EP0600799A1 - An active antenna with variable polarisation synthesis - Google Patents

Abstract

The invention relates to a UHF transmission/reception (T/R) circuit for an array antenna with polarisation synthesis, especially for a radar antenna. According to the invention, the required polarisation is obtained by applying two signals to a radiating element of the antenna, on two orthogonal access channels, having a controllable phase shift between the two channels, and the two channels operating simultaneously. In a preferred embodiment, the two transmission channels are equipped with two power amplifiers which each amplify a signal originating from an in-phase power divider or from a hybrid coupler, with a phase shift controllable by one or two bits, which adds a phase shift of 0, 90 or 180@, allowing the synthesis of orthogonal, linear or circular polarisations. According to one preferred embodiment, the circuit according to the invention is produced wholly or partly in monolithic (MMIC) technology. The invention relates also to an antenna including a T/R circuit having the above characteristics. <IMAGE>

Description

The invention relates to active antennas, which consist of a large number of radiating sources excited by microwave power amplifiers in transmission, or whose received signals are amplified by low noise amplifiers on reception. Such antennas are used in various applications such as telecommunications or radars; the invention will be particularly advantageous for radars. In the radar field, in fact, the usual architecture of a monostatic radar implies the use of a transmission channel and a reception channel which terminate on the same radiating source. Usually, a switch allows the selection of the transmission channel to transmit a radar signal in pulses, the time space between the transmission pulses being used to listen, by selecting the reception channel, the radar echoes which return. of the environment.

In the telecommunications sector, the increase in demand means that we are seeking better use of the radio spectrum. This concern results in the use of fine, orientable, and sometimes even polarized beams to allow the reuse of frequencies. These characteristics can advantageously be combined in realizations of array antennas. The invention will find an application in such telecommunications antennas, designed more particularly but not exclusively for transmission.

In the field of multistatic radars, transmitting and receiving antennas are spaced from one another, sometimes by the tens or even hundreds of kilometers. Network antennas can be designed to fulfill the two missions, transmission and reception, or they can be designed to fulfill only one of these two missions. A variant of the invention will be applicable for each of these possibilities.

The design of active antennas for monostatic radars has evolved considerably in recent years, and in the current state of the art, the radiating sources are connected to active transmission / reception modules (MAER or T \ R in English), produced in MMIC technology (Monolithic Microwave Integrated Circuits) or in hybrid technology. The transmission / reception switching is generally included in the active module, a schematic diagram of which is given in FIG. 1, with its location within the antenna.

FIG. 1 schematically shows an active radar antenna, operating alternately in transmission and in reception. The alternation of the transmission / reception functions is ensured by switches 25, 52 controlled by a synchronization clock 24. In this FIG. 1, orthogonal polarizations can be selected by the switch 26, for reception as for transmission. The phase and the gain are controllable by control means 23, both in transmission and in reception. The command values which will be supplied for controlling a given reception channel are not necessarily the same as for the same channel used for transmission.

à ${\text{S}}_{\text{ij}}^{\text{k}}$

, m' étant le nombre de colonnes de sources, dont seule la première et la deuxième sont (partiellement) représentées.In FIG. 1, a single active transmission / reception module is shown, comprising the controllable phase shifter 27 and a controllable attenuator 28, for adjusting the gain of the module. However, an active module is needed per channel and, in this example, there are several channels, each channel being connected to a radiating source composed of K elementary radiators. ${\text{S}}_{\text{ij}}^{\text{1}}$

at ${\text{S}}_{\text{ij}}^{\text{k}}$

, m 'being the number of source columns, of which only the first and the second are (partially) represented.

In transmission mode, the transmitter 21 supplies its signals to a distributor / combiner 22, which supplies the active I / O modules. The phase and the attenuation of the signal will be determined by the controllable phase shifter 27 and the controllable attenuator 28, according to the instructions. given by the control computer 23. Next, the switches 25 and 52 will be controlled by the clock 24 to engage the power channel, and the signal will be amplified by the power amplifier 29, before being sent to the sources radiant S _ij .

In reception mode, the receiver 31 receives the signals from the combiner / distributor 22, which are routed by the active E / R modules. In the E / R modules, the signals coming from the radiating sources S _ij are switched by the switches 25, 52 on the reception channel and pass through a low noise amplifier 30. Then, the phase shift and the attenuation are applied by the controllable phase shifter 27 and the controllable attenuator 28, controlled by the control computer 23.

This configuration allows the electronic scanning of the beam, in transmission and in reception thanks to the controllable phase shifters. The beams can also be formed, for example with steep flanks and weak side lobes, to improve the performance of the antenna with regard to the ambiguities of echoes, and in the presence of noise sources, thanks to the controllable phase shifters and attenuators. Finally, thanks to the switches 26, one of the two orthogonal polarizations can be selected, advantageous for the radar because the useful signal and the noise have different variations according to the polarization, which allows an optimization of the signal to noise ratio by acting on polarization.

   M est le facteur de mérite de l'antenne ;
   N est le nombre d'amplificateurs de puissance ;
   P_e représente la puissance émise par chaque amplificateur
   L_e représente les pertes après le (ou les) amplificateur(s) de puissance ;
   D_e et D_r représentent les directivités des diagrammes générés par le réseau des éléments rayonnants, respectivement en émission et en réception ;
   L_r représente les pertes avant le (ou les) amplificateur(s) faible bruit en réception ;
   FB représente le facteur de bruit de la chaîne réception. Si le gain du premier amplificateur faible bruit est suffisant, le facteur du bruit de la chaîne de réception est pratiquemet égal au facteur du bruit de l'amplificateur faible bruit.In fact, the performance of a radar is essentially characterized by a link budget which determines the ratio of useful signal to undesirable noise. The terms which depend on the microwave part of the radar are as follows: $${\text{M = NP}}_{\text{e}}{\text{- L}}_{\text{e}}{\text{+ D}}_{\text{e}}{\text{+ D}}_{\text{r}}{\text{- L}}_{\text{r}}\text{- FB; or :}$$

M is the antenna merit factor;
N is the number of power amplifiers;
P _e represents the power emitted by each amplifier
L _e represents the losses after the power amplifier (s);
D _e and D _r represent the directivities of the diagrams generated by the network of radiating elements, respectively in transmission and in reception;
L _r represents the losses before the low noise amplifier (s) on reception;
FB represents the noise factor of the reception chain. If the gain of the first low noise amplifier is sufficient, the noise factor of the reception chain is practically equal to the noise factor of the low noise amplifier.

It follows that, in order to have the best merit factor, it is sought to minimize the losses and the noise factor of the reception chain, while optimizing the transmitted power and the directivity of the radiation patterns. For a given elementary power P _e from a source of the network, the directivities as well as the term in N · P _e can be optimized with a larger number of sources.

The elementary sources, in the context of the present invention, are radiating elements capable of providing polarized radiation, the polarization of which can take at least two orthogonal values, for example horizontal (H) and vertical (V), or even circular polarizations right and left (R, L).

Cornets with square, circular or hexagonal mouths are radiating elements which can generate H or V polarizations. They are particularly suitable for high power antennas where ground is not a criticized element.

The printed radiating elements (known to a person skilled in the art by the English name "patch") are metal blocks photoetched on a thin dielectric substrate. with low microwave losses. They allow the production of radiant panels comprising a large number of elementary sources, these panels can be thin, light, and even conformable. To generate orthogonal polarizations with patches, it is enough to excite them by two points offset by 90 ° from the center of the patch, as shown in Figure 1. The connection between the MAER and the patch can be in coaxial line or in microstrip, for example. If a single MAER must control several patches, they can be grouped into sub-networks, connected to the MAER by microstrip online distributors for each H and V polarization.

To generate circular polarizations radiated by patches, it suffices the same excitations as those which are necessary to generate linear orthogonal polarizations; only the linear orthogonal excitations must be offset by 90 ° in phase, in addition to their physical offset by 90 ° around the center of the patch. This is easily obtained by using a 90 ° hybrid coupler, placed between the MAER and the patch, whose excitation on one of its inputs gives us the right circular polarization, and on the other of its inputs gives us the polarization left circular.

To excite horns in circular polarizations, it is known to use excitation by means of such orthomodes and polarizers. These techniques are well known to those skilled in the art, and it will not be necessary to explain them further for the proper understanding of the present invention.

Compared to the configuration of FIG. 1, it is known to make some modifications making it possible to improve the merit factor of the antenna by reducing the losses of the circuit between the sources of the antenna and the amplifiers. On the one hand, the E / R (transmit / receive) switches closest to the sources (item 52 in FIG. 1) can be replaced by circulators, more bulky and heavier, but with lower losses and better power handling. On the other hand, the switching between H and V polarizations can be carried out upstream of the power amplifier, as shown in FIG. 2. The losses L _e and L _r are thus reduced, but these chains must then be doubled amplification, as we see in Figure 2.

In Figure 2, we see that the same elements have the same references as in Figure 1; only the marks associated with one or the other of the amplifying chains carry indices which indicate to us their membership: the index "a" for the chain H, and the index "b" for the chain V. The command phase and amplitude attenuation is always performed by the control means 23, and the control of the H or V polarization, as well as the transmission or reception selection emanate from the clock 24, the output of which is connected to the polarization switch 26 and to the two E / R switches 25a, 25b.

quand elles sont alimentées par les amplificateurs de puissance, en cas de désadaptation de l'antenne. Ces moyens de protection sont des commutateurs 32a, 32b placés en shunt vers la masse, sur les entrées des amplificateurs faible bruit. Ces commutateurs sont également commandés par l'horloge 24, en même temps et en synchronisation avec les commutateurs E/R 25a, 25b. Les isolateurs facultatifs 33a, 33b, permettent d'évacuer vers la masse la puissance réfléchie (une deuxième fois) par ces moyens de protection 32a, 32b.The circuit of FIG. 2 furthermore comprises additional protection of the low noise amplifiers against possible untimely reflections coming from radiating sources. ${\text{S}}_{\text{ij}}^{\text{k}}$

when they are powered by power amplifiers, in case of antenna mismatch. These protection means are switches 32a, 32b placed in shunt to ground, on the inputs of the low noise amplifiers. These switches are also controlled by the clock 24, at the same time and in synchronization with the E / R switches 25a, 25b. The optional insulators 33a, 33b allow the reflected power (a second time) to be evacuated to ground by these protection means 32a, 32b.

In the transmission position of these switches 25a, 25b, one or the other of the power microwave amplifiers, 29a or 29b, will be activated, depending on the position of the polarization switch 26.

The microwave circulators 52a, 52b advantageously replace, on the amplifier chains H, V respectively, the switch 52 of the MAER of FIG. 1. The insertion losses of the circulators are lower than the losses caused by the conventional switches used in the MAERs.

In the reception position of these switches 25a, 25b, and possibly 32a, 32b, one or the other of the low noise microwave amplifiers, 30a or 30b, will be activated, depending on the position of the polarization switch 26.

In these systems known from the prior art, as we have presented them, there remain significant drawbacks due to the various switches necessary to effect either transmission, reception, or in H polarization, or in V or else in circular polarization D, ie in G.

If, according to a first solution of the prior art, the switches are located between the amplifiers and the radiating elements (FIG. 1), they severely strain the radar link budget (or the merit factor of the active antenna) , by their losses L _e and L _r which occur twice, in transmission and reception.

If, on the contrary and according to a second solution of the prior art, the switches are placed upstream of the power amplifiers, and downstream of the low noise amplifiers (FIG. 2), this first problem is avoided, but in this case it two amplifiers of each type are required for each radiating source, of which only one of the four operates at a given time, in turn according to the polarization and according to the emission or reception. The size and mass of the MAER are increased, without the power being. The merit factor is increased by the decrease in losses, since there is no longer a high level bias switch. This is particularly disadvantageous for embedded missions, all the more so for satellites than for aircraft. In addition, the MAERs in Figure 2 are likely to cost almost twice as much as those in Figure 1.

The invention overcomes these disadvantages of the prior art. According to the invention, a configuration of MAER is proposed which avoids the losses of the switches of the first solution, without increasing the mass and the bulk of the assembly, at equal power, as in the second solution.

For these purposes, the invention provides an alternating transmission and reception (E / R) microwave circuit for synthesis antenna with variable polarization synthesis, this E / R circuit able to supply excitation signals for at least two polarizations. orthogonal to radiating sources via two respective channels, these channels supplied respectively by two amplifying power transmission chains; this E / R circuit able to receive at least two signals having orthogonal polarizations detected by these same sources and supplying two low noise amplifier chains on reception; said E / R circuit comprising, in addition to the phase shifter located on the common channel intended to point or form the beam, at least one phase shifter controllable on a transmission channel, and at least one phase shifter controllable on a reception channel intended to choose the polarization ; said circuit characterized in that the two power amplifier chains operate simultaneously during transmission, and in that the two low noise amplifier chains operate simultaneously during reception.

According to a preferred characteristic, the polarizations H (horizontal) and V (vertical) are obtained by sum or difference of two orthogonal polarizations, inclined by 45 ° with respect to the horizontal: each of them is connected directly to one of the two-way E / R circuit.

According to an advantageous embodiment, the two power amplifying chains are supplied from a power divider in phase, allowing easy synthesis of orthogonal linear polarizations; according to another advantageous embodiment, the two power amplifying chains are supplied from a hybrid coupler with two outputs phase-shifted by 90 °, allowing easy synthesis of circular polarizations.

According to one characteristic, said phase shifters are digital controllable phase shifters of one bit, this bit corresponding according to its value, either to 0 °, or to 180 °.

According to a variant, said phase shifters are digital controllable phase shifters of one bit, this bit corresponding according to its value to either 0 ° or 90 °.

According to another characteristic, said phase shifters are two-bit digital controllable phase shifters, a first bit corresponding according to its value either to 0 or 180 ° and a second bit corresponding according to its value either to 0 ° or 90 °.

In this case, one of the following four polarizations is synthesized: linear H or V, circular right or left.

According to an advantageous embodiment, a variable attenuator makes it possible to adjust the gain of at least one power amplifier chain.

According to another advantageous embodiment, a variable attenuator makes it possible to adjust the gain of at least one low noise amplifier chain.

According to an efficient embodiment, said E / R circuit further comprises at least two phase shifters and at least two attenuators that can be controlled almost continuously, allowing the synthesis of any polarization, linear, circular, or elliptical.

According to a particular variant, said quasi-continuous control of the phase shifters and attenuators is of analog design.

According to a complementary variant, said quasi-continuous control of the phase shifters and attenuators is digital design, with a high number of bits, allowing the synthesis of any polarization, linear, circular, or elliptical.

The invention also relates to an antenna comprising E / R circuits according to one of the preceding embodiments or variants.

According to a variant of the antenna of the invention, the radiating sources are of the printed type (or patch in English).

According to another variant of the antenna, the radiating sources consist of annular slots photo-etched on one face of a dielectric substrate having low microwave losses, these slots being excited by lines photo-etched on the opposite face.

According to another variant of the above, the annular slots are excited by photo-etched lines on a suspended substrate.

According to one characteristic, the E / R circuits are produced in MMIC technology.

Alternatively, miniature circulators are added to MMIC circuits to increase the maximum allowable power.

According to a preferred embodiment, miniature duplexers comprising a circulator and an isolator are added to the circuits of the invention, in order to better isolate the transmission channels from the reception channels.

According to a last embodiment, the antenna according to the invention is self-adaptive in polarization, in order to be able to extract a useful radar signal in the presence of interference of any fixed polarization; to do this, the antenna detects the polarization of the jammer, and adapts the phases and possibly the amplitudes of the signals transmitted to work in a polarization orthogonal to that of the jammer.

• La figure 1, déjà décrite, représente schématiquement un exemple d'architecture d'une antenne active pour radar de l'art antérieur travaillant en polarisations linéaires orthogonales, avec ses MAER et ses sources rayonnantes ;
• La figure 2, déjà décrite, représente schématiquement un exemple d'un circuit E/R de l'art antérieur, ayant des pertes plus faibles que le circuit de la figure 1 ;
• La figure 3 représente schématiquement un exemple de circuit MAER selon l'invention ;
• La figure 4 représente schématiquement un deuxième exemple de circuit MAER selon l'invention, comprenant en plus les caractéristiques de la figure 2 ;
• La figure 5 représente schématiquement une variante de l'invention, capable de synthétiser une polarisation quelconque.
• La figure 6 représente schématiquement comme une variante de l'invention, un circuit hyperfréquence d'émission ou de réception, à synthèse de polarisation variable.

Other characteristics and advantages of the present invention will emerge from the detailed description which follows, with its annexed figures including:

• FIG. 1, already described, schematically represents an example of architecture of an active antenna for radar of the prior art working in orthogonal linear polarizations, with its MAERs and its radiating sources;
• FIG. 2, already described, schematically represents an example of an E / R circuit of the prior art, having lower losses than the circuit of FIG. 1;
• FIG. 3 schematically represents an example of a MAER circuit according to the invention;
• FIG. 4 schematically represents a second example of a MAER circuit according to the invention, further comprising the characteristics of FIG. 2;
• FIG. 5 schematically represents a variant of the invention, capable of synthesizing any polarization.
• FIG. 6 diagrammatically represents, as a variant of the invention, a transmission or reception microwave circuit, with variable polarization synthesis.

All the figures are given by way of non-limiting examples; a person skilled in the art will be able to learn from it the information he needs to generalize these examples to many other embodiments, without going beyond the ambit of the invention.

In all the figures, the same references designate the same elements, these elements being microwave functions, organized in a schematic flow diagram of the circuit. In the case where a function can be performed by one, among several components with a view to a similar result, this is indicated in the description which follows. Likewise, the figures represent general diagrams, therefore other variants on these diagrams can be produced without departing from the scope of the invention.

In FIG. 3, we see a first schematic example of a MAER circuit according to the invention. Compared to Figures 1 and 2 already described, we have simplified the diagram by ignoring the environment of the circuit shown; nevertheless, this circuit is intended to be installed in the same way as the circuits of the prior art, between a distributor / combiner (22 in FIG. 1) and a network of radiating sources S _ij . As in the previous figures, the variable attenuator 28 and phase shifter 27 are controlled by instructions given by the control computer (not shown), and the E / R switch 6 is controlled by a clock (not shown). The elements 35a, 35b correspond either to the E / R switches (52 in FIG. 1), or to the circulators (52a, 52b in FIG. 2), the function of which in both cases is to pass either the transmission power between the power amplifiers 29a, 29b and the corresponding radiating source S _i j, ie the reception signal between the radiating source S _ij and the low noise amplifiers 30a, 30b.

The elements 5a are distributors and the elements 5b are combiners, the nature of which will be discussed below.

The elements 1, 2, 3, 4 are phase shifters, including at least one phase shifter controllable on a transmission channel (s₁ or s₃), and at least one phase shifter controllable on a reception channel (s₂ or s₄). According to the invention, it is therefore possible that there are only two controllable phase shifters, for example 3 and 4, and that the elements 1, 2 can be removed from this diagram. Several variants of the invention can be built around this general diagram, in particular by playing on the different possibilities for these elements 1, 2, 3, 4; a number of these possibilities will be described later.

In a first variant of the invention, the element 5a is a power distributor and the element 5b is a power combiner, both operating in phase, that is to say that the phase of the signals s₁ and s₃ is the same, and that the signals s₂ and s₄ are combined in phase also. In this first variant, the simplest embodiment according to the invention, the elements 1 and 2 does not exist; and elements 3 and 4 are single-bit phase shifters, which introduce a phase shift of either 0 ° or 180 °, depending on the value of the control bit, supplied by control means not shown.

montrée sur la figure 3 est un "patch" gravé de forme carrée, dont l'orientation est significative de façon schématique. En effet, le carré est orienté avec ses diagonales respectivement à l'horizontale et à la verticale. Les lignes de propagation provenant des commutateurs ou circulateurs 35a, 35b vers le patch sont mutuellement perpendiculaires et orientées à 45° des diagonales du patch.The radiant source ${\text{S}}_{\text{ij}}^{\text{k}}$

shown in Figure 3 is an etched "patch" of square shape, the orientation of which is schematically significant. Indeed, the square is oriented with its diagonals respectively to the horizontal and to the vertical. The propagation lines coming from the switches or circulators 35a, 35b towards the patch are mutually perpendicular and oriented at 45 ° from the diagonals of the patch.

In an ideal circuit according to FIG. 3, ignoring the insertion losses and propagation delays in the phase shifters 3 and 4, the amplitude of the signals s₁ and s₃ is the same, and the signals s₂ and s₄ have the same amplitudes as well. If the phase shifter 3 is controlled, according to its control bit, at a value of 0 °, the two accesses are excited in phase by the two power amplifiers 29a, 29b, which results in a wave having a horizontal linear polarization. If on the other hand the phase shifter 3 is controlled, according to its control bit, at a value of 180 °, the two accesses are excited in phase opposition by the two power amplifiers 29a, 29b, which results in a wave having a polarization vertical linear.

In the same way for reception, if the phase shifter 4 is controlled, according to its control bit, at a value of 0 °, the two accesses which are excited in phase, and after amplification by the two low noise amplifiers 30a, 30b, are combined in phase by the combiner 5b, which corresponds to a wave having a linear polarization horizontal at the reception. If on the other hand the phase shifter 4 is controlled, according to its control bit, at a value of 180 °, the combiner 5b will have on its inputs the two signals s₂ and s₄ whose signal s₄ will have been subjected to a phase shift of 180 °, which means say that, only if the two accesses are excited in phase opposition, and after amplification by the two low noise amplifiers 30a, 30b, the result is obtained which corresponds to a wave having a vertical linear polarization.

In practice, to succeed exactly in the vector synthesis of the desired polarizations as described in the preceding paragraphs, it is necessary to take into account the insertion losses of the phase shifters 3, 4, as well as the gains and phases of insertion of the amplifiers 29a, 29b and 30a, 30b. For example, the real amplifiers will be paired (29a, b and 30a, b) so as to have the same gain and the same insertion phase, and the loss of the phase shifters 3,4 is compensated by a slight imbalance of the dividers 5a / Combiners 5b: for example if the phase shifters lose 1 dB, the dividers / combiners are designed to present the same difference between the amplitude of their two outputs / inputs (respectively). It should also be noted that the two states 0 and 180 ° of the phase shifters must have the same insertion loss, which is commonly achieved by those skilled in the art, whatever the technology used for these phase shifters. In the case where pairing of two amplifiers with the same gain and insertion phase would prove difficult (MMIC technology, for example), the balancing of the two channels must be carried out using the adjustment devices of these parameters, which will be added to the schematic circuit of Figure 3.

The schematic circuit of FIG. 3 can also provide orthogonal circular polarizations, with hybrid couplers at 90 ° 5a, 5b in place of the phase dividers / combiners considered above. With a hybrid coupler 5a on the transmission path, for example, the two power amplification chains will carry the same signal, except that the signal s₃ will be offset by + 90 ° in phase, compared to the signal s₁ (when the phase shifter 3 has a value of 0 °). Excitation of the patch by two orthogonal accesses, with a signal s₃ on the first access, offset by + 90 ° in phase with respect to the signal s₁ on the second orthogonal access, results in a wave having a right circular polarization, for example . By switching the control bit of the phase shifter 3, a phase shift of 180 ° is obtained on the signal s₃, which is equivalent to an offset of -90 ° with respect to the signal s₁. The result will be a radiated wave with a left circular polarization.

The reception channel can synthesize waves with right and left circular polarization in the same way, the design being perfectly symmetrical between the transmission and reception channels.

We have seen in this first example, the characteristics of the circuit according to the invention which give it its advantages compared to the prior art: the two amplification channels in parallel operate simultaneously, in transmission as in reception. This allows to obtain twice the power of the configuration of the prior art. In addition, the losses of the dividers and phase shifters do not intervene, neither in the radar link budget, nor in the figure of merit of the antenna, because they are located upstream of the power amplifiers in transmission, and downstream of the low noise amplifiers in reception.

Still with respect to this FIG. 3, we will discuss other possible variants of embodiments according to the invention. For example, it is obvious that the elements 35a, 35b can be E / R switches controlled by the clock (not shown), or they can be circulators, which allow the signal to pass through power amplifiers 29a, 29b to the radiating source S _ij , or vice versa, from the source S _ij to the low noise amplifiers 30a, 30b, but in no case will the signal be allowed to pass from power amplifiers 29a, 29b to low noise amplifiers 30a, 30b.

Still according to another variant of FIG. 3, the circuit can be endowed with the capacity to synthesize either orthogonal linear polarizations or orthogonal circular polarizations. To do this, it suffices to put phase shifters with two control bits in blocks 3, 4 on the diagram, with dividers / combiners in phase for the elements 5a, 5b. The first control bit, depending on its value, will give a phase of 0 ° or 180 ° as before, and to this phase will be added the phase controlled by the second control bit, of 0 ° or 90 °. If the second bit commands a phase shift of 0 °, we find ourselves in the previous case of orthogonal linear polarizations; if, on the other hand, the second control bit designates a 90 ° phase shift, the circuit is equivalent to that discussed before where the elements 5a, 5b were 90 ° hybrid couplers, that is to say that we find ourselves in a configuration which allows us to synthesize right and left circular polarizations.

We can obtain the same performances with an alternating circuit, in which the elements 5a, 5b are hybrid couplers at 90 °, and we put phase shifters 0 or 90 ° with a control bit on boxes 1, 2 of figure 3 , and phase shifters 0 or 180 ° with one control bit in boxes 3, 4 of the same figure. The result is identical to the result of the previous paragraph. This configuration makes it possible to obtain an additional production advantage, if the losses of the phase shifters 1, 2, 3, 4 are the same, since the hybrid couplers 5a, 5b can in this case be balanced couplers, more common components than unbalanced couplers.

This last observation leads us to give two more variants of the invention, still according to the FIG. 3. A variant allowing the synthesis of orthogonal linear polarizations, comprises two hybrid couplers 90 ° 5a, 5b, and four phase shifters 0 or 90 ° with a control bit 1, 2, 3, 4. As in the first variant described, a horizontal emission polarization is obtained if the phase shifter 1 has a phase shift of 0 ° and the phase shifter 3 has a phase shift of 90 ° (which is added to the 90 ° phase shift of the hybrid coupler); with the same thing on reception, with 0 ° on the phase shifter 2, and 90 ° on the phase shifter 4. The vertical polarization is obtained by reversing the phase shifts of the four phase shifters. As in the previous case, the realization can be simplified by the fact that with identical phase shifters on the four channels, it suffices to select components having the same losses and insertion phases to approach the ideal synthesis circuit of polarizations.

A last variant of Figure 3 will be to synthesize orthogonal circular polarizations, using the same trick as in the previous case: four phase shifters 1, 2, 3, 4 at 0 or 90 ° and at a control bit, but with dividers / combiners in phase 5a, 5b. In this case, a right circular polarization is obtained with a phase shift of 90 ° on the phase shifters 1, 3 and 0 ° on the phase shifters 2, 4; and conversely, a left circular polarization is obtained with a phase shift of 90 ° on the phase shifters 2, 4 and 0 ° on the phase shifters 1 and 3.

In FIG. 4, we see another variant of an E / R circuit according to the invention, or we have added to the circuit of the invention according to FIG. 3, the characteristics of the prior art according to FIG. 2. More precisely, to reduce the losses associated with switches in position 35a, 35b in FIG. 3, we have inserted circulators 52a, 52b in their place. This corresponds to one of the variants already discussed in the context of FIG. 3. But in addition to this, we have inserted, in the reception channel, protection against possible reflections from antenna mismatches. This protection is provided by switches 32a, 32b which are controlled by the clock to connect the inputs of the low noise amplifiers to ground during transmission. An additional advantage is obtained by the insertion of a second circulator on each reception channel 33a, 33b to evacuate any reflections coming from these switches 32a, 32b when they are closed, because possible reflections at this location would reduce the power especially if the direct and reflected signals combine in phase opposition.

In FIG. 5, the most general embodiment of a polarization synthesis circuit according to the invention is diagrammatically seen. Indeed, this circuit is capable of synthesizing any polarization: linear, circular or elliptical with arbitrary axes, and can easily pass among these possibilities by means of commands supplied to its phase shifters 27a, 27b and its attenuators 28a, 28b controllable from almost continuously. In this way, the instantaneous orientation of the polarization vector is given by the relative phases coming from the phase shifters 27a, 27b which can take arbitrary and time-varying values, and the relative amplitude of the signals passing through the variable attenuators can take also arbitrary and time-varying values, to determine the length of each of the two projections of the vector of the electric field, on the two orthogonal axes, corresponding to the polarizations generated on each of the accesses to the radiating elements. The polarization will be linear when this phase shift is 180 °; it will be circular if it is +/- 90 °, and the attenuations of the two channels are equal; we have an elliptical polarization in the case where the phase shift takes a different value, or linear, or else if the attenuations of the two channels are different.

In a practical embodiment of this variant, as shown in FIG. 5, we have chosen a design using two variable attenuators 28a, 28b and two variable phase shifters 27a, 27b. We could, of course, have used four of each with the configuration of Figure 3 or Figure 4, placing them, one of each, in boxes 1, 2, 3, 4 of these Figures 3 and 4. In the configuration of Figure 5 then, we added circulators 7a, 7b to separate the transmission signals from the reception signals according to their direction of propagation in the circuit.

The transmission signal arrives at a power divider, and is sent to the two circulators 7a, 7b after division in phase. Then we have two E / R circuits in parallel, the description of which conforms to the descriptions in the previous figures, with the same references representing the same elements in all the figures. These two circuits deliver signals on two orthogonal accesses to the radiating source S _ij , with a relative phase and a relative amplitude which are determined by the controllable attenuators and phase shifters 28a, 28b, and 27a, 27b respectively.

Conversely, the reception signal from the source S _ij is probed by the two orthogonal ports, and the two received signals are amplified separately by the low noise amplifiers 30a, 30b. Their relative amplitude and their relative phase are adjusted by the controllable attenuators and phase shifters 28a, 28b and 27a, 27b respectively, according to the polarization of the received wave that one wishes to look at. These signals are then transmitted, via the circulators 7a, 7b to separate reception channels for signal processing in an appropriate computer (not shown).

This possibility of synthesis of an arbitrary polarization makes it possible to obtain a self-adapting antenna, that is to say one which can be reconfigured to take account of a environment polluted by intentional or unintentional parasitic emissions. The principle consists of measuring the dominant polarization of the radio environment at the equipment operating frequency band, by putting the attenuators and phase shifters in a reference state. The polarization of the emission is then chosen to be orthogonal to this dominant polarization. This mode of operation can allow considerably improved operation in the presence of intentionally stationary polarization interference, or in the case where unwanted specular reflections mask a radar target of small equivalent surface, but not having a specularity.

In FIG. 6, we have shown schematically a simplest configuration of a microwave circuit according to the invention. Depending on the characteristics of the components used, this circuit will be suitable either for transmitting or for receiving microwave synthesis synthesis signals. Such circuits will find applications for multistatic radar antennas, for example, or even in telecommunications antennas.

According to a first example of implementation of the circuit shown in FIG. 6, this circuit would be intended for amplifying the signals for transmission. A low level signal arriving at the input of the variable attenuator 28, and attenuated by the latter, then propagated through a controllable phase shifter 27, so as to thus adjust the phase and the signal amplitude of this circuit relative to its position in the array of radiating elements of the array antenna (not shown). As in the previous figures (and in particular FIG. 3), the element 5 is a power divider, either a phase divider, or a hybrid coupler having a phase shift of 90 °.

.Blocks 1, 3 represent phase shifters controllable at 0, 1, or 2 bits, having values of phase shift of 0-0 °, 0-90 °, or 0-180 °, as in the description of figure 3. The construction of the circuit is strictly analogous to the description given for this figure 3, as regards the transmission channel . The components 20a, 20b are then power amplifiers, which feed the patches through channels inclined at 45 ° from the horizontal. ${\text{S}}_{\text{ij}}^{\text{k}}$

.

est acheminé par les voies d'accès inclinées à 45° par rapport à l'horizontale, vers les amplificateurs faible bruit 20a, 20b. Ensuite, les signaux amplifiés seront déphasés par 0, 90, 180, ou 270° (=-90°) par les déphaseurs commandables 1, 3 à 0, 1, ou 2 bits de commande. Apres déphasage, les signaux seront combinés soit en phase, soit avec un déphasage de 90°, grâce aux moyens 5 qui sont soit un combineur en phase, soit un coupleur hybride présentant un déphasage de 90° entre ses deux entrées. Les signaux seront ensuite acheminés à travers un déphasage et une atténuation commandable selon la position de l'élément rayonnant dans le réseau de l'antenne réseau.In a second example of implementation of the circuit shown in FIG. 6, this circuit would be intended for amplifying the signals for reception. A very low level signal arriving at the radiating element ${\text{S}}_{\text{ij}}^{\text{k}}$

is routed through the access channels inclined at 45 ° to the horizontal, to the low noise amplifiers 20a, 20b. Then, the amplified signals will be phase shifted by 0, 90, 180, or 270 ° (= -90 °) by the controllable phase shifters 1, 3 to 0, 1, or 2 control bits. After phase shift, the signals will be combined either in phase or with a phase shift of 90 °, by means 5 which are either a phase combiner or a hybrid coupler having a phase shift of 90 ° between its two inputs. The signals will then be routed through a phase shift and a controllable attenuation according to the position of the radiating element in the network of the network antenna.

Of course, the controllable phase shifters can be controlled almost continuously, as in the case of the previous FIG. 5, to allow greater flexibility in the synthesis of polarizations, if necessary.

In the examples shown in the figures, we have used to simplify the presentation, only the square patch as a radiating source, this patch being oriented with its horizontal and vertical diagonals. However, it is understood that the invention is situated at the level of the E / R circuit, and that the radiating sources can be of different types or of different orientations. For example, the patches can be oriented with the horizontal sides and vertical, and fed by orthogonal accesses along their diagonals. As already mentioned, the propagation lines leading to the accesses can also be of different types, for example coaxial, microstrip, triplate, ...

The radiating sources can also be annular slots photo-etched in an upper ground plane, excited by lines directed at 45 ° relative to the directions H and V, located in a lower plane, ie on the other face of the substrate comprising the plane mass and slots; either on a second suspended substrate, the two substrates kept spaced from each other by spacers or by a material having low microwave losses, such as foam or honeycomb. Such constructions of networks of radiating sources and their power supplies are well known to those skilled in the art, and are described for example in the Proceedings of Military Microwaves 1992 , "Antennas for space scatteromertes and SARS", by R. Petersson , the description of the prior art of which forms an integral part of the present application.

Other more conventional elements can also be used, such as horns with square, circular or hexagonal opening, which will be excited in two directions inclined by 45 ° with respect to the H and V polarizations. Another example of a radiating element, for to obtain a wider bandwidth, is the flared slot (in English: "notch antenna"), described in detail in the Proceedings of Antenna and Propagation Symposium, 1974 , IEEE, "A broadband stripline array element", by LR Lewis et al ., of which the description of the prior art forms an integral part of the present application.

The circuits presented by way of example in the figures can also be produced using different technologies without departing from the scope of the invention: if MMIC is a preferred technology for its low mass and size, as well as these production costs which remain Reasonable for large series production, higher transmitting power can be tolerated by using circulators instead of integrated switches downstream of the power amplifiers. The size and mass of these circulators are greater, but the losses are less than the losses of the MMIC switches.

On the other hand, certain performances can be optimized by an implementation in hybrid technology: discrete amplifiers can provide higher powers for transmission, and better noise factors for reception, than integrated amplifiers of MMIC technology. Depending on the implementation technology chosen, different options discussed in the description of Figure 3 will be preferred to others. The ultimate performance can be optimized according to the mission of the antenna, according to the many criteria mentioned. In all cases, the use of the E / R circuit according to the invention brings a significant improvement in the performances obtained, in particular in the ratio of useful signal to noise.

Claims (18)

Alternating transmission and reception (E / R) microwave circuit for a variable polarization synthesized network antenna, this E / R circuit capable of providing excitation signals for at least two orthogonal polarizations to radiating sources via two channels d 'respective access, these access channels supplied respectively by two amplifying power transmission chains; this E / R circuit able to receive at least two signals having orthogonal polarizations detected by these same sources and supplying two low noise amplifier chains on reception; said E / R circuit further comprising at least one phase shifter controllable on a transmission channel, and at least one phase shifter controllable on a reception channel, characterized in that the two power amplifier chains operate simultaneously during transmission, and in that the two low-noise amplifier chains operate simultaneously during reception. Circuit according to Claim 1, characterized in that the said two access channels are connected to radiating sources so as to generate polarizations inclined by 45 ° with respect to the horizontal, which makes it possible, by playing on the phase shifters, to synthesize the classic horizontal H or vertical V polarizations. E / R circuit according to any one of claims 1 or 2, characterized in that said two power amplifier chains are supplied from a power divider in phase, allowing easy synthesis of orthogonal linear polarizations. E / R circuit according to any one of Claims 1 to 3, characterized in that the said two power amplifier chains are supplied from a hybrid coupler with two phase-shifted outputs 90 °, allowing easy synthesis of circular polarizations. I / O circuit according to any one of claims 1 to 4, characterized in that said phase shifters are digitally controllable phase shifters of one bit, this bit corresponding according to its value, either to 0 ° or to 180 °. E / R circuit according to any one of Claims 1 to 4, characterized in that the said phase-shifters are digital controllable phase-shifters of two bits, of which a first bit corresponding according to its value is either 0 ° or 180 °, and a second corresponding bit according to its value either at 0 ° or 90 °, allowing to synthesize one of the following four classic polarizations: linear H or V, circular right or left. E / R circuit according to any one of Claims 1 to 4, characterized in that the said phase shifters are digitally controllable phase shifters of one bit, this bit corresponding according to its value to either 0 ° or 90 °. E / R circuit according to any one of Claims 1 to 7, characterized in that a variable attenuator makes it possible to adjust the gain of at least one of said power amplifier chains. E / R circuit according to any one of Claims 1 to 8, characterized in that a variable attenuator makes it possible to adjust the gain of at least one of said low noise amplifier chains. E / R circuit according to any one of Claims 1 to 9, characterized in that said E / R circuit further comprises at least two phase shifters and at least two attenuators which can be controlled almost continuously, allowing the synthesis of a polarization any, linear, circular, or elliptical. I / O circuit according to claim 10, characterized in that said quasi-continuous control of said phase shifters and said attenuators is of analog design. I / O circuit according to claim 10, characterized in that said quasi-continuous control of said phase shifters and said attenuators is of digital design, with a high number of bits, allowing the synthesis of any polarization, linear, circular, or elliptical . Array antenna with variable polarization synthesis on the radiating elements, characterized in that said antenna comprises transmission / reception circuits in accordance with any one of claims 1 to 12. Array antenna according to claim 13, characterized in that said antenna comprises radiating sources which are of the printed type (or "patch" in English). Array antenna according to claim 13, characterized in that said antenna comprises radiating sources which are annular slots photo-etched on one side of a dielectric substrate having low microwave losses, these slots being excited by lines photo-etched on the opposite side. Array antenna according to claim 15, characterized in that said slots are excited by photo-etched lines on a suspended substrate. E / R circuit according to any one of claims 1 to 12, characterized in that said circuit is produced in MMIC technology. Array antenna according to any one of Claims 13 to 16, characterized in that the said antenna is a self-adapting polarization antenna.

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