EP3179557B1 - Multi-band elementary radiating cell - Google Patents

Description

The present invention is in the field of radiating devices designed to operate in two distinct frequency bands. It applies in particular to dual-band radiating cells produced in printed technology, and used by radars with electronic scans for the surveillance of airspace. These radars operate in the S band, and in the band dedicated to IFF applications (English acronym for "Identification, Friend or Foe", or friend or enemy identification).

State-of-the-art electronic scanning radars consist of directional antennas made from radiating elements, or radiating cells, assembled within a network. The modification of the amplitude and the phase of each of the radiating elements of the network makes it possible to orient the direction of the radar beam.

The frequencies of interest for aerial surveillance applications are the S band, used for the primary radar, and in particular the sub-band 2.9GHz to 3.3GHz, as well as frequency bands of a few MHz or tens of MHz located around frequencies 1.03GHz and 1.09GHz, and used for IFF applications. Current radar equipment, whether it be ground speed radars or radars on board a carrier such as a vehicle, ship or aircraft, generally includes two independent systems: a rotary directive antenna dedicated to IFF applications and a array of radiant cells for the Band S radar. The rotary antenna is positioned above or next to the S band radar antenna. The two volumes are therefore added together, which can cause problems during transport or installation of antennas.

The invention seeks to solve the general problem of the multiplication of systems by proposing a radiating cell operating simultaneously and without interference, in two distinct frequency bands, in particular the S-band and the frequency band dedicated to IFF applications. Such a cell makes it possible to create a network radiating dual-band, thereby reducing the overall size of the radar system, as well as the installation complexity and associated usage constraints. The invention proposes a radiating cell for which the accesses to the different frequency bands are independent, which makes it possible to integrate the invention into existing radar devices in a transparent manner.

The use of dual-band or broadband radiating elements within radiating networks is a problem frequently encountered.

It is all the more complex that, when radiating elements are close, strong coupling phenomena appear. These coupling phenomena are all the more marked when the frequency ratio between the high band and the low band approaches an odd whole number. Indeed, the radiating elements are sized relative to the wavelength at which they operate. An element dimensioned to radiate in the low frequency band will generally have a size close to λ _B / 2, with λ _B the maximum wavelength of the low frequency band. Due to the ratio of the frequency bands, its size will also be N.λ _H / 2, with N the ratio of the frequency bands and λ _H the maximum wavelength of the high frequency band in the dielectric. Therefore, when N approaches an odd whole number, the device also radiates for the high frequency band, thus amplifying the coupling phenomena.

The use, within the same radiating cell of elements specific to each of the operating bands, separated by a gap making it possible to minimize the problems of coupling between elements, is not a solution to the problem when the radiating cell is implemented in a radiating network. Indeed, the size of the cell is constrained by the pitch of the lattice of the network, which is generally equal to λ / 2, with λ the wavelength in the air corresponding to the maximum frequency. Thus, when the frequency ratio between the high frequency band and the low frequency band increases, the radiating elements required by the low frequency band become incompatible with the size of this networking step. AT As an example, the step of networking a radiating mesh in S band at 3.3 GHz is around 5 cm. A patch suitable for the band S, when produced in the context of a substrate having a relative dielectric constant of 3.55, has dimensions of the order of 25mm x 25mm, compatible with the pitch of networking. A patch for IFF applications, due to the frequency ratio 3 between the two bands, will be 3 times larger (and with a surface area 9 times greater). It will then have a size of 75mm x 75mm. A device comprising an S band patch and a patch for IFF applications will therefore not be compatible with the pitch of the radiating mesh.

So the patent application US 2003/0164800 A1 presents a tri-band device operating in the AMPS (800-850 MHz), GPS (1.4 GHz) and PCS (1.85-1.99 GHz) bands from a patch antenna and two slots. The ratio of the operating frequencies not being odd multiples, the device does not have means for suppressing interference linked to the coupling between the radiating elements. In addition, the use of a slot tuned to the low frequency band makes it incompatible with its integration into a radiating mesh dimensioned with respect to the high frequency.

The Australian patent AU 2015101429 A4 presents a dual-band device operating in the Wifi bands at 2.4GHz and 5GHz. However, in this device, the frequency ratio is not an odd multiple, so it does not present any particular coupling problems. It also does not have independent access to each of the frequency bands: the radiating elements associated with each of the frequency bands cannot then be controlled independently.

A first known solution to the problem of making a bi-band cell of reduced dimensions consists in using a single broadband radiating element. Once networked, the result is a single broadband network, covering all the bands of interest. However, the production of such a radiating element proves to be complex when the band gap increases, and does not meet the need for independent access to each of the frequency bands.

To respond to the problem of the size of the network, a known solution consists in using, for the low frequency band, elements of the folded monopole or dipole type, or folded slots so as to be able to accommodate them in a reduced surface. The simultaneous use of a patch for the high frequency band, and a slot for the low frequency band is of practical interest, because the slot can be housed in the metallization of the patch, or in that of its plane of mass. Various solutions of this type have been explored, but they run up against the fact that, under these conditions, the radiating slots have a very narrow bandwidth, which limits their advantage.

The article "A Dual Band Quasi-Magneto-Electric Patch Antenna for X-band Phased Array", SE Valavan, Proceedings of the 44th European Microwave Conference 2014 , has overcome this limitation by using the coupling phenomena between the two elements. It proposes to disturb a radiating patch in the high frequency band by means of a slot housed inside the radiating surface of the patch. The response of the device, resulting from the coupling between the two elements, presents an operation in two distinct frequency bands whose central frequencies are distant from a ratio 1.5, but having significant bandwidths (greater than 5%).

• le rapport de bande vaut 1.5, ce qui ne permet pas de répondre aux applications radar Bande S et IFF, pour lesquels le rapport de bande de fréquences vaut 3,
• il ne répond pas au besoin d'avoir deux antennes séparées reliées chacune à un accès distinct, car il propose un système couplé ayant deux bandes de résonnance. Les amplitudes et phases des éléments rayonnants associés à chaque bande de fréquence ne peuvent alors pas être pilotées indépendamment. De plus, l'intégration d'une telle cellule dans des équipements existant requiert la séparation entre ces deux bandes, pour piloter séparément le signal en bande de fréquences haute et basse. Cette séparation requiert la réalisation d'un équipement supplémentaire à l'interface entre le réseau rayonnant et les équipements radio. Elle peut s'avérer délicate, la qualité des signaux résultants dépendant de la propreté du filtrage mis en œ uvre.

However, such a device has two major flaws:

• the band ratio is 1.5, which does not make it possible to respond to Band S and IFF radar applications, for which the frequency band ratio is 3,
• it does not meet the need to have two separate antennas each connected to a separate access, because it offers a coupled system having two resonance bands. The amplitudes and phases of the radiating elements associated with each frequency band cannot then be controlled independently. In addition, the integration of such a cell in existing equipment requires separation between these two bands, to drive the signal in high and low frequency bands separately. This separation requires the realization of equipment additional to the interface between the radiating network and the radio equipment. It can be delicate, the quality of the resulting signals depending on the cleanliness of the filtering implemented.

The invention addresses the problem posed by associating a radiating element in the high frequency band of the patch type, with at least one radiating element in the low frequency band of the folded slot type. This approach makes it possible to house the two radiating elements in a reduced size cell, compatible with a network of unit elements operating at the high frequency, that is to say less than a square with a side less than λ _H / 2.

The elements of the high frequency band (patch) and the low frequency band (slot) are each connected to a separate access, which allows them to be controlled independently in amplitude and in phase. Filters adapted to each of the frequency bands are implemented on each of the ports, so as to eliminate the undesirable contributions linked to the coupling resulting from the proximity between the radiating elements.

The invention therefore consists of a device radiating in two distinct frequency bands according to claim 1.

Advantageously, the slot-type element is housed in a ground plane of the device.

Advantageously, the one or more elements of the folded slot type are folded in a U shape and positioned at the periphery of the device.

According to one embodiment of the device, the number of slot-type elements is equal to the number of sub-bands of the low frequency band, said slot-type elements being supplied by the same second port.

According to another embodiment of the device, the number of slot-type elements is equal to the number of sub-bands of the low frequency band, said slot-type elements being supplied by different ports.

According to another embodiment, the device comprises a single slot-type element supplied by said second access to which it is connected by a resonator circuit, the coupling between said slot and said resonator circuit being adjusted to radiate in two distinct sub-bands of the low frequency band.

Advantageously, in this embodiment, the resonator circuit is a parallel resonator circuit comprising an inductor and a capacitor. The resonator is connected to the slit type element by a waveguide of length λ / 4, where λ is the wavelength associated with the center frequency of the low frequency band.

Advantageously, in all of the embodiments, the filter positioned between the patch-type element and the first access comprises a plurality of sections of microstrip line of different widths.

This property allows it to radiate only for one of the frequency bands when these are multiples of one another.

Advantageously, the device further comprises a low-pass filter positioned between the said slot-type element or elements and said second port, and configured to filter the high frequency band.

Advantageously, the device further comprises a second patch type element suitable for the high frequency band, said second patch type element being disposed above said first patch type element.

The device according to the invention can be implemented in a multilayer printed circuit for which said patch type element, said slit type element (s), and said filter positioned between the patch type element and the first access are in different layers of the circuit board.

This layer distribution makes it possible to limit the surface of the printed circuit as much as possible. It is possible because the radiating elements do not come to hide, the slit type element or elements being positioned on the periphery of the printed circuit, and therefore of the patch type element.

Thanks to the filter element of the high frequency band, the device according to the invention is adapted to operate when at least one frequency of the high frequency band is an odd integer multiple of a frequency of the frequency band low.

The device according to the invention is adapted to operate when the high frequency band comprises the band 2.9GHz - 3.3GHz.

It is also suitable for operating when at least one sub-band of the low frequency band is centered around a frequency chosen from the frequency 1030MHz and the frequency 1090MHz.

The device according to the invention can easily be produced in printed technology.

Finally, the invention relates to a radiating network configured to radiate in two distinct frequency bands, and characterized in that it comprises radiating cells conforming to the radiating device in two distinct frequency bands according to the invention.

It also addresses an electronic scanning radar configured to operate simultaneously in two different frequency bands, and characterized in that it comprises a radiating network as described by the invention.

• La figure 1 représente une cellule rayonnante selon un premier mode de réalisation de l'invention,
• La figure 2 représente la vue en éclaté d'une cellule rayonnante selon le premier mode de réalisation de l'invention,
• Les figures 3a et 3b représentent un exemple de coefficient de réflexion des entrées et de découplage, respectivement dans la bande de fréquences basse et dans la bande de fréquences haute, associés à chaque entrée d'une cellule rayonnante selon le premier mode de réalisation de l'invention,
• Les figures 4a et 4b représentent un exemple de diagrammes de rayonnements de l'entrée associée à la bande de fréquences basse d'une cellule rayonnante selon le premier mode de réalisation de l'invention,
• Les figures 5a et 5b représentent un exemple de diagrammes de rayonnements de l'entrée associée à la bande de fréquences haute d'une cellule rayonnante selon le premier mode de réalisation de l'invention,
• La figure 6 représente une cellule rayonnante selon un deuxième mode de réalisation de l'invention,
• Les figures 7a et 7b représentent un exemple de coefficient de réflexion des entrées et de découplage, respectivement dans la bande de fréquences basse et dans la bande de fréquences haute, associés à chaque entrée d'une cellule rayonnante selon le deuxième mode de réalisation de l'invention,
• Les figures 8a et 8b représentent un exemple de diagrammes de rayonnements de l'entrée associée à la bande de fréquences haute d'une cellule rayonnante selon le deuxième mode de réalisation de l'invention,
• Les figures 9a et 9b représentent un exemple de diagrammes de rayonnements de l'entrée associée à la bande de fréquences haute d'une cellule rayonnante selon le deuxième mode de réalisation de l'invention,
• La figure 10 représente une cellule rayonnante selon un troisième mode de réalisation.

The invention will be better understood and other characteristics and advantages will appear better on reading the description which follows, given without limitation, and thanks to the appended figures among which:

• The figure 1 represents a radiating cell according to a first embodiment of the invention,
• The figure 2 represents the exploded view of a radiating cell according to the first embodiment of the invention,
• The Figures 3a and 3b represent an example of reflection coefficient of the inputs and of decoupling, respectively in the low frequency band and in the high frequency band, associated with each input of a radiating cell according to the first embodiment of the invention,
• The Figures 4a and 4b represent an example of radiation diagrams of the input associated with the low frequency band of a radiating cell according to the first embodiment of the invention,
• The Figures 5a and 5b represent an example of radiation diagrams of the input associated with the high frequency band of a radiating cell according to the first embodiment of the invention,
• The figure 6 represents a radiating cell according to a second embodiment of the invention,
• The Figures 7a and 7b represent an example of reflection coefficient of the inputs and of decoupling, respectively in the low frequency band and in the high frequency band, associated with each input of a radiating cell according to the second embodiment of the invention,
• The Figures 8a and 8b represent an example of radiation diagrams of the input associated with the high frequency band of a radiating cell according to the second embodiment of the invention,
• The Figures 9a and 9b represent an example of radiation diagrams of the input associated with the high frequency band of a radiating cell according to the second embodiment of the invention,
• The figure 10 represents a radiating cell according to a third embodiment.

The descriptions of the embodiments set out below are dedicated to a particular mode of operation of the invention. This operating mode meets the needs of radar applications for airspace surveillance. The radiating cell presented below seeks to operate in a dissociated manner in the band 2.9GHz - 3.3GHz (sub-band of the S band dedicated to radar applications), as well as in two sub-bands of a few MHz in the frequency band dedicated to IFF applications, a first centered around the 1030MHz frequency and a second centered around the 1090MHz frequency. These two sub-bands correspond to the outward and return paths of the IFF applications.

However, the invention is not limited to this operation or to this type of application, and can be extended mutatis mutandis to other frequency bands, or to other embodiments in which the number of sub-bands chosen within the low frequency band varies.

In the examples presented, the ratio of the frequency bands, that is to say the ratio between the frequencies of the high frequency band and the frequencies of the low frequency band, is equal to about three. From this in fact, the coupling phenomena between the various radiating elements, introduced by their physical proximity, are reinforced. This is linked to the fact that, when the frequency ratio between the bands is an odd whole number, all the line-based resonant structures function naturally in the same way as the frequency f ₀ and all of its odd multiples. As a result, the radiating elements dimensioned for the IFF applications also radiate for the S band.

The figure 1 represents a radiating cell according to a first embodiment of the invention. This radiating cell 100, or antenna with printed radiating elements, is a printed circuit comprising multiple layers separated by a dielectric substrate, using distributed elements, that is to say microstrip lines (also designated by the English term “microstrip "). This technology is very widespread in microwave frequencies because, for high frequencies, the manipulation of waves from waveguides is simpler than the manipulation of currents and voltages. One of the layers of the printed circuit forms a ground plane.

The radiating cell comprises a radiating element 101 of the patch type. In distributed elements, a patch is a metallized layer of square or rectangular shape supplied. The dimensions of the patch are chosen so that it radiates in the high frequency band (S band). It is positioned in one of the layers of the circuit.

The radiating cell also includes two folded radiating slots 102. These slots have the behavior of dipoles, while being less sensitive to coupling phenomena. They are tuned to operate around the sub-bands of interest in the low frequency band (in the example, 1030MHz and 1090MHz). This agreement is achieved by dimensioning each one with respect to a wavelength close to the desired wavelength, the slit then having a length of λ / 2. In order to slightly decrease the size of the slits, tuning can be achieved by dimensioning them with respect to a wavelength slightly greater than the desired wavelength, then by adjusting their positions relative, the position of their exciter, and their position relative to the patch, so that the coupling phenomena push their operating frequency back onto the desired frequency. In the context of an IFF / Band S application, it is thus possible to use slots whose length is adapted to an operating frequency slightly greater than 1100 MHz, which makes them compatible, once folded in three in shape of U, of a mesh dimensioned compared to the frequency of 3.3 GHz, then to push back by coupling their operating frequency on the frequencies of interest 1030 MHz and 1090 MHz by adjusting their positions. The number of slots is adapted to the number of desired low frequency bands. The use of two slots folded in three in the shape of a U and a patch antenna makes it possible to accommodate the three radiating elements in a very reduced environment. It is also possible to fold the slots in more than three to make them fit into the radiating cell according to the invention.

The slots are produced by partial de-metallization of the ground plane of the cell. The excitation of the slots is carried out by a radiating strip 103 positioned between the two slots in one of the planes of the printed circuit, preferably the plane adjacent to the ground plane, and connected to the supply of the slots. The relative positioning of the two slots 102 and the exciter 103 creates coupling phenomena, both between the elements of the low frequency band, but also with the patch 101. Their positioning must therefore be adjusted in order to repel the artifacts generated by this coupling outside the useful bands. Adjusting the gap between the slits allows the resonant frequency of each slit to be adjusted and their operation to be pushed back to the triple frequency outside the high frequency band.

The exciter 103 is supplied by the low frequency band access 105, to which it is connected by a coaxial line 104 and a low pass filter 106.

This low-pass filter comprises, for example, two capacitors 107, which in printed technology take the form of open line sections. The role of the filter is to filter the components of the high frequency band due to the strong coupling between the slots and the patch.

The radiating element of the patch type 101 is supplied by the high frequency band access 109 to which it is connected by a coaxial line 108 and a filter 110.

The filter 110 has the role of filtering the components of the low frequency band due to the strong coupling between the slots and the patch.

The realization of a high pass or band pass filter requires a series capacitance series and parallel inductances difficult to achieve in distributed technology, and the size of the components, related to the low frequency band, presents the problem of size. An alternative way of making a bandpass filter then consists in inserting one or more short-circuited parallel waveguides, better known by the English name of stub.

A parallel waveguide acts as a series resonator circuit, and has a very small footprint. Its length is proportional to the wavelength in the dielectric of the frequency that it short-circuits. Thus, a stub made from a microstrip line section of length λ _B / 4, with λ _B the wavelength of the low frequency band, will play the role of short circuit in its resonance band. In the example, this is the low frequency band. However, resonant structures based on lines naturally function in the same way at the frequency f ₀ and for all the odd multiples of this frequency. This is the case in the example, where the ratio of the frequency bands is 3. Thus, such a stub will also play the role of short circuit for the high frequency band.

This problem is solved by implementing a variable stub whose total length is divided into several sections of different impedances (known in English as "stepped impedance"). Such a stub is dispersive. It is dimensioned so as to present a short circuit on its fundamental frequency, and an open circuit on its triple frequency. The filter 110 of the figure 1 has such a stub, consisting of several sections of microstrip line of different widths, and therefore having several distinct impedances. In the example, it has three different impedances, but the number of hops is a parameter specific to each implementation. Due to variable impedances, the system is not homogeneous, its electrical length no longer depends linearly on the frequency. Its size being λ _B / 4, it is tuned to block the components in the low frequency band, but is no longer suitable for the electrical length 3.λ _H / 4. It then performs well the desired functions of filtering the components of the low frequency band while letting the components of the high frequency band pass.

The different elements constituting the radiating cell according to the invention are arranged in different layers of the printed circuit. The figure 2 shows the exploded view of a radiating cell according to the first embodiment of the invention, in which the arrangement of the elements is intended to limit the size of the radiating cell.

In this nonlimiting example, the printed circuit comprises four layers. Each of the layers comprises a dielectric substrate on which an etched metal layer is deposited. The upper layer 201 comprises the patch type element 101 tuned to operate in the high frequency band.

The immediately lower layer 202 comprises the ground plane of the radiating cell, in which two slot-type elements 102, tuned for the low frequency bands, are produced by de-metallization of the ground plane. The slots are arranged so as not to be obstructed by the patch 101. An advantageous positioning then consists in placing them on the periphery of the radiating cell, opposite the patch.

The lower layer 203 comprises the slot exciter 103. Finally the lowest layer 204 comprises the low-pass filter element 106 connected on the one hand to the access 105 and on the other hand to the exciter 103 by the bias of a coaxial line, described under reference 104 in the figure 1 , allowing it to pass through the different layers of the printed circuit, and the band pass filtering elements 110 connected on the one hand to the access 109 and on the other hand to the patch 101 by means of a coaxial line 108.

The resulting radiating cell has a format slightly larger than the format of the S band patch. For example, in the specific case of operation for S band and IFF applications, the size of the patch band S is 25mm x 25mm. By using slots sized to operate at 1150 MHz, then by adjusting the position of the various elements of the device so as to radiate them in the desired frequency bands, or by using slots adjusted to the IFF frequency bands and folded in addition to three parts, the radiating cell resulting from the first embodiment takes up a space of 45mm x 45mm, ie λ _H / 2 x λ _H / 2.

This cell radiates simultaneously in the upper frequency band and in the lower frequency band, but has separate access to each of these bands. The different filtering elements ensure a strong decoupling between the two accesses.

Advantageously, it is possible to supplement the radiating cell with an additional layer 205, comprising a second patch antenna 206 adapted to the high frequency band. This additional layer is positioned on the highest layer 201, the second patch being superimposed on the first patch 101. This addition makes it possible to increase the bandwidth in the high frequency band, by playing on the coupling effects between the two patches , without changing the size of the cell.

The Figures 3a and 3b represent an example of reflection coefficient of the inputs and of decoupling, respectively in the low frequency band and in the high frequency band, associated with each input of a radiating cell according to the first embodiment of the invention.

The results are obtained by simulations using an electromagnetic simulation software by the finite element method.

The reflection coefficient of the inputs is representative of the power of the signal reflected as a function of the frequency. When this coefficient tends to 1 (ie OdB), then all of the signal power at the frequency concerned is rejected. The lower this coefficient, the better the antenna.

Decoupling measures the leakage power in the first antenna when the second antenna is working and vice versa. It is therefore representative of the performance of coexistence of the two types of radiating elements within the same cell.

In the figure 3a , the curve 301 represents the reflection coefficient of the access dedicated to the low frequency band, for the low frequency band (the frequency sub-bands envisaged in this embodiment are bands of a few MHz or tens of MHz around the frequencies 1.03GHz and 1.09GHz). This coefficient is less than - 10dB around the frequencies 1.03GHz and 1.09GHz. Dedicated access to the low frequency band is therefore suitable for IFF applications.

The curve 302 represents the reflection coefficient of the access dedicated to the high frequency band, for the low frequency band. In the 1.02GHz - 1.12GHz band, this coefficient is constant, and is equal to 1 (i.e. OdB). Dedicated access to the high frequency band therefore rejects all of the components of the low frequency band. It is not affected by coupling with the radiating elements in the low frequency band. This analysis is confirmed by measuring the decoupling 303 between the two inputs, which is greater than 24 dB across the band.

In the figure 3b , the curve 311 represents the reflection coefficient of the access dedicated to the low frequency band, for the high frequency band (the frequency band envisaged in this embodiment is the band 2.9GHz - 3.3GHz). This coefficient is constant, and is worth 1 (that is to say OdB). Dedicated access to the low frequency band therefore rejects all of the components of the high frequency band. It is then not affected by the coupling with the radiating elements in the high frequency band.

Curve 312 represents the reflection coefficient of the access dedicated to the high frequency band, for the high frequency band. In the 2.9GHz - 3.3GHz band, this coefficient is less than -12.5dB. The dedicated access to the high frequency band is therefore adapted to this frequency band. The decoupling 313 between the two antennas is greater than 25 dB in the band.

The Figures 4a and 4b represent an example of radiation diagrams of the input associated with the low frequency band of a radiating cell according to the first embodiment of the invention.

The figure 4a represents the radiation diagram in the horizontal plane of access to the low frequency band, for a frequency of 1.03GHz in main polarization (401) and crossed (403), as well as for a frequency of 1.09GHz in main polarization ( 402) and crossed (404). The cross-polarization response in this plane is almost zero (-30dB).

The main polarization of a radiating element is the axis on which the radiated electric field is maximum. Cross polarization is the axis perpendicular to the axis of the main polarization. These two axes lie in the plane perpendicular to the direction of propagation.

In the case of the device according to the invention, the main polarization is situated in the vertical plane (represented by the y axis in the figures), while the crossed polarization is situated in the horizontal plane (represented by the x axis in the figures).

The figure 4b represents the radiation diagram in the vertical plane of access to the low frequency band, for a frequency of 1.03GHz (411) and 1.09GHz (412). In this plane, the level of cross polarization is almost zero.

The radiation patterns observed on the access to the low frequency band in the horizontal and vertical plane vary in cosine θ for the main polarization, θ being the direction of observation. This characteristic is necessary for the production of an antenna with electronic scanning.

The Figures 5a and 5b represent an example of radiation diagrams of the input associated with the high frequency band of a radiating cell according to the first embodiment of the invention.

The figure 5a represents the radiation pattern in the horizontal plane of access to the high frequency band, for a frequency of 2.9GHz in main (501) and cross (502) polarization. The response according to the cross polarization is weak compared to the response according to the main polarization (typically 15dB to 30dB difference).

The figure 5b represents the radiation diagram in the vertical plane of access to the high frequency band, for a frequency of 2.9 GHz in main polarization (511). The response in cross polarization in this plane is negligible.

The radiation patterns observed in the high frequency band are characteristic of the radiation pattern of a patch. Indeed, this diagram has a variation close to a cosine function θ, necessary for the realization of an antenna with electronic scanning.

The figure 6 represents a radiating cell according to a second embodiment of the invention. This operating mode limits the number of sub-bands in the low frequency band to two.

Similarly to the first embodiment, the radiating cell 600 designed according to the second embodiment of the invention comprises a radiating element 101 of patch type tuned to the upper frequency band. This radiating element is supplied by the high band output 109 to which it is connected by means of a coaxial line 108 allowing it to pass through the different layers of the printed circuit, and of a filter 110 produced in the form of a stub. having several sections of variable impedance, making it possible to filter the low frequency band while passing for the high frequency band. Advantageously, a second patch type element, identical to the first, can be superimposed on the first patch type element 101, in order to widen the passband in the high frequency band.

The main difference between this embodiment and the first consists in that it contains only a single slit-type element 601, folded in a U, and positioned to be free from the masking represented by the patch (s) 101 The operating band of this element is then widened to the whole of the low frequency band, in order to to understand the two sub-bands required by IFF applications, by the association of a 602 resonator. The radiating slot, which forms a parallel resonator, can be supplemented by a series resonator placed in the output plane, or by a parallel resonator placed a quarter wave further. The resonator 602 is then placed at a distance L ₁ from the connector 104 connecting it to the exciter 103 of the slot, L ₁ being equal to λ / 4, where λ is the central wavelength of the low frequency band.

The slot 601 is not tuned to one of the sub-bands of the low frequency band, but to the central frequency, ie in the case of the example chosen, the frequency 1.06 GHz. It can also be tuned to a slightly higher frequency, so as to be compatible, once folded into three parts, of a mesh at the high frequency. The resonator 602 is designed to resonate at the same frequency. The action on the coupling between these two elements, that is to say the mismatch created between these two elements, will cause them to resonate around the frequencies sought. The coupling between the two elements is adjusted by varying the position of the exciter 103 of the slot. The slot 601, the resonator circuit 602 and the exciter 103 are therefore dimensioned and positioned so that the assembly resonates around the frequencies 1030MHz and 1090MHz, while allowing a strong mismatch in the intermediate frequency zone. The radiating element thus obtained is dual-frequency. This approach offers the advantage of only introducing a single radiating slit into the cell, and of reducing the interference between the slit and the patch, and therefore the coupling phenomena between the low frequency band and the high frequency band. . The positioning of the slot 601 and of the exciter 103 is therefore simplified compared to the first embodiment.

In the figure 6 , the resonator circuit 602 is of the parallel capacitance and inductance type. Inductance 603 is of low value. It is produced in the form of a microstrip line of length L ₂ connected to ground. The capacitor 604 is produced in the form of a short-circuited microstrip line of length L ₃ , L ₃ being much greater than L ₂ .

Advantageously, a low pass filter similar to the filter 106 of the first embodiment of the invention can be added to filter the components of the high bands linked to the coupling between the slot and the patch. However, such a filter is not essential in the second embodiment, the resonator circuit naturally performing the role of low pass filter.

In the second embodiment, the reduction in the number of radiating elements (slots) is compensated by an additional effort on the microwave circuit for adapting the slot.

The Figures 7a and 7b represent an example of reflection coefficient and decoupling associated with each input of a radiating cell according to the second embodiment of the invention. The results are obtained by simulations using an electromagnetic simulation software by the finite element method.

In the figure 7a , the curve 701 represents the reflection coefficient of the access dedicated to the low frequency band for the low frequency band (the frequency bands envisaged in this embodiment are bands of a few MHz or tens of MHz around the frequencies 1.03GHz and 1.09GHz). This coefficient is close to or less than -10dB around the frequencies 1.03GHz and 1.09GHz. Dedicated access to the low frequency band is therefore suitable for IFF applications.

The curve 702 represents the reflection coefficient of the access dedicated to the high frequency band, for the low frequency band. In the 1GHz - 1.15GHz band, this coefficient is constant, and is equal to 1 (i.e. OdB). Dedicated access to the high frequency band therefore rejects all of the components of the low frequency band. It is not affected by coupling with the radiating elements in the low frequency band. The decoupling 703 between the accesses of the slot and the patch is of the order of 30 dB.

In the figure 7b , the curve 711 represents the reflection coefficient of the access dedicated to the low frequency band, for the high frequency band (the frequency band envisaged in this embodiment is the band 2.9GHz - 3.3GHz). This coefficient is almost constant, and is equal to 1 (ie OdB) over almost the entire band. Dedicated access at the low frequency band therefore rejects all of the components of the high frequency band, it is not affected by the coupling with the radiating elements in the high frequency band.

Curve 712 represents the reflection coefficient of the access dedicated to the high frequency band. In the 2.9GHz - 3.3GHz band, this coefficient is much lower than -12.5dB. The dedicated access to the high frequency band is therefore adapted to this frequency band.

The decoupling 713 between the 2 antennas is greater than 12.5 dB in the band.

The Figures 8a and 8b represent an example of radiation diagrams of the input associated with the low frequency band of a radiating cell according to the second embodiment of the invention.

The figure 8a represents the radiation diagram in the horizontal plane of access to the low frequency band, for a frequency of 1.03GHz in main polarization (801) and crossed (803), as well as for a frequency of 1.09GHz in main polarization ( 802) and crossed (804). The response according to the main polarization in this plane is almost zero (-30dB).

The figure 8b represents the radiation diagram in the vertical plane of access to the low frequency band, for a frequency of 1.03GHz in main polarization (811), as well as for a frequency of 1.09GHz in main polarization (812). In this plane, the cross polarization is negligible.

The radiation patterns observed on the access to the low frequency band in the first and second plan vary in cosine θ for the main polarization, θ being the direction of observation. This characteristic is necessary for the production of an antenna with electronic scanning.

The Figures 9a and 9b represent an example of radiation diagrams of the input associated with the high frequency band of a radiating cell according to the first embodiment of the invention,

The figure 9a represents the radiation diagram in the horizontal plane of access to the high frequency band, for a frequency of 2.9 GHz in main (901) and cross (902) polarization. The response according to the cross polarization is weak compared to the response according to the main polarization (typically 30dB difference).

The figure 9b represents the radiation diagram in a vertical plane of access to the high frequency band, for a frequency of 2.9 GHz in main polarization (911). There is no cross polarization response in this plane of the cell.

The radiation patterns observed in the high frequency band are characteristic of the radiation pattern of a patch. Indeed, this radiation diagram in the foreground has a variation in cosine θ characteristic of a patch antenna, and necessary for the realization of an antenna with electronic scanning.

The figure 10 represents a radiating cell according to a third embodiment of the invention. It is a variant of the first embodiment, which comprises a radiating element of the slit type for each of the sub-bands envisaged in the low frequency band.

This embodiment differs from the first in that the two slot-type elements 1001 and 1011 are dissociated and placed on each side of the patch-type element, always on the periphery of the radiating cell so as not to be masked by the patch. This distance between the two slots makes it possible to reduce the coupling phenomena between them. Each of the slots is tuned relative to the center frequency of one of the sub-bands of the low frequency band, or reduced to this frequency by coupling. Finally, each of the slots is connected to a separate access. The radiating cell then has three accesses: a first access to the high frequency band, and an access for each of the sub-bands of the low frequency band.

In this embodiment, the first slot 1001 is supplied by the access 1003 to which it is connected by means of an exciter 1002, a coaxial line 1004, and a low pass filter 1005.

In a completely identical manner, the second slot 1011 is supplied by the access 1013 to which it is connected by means of an exciter 1012, a coaxial line 1014, and a low pass filter 1015.

The invention also includes a radiating network produced from dual-band radiating cells as defined above. Each of the cells can then be controlled in amplitude and / or in phase in each of the bands of interest, that is to say in the specific example, in the S band (and more particularly the 2.9GHz-3.3GHz subband) and in the band dedicated to IFF applications (1.03GHz and 1.09GHz).

Finally, it consists of a dual-band radar comprising a single electronic scanning antenna, the antenna being produced from the radiating network described above, and operating independently in the two frequency bands.

Claims (17)

1. Radiating device operating in two distinct frequency bands, a high frequency band and at least one sub-band of a low frequency band, the said device being characterized in that it comprises:

   • at least one element of patch type (101) adapted to the high frequency band and connected to a first access (109),

   • at least one element of folded slot type (102), adapted to the low frequency band and connected to a second access (105) different from the said first access,

   • a filter (110) positioned between the said element of patch type and the said first access, configured to filter the low frequency band and to be passing for the high frequency band,

   and in that the elements of which it consists are positioned in a surface area of less than or equal to a square of edge λ/2, where λ is the wavelength corresponding to the maximum frequency of the high frequency band.
2. Radiating device according to the preceding claim, in which the said element of slot type (102) is accommodated in a ground plane of the device.
3. Radiating device according to one of the preceding claims, in which the said element or elements of folded slot type (102) are folded into a U shape and positioned at the periphery of the device.
4. Radiating device according to one of the preceding claims, in which the number of elements of slot type is equal to the number of sub-bands of the low frequency band, the said elements of slot type being feed by one and the same second access.
5. Radiating device according to one of claims 1 to 3, in which the number of elements of slot type is equal to the number of sub-bands of the low frequency band, the said elements of slot type being feed by different accesses.
6. Radiating device according to one of claims 1 to 3, comprising a single element of slot type (601) feed by the said second access (109) to which it is connected by a resonator circuit (602), the coupling between the said slot and the said resonator circuit being adjusted to radiate in two distinct sub-bands of the low frequency band.
7. Radiating device according to claim 6, in which the said resonator circuit (602) is a parallel resonator circuit comprising an inductor (603) and a capacitor (604), the said resonator being connected to the element of slot type (601) by a waveguide of length λ/4, where λ is the wavelength associated with the central frequency of the low frequency band.
8. Radiating device according to one of the preceding claims, in which the said filter (110) positioned between the element of patch type (101) and the first access (109) comprises a plurality of segments of microstrip line of different widths.
9. Radiating device according to one of the preceding claims, furthermore comprising a low-pass filter (106) positioned between the said element or elements of slot type (102) and the said second access (105), and configured to filter the high frequency band.
10. Radiating device according to one of the preceding claims, furthermore comprising a second element (206) of patch type adapted to the high frequency band, the said second element of patch type being disposed above the said first element of patch type.
11. Radiating device according to one of the preceding claims, implemented in a multilayer printed circuit for which the said element of patch type (101), the said element or elements of slot type (102), and the said filter (110) positioned between the element of patch type and the first access, are in different layers (201, 202, 203, 204) of the printed circuit.
12. Radiating device according to the preceding claim, in which at least one frequency of the high frequency band is an odd integer multiple of a frequency of the low frequency band.
13. Radiating device according to the preceding claim, in which the high frequency band comprises the 2.9GHz - 3.3GHz band.
14. Radiating device according to one of the preceding claims, in which a sub-band of the low frequency band is centred around a frequency chosen from among the frequency 1,030MHz and the frequency 1,090MHz.
15. Radiating device according to one of the preceding claims, produced using printed technology.
16. Radiating array configured to radiate in two distinct frequency bands, characterized in that it comprises radiating devices according to one of the preceding claims.
17. Electronic scanning radar configured to operate simultaneously in two different frequency bands, and characterized in that it comprises a radiating array according to Claim 16.

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