FR2693039A1 - Microwave spatial attenuation panel. - Google Patents

Abstract

The invention relates to a microwave spatial attenuator panel. According to the invention, two conjugate networks of parallel son-diodes are used, arranged one behind the other on support panels 2, 2 'at a distance of a quarter of the electromagnetic wavelength that is to be absorbed or allowed to pass. , and one controls by an electric switch 4 strong currents or weak combined currents I1, I2 in each of the panels depending on whether it is desired that the panel is active or passive. The invention applies in particular to the protection of microwave antennas against parasitic echo effects.

Description

i

  The main subject of the present invention is an electrically controlled microwave frequency attenuator panel.

  than. More specifically, the invention relates to a

  an electrically controlled microwave controlled attenuator, capable of passing electromagnetic waves emitted or received through it without significant attenuation or deformation when in a first electrical state,

  and to block and absorb substantially completely, when in a second electrical state.

  It is already known, as described in the French patent number 79 02918 filed by the same applicant on February 5, 1979 for a "microwave adaptive spatial filter", a device for attenuating or canceling certain secondary lobes of the

  radiation diagram of a microwave antenna According to this patent, the device is composed of parallel conductive wires

  parallel to the electric field vector E of the wave emitted by the antenna, these son carrying diodes placed in series and distributed in a constant pitch on each of the wires Each diode-carrying wire is supplied with electric power of polarization diodes in the forward direction, via a switch which allows to vary the intensities of this DC current in a wide range of values of microamper to ten milliamperes By modulating the amplitude of the current flowing through these son, according to some laws, one creates "holes" in the directions of the side lobes that one wants to attenuate This device is effective if the direction of the waves that one wants to attenuate is relatively delimited By cons, if several directions must be obscured or if the directional ranges are too large, the device is no longer effective and significant parasitic phenomena are generated which no longer allow a good do not exploit the results. According to the present invention, the microwave frequency attenuation panel uses, as the device of the aforementioned patent, at least one network of rows of wires or trunks.

  of parallel conductor wires stretched in a sensible plane

  parallel to the electric field vector E of the said waves

  electromagnetic waves, and said wires are interrupted from

  2 in distance by controllable resistance elements va-

  particularly such as diodes. The device according to the invention is characterized in that it comprises at least two networks of aforementioned son disposed one behind the other at a distance (measured in free space constant dielectric = 1) substantially equal to a quarter of the length of electromagnetic waves that we want to absorb or pass, and said networks are connected to at least one switch which induces, at least when the panel is absorbing, electric currents whose value is determined according to a defined relationship of one network to another, the value of

  this relation being a function of the construction characteristics of the panel. In such conditions, when ordered by the

  mutator the passage of currents of great intensity (for example several milliamps) in the son, one has a panel perfectly transparent to the electromagnetic waves of the antenna (very low reflection coefficient: TOS <to 1.1). On the other hand, when passing the aforementioned weak conjugated electric currents into said wires, a highly absorbent panel is obtained which will virtually obscure

  all the waves coming from a direction detuned for example 400 with respect to the axis of emission of the antenna, without introducing any significant disturbance of the main lobe. In other words, the panel of the invention has a wide dynamic of attenuation as a function of the currents circulating

  the diode wires (> 20 d B), without inducing a phase shift in the transmission and while maintaining a low reflection coefficient (TOS <1.2 corresponding to 1 hundredth of energy lost) 30 and this in a frequency band greater than 10%.

  This spatial attenuator panel makes it possible to envisage all kinds of applications, in particular the blocking of the secondary lobes.

  a mechanical or electronic scanning antenna in the area other than that referred to by the antenna as will be more clearly apparent from the description which follows.

  According to another characteristic of the invention, the performance of the panel is considerably improved by pre-

  indicating, transversely to the networks of parallel wires, and preferably oriented substantially perpendicular thereto, substantially continuous metal strips or tracks, separating said controllable resistance elements mounted on said

son from one element to the next.

  When this is done, the para-

  secondary sites of resonance that can appear between the son and the diodes On the other hand, it is advantageous to use these tracks for the current supply required of said son,

  to obtain at will the transparency of the panel or

milk the absorption.

  The invention also aims at a method of using such a panel which is characterized in that when it is desired to make the panel transparent to electromagnetic waves, a large current is passed through the networks, for example several milliamperes, while when you want to make the

  absorbent panel is passed through the two networks.

  low current currents defined in

  according to the characteristics of the construction of the panel, occult-

  in these conditions most of the electromagnetic waves

  magnetic signals transmitted and / or received passing through the panel without introducing significant disturbance or modification of the main lobe of the antenna when it is detuned from

at the panel.

  The invention, its implementation and its applications appear

  will become clearer with the help of the description that will

  follow, made with reference to the accompanying drawings in which Figure 1 shows in schematic view the general principle of construction of a son network used in the construction of a panel according to the invention; Figure 2 shows as Figure 1 a diagram of an alternative embodiment of such a network, this view being made in the direction of the arrow II of Figure 3; Figure 3 is a sectional view taken substantially along the plane III / III of Figure 2; Figure 4 shows, seen from the other side according to the arrow IV of Figure 3 the same network; FIG. 5 is a schematic view of another network providing a different grouping of the power supplies of the diode-carrying wires 4;

  FIG. 6 is a cut-away perspective view of an embodiment of a network corresponding to the diagram of FIG.

  re 5; FIG. 7 shows on a smaller scale a panel consisting of two juxtaposed networks of the type illustrated in FIGS.

  5 and 6, the operation of this panel being controlled by an electronic switch; FIG. 8 shows an application of such a panel mounted on the protective radome of an airborne radar;

  Figure 9 shows the attenuation effect of a panel tuned to an antenna on its side lobes.

  According to the embodiment illustrated in FIG. 1, a grating according to the invention comprises electrical conductor wires 101, 10, 103, stretched in a plane substantially parallel to the electric field vector E of the electromagnetic waves that are wants to absorb or pass. On these conductor wires are mounted in series at a distance distance variable controllable resistance elements such as diodes 111, 121, 131, 102, 1121 132, on the other hand are provided transversely to the network of parallel son, and preferably oriented perpendicularly to them, metal strips or tracks marked 20, 21, 24 These metal tracks separate the con-25 control elements such as 11, 1121 adjacent elements 121, 122, In the illustrated example, the tracks end 20,24 serve respectively to supply electrical power to the son supplied in parallel between these two tracks The electric generator-power supply can thus simply be connected as illustrated at 30 and 31 respectively to the track 20

  serving as an entrance manifold and at runway 24 serving as a

output reader.

  Under these conditions, it is possible to order the

  passing through the parallel wire network 101, 1021 103, electric currents of determined intensity.

  In contrast to what was done in the aforementioned French patent 79 02918 where the amplitude of the current passing through the network of the wires was modulated, so as to be able to conceal certain

  According to the invention, some secondary lobes of an antenna are passed either a relatively high current (several milliamps) in the wire network or a low current (a few microamperes).

  If, in addition, care is taken, in accordance with the invention, to place parallel to this network, a second similar network

  (not shown in FIG. 1) separated from the first network by a distance (measured in free space, that is to say with a coeffi-

  dielectric value equal to 1) substantially equal to one quarter of the electromagnetic wavelength of the waves that are to be absorbed.

  sorb or let pass, we note the following phenomena. In the case where the intensity which crosses the networks is relatively large, of the order of several milliamonds.

  fathers, the panel consisting of the two networks thus juxtaposed istransparent said electromagnetic waves; everything happens as if there were no interception networks; this is also true if there is only one network. If on the other hand it passes in the two networks of weak currents, of the order of a few microamperes, the panel is very strongly absorbent; it will absorb in general and commonly 99% of the power received; however, if the currents flowing through each of the two networks have two specific conjugate values which are a function of the construction characteristics of each of the networks, and which can be determined, for example, experimentally, it is found that a microwave antenna de-emphasized by As an example of 50 with respect to the panel, due to the presence of the panel, no significant change in its emission spectrum will occur, and more particularly the main lobes of the antenna, the secondary lobes corresponding to the angle of view of the panel versus

  the antenna being almost completely absorbed. In other words, by making use of a panel consisting of two conjugated networks placed one behind the other at a distance equal to one quarter of the transmission wavelength of the antenna. and by passing through these networks

  With a determined conjugate intensity, it is possible to neutralize and obscure an entire region that is detuned with respect to a scanning direction 6 of the antenna by simply interposing between the

  center of the antenna and the directions that one wants to hide a panel according to the invention. Reference is now made to Figures 2 to 4 in

  which illustrates an embodiment of a network very similar to that of Figure 1, and that differs only in that the intermediate metal tracks 21, 22, 23 are interrupted distance distance, for example once between each pair of adjacent rows of wires such as 101, 102 'Only the end tracks 20, 24 serving as a current collector are continuous This modification improves a good and even distribution of the currents in the wires However, the intermediate metal tracks 21, 22, 23 formed juxtaposed trunks 211, 212, 221, 2221,

  If they are radioelectrically continuous, one advantageously has on the other side of the support plate 1

  buckets of threads and metal tracks of the counterpoisers 21 ', 22', 23 'which are deposited at least substantially as illustrated in FIG. 4 opposite the intervals or cuts formed on

tracks 21, 22, 23.

  Reference will now be made to FIG. 5, in which another feed group of the network of wires stretched parallel to the electric field vector E has been illustrated. In this example, the parallel wires consist of

  aligned sections such as 401, 411, 421, 1402, 412, 422, 403 etc., 40 n, 41 n, although in the figure it has been shown that each

  Since the wire consists of three successive sections, it is obvious that the number of these sections can be arbitrary and that in practice it will be much larger. On each section of wire is mounted a controllable resistance element such as a diode 501, 511.50 N, 51 n,

  Note that from one row of parallel son to the next the diodes are mounted in the opposite direction. Each section of wire is connected, from one row to the next

  (the rows being arranged parallel to the electric field vector E) by a section of metal track as the tracks of the preceding figures These sections have been identified in FIG. 5 6001, 6023 61121 61341 65121, 65 nl, n (in this numbering the index numbers refer to the rows of wires connected by the corresponding track section). The power supply of these sections can then be done simply by means of two respective inlet 70 and outlet 71 collectors connected to the appropriate sections.

  such that 601, 6201 '64 1, 60 n, 62 n, 64 n It is found that in such an arrangement all the diodes are connected in series between two adjacent rows of tracks such as 60-61, 62-63, FIGS. 6 and 7 illustrate a practical embodiment of such a network and a panel microwave attenuator cons-

  according to the invention of two such juxtaposed networks. To avoid overloading the figure, only some

  sections of tracks, diodes, and sections of wires, the concordance of FIGS. 5 and 6 appearing in any case clearly

  is lying. The tracks sections can be formed in practice by copper-plated metal deposits of 35 microns thick covered with a gold layer of 11 microns. The inlet and outlet current collectors such as 70, 71 are formed by metal tracks deposited on the other side of the dielectric support panel 2 which may have a thickness of for example 1.2 millimeters and be made of a mixture of glass and teflon, having a low loss tangent of -3 to 2 and a dielectric constant of the order of

2.55 to 3000 MHZ.

  The connection between the collectors 70 and the track sections such as 6001 6201 is made by metallized holes

  3 may have a diameter of 0.3 millimeters.

  The distance between two rows of diode wires may be five centimeters. The distance between two metal tracks

  between which are mounted the diode wires may be 1.5 centimeters, the width of said tracks may be of

  in order of magnitude The distance separating two adjacent metal tracks not joined by diode wires, such as

  and 62 for example is preferably reduced for example to 0.5 centimeter, the spacing having been exaggerated in the drawing.

  The networks are advantageously constituted by the technique of printed circuits, the diameter of the wires deposited can

  to be 0.5 millimeters. In use in a frequency band of 3000 MHZ (S-band) corresponding to a wavelength of the order of centimeters, the panel will consist of two such juxtaposed networks separated by a distance substantially equal to a quarter of the length d In this example, the diode is used as a diode. For example, PIN diodes 5082-3080 having a total capacitance of 0.21 μF are used unless

  V and a breakdown voltage greater than 350 volts for a current of 10 microamperes.

  Under such conditions, for a band of use of 2900 to 3100 MHz, the panel can present two states:

  state number 1: the networks being supplied with current close to the saturation Il = I 2 = 20 m A, it is passive

  It can pass more than 99% of the energy of the electromagnetic waves that pass through it and without inducing any deformation of these waves.

  state number 2 the networks being traversed by conjugated currents Il = 200 microamperes and I 2 = 800 microamps

  The panel is active with an attenuation greater than 25 to 25 dB, absorbing more than 99% of the power of the electromagnetic waves passing through it.

  The currents in question are supplied to the networks by any appropriate electronic power supply device 4 as shown diagrammatically in FIG. 7. Such a panel, as it appears more clearly in FIG. 9, shows that if the antenna is detuned for example from 500 relative to the panel, there is no significant change in the emission spectrum of the antenna in the vicinity of the lobe

  the panel is passive (outer curve) or active (inner curve). On the other hand, when the panel is active, there is practically total absorption of the secondary lobes.

  of the antenna in the region of the panel located between 45 and 90 of the antenna axis, which is reflected in the curve of Figure 9 by the hatched area representative of the energy of the antenna.

  9 waves absorbed in this region.

  Such a panel can receive many immediate applications. For example, as illustrated in FIG. 8, it can be mounted in an airborne radome 5 and disposed at the bottom as schematized at 6 to obscure the spurious effects coming from the earth, allowing thus a better work of the antenna 7, carrying out an objective search in the site plan for example between the positions 7, 7 'of the flat antenna illustrated here. The emitted microwave wave is linearly-polarized polarization. , the electric field vector E being in the site plan In such a search function, the panel is active,

  The passage of the conjugate currents of determined value as indicated above is then applied. If one wants to carry out a ground search, the passive panel is made by passing a large current in the diode wires (generally the saturation current of the diodes). making the panel transparent.

  The panel can also find application in particular on fixed speed radars on the ground to avoid harmful interference.

  For example, other nearby radars or nearby metal constructions such as hangars which would otherwise induce harmful spurious effects.

  Of course, the invention is not limited to the illustrated and described embodiments that have not been given

  By way of example, the invention comprises all the equivalent techniques of the means described and their combinations if they are carried out according to its spirit and implemented.

  within the scope of the following claims. Thus, in particular, although the invention has been described with reference to flat panels, the panels can be

  Bés for example cylindrically or spherically without modification especially to adapt to the curvature of the radome protection.

antenna.

Claims (8)

  1 Electrically controlled microwave frequency attenuator panel capable of passing emitted or received electromagnetic waves passing through it without attenuation   or deformation-important when in a first electrical state and block and absorb substantially completely when in a second electrical state, said pan-   the water being of the type using at least one network of rows of son or sections of parallel conductive wires stretched in a plane substantially parallel to the electric field vector E of said waves, said wires being interrupted remotely by controllable resistance elements , varia-   In particular, such panels are characterized in that it comprises at least two aforementioned networks of wires 101, 1021 * 401, 411, 402, 4121 arranged one behind the other at a distance ( measured in free space dielectric coefficient = 1) substantially equal to a quarter of the   length of the electromagnetic waves that we want to absorb or pass, and said networks are connected to at least one switch 4 which induces at least when the panel is absorbing 20 electric currents II, I 2 whose value is deter- in a defined relationship from one network to another, the   their relationship is a function of the construction characteristics of the panel. 2 Panel according to claim 1, characterized in that it provides, transversely to the parallel son networks, and preferably oriented substantially perpendicular to   they, metal strips or tracks 20, 21,, 60, 61, 62, substantially continuous forming waveguides electromagnetically separating said controllable resistance elements 111, 30, 112, 121, 122, 501, 5021, 51, 512 mounted on the said wires from one element to the next.   Panel according to claim 2, characterized in that said wires are mounted with their controllable resistance elements on one side of a dielectric panel 1, 2 of suitable quality, and said tracks are mounted perpendicularly to said wires on one side and / or the other of said dielectric panel. Panel according to claim 2 or claim 3, characterized in that said tracks are in electrical contact with said wires on one side of said dielectric panel. Panel according to claim 4, characterized in that said tracks 21, 22, 23 except the two end tracks 20, 24, of an array which serve as collectors respectively of supply and of control current output are interrupted by THE DISTANCES   this in distance, for example once between each pair of adjacent rows of son. 6. Panel according to one of the preceding claims,   characterized in that said controllable resistance elements are connected in series in groups, for example from ten to twenty, and said groups are electrically powered in parallel. 7 Panel according to claim 6, characterized in that said groups are formed in rows between two aforementioned adjacent tracks 6 O-61, 62-63, said diodes 501, 502 ', 511, 512 * are mounted alternately in one direction and in the other on said wires, and each track is formed of separate, successive sections 600 1, 6023, 60 n20 6112 and 6134 (which are each in electrical contact with two adjacent diodes 501, 502 except for the sections   ends 6001, 60 n, 62 1, 62 n, which are in contact with the energizing collector 70, 71 of said wires which are in contact only with the end diode 501, 50 n, 511, 51 n25 from the row.   8 panel according to claim 5 or claim 7, characterized in that the right of cuts formed on said   tracks are provided on the other side of the panel of short track sections ensuring the continuity -radioelectric of the-track.30 9 A method of using a microwave frequency attenuator panel according to one of the preceding claims, cat.   characterized in that said panel being associated with a transmitting-receiving antenna, when it is desired to make the panel transparent to the electromagnetic waves, an im-35 carrying current is passed through the networks, for example several milliamonds. -   fathers while when one wants to make the absorbent panel one there   In both conjugate networks, the intensities   conjugated current types defined according to the characteristics   of the panel, obscuring under these conditions most of the electromagnetic waves emitted and / or received that pass through the panel without introducing disturbance   or significant modification of the main lobe of the antenna during   that it is depointed with respect to the panel.   Application of a panel according to one of the claims   1 to 8 to the radomes protecting the transmitting and / or receiving antennas of microwave electromagnetic waves in order to   to mitigate parasitic reflection and interference effects   coming from a region of the space distanced from the main lobe of the antenna, characterized in that said panel is disposed near the antenna in said radome in the   direction of the region whose effects are to be suppressed.