Active microwave reflector for antenna with electronic scanning - Google Patents

Description

The subject of the invention is an active microwave reflector with electronic scanning, capable of being illuminated by a wave source microwave to form an antenna.

Electronic scanning antennas are commonly made up of a set of radiating elements emitting a wave microwave whose phase is electronically controllable, independently for each element or group of elements. An antenna whose beam is capable of scanning space in two directions orthogonal (2D) requires a large number of radiating elements; their cost, that of the phase shifters and associated electronics generally makes this very expensive type of antenna.

EP-A-595726 discloses an electronic scanning antenna comprising a network of photodetector phase-shifting elements which can operate in transmission as microwave lens or, with metallization or a network of metallic wires, such as active microwave reflector.

Document FR-A-2 708 808 describes a phase-shifting panel with four phase states and its application to a microwave lens, the panel comprising conductive wires arranged parallel to the direction of the electric field of an incident wave, each wire carrying at at least two diodes mounted in opposition and supplied by control conductors.

The object of the invention is to allow the realization of an antenna with 2D electronic scanning for a cost which is significantly lower, at performance comparable to that of known antennas.

To this end, the antenna according to the invention consists of a source linearly polarized wave wave, illuminating an active reflector microwave. The active reflector according to the invention comprises an assembly of elementary cells each comprising a microwave circuit phase shifter arranged in front of a conducting plane. The phase shifter has conductive wires arranged on a support, the wires each comprising at at least two semiconductor elements with two states, diodes for example, and being connected to conductors enabling the state of the diodes independently of each other, each of the diodes can be in the on or blocked state; we thus obtain four possible states and geometric and electrical characteristics of the cell are such that at each of these states corresponds to a given phase shift value. Finally, between the cells, microwave decoupling means are provided which consist in particular in forming between two neighboring cells, guides waves whose walls are parallel to the polarization of the wave and whose the spacing is such that it prohibits the propagation of the wave.

• la figure 1, le schéma général de l'antenne selon l'invention ;
• la figure 2, un schéma vu de dessus du réflecteur actif selon l'invention ;
• la figure 3, le schéma vu en coupe d'un mode de réalisation du réflecteur actif ;
• la figure 4, un mode de réalisation d'un circuit hyperfréquence utilisé dans le réflecteur actif ;
• la figure 5, le circuit équivalent du circuit hyperfréquence précédent ;
• la figure 6, un mode de réalisation pratique d'un élément de découplage des cellules entre elles ;
• la figure 7, un autre mode de réalisation du circuit hyperfréquence, permettant de réaliser une antenne bi-polarisation.

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

• Figure 1, the general diagram of the antenna according to the invention;
• FIG. 2, a diagram seen from above of the active reflector according to the invention;
• FIG. 3, the diagram seen in section of an embodiment of the active reflector;
• FIG. 4, an embodiment of a microwave circuit used in the active reflector;
• Figure 5, the equivalent circuit of the previous microwave circuit;
• FIG. 6, a practical embodiment of an element for decoupling the cells from one another;
• FIG. 7, another embodiment of the microwave circuit, making it possible to produce a bi-polarization antenna.

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

Figure 1 schematically illustrates the principle used by the antenna according to the invention.

The antenna is formed by a source S of microwave wave O ₁ with linear polarization, parallel to a predefined direction OY, which illuminates an active reflector RA located in a plane, for example XOY containing the direction OY.

The reflector RA is shown diagrammatically in FIG. 2, seen from above (in the XOY plane).

It consists of a set of elementary cells C, arranged side by side and separated by zones 20, used for the microwave decoupling of cells. Each cell is capable of reflect the wave it receives with a controllable phase value electrically, according to a process described later.

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 O ₂ (FIG. 1) in the desired direction.

Figure 3 is a schematic sectional view (in a YOZ plane normal to plane XOY) of an embodiment of the active reflector RA.

The reflector RA is composed of a microwave circuit CH, receiving the incident wave O ₁ , for example substantially planar, and of a conductive plane CC, arranged substantially parallel to the circuit CH, at a predefined distance d from the latter.

The function of the CC conducting plane is to reflect waves microwave. It can be constituted by any known means, for example parallel wires or a sufficiently tight mesh, or a continuous plane. The CH circuit and the CC plane are preferably made on two sides of a dielectric support 32, of the printed circuit type.

The RA reflector further comprises, preferably on the same printed circuit 32, which is then a multilayer circuit, the electronic circuit (components and interconnections) required to control the values of phase. In the figure, there is shown a multilayer circuit whose face front 30 carries the CH circuit, the rear face 31 carries components 132, and the intermediate layers form the plane CC and by example two PI plans for interconnecting components 132 to the CH circuit.

FIG. 4 represents an embodiment of the circuit microwave CH.

The CH circuit consists of elementary phase shifters D made on the surface 30 and separated by decoupling zones. Each phase shifter D, associated with the corresponding part of the DC conductor plane, forms one of the elementary cells C in FIG. 2.

A D comprises one or more wires F (only one in FIG. 4), substantially parallel to the direction OY and each carrying at least two semiconductor elements with two states, D ₁ and D ₂ , for example diodes, for example connected in opposition, for example by their cathode. The supply voltage of the diodes D ₁ and D ₂ is brought by control conductors which are substantially parallel to each other and perpendicular to the wires F, marked CD. There are at least three, or four as shown in the figure, so as to control the diodes independently of one another.

The phase shifters D are surrounded by conductive zones arranged towards their periphery, marked 74 in a direction parallel to OX and 75 in a direction parallel to OY, used for decoupling as explained below.

The CD conductors are connected to the electronic circuit carried by the reflector, via metallized holes 40 (41) made at the level of the conductive zones 75 but of course electrically isolated of the latter (for example for an interruption 43 of the zone 75).

For the clarity of the figures, the surface of the various conductors, for example made in the form of metallic deposits on the surface 30, is shown hatched although not seen in section.

To describe the functioning of a cell, it is first of all necessary to consider the equivalent circuit of a phase shifter D, such that shown in Figure 5.

The incident microwave wave, of polarization (electric field vector) rectilinear and parallel to OY and to the wires F, is received on terminals B ₁ and B ₂ and meets four capacitors C _O , C _I1 , C _I2 , C _I3 in series , connected in parallel on terminals B ₁ and B ₂ . The capacitance C _O represents the linear decoupling capacity between the extreme CD conductors and the conductive zones 74; the capacitance C _I1 is the linear capacitance between the conductors CD surrounding the diode D ₁ , the capacitance C _I3 , the linear capacitance between the central conductors CD, and the capacitance C _I2 , the equivalent of C _I1 for the diode D ₂ .

• 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 diode D1, also represented by its equivalent diagram. The latter consists of an inductor L ₁ , inductor of the diode D ₁ taking into account its connection wire (F), in series with:

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

In the same way, at the terminals of the capacitor C _I2 is connected a diode D ₂ represented by its equivalent diagram. The latter is analogous to that of diode D ₁ , 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 , C _I2 and C _I3 .

The operation of the phase shifter D is explained below by considering, in a first step, the behavior of such a circuit in the absence of the diode D ₂ and the central CD conductors, which returns to the equivalent diagram of the figure 5 to delete the block D _{2 as} well as the capacities C _I2 and C _I3 .

When the diode D1 is forward biased, the susceptance (B _d1 ) of the circuit of FIG. 5 (modified) is written: B d1 = ZC 0 .ω. 1 - LC I1 ω 2 LC I1 ω 2 + LC 0 ω 2 - 1 where Z is the impedance of the incident wave and ω is the pulsation corresponding to the center frequency of the operating band of the device.

We choose for example the parameters of the circuit to have B _d1 ≅ 0, that is to say that, by neglecting its conductance, the circuit is adapted or, in other words, that it is transparent to the wave incident microwave, introducing neither parasitic reflection nor phase shift (d _d1 = 0). More precisely, we choose: LC I1 ω 2 = 1 which leads to B _d1 ≅ 0, whatever the value of the capacity C _{i1 in particular} .

When the diode D ₁ is reverse biased, the susceptance (B _r2 ) of the circuit is written: B Γ1 = ZC 0 .ω. 1 - LC I1 ω 2 + (C I1 / This) LC I1 ω 2 + LC 0 ω 2 - 1 + VS 0 + C I1 VS i

The capacitance C _I1 being fixed previously, it appears that one can adjust the value of the susceptance B _r1 by action on the value of the capacitance C _i , that is to say the choice of the diode D ₁ .

If now, in a second step, we take into consideration the existence of the diode D ₂ and the central CD conductors, we see that, by analogous reasoning, we obtain two other distinct values for the susceptance, depending on whether the diode D ₂ is polarized in direct or reverse.

It thus appears that a phase shifter D can have four different values for its susceptance B _D (denoted B _D1 , B _D2 , B _D3 and B _D4 ) depending on the command (direct or reverse polarization) applied to each of the diodes D ₁ and D ₂ . These values are a function of the parameters of the circuit of FIG. 5, that is to say of the values chosen for the geometric (dimensions, shapes and spacings of the different conductive surfaces) and electrical (electrical characteristics of the diodes) parameters of the phase shifter.

If, now, we study the behavior of the whole cell, i.e. the phase shifter D and the conductive plane CC, we must take into account the susceptance due to the plane CC, brought back into the plane of the phase shifter and marked B _CC , which is written: B CC = -cotg 2πd λ where λ is the wavelength corresponding to the pulsation ω.

The cell susceptance B _C is then given by: B VS = B D + B CC

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

We also know that the phase shift (dϕ) imparted by an admittance (Y) to a microwave wave is of the form: dϕ = 2 arctg Y

It thus appears that, by neglecting the real part of the admittance of a cell, we have dϕ ≅ 2 arctg B VS and that four possible values (dϕ ₁ - dϕ ₄ ) of phase shift per cell 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 evenly distributed, for example but not necessarily: 0, 90 °, 180 °, 270 °.

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

Furthermore, in the case where a cell has more than one wire F charged with diodes, operation and determination of parameters are of the same type, provided that the circuit is modified accordingly equivalent and take into account the interaction between the diode wires.

The active reflector according to the invention also comprises means of decoupling between C cells.

The microwave wave received by the cells is linearly polarized, parallel to the OY direction. It is desirable that this wave does not propagate from one cell to another, in the direction OX. To avoid such propagation, the invention provides for having a conductive zone 75 substantially in the form of a strip, produced by metallic deposition on the surface 30 for example, between the cells, parallel to the direction OY. This strip 75 forms, with the reflective plane CC which is below, a space of the waveguide type whose width is the distance d. According to the invention, the distance d is chosen so that it is less than λ / 2, knowing that a wave whose polarization is parallel to the bands cannot 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 less 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 the phase shifts dϕ ₁ - dϕ ₄ . In addition, the strip 75 must have a width e , in the direction OX, sufficient for the effect described above to be appreciable. In practice, the width e may be of the order of λ / 15.

Furthermore, it can be created parasitically in a cell, a wave whose polarization would be directed in the direction OZ (normal to OX and OY directions). It is also desirable to avoid its spread to neighboring cells.

As for neighboring cells in the OX direction, we can use as shown in Figure 4 the metallized holes 40-41 of connection of CD conductors to the electronic control circuit. In effect, these being parallel to the polarization of the stray wave, they are equivalent to a conductive plane forming shielding if they are sufficiently close together (at a distance from each other much less than the operating wavelength of the reflector), therefore numerous, for the operating wavelengths of the reflector. If this condition is not met, we can of course form holes additional metallized, having no connection function It is note that these metallized holes 40-41 are preferably made at the level of the bands 75 so as not to disturb the operation of the cells.

Finally, with regard to neighboring cells in the direction OY, you can either use metallized holes similar to holes 40-41 but aligned in the OX direction, or have a conductive surface continues in the XOZ plane, as illustrated in Figure 6, where we have shown plates 61 extending parallel to the XOZ plane from of the plane CC (the intersection of these plates 61 with the surface 30 forms zones 74 of FIG. 4). These plates can advantageously be extend beyond the surface 30, over a height which is not critical, which can for example be less than λ / 10, equal to λ / 10 or a few multiples of λ / 10, to improve decoupling.

FIG. 7 represents another embodiment of the circuit microwave CH, allowing to realize a bipolarization antenna.

In this figure, there is shown in perspective a single cell C. The phase shifting circuit carried on the surface 30 of the substrate 32 now consists of two wires F ₁ , F ₂ , each carrying two semiconductor elements such as diodes (D ₁₁ , D ₂₁ , D ₁₂ , D ₂₂ ), connected for example to the same central conductor 71 itself connected by a metallized hole 72 to the electronic circuit for controlling the reflector. Each of the diode wires acts here on the only waves whose polarization has a component which is parallel to them, according to the same process as that which was described previously, subject to taking into account the differences in the geometry of the conductors.

Claims (8)

1. Active microwave reflector, capable of receiving an electromagnetic wave linearly polarized in a first given direction (OY), comprising a set of elementary cells (C) positioned beside one another on a surface,
      each cell comprising a phase-shifter microwave circuit (D) and a conductive plane (CC) that is positioned substantially parallel to the microwave circuit, at a predefined distance (d) from this circuit, characterized in that the predefined distance (d) is less than half the shortest wavelength of the operating band of the reflector,
      the phase-shifter circuit comprising a dielectric support (32), at least one electrically conductive wire (F) substantially parallel to the given direction, positioned on the support and bearing at least two two-state semiconductor elements (D₁, D₂), the wire being connected to control conductors (CD) for the semiconductor elements that are substantially normal to the wires (F), the control conductors being at least three in number in order to control the state of the semiconductor elements independently of one another, and two first conductive zones (74) positioned towards the periphery of the cell so as to be substantially parallel to the control conductors,
      the geometrical and electrical characteristics of the cell being such that, corresponding to each of the states of the semiconductor elements there is a given value of the phase shift (d₁, d₂, d₃, d₄) of the electromagnetic wave that is reflected by the cell,
      the reflector furthermore including an electronic circuit for controlling the state of the semiconductor elements, this being connected to the control conductors, and means of microwave decoupling between the cells, these means comprising a second conductive zone (75) positioned between each cell, parallel to the given direction, this second conductive zone forming, with the conductive plane, a guided space in which the wave cannot propagate.
2. Reflector according to Claim 1, characterized in that the dielectric support (32) is of the multilayer printed circuit type, a first face (30) bearing having the microwave circuit, a first intermediate layer bearing the conductive plane and the second face (31) bearing components of the control circuit.
3. Reflector according to Claim 2, characterized in that the dielectric support (32) furthermore comprises at least one second intermediate layer (PI) bearing interconnections of the control circuit.
4. Reflector according to either of Claims 2 and 3, characterized in that it comprises metallised holes (40, 41), made in the dielectric support (32), in a second direction (OZ), substantially normal to the first direction, at a distance from one another that is far smaller than the electromagnetic wavelength, at least some of these metallised holes providing a link between the control circuit and the control conductors.
5. Reflector according to Claim 4, characterized in that the metallised holes (40, 41) are made in the second conductive zone (75) but without any electrical contact with this zone.
6. Reflector according to one of the preceding claims, characterized in that the first conductive zones (74) are extended by conductive planes (61) substantially perpendicular to the first direction (OY), extending at least between the conductive plane (CC) and the phase-shifter circuit (D).
7. Reflector according to one of the preceding claims, characterized in that the semiconductor elements are diodes.
8. Microwave antenna with electronic scanning, characterized in that it includes a reflector (RA) according to one of the preceding claims and a microwave source illuminating the reflector.

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