EP1157444B1 - Antenna with double-band electronic scanning, with active microwave reflector - Google Patents

Description

The present invention relates to a scanning antenna dual-band electronics, with active microwave reflector. It applies especially for microwave applications requiring two bands emission conditions also subject to very low production conditions costs. It can for example be applied for individual stations of communication with scrolling satellites, and more generally for many types of multimedia applications.

It is known to produce antennas comprising a reflector active microwave. The latter, also called "reflect array" in the Anglo-Saxon literature, is a network with controllable phase shifters electronically. This network extends in a plane and includes a network phase control elements, or phased network, arranged in front of means reflectors, constituted for example by a metallic plane forming a plane of mass. The reflective network notably includes elementary cells each carrying out reflection and phase shift, variable on command electronic, of the microwave wave it receives. Such an antenna brings great beam agility. A primary source, such as a cone, arranged in front of the reflective network emits waves towards the latter microwave.

Mass applications are possible for such antennas, in particular with the advent of interactive multimedia activities via satellite communications networks. To ensure continuity of a communications network, scrolling satellites are arranged around the earth. The ground antennas must follow the satellites. For switch from one satellite to another without phase jumps, the antennas transmit and receive on two frequency bands, with phase shifts different between these two bands.

Document presents scanning antenna electronic likely to operate in two crossed polarizations.

An object of the invention is to produce a scanning antenna dual-band electronics with reflective grating intended in particular for mass applications, and therefore of low production cost.

To this end, the invention relates to a scanning antenna electronic, characterized in that it comprises at least two sources microwave emitting in different frequency bands and having opposite circular polarizations, an active reflective grating comprising elementary cells illuminated by sources and a rotator polarization, interposed between the reflective grating and the sources, transforming circular polarizations into two linear polarizations crossed, an elementary cell comprising two transverse phase shifters, the first phase shifter acting on waves of linear polarization and the second phase shifter acting on the waves of the other linear polarization.

• la figure 1, un exemple de réalisation d'une antenne à balayage électronique à réseau réflecteur actif ;
• la figure 2, par une vue schématique, une illustration du principe de fonctionnement d'une antenne selon l'invention ;
• la figure 3, une vue partielle de la face avant d'un exemple de réseau réflecteur actif utilisé dans une antenne selon l'invention ;
• la figure 4, une vue partielle en coupe d'un exemple de réseau actif utilisé dans une antenne selon l'invention ;
• la figure 5, une vue détaillée en perspective, d'un exemple de réalisation d'une cellule élémentaire d'un réseau réflecteur actif utilisé dans une antenne selon l'invention ;
• la figure 6, à titre d'exemple, une illustration d'une cellule élémentaire munie d'une protection contre les propagations parasites vers et venant de cellules voisines ;
• la figure 7, un schéma électrique équivalent d'un déphaseur d'une cellule élémentaire.

Other objects, features and results of the invention will become apparent with the aid of the description which follows given by way of example and made with reference to the appended drawings which represent:

• FIG. 1, an exemplary embodiment of an electronic scanning antenna with an active reflecting array;
• Figure 2, in a schematic view, an illustration of the operating principle of an antenna according to the invention;
• FIG. 3, a partial view of the front face of an example of an active reflecting array used in an antenna according to the invention;
• Figure 4, a partial sectional view of an example of active network used in an antenna according to the invention;
• FIG. 5, a detailed perspective view, of an embodiment of an elementary cell of an active reflective network used in an antenna according to the invention;
• FIG. 6, by way of example, an illustration of an elementary cell provided with protection against parasitic propagations to and from neighboring cells;
• Figure 7, an equivalent electrical diagram of a phase shifter of an elementary cell.

Figure 1 schematically illustrates an example of realization of an electronic scanning antenna with active reflective array where the microwave distribution is for example of the so-called optical type, that is to say for example ensured using a primary source illuminating the reflective network. For this purpose, the antenna includes a primary source 1, for example a cornet. Primary source 1 emits microwave waves 3 towards the active reflective network 4, arranged in the Oxy plane. This network reflector 4 comprises a set of elementary cells carrying out the reflection and phase shift of the waves it receives. So by order phase shifts printed on the wave received by each cell, it is possible as is known, to form a microwave beam in the direction desired.

An antenna according to the invention comprises at least two elementary sources, for example of reverse circular polarizations, to illuminate the active reflector 4 whose elementary cells moreover have a given architecture. In addition, the two sources emit waves in different frequency bands. Figure 2 schematically illustrates such an antenna. The latter therefore comprises two sources S _D , S _G , for example horns, with respective right and left polarizations. These horns illuminate an active reflective network 4 as described above. A polarization rotation grid 21 is disposed in front of this reflector 4, and interposed between the latter and the sources S _D , S _G. The polarization rotation grid transforms the circularly polarized waves emitted by these sources into linearly polarized waves. An antenna according to the invention may also include elementary linear sources, of crossed polarizations. In this case, there is no need to use a polarization rotation grid.

Figure 3 schematically shows part of the network reflector 4 in the Oxy plane, from a top view, according to F. Le reflector comprises a set of elementary cells 10 arranged side by side side by side and separated by zones 20, used for decoupling cell microwave. These cells 10 carry out the reflection and the phase shift of the waves they receive. An elementary cell 10 includes a phase shifting microwave circuit arranged in front of a plane driver. More specifically, as will appear later, the circuit microwave has two transverse phase shifters, each dedicated to linear polarization.

FIG. 4 is a schematic sectional view, in the Oxz plane, of a possible embodiment of the active reflector 4. The reflector 4 consists of a microwave circuit distributed in the elementary cells 10 and of a conducting plane 42, disposed substantially parallel to the microwave circuit 41, at a predefined distance d. This microwave circuit receives the incident waves, for example substantially planar, emitted by the aforementioned sources S _D , S _G.

The function of the conducting plane 42 is in particular to reflect the microwave waves. It can be constituted by any known means, by example of parallel wires or a sufficiently tight mesh, or a plane continued. The microwave circuit 41 and the conductive plane 42 are of preferably made on two sides of a dielectric support 43, for example of the printed circuit type. The reflector 4 also comprises, preferably on the same printed circuit 43, which is then a multilayer circuit, the circuit electronics required to control phase values. On the face 4, a multilayer circuit is shown, the front face 44 of which carries the circuit microwave 41, the rear face 45 carries components 46 of the circuit aforementioned control electronics, and the intermediate layers form the conducting plane 42 and for example two interconnection plans 47 of the components 46 to the microwave circuit 41.

Figure 5 shows, schematically, an example of production of an elementary cell 10 of an antenna according to the invention. A cell includes a phase shift microwave circuit, forming part of the microwave circuit mentioned in relation to Figure 4. The phase shifter comprises conductive wires 51, 51 ′ arranged on a support, for example on the front face 44 of the multilayer circuit 43. The wires 51, 51 ′ have each at least two semiconductor elements with two states 521, 521 ′, 522, 522 ', diodes for example. The embodiment of Figure 5 is consists of two conductive wires, each comprising two diodes in series, cross-wired and interconnected by a central conductor control 53. The diodes being arranged on the front face of the circuit multilayer, the central conductor 53 is for example itself connected to a metallized hole 531 which connects the conductive wires 51, 51 'to the circuit electronic control arranged on the rear face 45 of the multilayer circuit, via the interconnection circuits. The central conductor 53 is connected to the four diodes 521, 521 ', 522, 522' of the phase shifter, being wired between the two diodes of each of the conductive wires 51. The ends of these the latter are also each connected to a control conductor 54 connected for example itself to a metallized hole 541 made in the circuit multilayer 43. The ends of the conducting wires 51, 51 ′ are thus connected to the electronic control circuit. The state, passing or blocked, of each of the four diodes can then be controlled by the electronic circuit of ordered. Each of the diode wires acts on the only waves whose polarization, i.e. the electric field vector, has a component which is parallel to it. Thus, the polarization rotation grid 21 transforms by example right circular polarization in parallel linear polarization to a conducting wire 51 while it transforms the circular polarization left in a linear polarization parallel to the other conductive wire 51 ', a wire conductor 51 being for example parallel to the direction Ox and the other wire conductor 51 ′ being for example parallel to the direction Oy.

It is desirable that a wave received by a cell elementary 10 does not spread to other neighboring cells. For avoid such propagation, the invention provides decoupling zones 20 which separate the 10 cells. In particular, with regard to a wave microwave received by the elementary cells 10, polarized linearly and parallel to the direction Oy, it is desirable that this wave does not propagate from one cell to another, in the direction Ox. Of even, it is desirable that a received wave linearly polarized at the direction Ox does not propagate from one cell to another in the direction Oy.

Figure 6 shows a possible embodiment of these decoupling zones 20. A decoupling zone 20 surrounding a cell elementary comprises a conductive strip 62. For reasons space but also so as not to disturb the operation of cells, the end conductors 54 which connect the conductive wires to the electronic control circuit are for example preferably located in the conductive strip 62, without however being electrically connected to the latter. For this purpose, provision is made for an interruption of the band around end conductors 54.

The conductive strip 62 is for example produced by deposition metallic on the front face 44, between the cells, parallel to the directions Ox and Oy. This strip 62 forms, with the reflective plane 42 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 tapes cannot be spread in such a space. In practice, the reflector according to the invention operates in a certain band of frequencies and we choose d so that it is less than the smallest of the wavelengths of the two bands. In addition, strip 62 must have a sufficient width for the effect described above to be appreciable. In practical, the width maybe 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 in directions Ox and Oy. It is also desirable to avoid its propagation to neighboring cells. For this, we can use as shown FIG. 6 the metallized holes 541 for connecting the conductors 54 to the circuit control electronics. Indeed, these being parallel to the polarization of the stray wave, they are equivalent to a conducting plane forming a shield if they are close enough (at a distance one of the 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 61, having no connection function. Yes these open into the conductive strip 62, they are then contactless electric with the latter.

To describe the operation of a cell, it is necessary to consider the equivalent circuit of a phase shifter 10 as shown in FIG. 7. The equivalent circuit relates to a conducting wire 51 and its two diodes 521, 522, in fact what corresponds to a phase shifter, associated with a given polarization and therefore with a given frequency band. The incident microwave wave, of linear polarization and parallel to Oy and to the wires 51 is received on terminals B ₁ and B ₂ and meets three capacitors C _o , C _I1 , C _I2 in series, connected in parallel on the terminals B ₁ and B ₂ . The capacitance C ₀ represents the linear decoupling capacitance between the end conductors 54 and the conductive strip 62 of the decoupling zone 20. The capacitance C _I1 is the linear capacitance between the end conductor 54 connected to the first diode 521 and the central conductor 53. The capacitance C _I2 is the linear capacitance between the end conductor 54 connected to the second diode 522 and the central conductor 53.

• 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 521 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 521, also represented by its equivalent diagram. The latter consists of an inductor L, inductor of the diode 521 taking into account its connection wire, in series with:

• either a capacitance C _i1 (diode junction capacitance) in series with a resistor R _i1 (reverse resistance),
• or a resistor R _d1 (direct resistance of the diode), depending on whether the diode 521 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 the second diode 522 represented by its equivalent diagram. The latter is analogous to that of the first diode 521, 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 C _I2 .

The operation of the phase shifter 10 is explained below by considering, in a first step, the behavior of such a circuit in the absence of the second diode 522, which returns to the equivalent diagram of FIG. 7 to remove the 522 as well as the capacity C _I2 .

When the first diode 521 is forward biased, the susceptance B _d1 of the circuit of FIG. 7 (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 one of the two operating bands of the antenna. By way of example, it is considered that the first conducting wire 51 receives the waves emitted by the right circular polarization source S _D.

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 _ϕd1 = 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 first diode is reverse biased, the susceptance B _r1 of the circuit is written: B r1 = 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 521.

If now, in a second step, we take into considering the existence of the second diode 522, we see that, by a analogous reasoning, we obtain two other distinct values for the susceptance, depending on whether diode 522 is forward or reverse bias.

It thus appears that a phase shifter of a cell 10, this phase shifter corresponding to a conducting wire 51, 51 ′, can have four different values for its susceptance B _D (denoted B _D1 , B _D2 , B _D3 and B _D4 ) according to the command (direct or reverse polarization) applied to each of the diodes 521, 522. These values are a function of the parameters of the circuit of FIG. 7, that is to say of the values chosen for the geometric parameters (dimensions, shapes and spacings different conductive) and electrical surfaces (electrical characteristics of the diodes) of the phase shifter. In particular, it is necessary to take into account the definition constraint of the conductive strip 62 mentioned previously when determining the various parameters for fixing the phase shifts d _ϕ1 - d _ϕ4

If, now, we study the behavior of the whole of cell 10, that is to say the phase shifter in association with the conducting plane 42, we must take into account the susceptance due to this plane 42, brought back in the plan of the phase shifter and noted 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 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: d φ ≅ 2 arctg B VS and that four possible values (d _ϕ1 - d _ϕ4 ) 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 d _ϕ1 - d _ϕ4 are _evenly distributed, for example but not necessarily: 0, 90 °, 180 °, 270 °. These four states correspond to a digital control coded on two bits. It is possible to extend a three-bit command corresponding to eight states, phase shifted for example each by 45 °, by adding for example a diode on the conductive wire 51.

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 d _ϕ1 -d _ϕ4 is fulfilled.

The operation of an elementary cell along its second conducting wire 51 ′ can be described in a similar manner, for the waves emitted by the second source, for example S _G , in another frequency band. Thus, according to the invention, the active network 4 is illuminated by two sources S _D , S _G emitting respectively in right and left circular polarization and in two different frequency bands, the polarization rotation grid 21 transforming these two circular polarizations into two crossed linear polarizations allowing the cells of the active network 4 to act independently on two polarizations and in different frequency bands. An elementary cell 10 in fact comprises two transverse phase shifters, preferably controllable, the first phase shifter 51, 521, 522 acting on the waves of a linear polarization and the second phase shifter 51 ', 521', 522 'acting on the waves of the other linear polarization. In particular, to act on a given polarization wave, a phase shifter, and therefore its conducting wire, is substantially parallel to the direction of this polarization. To this end, the polarization rotation grid 21 is arranged in such a way that the linear polarizations obtained from the circular polarizations are very substantially parallel to the phase shifters concerning them.

After reflection and phase shift on the active reflector 4, the waves again cross the polarization rotation grid 21. The crossed linear polarizations then become polarizations again left and right circular, vertical polarization being for example transformed into a right circular polarization and a polarization horizontal being for example transformed into a circular polarization left. The polarization rotation grid can be a rotator of any polarization, in particular, it can be a meandering grid or a wire grid.

The invention advantageously makes it possible to operate on two frequency bands and adjust the phase shifts of the waves reflected by the active network, independently from one band to another. Knowing that these phase shifts determine the direction of the beams emitted by the antenna, it is so easy and quick to change the direction of the beam for the two bands frequencies. This is particularly well suited for tracking traveling satellites arranged around the Earth used in particular for all kinds of multimedia applications. Finally, an antenna according to the invention is well suited for mass use, i.e. intended for a large audience, insofar as it can be carried out at low cost. Indeed, it does not contain expensive or complex components to install artwork. In particular, the active network, consisting of a printed circuit multilayer with components arranged on these front and rear faces is not expensive. In addition, it is perfectly suited to a production of large series. Finally, the polarization rotation grid, used in the case in particular where the elementary sources are polarized circular as is the case for example for applications multimedia is also inexpensive.

Claims (10)

1. Electronic scanning antenna, comprising at least two microwave sources (S_D, S_G) transmitting in different frequency bands, an active reflecting array (4) comprising elementary cells (10) illuminated by the sources (S_D, S_G), characterized in that the waves from the two microwave sources have crossed polarizations, an elementary cell (10) comprising a conducting plane (42) and two transverse phase shifters, the first phase shifter (51, 521, 522) being substantially parallel to one linear polarization and the second phase shifter (51', 521', 522') being substantially parallel to the other linear polarization, the conducting plane (42) being placed substantially parallel to the phase shifters, a phase shifter comprising at least one dielectric support (43), at least one conducting wire (51) placed on the support and bearing at least two semiconducting elements (521, 522) with two states, the wire being connected to control conductors (53,54) of the semiconducting elements connected to an electronic control circuit, the characteristics of the cell being such that a given phase shift value (d_ϕ1, d_ϕ2, d_ϕ3, d_ϕ4) of the electromagnetic wave reflected by the cell (10) whose polarization is substantially parallel to the conducting wire (51), corresponds to each of the states of the semiconducting elements.
2. Antenna according to Claim 1, characterized in that since one of the control conductors (53) is central and each phase shifter comprises two semiconducting elements, the central conductor (53) is connected to the four semiconducting elements.
3. Antenna according to either of the preceding claims, characterized in that the elementary cells (10) are separated by microwave decoupling regions (20), a decoupling region comprising a conducting band (62) surrounding a cell substantially parallel to the polarization directions and forming, with the conducting plane (42), a guided space where a wave of the two frequency bands cannot be propagated.
4. Antenna according to any one of the preceding claims, characterized in that since the support (43) is of the multilayer printed circuit type, a first face (44) of which bears the microwave circuits, a first interlayer bears the conducting plane (42) and the second face (45) bears components (46) of the electronic control circuit.
5. Antenna according to Claim 4, characterized in that the dielectric support (43) comprises in addition at least a second interlayer (47) bearing interconnections of the electronic control circuit.
6. Antenna according to either of Claims 4 and 5, characterized in that the microwave decoupling region (20) comprises plated-through holes (541, 61), made in the dielectric support (43) at a distance one from the other of less than the electromagnetic wavelength.
7. Antenna according to Claim 6, characterized in that some of the plated-through holes (541) provide the connection between the control circuit and control conductors (54).
8. Antenna according to either of Claims 6 and 7, characterized in that the plated-through holes (541, 61) are made in the conducting band (62) but without electrical contact with the latter.
9. Antenna according to any one of the preceding claims, characterized in that the semiconducting elements are diodes.
10. Antenna according to any one of the preceding claims, characterized in that the sources have opposite circular polarizations, it comprises a polarization rotator (21) inserted between the reflecting array (4) and the sources, changing the circular polarizations into two crossed linear polarizations.

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