EP0991135B1 - Selective antenna with frequency switching - Google Patents

Selective antenna with frequency switching Download PDF

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Publication number
EP0991135B1
EP0991135B1 EP19990402412 EP99402412A EP0991135B1 EP 0991135 B1 EP0991135 B1 EP 0991135B1 EP 19990402412 EP19990402412 EP 19990402412 EP 99402412 A EP99402412 A EP 99402412A EP 0991135 B1 EP0991135 B1 EP 0991135B1
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EP
European Patent Office
Prior art keywords
antenna
slot
length
slots
radiating
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EP19990402412
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German (de)
French (fr)
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EP0991135A1 (en
Inventor
Laurent Yvelin
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Thales SA
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Thales SA
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
    • H01Q9/04—Resonant antennas
    • H01Q9/06—Details
    • H01Q9/14—Length of element or elements adjustable
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q13/00—Waveguide horns or mouths; Slot antennas; Leaky-waveguide antennas; Equivalent structures causing radiation along the transmission path of a guided wave
    • H01Q13/10—Resonant slot antennas
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q13/00—Waveguide horns or mouths; Slot antennas; Leaky-waveguide antennas; Equivalent structures causing radiation along the transmission path of a guided wave
    • H01Q13/10—Resonant slot antennas
    • H01Q13/18—Resonant slot antennas the slot being backed by, or formed in boundary wall of, a resonant cavity ; Open cavity antennas

Definitions

  • the invention relates to the field of antennas with radiating slots.
  • An antenna with radiating slots is a resonant antenna and therefore highly selective in frequency.
  • the frequency bandwidth of such an antenna is generally low.
  • the bandwidth is the frequency range on which the operation of the antenna remains sufficiently stable, both in radiation pattern and adaptation.
  • IFF friend or friend identification
  • These solutions may sometimes encounter congestion considerations, particularly in the case of antennas embedded on a weapon aircraft, for example.
  • a U.S. Patent 5,754,143 discloses a meander slot antenna having microwave diodes.
  • the invention proposes an antenna capable of operating at several distinct frequencies by switching, while maintaining in a given rectilinear polarization a similar given radiation pattern for each of the frequencies, while maintaining a low level of cross polarization.
  • the developed length of a radiating slot is the sum of all the median lengths of each of the folded elements of the slot if it has several, otherwise the developed length merges with the median length of the slot.
  • This form of radiating slot makes it possible to maintain a low cross polarization.
  • the electronic circuits are synchronized so that the radiating slots have between them substantially the same radioelectric length, and in that the reduction in radio length is sufficiently small for the radiation pattern of the antenna remains substantially stable.
  • the radiating slots of the antenna are excited by coupling with a microstrip line which remains unchanged whatever the blocked state or passing electronic devices.
  • FIGS. 1 to 5 describe the preferred embodiment of the invention in which the electronic circuits are synchronized so that the radiating slots have substantially the same radio frequency between them.
  • the figure 1 schematically represents a preferred general structure of an antenna according to the invention.
  • the antenna is seen in profile.
  • the antenna comprises sequentially, from the outer side to the inner side of the antenna, a radome 1, a conductive surface 2 connected to ground, a dielectric substrate 3, a conductive cavity 5, preferably metal, also connected to ground .
  • Radiant slots are etched on the conductive surface 2.
  • a feed line 4 which is advantageously a microstrip line.
  • This microstrip line 4 is preferably deposited in the form of a printed circuit.
  • the electronic circuits, not shown here, associated with the radiating slots of the antenna comprise electronic devices.
  • the electronic devices are advantageously mounted on the surface of another printed circuit comprising the electronic circuits and etched on the same face of the substrate 3 as the line 4, but independently of the line 4.
  • the antenna then has only three elements. mechanically distinct which are the radome 1, the substrate 3 with on one of its faces the conductive surface 2 and on the other side a printed circuit comprising the electronic circuits and the supply line 4, and the cavity 5.
  • the slots can be machined in the bulk of the metal structure of the waveguide, and the electronic circuits can then be etched on a substrate. glued on the conductive surface of the slots.
  • the thickness and the dielectric constant of the substrate 3 and the radome 1 significantly influence the resonance wavelength, and therefore the slot radio frequency. Indeed, the higher these thicknesses and these dielectric constants, more for a given resonance frequency of the slot, the physical dimensions of the slot are small, which allows a smaller footprint of each slot. However, the bandwidth of the antenna then decreases as well.
  • the substrate 3 has a large thickness, of the order of 2 mm, and a high relative dielectric constant, of the order of 10.
  • the radome 1, protective element of the antenna preferably plated on the conductive surface 2 can also cause significant ohmic losses when its thickness is too high. In this preferred example chosen, the radome has a thickness of 4 mm and its material is stratified epoxy glass.
  • the cavity 5 makes it possible to eliminate the radiation of the antenna towards the rear, that is to say on the side opposite to the radome 1.
  • the presence of a cavity increases the frequency selectivity of a radiating slot antenna .
  • the gain in space at the thickness of the antenna is to the detriment of the surface clutter of the antenna and to the detriment of the width of its bandwidth.
  • the Figure 2A schematically represents a radiating slot 20 of the antenna and the nonlinear electronic circuit 70 associated with the slot 20, a preferred embodiment of an antenna according to the invention.
  • the slot 20 is seen from above with respect to the figure 1 ; it is etched in the conductive surface 2.
  • the electronic circuit 70 on the example of the Figure 2A has only one electronic device 70a with which it merges.
  • the electronic circuit 70 is controlled by a control device 6 which is preferably common to several electronic circuits 70.
  • the control device 6 comprises for example a control line 61 and a high-frequency decoupling inductor 62 whose slots 20 are headquarters.
  • the electronic device 70a preferably comprises a wire link 71 connecting two points 74 and 75 of the perimeter 21 of the slot 20.
  • the wire link 71 preferably comprises a diode 72 and a capacitance 73 for decoupling the ground to which the conductive surface is connected. 2.
  • the slot 20, perimeter 21 corresponding to a given radio length comprises a central bar 22 and a transverse bar 23 having flared sides 24.
  • the electronic device 70a has two states: a locked state and a on state.
  • the blocked state does not modify the radioelectric length of the slot 20.
  • the on state decreases the radioelectric length of the slot 20 by shortening the perimeter 21 of the slot 20 by a short circuit made between two points 74 and 75 of the perimeter 21.
  • the slot 20 has the greatest radio length when the electronic device 70a is in the off state.
  • the change of state of the electronic device 70a switches between two states that are geometrically different from the slot 20.
  • Figures 2B and 2C schematically represent the two states of the electronic device 70a according to the invention, the blocked state is represented on the Figure 2B and the state passing on the Figure 2C .
  • the effective perimeter 21 of the slot 20 is shown in solid lines in each of the states of the electronic device 70a.
  • the distance of shortening distance of the crossbar 23, corresponds to a decrease in the radioelectric length of the slot 20.
  • the decrease in the radioelectric length of the slot 20 must be sufficiently small for the antenna radiation pattern remains substantially stable, that is to say has a stability considered sufficient in the application in question, even in the case where the supply line 4 remains identical for the two states of the electronic device 70a.
  • the electronic circuits 70 are synchronized so that the slots 20, of a multi-slot antenna, have between them substantially the same radio length, that is to say have radio lengths considered sufficiently close in the intended application, for example by having a common control device 6 which then allows for example a common voltage control of all the Electronic circuits 70.
  • the value of substantially in the expression "substantially the same radio-frequency length" depends on the allowable tolerances in the intended application. Similarly in the more general case of radiating slots switching from one state to another "substantially at the same time", the value of "substantially” depends on the allowable tolerances in the intended application.
  • the perimeters 21 and the distances d are substantially equal for all the slots 20 of the antenna.
  • the conductive surface 2 connected to ground, establishes an electromagnetic shield against strong fields at frequencies below the resonant frequency of the slots 20.
  • This screen protects all the electronic elements that are behind the conductive surface 2 and in particular behind the substrate 3.
  • the slot 20 may have various shapes.
  • the folded T shape shown on the FIGS. 2A, 2B and 2C is a preferred form.
  • D1 be a first direction and D2 a second direction orthogonal to D1.
  • the slots 20, only one of which is shown on the FIGS. 2A to 2C are aligned in the direction D1.
  • the slot 20 comprises two bars 22 and 23; a transverse bar 23 parallel to the direction D1 connected at its center to a central bar 22 parallel to the direction D2. This refolding makes it possible to reduce the bulk in the direction D2 with respect to a straight slot in the direction D2 of the same radio length, to the detriment of a reduction in the bandwidth.
  • the T-shape results in a radiated cross polarization, that is to say here a polarization in the direction D2, which is markedly inferior to that resulting from other types of shape.
  • a conventional L-shaped for example which can be explained by the presence of currents in opposition in the two branches of the crossbar 23 located on either side of the center of the crossbar 23.
  • the central bar 22 must be sufficiently thin, that is to say that the ratio between its width and its length must be sufficiently small, so that the slot 20 has a slot behavior radiating especially a rectilinear polarization parallel to the direction D1 perpendicular to its length .
  • the ratio of the length of the central bar 22 to the length of the crossbar 23 is sufficiently large for the radiating slot to radiate with a rectilinear polarization substantially parallel to direction D1, that is to say comprising a cross-polarization level sufficiently low for the considered application.
  • the term “substantially” depends on the intended application and allowable tolerances for cross polarization level. The more the radio currents whose radiating slot is the seat are located in the central bar 22 and the more the direction of polarization of the field radiated by the slot 20 will be parallel to the direction D1.
  • the length of the central bar 22 is substantially one third of the perimeter 21 of the slot 20.
  • the transverse bar 23 flares towards its ends, as shown on the Figure 2A the oblique side 24 of the transverse bar 23. It is found that this flare widens the bandwidth of the antenna. This flaring can also be performed along the other side of the crossbar 23 or even simultaneously along both sides of the crossbar 23, but in these two cases, the gain in space in the direction D1 is a little more weak than in the case shown on the Figure 2A .
  • the T-shaped slot is no longer symmetrical, the two branches of the cross bar 23 are no longer the same length; as explained above, the distance d is chosen to be sufficiently small relative to the length of the transverse bar 23 so that the radiation pattern of the antenna remains substantially stable.
  • two electronic devices such as the device 70a, which could be placed each at a distance d / 2 from the ends of the crossbar 23.
  • the wired link 71 shortens the crossbar 23 and therefore decreases the perimeter 21 of the slot 20.
  • the wire link 71 is parallel to the direction D2 and is located sufficiently in the vicinity of the plane of the conductive surface 2 for the short circuit thus produced is effective and that the radioelectric length of the slot is reduced without appearance parasitic inductive effects.
  • the wired link 71 can be made on one or the other face of the substrate 3.
  • a preferred embodiment of wired connection 71 is given to the 2D figure .
  • the wire connection 71 is made in the form of metal etching on the substrate face 3 which is situated on the opposite side to the conductive surface 2.
  • Figure 2A it preferably comprises a diode 72 and a decoupling capacitor 73 in series.
  • the capacity 73 is for example 500pF in the preferential frequency domain of use located around 1 GHz.
  • Metallic holes 71a and 71b connect the wire connection 71 respectively to the short-circuit points 74 and 75 located on the conductive surface 2.
  • the diode 72 is a microwave diode with two states of polarization.
  • the diode 72 generally a PIN diode, advantageously has the following characteristics: a fast switching time, for example less than 1 ⁇ s, a significant reverse-voltage withstand, for example from 500 to 1000 volts, a relatively low direct polarization equivalent resistance for example 0.6 ohms, a very low inverse capacity, for example 0.4 pF.
  • the control line 61 carries control signals of this diode, for example a voltage of -50 volts for the off state and a current of 50 mA for the on state.
  • the figure 3 schematically represents a top view of a preferred antenna according to the invention.
  • the antenna preferably comprises two slots 20 with associated electronic circuits 70 similar to that of the Figure 2A .
  • the slots 20, whose central bars 22 are parallel to the direction D2, are aligned in the direction D1 which is the direction of polarization of the radiation emitted by the slots 20.
  • the alignment thus obtained has a small surface area and allows to achieve undersized antennas whose dimensions are of the order of the slit resonance wavelength fraction, for example example of the order of half in the direction D1 and the third in the direction D2.
  • a partition 51 preferably located equidistant from the central bars 22 of the two slots 20, parallel to the direction D2 and perpendicular to the plane of the figure 3 separates the cavity 5 into two parts. Partition 51 is shown on the figure 3 in dotted lines. The partition 51 is also connected to the ground, in order to reduce or even eliminate the intracavity couplings, that is to say inside the cavity 5, between the slots 20, for example via holes metallized through the substrate 3 and establishing an electrical contact between the conductive partition 51 and the conductive surface 2.
  • the control line 61 is connected to the partition 51 by a capacitor 63 decoupling.
  • the partition 51 has a hole 52 passing a feed line 4.
  • the feed line 4 is shown in dashed lines.
  • the slots 20 are fed in series.
  • the difference in excitation phase imposed between the slots 20 by the power supply line 4 partially allows to detach, relative to the normal to the antenna surface, the main lobe of the beam radiated by the antenna.
  • the normal to be considered is the vertical to the mean plane at the point 0 and passing through the point 0.
  • the misalignment is also linked to an extracavity coupling effect between the slots 20, especially when they are very close to each other, which will be examined later.
  • the central bars 22 are spaced substantially a quarter of the resonant wavelength of the slots 20, which allows by establishing an excitation phase difference of about 90 degrees between the two slots 20 of the antenna greatly reduce radiation losses to the rear of the main lobe, that is to say towards the source of the supply line 4 described below.
  • Such a combination of two slots 20 allows the radiation of a main lobe at high inclination with respect to the conductive surface 2.
  • the feed line 4 has different sections and ends with an open circuit termination 44. From the source, not represented on the figure 3 , feed line 4 has sections 41 intermediates, on the one hand between the source and the first slot 20, and on the other hand between the two slots 20. Between the intermediate sections 41 and the slots 20, the supply line 4 comprises adaptation sections 42 impedance, to achieve an adaptation between the impedance of the intermediate sections 41, for example 50 ohms, and the impedance of the slots 20 seen by the supply line 4.
  • the impedance matching is obtained by preferably playing on the width of the different sections of the supply line 4.
  • the realization of the adaptation of the power line 4 results from a compromise between the adaptation to the different radio lengths of the slots 20, so that during the changes of state of the electronic circuits 70, the power line 4 remains adapted and that the misalignment of the beam is substantially maintained so that the radiation pattern remains substantially stable.
  • the adaptation makes it possible to keep a TOS, standing wave ratio, relatively low.
  • the supply line 4 is coupled to the slots 20 via coupling sections 43 which excite the slots 20.
  • Each section 43 is preferably located in the vicinity of the end of the central bar 22 located on the side opposite the bar. 23.
  • the example of figure 3 shows an optimal excitation called "maximum offset", that is to say at the end of the slot.
  • maximum offset that is to say at the end of the slot.
  • slot-end excitation requires a slightly smaller slot size than for excitation elsewhere in the slot.
  • a gain in surface area for the antenna is performed by capacitive coupling.
  • phase shift imposed by the power line sections 4 located between the two slots 20 is partially responsible for the pointing effect of the beam of the antenna.
  • Another important effect that occurs in the pointing is the extracavity coupling, that is to say external to the cavity, between the slots 20, the intracavity coupling having been virtually eliminated by the partition 51 connected to ground.
  • this coupling must be taken into consideration for each of the frequencies radiated by the antenna so that the desired pointing effect corresponding to a specific radiation pattern depends on the intended application. , obtained for all circuit states 70, which states correspond to given radio slot lengths and therefore to frequencies radiated by the antenna.
  • the radiation patterns obtained with the preferred antenna represented on the figure 3 are represented on the figure 4 .
  • the figure 4 schematically represents the radiation patterns at the two distinct frequencies F1 and F2 which respectively correspond to the blocked and passing states of the electronic devices 70a.
  • the radiation patterns are represented in the plane P of the figure 3 , the plane P being shown in phantom and passing at the middle of the central bars 22 of the slots 20, parallel to the direction D1, and perpendicular to the plane of the figure 3 which plane corresponds to the average plane of the antenna at these environments.
  • the antenna is not necessarily flat, it can also be shaped to a particular surface, as in a preferential application discussed later.
  • the curves are in solid lines for the frequency F1 and in dashed lines for the frequency F2.
  • the preferred field of application of the invention is the L band around 1GHz.
  • the bandwidth around each of these frequencies is about 20 MHz, or about 2%, which means that the pattern of the radiation patterns is substantially stable in these two bandwidths.
  • the curves of the figure 4 show that it is possible to obtain stable and similar radiation patterns on narrow bandwidths, about 2%, around substantially distant frequencies, their relative distance is about 6%. To achieve this operating result only by continuously broadening a bandwidth around a center frequency of approximately 1060 MHz, a band would have had to be equivalent pass rate of 8%, significantly more than bandwidths of 2%.
  • TOS readings, standing wave ratios show that the bandwidths in radiation pattern are also the bandwidths in TOS for the antenna considered at the time. figure 3 .
  • the figure 5 represents an electronic circuit variant 70 comprising several electronic devices, here for example three, the devices 70a, 70b and 70c being similar to that of the figure 3 and respectively located at distances d1, d2, d3.
  • the slots 20 then have a stable radiation pattern for a plurality of frequencies, the frequencies corresponding to different perimeter sizes 21 of the slots being obtainable with the electronic devices 70a-70c.
  • This variant makes it possible, for example, to operate the antenna in frequency evasion mode or in automatic frequency tuning correction mode.
  • the frequency evasion mode naturally requires a short frequency switching period.
  • the automatic frequency tuning correction mode related to the drift of the characteristics of the antenna according to certain parameters, such as the temperature for example, can generally operate with a much longer switching period.
  • the antenna is shaped on the surface of an aircraft, which allows it to have, in view of its misalignment of 40 ° to 50 °, an angle of inclination of the beam in site low compared to the horizontal angle which corresponds to an observation towards the front of the aircraft.
  • Several antennas of this type for example four, may be aligned parallel to the direction D2, thereby forming an electronically controllable array for scanning the beam in the azimuth plane of the aircraft.
  • Each pointed beam of the array advantageously covers a sector limited in azimuth of the observation space which is thus covered by an electronic scanning of all the beams.
  • One or more antenna arrays previously described make it possible, for example, to produce an identification system, of the IFF type (lFF having been defined above) operating at two frequencies F1 and F2, using shaped antennas, and covering the space in space. before the aircraft on a given angular sector in site and in azimuth.
  • the identification system is an air-to-air system as well as an air-ground system.

Description

L'invention concerne le domaine des antennes à fentes rayonnantes. Une antenne à fentes rayonnantes est une antenne résonante donc fortement sélective en fréquence. La bande passante en fréquence d'une telle antenne est généralement faible. La bande passante est le domaine de fréquences sur lequel le fonctionnement de l'antenne reste suffisamment stable, tant en diagramme de rayonnement qu'en adaptation. Dans certaines applications, telles que l'IFF (« identification friend or foe » qui signifie « identification ami ou ennemi »), il est nécessaire de pouvoir faire rayonner l'antenne selon deux bandes de fréquences proches, mais distinctes. Il est alors possible soit d'utiliser deux antennes très sélectives en fréquence fonctionnant chacune dans une bande de fréquence, soit une seule antenne avec une bande passante plus large englobant les deux bandes précédentes. Ces solutions peuvent parfois se heurter à des considérations d'encombrement, notamment dans le cas d'antennes embarquées sur un avion d'arme par exemple.The invention relates to the field of antennas with radiating slots. An antenna with radiating slots is a resonant antenna and therefore highly selective in frequency. The frequency bandwidth of such an antenna is generally low. The bandwidth is the frequency range on which the operation of the antenna remains sufficiently stable, both in radiation pattern and adaptation. In some applications, such as the IFF ("friend or friend identification"), it is necessary to be able to radiate the antenna in two bands of close but distinct frequencies. It is then possible to use two very frequency selective antennas each operating in a frequency band, or a single antenna with a wider bandwidth encompassing the two previous bands. These solutions may sometimes encounter congestion considerations, particularly in the case of antennas embedded on a weapon aircraft, for example.

Il est connu de réduire l'encombrement de l'antenne en repliant ses fentes. Cependant les formes de fentes obtenues font généralement apparaître une polarisation croisée souvent indésirable, ainsi que d'éventuels modes parasites de rayonnement, et réduisent alors la bande passante de l'antenne.It is known to reduce the size of the antenna by folding its slots. However, the slot shapes obtained generally show an often undesired cross polarization, as well as possible parasitic radiation modes, and then reduce the bandwidth of the antenna.

Un brevet US 5 754 143 décrit une antenne à fente en méandre comportant des diodes hyperfréquence.A U.S. Patent 5,754,143 discloses a meander slot antenna having microwave diodes.

L'invention propose une antenne susceptible de fonctionner à plusieurs fréquences distinctes par commutation, tout en conservant selon une polarisation rectiligne donnée un diagramme de rayonnement donné similaire pour chacune des fréquences, tout en maintenant un niveau de polarisation croisée faible.The invention proposes an antenna capable of operating at several distinct frequencies by switching, while maintaining in a given rectilinear polarization a similar given radiation pattern for each of the frequencies, while maintaining a low level of cross polarization.

La longueur développée d'une fente rayonnante est la somme de toutes les longueurs médianes de chacun des éléments repliés de la fente si celle-ci en comporte plusieurs, sinon la longueur développée se confond avec la longueur médiane de la fente. Plus la fente est fine, c'est-à-dire plus le rapport entre ses deux dimensions est grand, plus la valeur de sa longueur développée se confond avec celle de son demi-périmètre.The developed length of a radiating slot is the sum of all the median lengths of each of the folded elements of the slot if it has several, otherwise the developed length merges with the median length of the slot. The slighter the slit, that is, the greater the ratio between its two dimensions, the more the value of its developed length merges with that of its half-perimeter.

Selon l'invention, il est prévu une antenne à fentes rayonnantes gravées dans une surface conductrice reliée à la masse, les fentes rayonnantes ayant un périmètre correspondant à une longueur radioélectrique donnée, l'antenne comportant des circuits électroniques non linéaires, un circuit électronique étant associé à chaque fente rayonnante et comportant au moins un dispositif électronique à deux états, un état bloqué qui ne modifie pas la longueur radioélectrique de la fente, et un état passant qui diminue la longueur radioélectrique de la fente en raccourcissant le périmètre de la fente par court-circuit réalisé entre deux points dudit périmètre, en ce que les circuits électroniques sont synchronisés pour que les fentes rayonnantes commutent d'un état à un autre sensiblement au même instant, et en ce que les diminutions des longueurs radioélectriques des fentes sont suffisamment faibles pour que les diagrammes de rayonnement de l'antenne restent sensiblement stables caractérisé en ce que les fentes rayonnantes étant alignées selon une première direction, chaque fente rayonnante est en forme de T, le T comportant une barre transversale selon la première direction reliée au niveau de son centre à une barre centrale selon une deuxième direction orthogonale à la première direction.According to the invention, there is provided an antenna with radiating slots etched in a conductive surface connected to the ground, the slots radiators having a perimeter corresponding to a given radio length, the antenna comprising non-linear electronic circuits, an electronic circuit being associated with each radiating slot and comprising at least one electronic device with two states, a locked state which does not modify the length radio frequency of the slot, and an on state that decreases the radioelectric length of the slot by shortening the perimeter of the slot by short circuit realized between two points of said perimeter, in that the electronic circuits are synchronized so that the radiating slots switch d one state to another at substantially the same instant, and in that the decreases in the radio lengths of the slots are small enough so that the radiation patterns of the antenna remain substantially stable, characterized in that the radiating slots being aligned according to a first direction, every radiant slit is T-shaped, the T having a transverse bar in the first direction connected at its center to a central bar in a second direction orthogonal to the first direction.

Cette forme de fente rayonnante permet de maintenir une polarisation croisée faible.This form of radiating slot makes it possible to maintain a low cross polarization.

Selon un mode de réalisation préférentiel de l'invention, les circuits électroniques sont synchronisés pour que les fentes rayonnantes présentent entre elles substantiellement la même longueur radioélectrique, et en ce que la diminution de longueur radioélectrique est suffisamment faible pour que le diagramme de rayonnement de l'antenne reste sensiblement stable. De préférence, les fentes rayonnantes de l'antenne sont excitées par couplage avec une ligne microruban qui reste inchangée quelque soit l'état bloqué ou passant des dispositifs électroniques.According to a preferred embodiment of the invention, the electronic circuits are synchronized so that the radiating slots have between them substantially the same radioelectric length, and in that the reduction in radio length is sufficiently small for the radiation pattern of the antenna remains substantially stable. Preferably, the radiating slots of the antenna are excited by coupling with a microstrip line which remains unchanged whatever the blocked state or passing electronic devices.

L'invention sera mieux comprise et d'autres particularités et avantages apparaîtront à l'aide de la description ci-après et des dessins joints, donnés à titre d'exemples, où :

  • la figure 1 représente schématiquement une vue en coupe d'un mode de réalisation d'une antenne selon l'invention ;
  • la figure 2A représente schématiquement une fente et le circuit électronique associé, d'un mode de réalisation d'une antenne selon l'invention ;
  • les figures 2B et 2C représentent schématiquement deux états d'un mode de réalisation d'un dispositif électronique selon l'invention, respectivement l'état bloqué et l'état passant ;
  • la figure 2D représente schématiquement un mode de réalisation préférentiel d'un dispositif électronique selon l'invention ;
  • la figure 3 représente schématiquement une vue de dessus d'un mode de réalisation d'une antenne selon l'invention ;
  • la figure 4 représente schématiquement les diagrammes de rayonnement d'un mode de réalisation d'une antenne selon l'invention, à deux fréquences distinctes ;
  • la figure 5 représente une variante d'un circuit électronique d'une antenne selon l'invention.
The invention will be better understood and other features and advantages will become apparent from the following description and accompanying drawings, given by way of example, where:
  • the figure 1 schematically represents a sectional view of an embodiment of an antenna according to the invention;
  • the Figure 2A schematically shows a slot and the associated electronic circuit, an embodiment of an antenna according to the invention;
  • the Figures 2B and 2C schematically represent two states of an embodiment of an electronic device according to the invention, respectively the locked state and the on state;
  • the 2D figure schematically represents a preferred embodiment of an electronic device according to the invention;
  • the figure 3 schematically represents a top view of an embodiment of an antenna according to the invention;
  • the figure 4 schematically represents the radiation patterns of an embodiment of an antenna according to the invention, at two distinct frequencies;
  • the figure 5 represents a variant of an electronic circuit of an antenna according to the invention.

Les figures 1 à 5 décrivent le mode de réalisation préférentiel de l'invention dans lequel les circuits électroniques sont synchronisés pour que les fentes rayonnantes présentent entre elles substantiellement la même longueur radioélectrique.The Figures 1 to 5 describe the preferred embodiment of the invention in which the electronic circuits are synchronized so that the radiating slots have substantially the same radio frequency between them.

La figure 1 représente schématiquement une structure générale préférentielle d'une antenne selon l'invention. L'antenne est vue de profil. L'antenne comporte séquentiellement, du côté extérieur vers le côté intérieur de l'antenne, un radôme 1, une surface conductrice 2 reliée à la masse, un substrat 3 diélectrique , une cavité 5 conductrice, de préférence métallique, également reliée à la masse. Des fentes 20 rayonnantes sont gravées sur la surface conductrice 2. Dans la cavité 5, sur la face du substrat 3, du côté opposé à celui de la surface conductrice 2, est déposée une ligne d'alimentation 4 qui est avantageusement une ligne microruban. Cette ligne microruban 4 est préférentiellement déposée sous la forme d'un circuit imprimé. Les circuits électroniques, non représentés ici, associés aux fentes rayonnantes de l'antenne, comportent des dispositifs électroniques. Les dispositifs électroniques sont avantageusement montés en surface d'un autre circuit imprimé comportant les circuits électroniques et gravé sur la même face du substrat 3 que la ligne 4, mais de manière indépendante de la ligne 4. L'antenne ne comporte alors que trois éléments mécaniquement distincts qui sont le radôme 1, le substrat 3 avec sur l'une de ses faces la surface conductrice 2 et sur l'autre face un circuit imprimé comprenant les circuits électroniques et la ligne 4 d'alimentation, et la cavité 5.The figure 1 schematically represents a preferred general structure of an antenna according to the invention. The antenna is seen in profile. The antenna comprises sequentially, from the outer side to the inner side of the antenna, a radome 1, a conductive surface 2 connected to ground, a dielectric substrate 3, a conductive cavity 5, preferably metal, also connected to ground . Radiant slots are etched on the conductive surface 2. In the cavity 5, on the face of the substrate 3, on the side opposite to that of the conductive surface 2, is deposited a feed line 4 which is advantageously a microstrip line. This microstrip line 4 is preferably deposited in the form of a printed circuit. The electronic circuits, not shown here, associated with the radiating slots of the antenna, comprise electronic devices. The electronic devices are advantageously mounted on the surface of another printed circuit comprising the electronic circuits and etched on the same face of the substrate 3 as the line 4, but independently of the line 4. The antenna then has only three elements. mechanically distinct which are the radome 1, the substrate 3 with on one of its faces the conductive surface 2 and on the other side a printed circuit comprising the electronic circuits and the supply line 4, and the cavity 5.

Dans une variante de l'invention utilisant une structure de guide d'onde à fentes rayonnantes par exemple, les fentes peuvent être usinées dans la masse de la structure métallique du guide d'onde, et les circuits électroniques peuvent alors être gravés sur un substrat collé sur la surface conductrice des fentes.In a variant of the invention using a radially slotted waveguide structure for example, the slots can be machined in the bulk of the metal structure of the waveguide, and the electronic circuits can then be etched on a substrate. glued on the conductive surface of the slots.

L'épaisseur et la constante diélectrique du substrat 3 et du radôme 1 influencent de manière importante la longueur d'onde de résonance, et donc la longueur radioélectrique de fente. En effet, plus ces épaisseurs et ces constantes diélectriques sont élevées, plus pour une fréquence de résonance donnée de la fente, les dimensions physiques de la fente sont petites, ce qui permet un encombrement moindre de chaque fente. Cependant, la bande passante de l'antenne diminue alors également. Dans un exemple préférentiel, pour des fréquences autour de 1GHz, le substrat 3 a une forte épaisseur, de l'ordre de 2mm, et une constante diélectrique relative élevée, de l'ordre de 10. Le radôme 1, élément protecteur de l'antenne de préférence plaqué sur la surface conductrice 2, peut aussi entraîner des pertes ohmiques importantes lorsque son épaisseur est trop élevée. Dans cet exemple préférentiel choisi, le radôme a une épaisseur de 4mm et son matériau est du verre-époxyde stratifié.The thickness and the dielectric constant of the substrate 3 and the radome 1 significantly influence the resonance wavelength, and therefore the slot radio frequency. Indeed, the higher these thicknesses and these dielectric constants, more for a given resonance frequency of the slot, the physical dimensions of the slot are small, which allows a smaller footprint of each slot. However, the bandwidth of the antenna then decreases as well. In a preferred example, for frequencies around 1 GHz, the substrate 3 has a large thickness, of the order of 2 mm, and a high relative dielectric constant, of the order of 10. The radome 1, protective element of the antenna preferably plated on the conductive surface 2, can also cause significant ohmic losses when its thickness is too high. In this preferred example chosen, the radome has a thickness of 4 mm and its material is stratified epoxy glass.

La cavité 5 permet de supprimer le rayonnement de l'antenne vers l'arrière, c'est-à-dire du côté opposé au radôme 1. La présence d'une cavité 5 accroît la sélectivité en fréquence d'une antenne à fentes rayonnantes. Moins la cavité 5 est profonde, plus pour une fréquence de résonance donnée de la fente, les dimensions de la fente augmentent, et plus la bande passante en fréquence diminue. Le gain de place au niveau de l'épaisseur de l'antenne se fait au détriment de l'encombrement de surface de l'antenne et au détriment de la largeur de sa bande passante.The cavity 5 makes it possible to eliminate the radiation of the antenna towards the rear, that is to say on the side opposite to the radome 1. The presence of a cavity increases the frequency selectivity of a radiating slot antenna . The less the cavity 5 is deep, the more for a given resonance frequency of the slot, the dimensions of the slot increase, and the lower the frequency bandwidth decreases. The gain in space at the thickness of the antenna is to the detriment of the surface clutter of the antenna and to the detriment of the width of its bandwidth.

La figure 2A représente schématiquement une fente rayonnante 20 de l'antenne et le circuit électronique 70 non linéaire associé à la fente 20, d'un mode de réalisation préférentiel d'une antenne selon l'invention. La fente 20 est vue de dessus par rapport à la figure 1 ; elle est gravée dans la surface conductrice 2. Le circuit électronique 70 sur l'exemple de la figure 2A ne comporte qu'un seul dispositif électronique 70a avec lequel il se confond. Le circuit électronique 70 est commandé par un dispositif 6 de commande qui est de préférence commun à plusieurs circuits électroniques 70. Le dispositif 6 de commande comporte par exemple une ligne de commande 61 et une inductance 62 de découplage des hautes fréquences dont les fentes 20 sont le siège. Le dispositif électronique 70a comporte préférentiellement une liaison filaire 71 reliant deux points 74 et 75 du périmètre 21 de la fente 20. La liaison filaire 71 comporte de préférence une diode 72 et une capacité 73 de découplage de la masse à laquelle est reliée la surface conductrice 2. Dans la forme préférentielle en T de la fente 20 représentée sur la figure 2A, la fente 20, de périmètre 21 correspondant à une longueur radioélectrique donnée, comporte une barre centrale 22 et une barre transversale 23 ayant des côtés évasés 24. Les différents éléments vont être décrits plus en détail ci-après.The Figure 2A schematically represents a radiating slot 20 of the antenna and the nonlinear electronic circuit 70 associated with the slot 20, a preferred embodiment of an antenna according to the invention. The slot 20 is seen from above with respect to the figure 1 ; it is etched in the conductive surface 2. The electronic circuit 70 on the example of the Figure 2A has only one electronic device 70a with which it merges. The electronic circuit 70 is controlled by a control device 6 which is preferably common to several electronic circuits 70. The control device 6 comprises for example a control line 61 and a high-frequency decoupling inductor 62 whose slots 20 are headquarters. The electronic device 70a preferably comprises a wire link 71 connecting two points 74 and 75 of the perimeter 21 of the slot 20. The wire link 71 preferably comprises a diode 72 and a capacitance 73 for decoupling the ground to which the conductive surface is connected. 2. In the preferred T-shape of the slot 20 shown in FIG. Figure 2A , the slot 20, perimeter 21 corresponding to a given radio length, comprises a central bar 22 and a transverse bar 23 having flared sides 24. The various elements will be described in more detail below.

Le dispositif électronique 70a a deux états : un état bloqué et un état passant. L'état bloqué ne modifie pas la longueur radioélectrique de la fente 20. L'état passant diminue la longueur radioélectrique de la fente 20 en raccourcissant le périmètre 21 de la fente 20 par court-circuit réalisé entre deux points 74 et 75 du périmètre 21. Donc la fente 20 a la plus grande longueur radioélectrique lorsque le dispositif électronique 70a est dans l'état bloqué. Le changement d'état du dispositif électronique 70a réalise une commutation entre deux états géométriquement différents de la fente 20. Les figures 2B et 2C représentent schématiquement les deux états du dispositif électronique 70a selon l'invention, l'état bloqué est représenté sur la figure 2B et l'état passant sur la figure 2C. Le périmètre 21 effectif de la fente 20 est représenté en traits pleins dans chacun des états du dispositif électronique 70a. La distance d, distance de raccourcissement de la barre transversale 23, correspond à une diminution de la longueur radioélectrique de la fente 20. La diminution de la longueur radioélectrique de la fente 20 doit être suffisamment faible pour que le diagramme de rayonnement de l'antenne reste sensiblement stable, c'est-à-dire présente une stabilité considérée comme suffisante dans l'application considérée, même dans le cas où la ligne 4 d'alimentation reste identique pour les deux états du dispositif électronique 70a.The electronic device 70a has two states: a locked state and a on state. The blocked state does not modify the radioelectric length of the slot 20. The on state decreases the radioelectric length of the slot 20 by shortening the perimeter 21 of the slot 20 by a short circuit made between two points 74 and 75 of the perimeter 21. Thus, the slot 20 has the greatest radio length when the electronic device 70a is in the off state. The change of state of the electronic device 70a switches between two states that are geometrically different from the slot 20. Figures 2B and 2C schematically represent the two states of the electronic device 70a according to the invention, the blocked state is represented on the Figure 2B and the state passing on the Figure 2C . The effective perimeter 21 of the slot 20 is shown in solid lines in each of the states of the electronic device 70a. The distance of shortening distance of the crossbar 23, corresponds to a decrease in the radioelectric length of the slot 20. The decrease in the radioelectric length of the slot 20 must be sufficiently small for the antenna radiation pattern remains substantially stable, that is to say has a stability considered sufficient in the application in question, even in the case where the supply line 4 remains identical for the two states of the electronic device 70a.

Les circuits électroniques 70 sont synchronisés pour que les fentes 20, d'une antenne à plusieurs fentes, présentent entre elles substantiellement la même longueur radioélectrique, c'est-à-dire présentent des longueurs radioélectriques considérées comme suffisamment proches dans l'application envisagée, par exemple en ayant un dispositif 6 de commande commun lequel permet alors par exemple une commande en tension commune de tous les circuits électroniques 70. La valeur du substantiellement dans l'expression « substantiellement la même longueur radioélectrique » dépend des tolérances admissibles dans l'application envisagée. De même dans le cas plus général de fentes rayonnantes commutant d'un état à un autre « sensiblement au même instant », la valeur du « sensiblement » dépend des tolérances admissibles dans l'application envisagée. De préférence, les périmètres 21 et les distances d sont substantiellement égaux pour toutes les fentes 20 de l'antenne.The electronic circuits 70 are synchronized so that the slots 20, of a multi-slot antenna, have between them substantially the same radio length, that is to say have radio lengths considered sufficiently close in the intended application, for example by having a common control device 6 which then allows for example a common voltage control of all the Electronic circuits 70. The value of substantially in the expression "substantially the same radio-frequency length" depends on the allowable tolerances in the intended application. Similarly in the more general case of radiating slots switching from one state to another "substantially at the same time", the value of "substantially" depends on the allowable tolerances in the intended application. Preferably, the perimeters 21 and the distances d are substantially equal for all the slots 20 of the antenna.

La surface conductrice 2, reliée à la masse, établit un écran de protection électromagnétique contre les champs forts aux fréquences inférieures à la fréquence de résonance des fentes 20. Cet écran protège tous les éléments électroniques qui sont derrière la surface conductrice 2 et en particulier derrière le substrat 3.The conductive surface 2, connected to ground, establishes an electromagnetic shield against strong fields at frequencies below the resonant frequency of the slots 20. This screen protects all the electronic elements that are behind the conductive surface 2 and in particular behind the substrate 3.

La fente 20 peut présenter diverses formes. La forme repliée en T représentée sur les figures 2A, 2B et 2C est une forme préférentielle. Soit D1 une première direction et D2 une deuxième direction orthogonale à D1. Les fentes 20, dont une seule est représentée sur les figures 2A à 2C, sont alignées selon la direction D1. La fente 20 comporte deux barres 22 et 23 ; une barre transversale 23 parallèle à la direction D1 reliée au niveau de son centre à une barre centrale 22 parallèle à la direction D2. Ce repliement permet de diminuer l'encombrement selon la direction D2 par rapport à une fente rectiligne selon la direction D2 de même longueur radioélectrique, au détriment d'une réduction de la bande passante. De plus, à fréquences de résonance égales, on constate que le périmètre d'une fente en T est inférieur au périmètre d'une fente rectiligne, ce qui peut s'expliquer par un phénomène de couplage entre la barre transversale 23 d'une part et la barre centrale 22 d'autre part. Ceci amène une réduction supplémentaire d'encombrement.The slot 20 may have various shapes. The folded T shape shown on the FIGS. 2A, 2B and 2C is a preferred form. Let D1 be a first direction and D2 a second direction orthogonal to D1. The slots 20, only one of which is shown on the FIGS. 2A to 2C , are aligned in the direction D1. The slot 20 comprises two bars 22 and 23; a transverse bar 23 parallel to the direction D1 connected at its center to a central bar 22 parallel to the direction D2. This refolding makes it possible to reduce the bulk in the direction D2 with respect to a straight slot in the direction D2 of the same radio length, to the detriment of a reduction in the bandwidth. Moreover, at equal resonance frequencies, it can be seen that the perimeter of a T-slot is smaller than the perimeter of a straight slot, which can be explained by a coupling phenomenon between the transverse bar 23 on the one hand and the central bar 22 on the other hand. This brings a further reduction in size.

On constate également que la forme en T aboutit à une polarisation croisée rayonnée, c'est-à-dire ici une polarisation selon la direction D2, nettement inférieure à celle résultant d'autres types de forme comme une forme classique en L par exemple, ce qui peut s'expliquer par la présence de courants en opposition dans les deux branches de la barre transversale 23 situées de part et d'autre du centre de la barre transversale 23. La barre centrale 22 doit être suffisamment fine, c'est-à-dire que le rapport entre sa largeur et sa longueur doit être suffisamment faible, pour que la fente 20 aie un comportement de fente rayonnant surtout une polarisation rectiligne parallèle à la direction D1 perpendiculaire à sa longueur. De préférence également, le rapport de la longueur de la barre centrale 22 sur la longueur de la barre transversale 23 est suffisamment grand pour que la fente 20 rayonnante rayonne avec une polarisation rectiligne sensiblement parallèle à direction D1, c'est-à-dire comportant un niveau de polarisation croisée suffisamment faible pour l'application considérée. Le terme « sensiblement » dépend de l'application envisagée et des tolérances admissibles en matière de niveau de polarisation croisée. Plus les courants radioélectriques dont la fente 20 rayonnante est le siège sont localisés dans la barre centrale 22 et plus la direction de polarisation du champ rayonné par la fente 20 sera parallèle à la direction D1. Avantageusement, la longueur de la barre centrale 22 vaut sensiblement un tiers du périmètre 21 de la fente 20.It can also be seen that the T-shape results in a radiated cross polarization, that is to say here a polarization in the direction D2, which is markedly inferior to that resulting from other types of shape. as a conventional L-shaped for example, which can be explained by the presence of currents in opposition in the two branches of the crossbar 23 located on either side of the center of the crossbar 23. The central bar 22 must be sufficiently thin, that is to say that the ratio between its width and its length must be sufficiently small, so that the slot 20 has a slot behavior radiating especially a rectilinear polarization parallel to the direction D1 perpendicular to its length . Also preferably, the ratio of the length of the central bar 22 to the length of the crossbar 23 is sufficiently large for the radiating slot to radiate with a rectilinear polarization substantially parallel to direction D1, that is to say comprising a cross-polarization level sufficiently low for the considered application. The term "substantially" depends on the intended application and allowable tolerances for cross polarization level. The more the radio currents whose radiating slot is the seat are located in the central bar 22 and the more the direction of polarization of the field radiated by the slot 20 will be parallel to the direction D1. Advantageously, the length of the central bar 22 is substantially one third of the perimeter 21 of the slot 20.

De préférence, la barre transversale 23 s'évase vers ses extrémités, comme le montre sur la figure 2A le côté oblique 24 de la barre transversale 23. On constate que cet évasement élargit la bande passante de l'antenne. Cet évasement peut être réalisé également le long de l'autre côté de la barre transversale 23 ou bien même simultanément selon les deux côtés de la barre transversale 23, mais dans ces deux cas, le gain en encombrement selon la direction D1 est un peu plus faible que dans le cas représenté sur la figure 2A.Preferably, the transverse bar 23 flares towards its ends, as shown on the Figure 2A the oblique side 24 of the transverse bar 23. It is found that this flare widens the bandwidth of the antenna. This flaring can also be performed along the other side of the crossbar 23 or even simultaneously along both sides of the crossbar 23, but in these two cases, the gain in space in the direction D1 is a little more weak than in the case shown on the Figure 2A .

Lorsque le dispositif électronique 70a est dans l'état passant comme sur la figure 2C, la fente en forme de T n'est plus symétrique, les deux branches de la barre transversale 23 n'ont plus la même longueur ; comme expliqué ci-dessus, la distance d est choisie suffisamment faible par rapport à la longueur de la barre transversale 23 pour que le diagramme de rayonnement de l'antenne reste sensiblement stable. Dans une variante de réalisation, on peut utiliser deux dispositifs électroniques tel que le dispositif électronique 70a, qui pourraient être placés chacun à une distance d/2 des extrémités de la barre transversale 23.When the electronic device 70a is in the on state as on the Figure 2C , the T-shaped slot is no longer symmetrical, the two branches of the cross bar 23 are no longer the same length; as explained above, the distance d is chosen to be sufficiently small relative to the length of the transverse bar 23 so that the radiation pattern of the antenna remains substantially stable. In an alternative embodiment, it is possible to use two electronic devices such as the device 70a, which could be placed each at a distance d / 2 from the ends of the crossbar 23.

La liaison filaire 71 raccourcit la barre transversale 23 et donc diminue le périmètre 21 de la fente 20. Préférentiellement, la liaison filaire 71 est parallèle à la direction D2 et est située suffisamment dans le voisinage du plan de la surface conductrice 2 pour que le court-circuit ainsi réalisé soit efficace et que la longueur radioélectrique de la fente soit réduite sans apparition d'effets inductifs parasites. La liaison filaire 71 peut être réalisée sur l'une ou l'autre face du substrat 3. Un exemple préférentiel de réalisation de liaison filaire 71 est donné à la figure 2D. La liaison filaire 71 est réalisée sous forme de gravure métallique sur la face substrat 3 qui est située du côté opposé à la surface conductrice 2. Comme sur la figure 2A, elle comporte de préférence une diode 72 et une capacité 73 de découplage en série. La capacité 73 vaut par exemple 500pF dans le domaine fréquentiel préférentiel d'utilisation situé autour de 1 GHz. Des trous métallisés 71a et 71b relient la liaison filaire 71 respectivement aux points de court-circuit 74 et 75 situées sur la surface conductrice 2.The wired link 71 shortens the crossbar 23 and therefore decreases the perimeter 21 of the slot 20. Preferably, the wire link 71 is parallel to the direction D2 and is located sufficiently in the vicinity of the plane of the conductive surface 2 for the short circuit thus produced is effective and that the radioelectric length of the slot is reduced without appearance parasitic inductive effects. The wired link 71 can be made on one or the other face of the substrate 3. A preferred embodiment of wired connection 71 is given to the 2D figure . The wire connection 71 is made in the form of metal etching on the substrate face 3 which is situated on the opposite side to the conductive surface 2. Figure 2A it preferably comprises a diode 72 and a decoupling capacitor 73 in series. The capacity 73 is for example 500pF in the preferential frequency domain of use located around 1 GHz. Metallic holes 71a and 71b connect the wire connection 71 respectively to the short-circuit points 74 and 75 located on the conductive surface 2.

La diode 72 est une diode hyperfréquence à deux états de polarisation. La diode 72, généralement une diode PIN, a avantageusement les caractéristiques suivantes : un temps de commutation rapide, par exemple inférieur à 1µs, une tenue en tension inverse importante, de 500 à 1000 volts par exemple, une résistance équivalente en polarisation directe relativement faible, par exemple 0,6 ohms, une capacité inverse très faible, par exemple 0,4 pF. La ligne de commande 61 véhicule des signaux de commande de cette diode, par exemple une tension de -50 volts pour l'état bloqué et un courant de 50 mA pour l'état passant.The diode 72 is a microwave diode with two states of polarization. The diode 72, generally a PIN diode, advantageously has the following characteristics: a fast switching time, for example less than 1 μs, a significant reverse-voltage withstand, for example from 500 to 1000 volts, a relatively low direct polarization equivalent resistance for example 0.6 ohms, a very low inverse capacity, for example 0.4 pF. The control line 61 carries control signals of this diode, for example a voltage of -50 volts for the off state and a current of 50 mA for the on state.

La figure 3 représente schématiquement une vue de dessus d'une antenne préférentielle selon l'invention. L'antenne comporte préférentiellement deux fentes 20 avec des circuits électroniques 70 associés semblables à celui de la figure 2A. Les fentes 20, dont les barres centrales 22 sont parallèles à la direction D2, sont alignées selon la direction D1 qui est la direction de polarisation du rayonnement émis par les fentes 20. L'alignement ainsi obtenu présente un faible encombrement surfacique et permet de réaliser des antennes sous-dimensionnées dont les dimensions sont de l'ordre de la fraction de longueur d'onde de résonance de fente, par exemple de l'ordre de la moitié selon la direction D1 et du tiers selon la direction D2.The figure 3 schematically represents a top view of a preferred antenna according to the invention. The antenna preferably comprises two slots 20 with associated electronic circuits 70 similar to that of the Figure 2A . The slots 20, whose central bars 22 are parallel to the direction D2, are aligned in the direction D1 which is the direction of polarization of the radiation emitted by the slots 20. The alignment thus obtained has a small surface area and allows to achieve undersized antennas whose dimensions are of the order of the slit resonance wavelength fraction, for example example of the order of half in the direction D1 and the third in the direction D2.

Une cloison 51, située de préférence à égale distance des barres centrales 22 des deux fentes 20, parallèle à la direction D2 et perpendiculaire au plan de la figure 3, sépare la cavité 5 en deux parties. La cloison 51 est représentée sur la figure 3 en traits pointillés. La cloison 51 est également reliée à la masse, afin de réduire voire d'éliminer les couplages intracavité, c'est-à-dire à l'intérieur de la cavité 5, entre les fentes 20, par exemple par l'intermédiaire de trous métallisés traversant le substrat 3 et établissant un contact électrique entre la cloison 51 conductrice et la surface conductrice 2. La ligne de commande 61 est reliée à la cloison 51 par une capacité 63 de découplage. La cloison 51 comporte un trou 52 laissant passer une ligne 4 d'alimentation.A partition 51, preferably located equidistant from the central bars 22 of the two slots 20, parallel to the direction D2 and perpendicular to the plane of the figure 3 separates the cavity 5 into two parts. Partition 51 is shown on the figure 3 in dotted lines. The partition 51 is also connected to the ground, in order to reduce or even eliminate the intracavity couplings, that is to say inside the cavity 5, between the slots 20, for example via holes metallized through the substrate 3 and establishing an electrical contact between the conductive partition 51 and the conductive surface 2. The control line 61 is connected to the partition 51 by a capacitor 63 decoupling. The partition 51 has a hole 52 passing a feed line 4.

Sous le substrat 3 non représenté sur la figure 3, est située la ligne 4 d'alimentation des fentes 20, avantageusement une ligne microruban. La ligne 4 d'alimentation est représentée en traits pointillés. Les fentes 20 sont alimentées en série. La différence de phase d'excitation imposée entre les fentes 20 par la ligne 4 d'alimentation permet en partie de dépointer, par rapport à la normale à la surface de l'antenne, le lobe principal du faisceau rayonné par l'antenne. Dans le cas où l'antenne n'est pas complètement plane, la normale à considérer est la verticale au plan moyen au point 0 et passant par le point 0. Le dépointage est aussi lié à un effet de couplage extracavité entre les fentes 20, surtout lorsque celles-ci sont très proches l'une de l'autre, qui sera examiné ultérieurement. Les barres centrales 22 sont espacées sensiblement d'un quart de la longueur d'onde de résonance des fentes 20, ce qui permet par l'établissement d'une différence de phase d'excitation d'environ 90 degrés entre les deux fentes 20 de l'antenne de diminuer fortement les pertes par rayonnement vers l'arrière du lobe principal, c'est-à-dire en direction de la source de la ligne 4 d'alimentation décrite ci-après. Une telle combinaison de deux fentes 20 permet le rayonnement d'un lobe principal à forte inclinaison par rapport à la surface conductrice 2.Under the substrate 3 not shown on the figure 3 , is located the feed line 4 slots 20, preferably a microstrip line. The feed line 4 is shown in dashed lines. The slots 20 are fed in series. The difference in excitation phase imposed between the slots 20 by the power supply line 4 partially allows to detach, relative to the normal to the antenna surface, the main lobe of the beam radiated by the antenna. In the case where the antenna is not completely flat, the normal to be considered is the vertical to the mean plane at the point 0 and passing through the point 0. The misalignment is also linked to an extracavity coupling effect between the slots 20, especially when they are very close to each other, which will be examined later. The central bars 22 are spaced substantially a quarter of the resonant wavelength of the slots 20, which allows by establishing an excitation phase difference of about 90 degrees between the two slots 20 of the antenna greatly reduce radiation losses to the rear of the main lobe, that is to say towards the source of the supply line 4 described below. Such a combination of two slots 20 allows the radiation of a main lobe at high inclination with respect to the conductive surface 2.

La ligne 4 d'alimentation comporte différents tronçons et se termine par une terminaison 44 en circuit ouvert. A partir de la source, non représentée sur la figure 3, la ligne 4 d'alimentation comporte des tronçons 41 intermédiaires, d'une part entre la source et la première fente 20, et d'autre part entre les deux fentes 20. Entre les tronçons 41 intermédiaires et les fentes 20, la ligne 4 d'alimentation comporte des tronçons 42 d'adaptation d'impédance, pour réaliser une adaptation entre l'impédance des tronçons 41 intermédiaires, valant par exemple 50 ohms, et l'impédance des fentes 20 vue par la ligne 4 d'alimentation. L'adaptation d'impédance est obtenue en jouant de préférence sur la largeur des différents tronçons de la ligne 4 d'alimentation. La réalisation de l'adaptation de la ligne 4 d'alimentation résulte d'un compromis entre l'adaptation aux différentes longueurs radioélectriques des fentes 20, afin que lors des changements d'état des circuits électroniques 70, la ligne 4 d'alimentation reste adaptée et que le dépointage du faisceau soit sensiblement conservé pour que le diagramme de rayonnement reste sensiblement stable. L'adaptation permet de conserver un TOS, taux d'ondes stationnaires, relativement faible.The feed line 4 has different sections and ends with an open circuit termination 44. From the source, not represented on the figure 3 , feed line 4 has sections 41 intermediates, on the one hand between the source and the first slot 20, and on the other hand between the two slots 20. Between the intermediate sections 41 and the slots 20, the supply line 4 comprises adaptation sections 42 impedance, to achieve an adaptation between the impedance of the intermediate sections 41, for example 50 ohms, and the impedance of the slots 20 seen by the supply line 4. The impedance matching is obtained by preferably playing on the width of the different sections of the supply line 4. The realization of the adaptation of the power line 4 results from a compromise between the adaptation to the different radio lengths of the slots 20, so that during the changes of state of the electronic circuits 70, the power line 4 remains adapted and that the misalignment of the beam is substantially maintained so that the radiation pattern remains substantially stable. The adaptation makes it possible to keep a TOS, standing wave ratio, relatively low.

La ligne 4 d'alimentation est couplée aux fentes 20 par l'intermédiaire de tronçons 43 de couplage qui excitent les fentes 20. Chaque tronçon 43 est préférentiellement situé au voisinage de l'extrémité de la barre centrale 22 située du coté opposé à la barre transversale 23. L'exemple de la figure 3 montre une excitation optimale dite en « offset maximum », c'est-à-dire en extrémité de fente. A longueur d'onde de résonance de fente donnée, une excitation en extrémité de fente requiert une taille de fente légèrement plus petite que pour une excitation réalisée ailleurs dans la fente. D'où à nouveau, un gain en encombrement surfacique pour l'antenne. La ligne 4 d'alimentation et les fentes 20 étant situées de part et d'autre du substrat 3, l'excitation est réalisée par couplage capacitif.The supply line 4 is coupled to the slots 20 via coupling sections 43 which excite the slots 20. Each section 43 is preferably located in the vicinity of the end of the central bar 22 located on the side opposite the bar. 23. The example of figure 3 shows an optimal excitation called "maximum offset", that is to say at the end of the slot. At a given slot resonance wavelength, slot-end excitation requires a slightly smaller slot size than for excitation elsewhere in the slot. Hence again, a gain in surface area for the antenna. The supply line 4 and the slots 20 being located on either side of the substrate 3, the excitation is performed by capacitive coupling.

Le déphasage imposé par les tronçons de ligne 4 d'alimentation situées entre les deux fentes 20 est partiellement responsable de l'effet de pointage du faisceau de l'antenne. Un autre effet important qui intervient dans le pointage est le couplage extracavité, c'est-à-dire externe à la cavité, entre les fentes 20, le couplage intracavité ayant été pratiquement supprimé par la cloison 51 reliée à la masse. Dans l'adaptation de la ligne 4 d'alimentation, ce couplage doit être pris en considération pour chacune des fréquences rayonnées par l'antenne afin que l'effet de pointage recherché, correspondant à un diagramme de rayonnement spécifique dépendant de l'application envisagée, soit obtenu pour toutes les états des circuits électroniques 70, lesquels états correspondent à des longueurs radioélectriques de fente données et donc à des fréquences rayonnées par l'antenne.The phase shift imposed by the power line sections 4 located between the two slots 20 is partially responsible for the pointing effect of the beam of the antenna. Another important effect that occurs in the pointing is the extracavity coupling, that is to say external to the cavity, between the slots 20, the intracavity coupling having been virtually eliminated by the partition 51 connected to ground. In the adaptation of the power supply line 4, this coupling must be taken into consideration for each of the frequencies radiated by the antenna so that the desired pointing effect corresponding to a specific radiation pattern depends on the intended application. , obtained for all circuit states 70, which states correspond to given radio slot lengths and therefore to frequencies radiated by the antenna.

Les diagrammes de rayonnement obtenus avec l'antenne préférentielle représentée sur la figure 3 sont représentés sur la figure 4. La figure 4 représente schématiquement les diagrammes de rayonnement aux deux fréquences distinctes F1 et F2 qui correspondent respectivement aux états bloqué et passant des dispositifs électroniques 70a. Les diagrammes de rayonnement sont représentés dans le plan P de la figure 3, le plan P étant représenté en traits mixtes et passant au niveau des milieux des barres centrales 22 des fentes 20, parallèle à la direction D1, et perpendiculaire au plan de la figure 3 lequel plan correspond au plan moyen de l'antenne au niveau de ces milieux. En effet, l'antenne n'est pas nécessairement plane, elle peut aussi être conformée à une surface particulière, comme dans une application préférentielle examinée ultérieurement. Les courbes sont en traits pleins pour la fréquence F1 et en traits pointillés pour la fréquence F2. Ces courbes représentent un gain relatif en décibel sur l'axe des ordonnées, en fonction de l'angle entre la direction d'observation dans le plan P et la verticale au plan de la figure 3 passant par le point O visible sur la figure 3, angle exprimé en degrés. Le point O est à égale distance des deux barres centrales 22. L'angle de dépointage obtenu est important, l'angle de dépointage étant l'angle pour lequel la valeur du gain relatif est maximale ; il peut atteindre 40° à 50°.The radiation patterns obtained with the preferred antenna represented on the figure 3 are represented on the figure 4 . The figure 4 schematically represents the radiation patterns at the two distinct frequencies F1 and F2 which respectively correspond to the blocked and passing states of the electronic devices 70a. The radiation patterns are represented in the plane P of the figure 3 , the plane P being shown in phantom and passing at the middle of the central bars 22 of the slots 20, parallel to the direction D1, and perpendicular to the plane of the figure 3 which plane corresponds to the average plane of the antenna at these environments. Indeed, the antenna is not necessarily flat, it can also be shaped to a particular surface, as in a preferential application discussed later. The curves are in solid lines for the frequency F1 and in dashed lines for the frequency F2. These curves represent a relative gain in decibel on the ordinate axis, as a function of the angle between the direction of observation in the plane P and the vertical direction of the plane. figure 3 passing through the visible point O on the figure 3 angle expressed in degrees. The point O is equidistant from the two central bars 22. The misalignment angle obtained is important, the misalignment angle being the angle for which the value of the relative gain is maximum; it can reach 40 ° to 50 °.

Le domaine préférentiel d'application de l'invention est la bande L autour de 1GHz. Les fréquences de l'exemple préférentiel d'application sont les fréquences F1 = 1030 MHz et F2= 1090 MHz, espacées de 60 MHz. La bande passante autour de chacune de ces fréquences est d'environ 20 MHz, soit environ 2%, ce qui signifie que l'allure des diagrammes de rayonnement est sensiblement stable dans ces deux bandes passantes. Les courbes de la figure 4 montrent qu'il est possible d'obtenir des diagrammes de rayonnement stables et similaires sur des bandes passantes étroites, environ 2%, autour de fréquences sensiblement éloignées, leur éloignement relatif est d'environ 6%. Pour obtenir ce résultat de fonctionnement uniquement par élargissement continu d'une bande passante autour d'une fréquence centrale d'environ 1060 MHz, il aurait fallu obtenir une bande passante équivalente de 8%, soit nettement plus que les bandes passantes de 2%. Des relevés de TOS, taux d'ondes stationnaires, montrent que les bandes passantes en diagramme de rayonnement sont également les bandes passantes en TOS pour l'antenne considérée à la figure 3.The preferred field of application of the invention is the L band around 1GHz. The frequencies of the preferred example of application are the frequencies F1 = 1030 MHz and F2 = 1090 MHz, spaced 60 MHz. The bandwidth around each of these frequencies is about 20 MHz, or about 2%, which means that the pattern of the radiation patterns is substantially stable in these two bandwidths. The curves of the figure 4 show that it is possible to obtain stable and similar radiation patterns on narrow bandwidths, about 2%, around substantially distant frequencies, their relative distance is about 6%. To achieve this operating result only by continuously broadening a bandwidth around a center frequency of approximately 1060 MHz, a band would have had to be equivalent pass rate of 8%, significantly more than bandwidths of 2%. TOS readings, standing wave ratios, show that the bandwidths in radiation pattern are also the bandwidths in TOS for the antenna considered at the time. figure 3 .

La figure 5 représente une variante de circuit électronique 70 comportant plusieurs dispositifs électroniques, ici par exemple trois, les dispositifs 70a, 70b et 70c étant similaires à celui de la figure 3 et respectivement situés à des distances d1, d2, d3. Les fentes 20 ont alors un diagramme de rayonnement stable pour plusieurs fréquences, les fréquences correspondant aux différentes tailles de périmètre 21 des fentes 20 pouvant être obtenues avec les dispositifs électroniques 70a à 70c. Cette variante permet par exemple de faire fonctionner l'antenne en mode évasion de fréquence ou en mode correction automatique d'accord en fréquence. Le mode évasion de fréquence requiert par nature une période de commutation en fréquence courte. Le mode correction automatique d'accord en fréquence, lié à la dérive des caractéristiques de l'antenne en fonction de certains paramètres, comme la température par exemple, pourra généralement fonctionner avec une période de commutation beaucoup plus longue.The figure 5 represents an electronic circuit variant 70 comprising several electronic devices, here for example three, the devices 70a, 70b and 70c being similar to that of the figure 3 and respectively located at distances d1, d2, d3. The slots 20 then have a stable radiation pattern for a plurality of frequencies, the frequencies corresponding to different perimeter sizes 21 of the slots being obtainable with the electronic devices 70a-70c. This variant makes it possible, for example, to operate the antenna in frequency evasion mode or in automatic frequency tuning correction mode. The frequency evasion mode naturally requires a short frequency switching period. The automatic frequency tuning correction mode, related to the drift of the characteristics of the antenna according to certain parameters, such as the temperature for example, can generally operate with a much longer switching period.

Dans une application de l'invention, l'antenne est conformée à la surface d'un avion, ce qui lui permet d'avoir, compte tenu de son dépointage de 40° à 50°, un angle d'inclinaison du faisceau en site faible par rapport à l'horizontale, angle qui correspond à une observation vers l'avant de l'avion. Plusieurs antennes de ce type, par exemple quatre, peuvent être alignées parallèlement à la direction D2, formant ainsi un réseau pouvant être commandé électroniquement afin de réaliser un balayage du faisceau dans le plan azimuth de l'avion. Chaque faisceau pointé du réseau couvre avantageusement un secteur limité en azimut de l'espace d'observation qui est ainsi couvert par un balayage électronique de l'ensemble des faisceaux. Un ou plusieurs réseaux d'antennes précédemment décrits permettent de réaliser par exemple un système d'identification, du type IFF (lFF ayant été défini plus haut) fonctionnant à deux fréquences F1 et F2, utilisant des antennes conformées, et couvrant l'espace en avant de l'avion sur un secteur angulaire donné en site et en azimut. Le système d'identification est aussi bien un système air-air qu'un système air-sol.In one application of the invention, the antenna is shaped on the surface of an aircraft, which allows it to have, in view of its misalignment of 40 ° to 50 °, an angle of inclination of the beam in site low compared to the horizontal angle which corresponds to an observation towards the front of the aircraft. Several antennas of this type, for example four, may be aligned parallel to the direction D2, thereby forming an electronically controllable array for scanning the beam in the azimuth plane of the aircraft. Each pointed beam of the array advantageously covers a sector limited in azimuth of the observation space which is thus covered by an electronic scanning of all the beams. One or more antenna arrays previously described make it possible, for example, to produce an identification system, of the IFF type (lFF having been defined above) operating at two frequencies F1 and F2, using shaped antennas, and covering the space in space. before the aircraft on a given angular sector in site and in azimuth. The identification system is an air-to-air system as well as an air-ground system.

Claims (12)

  1. Antenna with radiating slots (20) etched in an earthed conducting surface (2), the radiating slots (20) having a perimeter (21) corresponding to a given radioelectric length, the antenna comprising non-linear electronic circuits (70), an electronic circuit (70) being associated with each radiating slot (20) and comprising at least one electronic device (70a, 70b, 70c) with two states, a disabled state which does not modify the radioelectric length of the slot (20) and an enabled state which decreases the radioelectric length of the slot (20) by shortening the perimeter (21) of the slot (20) by a short-circuit effected between two points (74 and 75) of the said perimeter (21), the electronic circuits (70) being synchronized so that the radiating slots (20) switch from one state to another substantially at the same instant, and the decreases in the radioelectric lengths being small enough for the radiation patterns of the antenna to remain substantially stable, characterized in that since the radiating slots (20) are aligned along a first direction (D1), each radiating slot (20) is T-shaped, the T comprising a transverse bar (23) in the first direction (D1) linked at its centre to a central bar (22) in a second direction (D2) orthogonal to the first direction (D1).
  2. Antenna according to Claim 1, characterized in that the electronic circuits (70) are synchronized so that the radiating slots (20) exhibit between them substantially the same radioelectric length and in that the decrease (d, d1, d2, d3) in radioelectric length is small enough for the radiation pattern of the antenna to remain substantially stable.
  3. Antenna according to either of Claims 1 to 2, characterized in that the electronic device (70a, 70b, 70c) comprises a microwave diode (72) with two polarization states.
  4. Antenna according to any one of the preceding claims, characterized in that the electronic device (70a, 70b, 70c) comprises a wire link 71 substantially parallel to the first direction (D1) and effecting, when the electronic device (70a, 70b, 70c) is in the enabled state, the short-circuit between two points (74 and 75) of the transverse bar (23).
  5. Antenna according to Claim 4, characterized in that the ratio of the length of the central bar (22) to the length of the transverse bar (23) is large enough for the slot (20) to radiate according to a linear polarization substantially parallel to the first direction (D1).
  6. Antenna according to Claim 5, characterized in that the length of the central bar (22) is substantially equal to one third of the perimeter (21) of the radiating slot (20).
  7. Antenna according to any one of the preceding claims, characterized in that the antenna comprises a feed line (4) which feeds in series all the radiating slots (20) in the vicinity of the end of their central bar (22) situated on the opposite side from their transverse bar (23).
  8. Antenna according to any one of the preceding claims, characterized in that the transverse bar (23) flares out towards its ends.
  9. Antenna according to any one of the preceding claims, characterized in that the antenna comprises two radiating slots (20) whose central bars (22) are spaced apart substantially by one quarter of the resonance wavelength of the radiating slots (20).
  10. Antenna according to any one of the preceding claims, comprising sequentially a radome (1), the earthed conducting surface (2), a dielectric substrate (3) and a metallic cavity (5), characterized in that a microstrip feed line (4) is situated in the metallic cavity (5) on the opposite face of the substrate (3) from that where the radiating slots (20) are situated, and in that the cavity (5) is partitioned so as to decrease the coupling between radiating slots (20).
  11. Antenna according to any one of the preceding claims, characterized in that each electronic circuit (70) comprises several electronic devices (70a, 70b, 70c) in such a way that the antenna operates in frequency evasion mode or in automatic frequency-tuning correction mode.
  12. Antenna array, characterized in that the array comprises several antennas according to any one of Claims 1 to 11, a given observation space consisting of observation sectors being covered by electronic scanning of the antenna array, each observation sector being covered by a position of the scan beam of the array.
EP19990402412 1998-10-02 1999-10-01 Selective antenna with frequency switching Expired - Lifetime EP0991135B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9812381A FR2784236B1 (en) 1998-10-02 1998-10-02 ANTENNA WITH FREQUENCY SWITCHING
FR9812381 1998-10-02

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EP0991135A1 EP0991135A1 (en) 2000-04-05
EP0991135B1 true EP0991135B1 (en) 2009-02-11

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DE (1) DE69940393D1 (en)
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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6150989A (en) * 1999-07-06 2000-11-21 Sky Eye Railway Services International Inc. Cavity-backed slot antenna resonating at two different frequencies
DE10047903A1 (en) * 2000-09-27 2002-04-25 Siemens Ag Mobile radio transceiver with tunable antenna
US6388631B1 (en) * 2001-03-19 2002-05-14 Hrl Laboratories Llc Reconfigurable interleaved phased array antenna
US6965349B2 (en) 2002-02-06 2005-11-15 Hrl Laboratories, Llc Phased array antenna
NL2019472B1 (en) * 2017-08-31 2019-03-11 The Antenna Company International N V Antenna suitable to be integrated in a printed circuit board, printed circuit board provided with such an antenna
EP3676910A1 (en) * 2017-08-31 2020-07-08 The Antenna Company International N.V. Antenna suitable to be integrated in a printed circuit board, printed circuit board provided with such an antenna

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4733245A (en) * 1986-06-23 1988-03-22 Ball Corporation Cavity-backed slot antenna
FR2669776B1 (en) * 1990-11-23 1993-01-22 Thomson Csf SLOTTED MICROWAVE ANTENNA WITH LOW THICKNESS STRUCTURE.
JPH0514034A (en) * 1991-06-27 1993-01-22 Nissan Motor Co Ltd Polarized wave generator
JP3224323B2 (en) * 1994-04-06 2001-10-29 日本電信電話株式会社 Antenna circuit
US5754143A (en) * 1996-10-29 1998-05-19 Southwest Research Institute Switch-tuned meandered-slot antenna

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EP0991135A1 (en) 2000-04-05
FR2784236A1 (en) 2000-04-07
ES2321891T3 (en) 2009-06-12
DE69940393D1 (en) 2009-03-26
FR2784236B1 (en) 2006-06-23

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