GB2266995A - Microwave spatial attenuator panel - Google Patents

Abstract

Two conjugate networks of parallel wired-diodes are used which are disposed successively on support panels 2, 2' spaced by one-quarter of the electromagnetic wavelength of a wave which is to be absorbed or passed, and a switch 4 is used to control conjugate weak currents or heavy currents I1, I2 in each of the panels according as the panel is to be active or passive. The invention is applied particularly to protecting microwave antennas against interference echo effects. <IMAGE>

Description

TITLE "MICROWAVE SPATIAL ATTENUATOR PANEL" DESCRIPTION The invention relates mainly to an electricallycontrolled microwave spatial attenuator panel.

More specifically the invention relates to an electrically-controlled microwave spatial attenuator panel capable of conveying transmitted cr received electromagnetic waves through it without substantial attenuation or deformation when it is in a first electrical state and to stop them and absorb them almost totally when it is in a second electrical state.

.k device for attenuating or eliminating some side lobes of the radiation diagram of a microwave antenna is known, as described in French patent specification 79 02918 filed by the present applicants on 5 rebruavy t979 for a microwave matching spatial filter. According to the cited specification the device is made up of parallel conductive wires parallel to the electric field vector E of the wave transmitted by the antenna, the wires wearing diodes disposed in series and distributed at constant intervals on each wire.Each diode-bearing wire is supplied with electric current polarising the diodes in the forward direction, via a switch which is adapted to vary the intensity of the direct current over a wide range of values, from a microampere to about 10 milliamperes. The amplitude of the current travelling through the wires can be modified in accordance with certain laws to produce "holes" in the directions of the side-lobes to be attenuated. The device is efficient if the waves to be attenuated are in a relatively delimited direction. Cn the other hand.

if a number of directions have to be cut off or if the directional xanges are too large, the device is inefficient and serious interference is produced and prevents the results from being efficiently used.

The microwave spatial attenuator panel according to the invention, like the device in the cited specification, uses at least one network of rows of parallel conductive wires or portions of wires stretched in a plane substantially parallel to the electric field vector E of the electromagnetic waves, and the wires are interrupted at intervals by variable controllable resistance components, more particularly diodes.

The device according to the invention is characterised in that it comprises at least three networks of the aforementioned wires, disposed one behind the other at a distance (measured in free space, dielectric coefficient = 1) substantially equal to a quarter of the wavelength of the electromagnetic waves to be absorbed or conveyed, and the networks are connected to at least one switch which, at least When the panel is absorbent, induces electric currents having a value fixed by a function defined for each network, the value of the function being dependent on the constructional characteristics of the panel.

Under these conditions, when the switch sends a current of considerable intensity (e.g. a number of mil.ti- a:nperes) through the wires1 the panel is copletery transparent to electromagnetic waves from the antenna (very low reflection coefficient: TOS 1.1).

On the other hand when the aforementioned weak conjugate electric currents are conveyed through the wires the panel has very high absorption and cuts off substantially all the waves coming from a direction off centre by e.g.

400 relative to the transmission axis of the antenna, without substantially perturbing the main lobe.

In other words, the panel according to the invention has a wide dynamic range ( > 20 dB) of attenuation depending on the currents travelling through the diode wires without inducing a phase shift during tranmission and so as to preserve a low reflection coefficient (TOS 4 1.2 corresponding to one hundredth or- energy lost) in a frequency band of above 10%.

The spatial attenuator panel can have all kinds or applications, e.g. for shuttling off side-lobes of a mechanical or electronic scanning antenna ir. regions other than that at which the antenna is aimed. This will be shown more clearly from the following description.

According to another feature of the invention, the performance of the panel is considerably improved in that metal tapes or tracks are disposed at an angle to the networks of parallel wires and preferably substantially perpendicular thereto, the trade being substantially continuous and forming wave guides and electromagnetically separating the aforementioned controllable resistance components mounted on the aforementioned wires from the adjacent component.

This eliminates secondary interference from resonance between the wires and diodes. The tracks are also advantageously used for supplying the required electricity to the wires so as to make the panel transparent or absorptive as required.

The invention also relates to a method of using an aforementioned panel characterised in that when it is desired to make the panel transparent to electromagnetic waves a large current, e.g. of a number of milliamperes, is conveyed through the networks, whereas in order to make the panel absorbent, weak conjugate currents are conveyed through the two conjugate networks, the intensity being defined in accoroance with the constructional characteristics of the ranel, which under these conditions cuts off most of the transmitted and/or received electromagnetic waves travelling through it without introducing any substantial perturbation or modification in the main lobe of the antenna when aimed away from the panel The invention, the manner of working it and its applications will be more clearly understood from the following description with reference to the accompanying drawings in which: : Fig. 1 diagrammatically shows the basic construction of a network o wires for constructing a panel according to the invention; Fig. 2 i a diagram corresponding to Fig. 1 of an embodiment of a network, shown in the direction of arrow II in rig. 3:: Fig. 3 shows a section substantially along plane III-III of Fig. 2; Fig. 4 shows tile same network from tile other side, along arrow IV in Fig. 3; Fig. 5 is a diagram of another network for differently grouping the power supplies to the diode-bearing wires Fig. 6 is a cut-away view in perspective of an embodiment of a networks corresponding to Fig. 5 Fig. 7 is a smaller-scale view of a panel made up of two juxtaposed networks of the kind illustrated in Figs. 5 and 5, the panel being operated via an electronic switch;; Fig O slows an application of an aforementioned panel, mounted on a radome for protecting radar equipment carried by an aircraft, and Fig. 9 shows the attenuating effect of a panel tuned to the side lobes of an antenna.

In the embodiment illustrated in Fig. I, a network according to the invention comprises electrically conductive wires 101, 102, 103,........ stretched in a plane substantially parallel to the electric field vector E of the electromagnetic waves which are to be absorbed or conveyed.

Variable controllable resistance components such as diodes 111, 121, 131,........ 102, 112, 132...... art mounted at intervals on the conductive wires. Metal tapes or tracks 20, 21,......., 24 are disposed at an angle to the network of parallel wires and preferably substantially perpendicular thereto. The metal tracks separate the controllable resistance compenents 111, 112,......... from the adjacent components 121, 122, In the illustrated example, the end tracks 20 and 24 are used for supplying electric power to the wires supplied in parallel between them.Onus, the electric supply generator can sirriply be connected as illustrated, i.e. at 30 to the input collector track 20 and at 31 to the output collector track 24.

Under these conditions, electric currents having a given intensity can be switched into the network of parallel wires 101, 102, lO3,.......

In the cited French patent specification 79 02913 the amplitude or the current travelling through the network of wires was modified 50 as to cut out some of the side-lobes of an antenna. By contrast, according to the inventions the network of wires is supplied either with a relatively strong current (a number of milliamperes) or a weak current (a zew microanneres) If also, according to the invention, a second similar network (not shown in Fig. 1) is placed prallel to the first network and separated therefrom by a distance (measured in free space, i.e. with a dielectric coefficient of 1) substantially equal to a quarter of the electromagnetic wavelength of the waves to be absorbed or conveyed, the following phenomena will be observed: 1. If the current through the networks is relatively strong, of the order of a few milliartiperes, the panel made up of the two thus-juxtaposed networks will be transparent to the electromagnetic waves. The situation will therefore be the same as if there were no intercepting networks, and the same will of course be true if there is only one network.

2. If on the oEr hand weak currents of the order of a few microamperes are supplied to the two networks, the panel becomes very highly absorbent; in general it will usually absorb 99% of the received power. However, if the currents through the two networks have two specific conjugated values (which depend on the constructional characteristics of each network and can be found e.g. by experiment) it will be seen that a microwave antenna offset e.g. by 500 -from the panel will not, as a result of the presence of the panel suffer any substantial change in its remission spect::i or swore particularly in its main lobds, whereas the side lobes corresponding to the angle of sight of the panel relative to the antenna will be almost totally absorbed. In other words, a panel comprising two conjugate networks placed one behind the other at a distance equal to half the transmission wavelength of the antenna, the networks being supplied with weak currents having a given conjugate intensity, can be used to neutralize and shut off an entire region which is off-centre relative to a scanning direction of the antenna, simply by interposing a panel according to the invention between the centre of the antenna and the directions to be shut off.

We now refer to Figs. 2 - 4, which illustrate an embodiment of a network very similar to Fig. 1, the only difference being that the intermediate metal tracks 21, 22, 23 are periodically interrupted, e.g. once between each pair of adjacent rows of wires such as l01, 102. The only continuous tracks are the end trades 20, 24, which serve as current collectors. This modificasation improves the uniform distribution of currant in the wires, In order1 however, to ensure that the intermediate metal tracks 21, 22, 23 formed from juxtaposed portions 211, 212....

..221, 222,........ are radio-electrically continuous, counter-tracks 21', 22' and 23' are advantageously disposed on the other side of the plate 1 bearing the networks of wires and metal tracks, the counter-tracks being disposed at least substantially as illustrated in Fig 4, opposite the spaces or cuts in tracks 21, 22 and 23.

We now refer to Fig. 5, which illustrates another manner of grousing the power supply to a network of wires stretched parallel to the electric field vector 3.

In this example, the parallel wires are made up of aligned portions 401, 411, 421,......, 402, 412, 422, ........

403, etc, 40n', 41n'...... In the drawing each wire is made - up of three successive portions, but of course there can be any number of portions and in practice the number will be much larger.

A controllable resistance component such as a diode 501, 511,......., 50n, 51n,.... is mounted on each portion of wire. Note that the didres in one row of parallel wires are mounted in the opposite direction from the diodes in the next row.

Each portion of wire is connected from one row to the next (the rows are disposed parallel to the electric f4e'.d vector E) by a portion of metal track similar to the tracks in the preceding drawing. In Fig. 5 the t.~acXQ are marked 6001, 6023......... 6112, 6134,...... 6512,......., 65n-1, n.

In these numbers, the subscripts denote the rows of wires connected by the corresponding track portion.

The portions can then be electrically energized simply via an input collector 70 and an output collector 71 connected to appropriate portions such as 6001, 62015 6401, 60n, 62n, 64n. *Note that in a circuit of this kind, all the diodes are mounted in series between t'o adjacent rows of tracks such as 60-61. 62-63,.....

Figs. 6 and 7 illustrate an embodiment of an afore mentioned network and a microwave attenuator panel constructod according to the invention from two juxtaposed networks of the aforementioned kind.

For simplicity, the drawing shows only some track portions, diodes and portions of wires, but its correspondance with rigs. 5 and 6 is clear.

In practice, the track portions can be metal deposits comprising copper 35 microns thick covered with an 11-micron layer of gold. The input and output current collectors, e.g. 70 and 71, comprise metal tracks deposited on the other side of the dielectric panel support 2, which can have a thickness of e.g. 1.2 mm and be made of a mi:ure of glass and teflon having a low loss tangent of 2.10 and a dielectric constant of the order of 2.55 to 3 000 MHz.

The collectors 70 are connected to the track portions such as 6001, 6201 by metallieed holes 3 which can have a diameter of 0.3 mm.

The distance between two rows of diode wires can be 5 centimetres. The distance between t.n metal tracks between which the diode wires are mounted can be 1. 1.5 centimetres, and the width of the tracks can be of the same order. The distance between two adjacent metal tracks not joined by a diode wire, e.g. 61 and 62, is preferably reduced to e.g. 0.5 cm. The spacing has been exaggerated in the drawing.

Advantagensly the networks are made by the printedcircuit technique ; the diameter of the deposited wires can be 0.5 mm.

If u in a frequency band of 3 000 MHz (S band) corresponding to a wavelength of the order of 10 cn, the panel will be made up of two of the aforementioned juxtaposed networks separated by a distance substantially equal to a quarter wavelength, i.e. 2.5 cm in the chosen example.

The diodes can be e.g. PIN 5082-3080 diodes having a total capacitance of 0.21 pF at below 50 V and a breakdown voltage above 350 V for a current of 10 microamperes.

Under such conditions, when used in a band of 2900 to 3100 MHz, the panel can have the following two states: State No.1. The networks are supplied with nearly the saturation current: Ii = 12 = 20 mA. The panel is passive and transmits more than 99% of the energy of the electromagnetic waves passing through it without inducing any deformation thereof.

State No.2. The networks are supplied with conjugated currents I1 = 200 mA and 12 = 800 mA, The panel is active and has an attenuation above 25 dB, absorbing more than 99% of the power of electrom@netic waves travelling through it.

The currents in question are supplied to the networks by any appropriate electronic supply device 4 as diagrammatically shown in Fig. 7.

The aforementioned panel, as shown more clearly in Fig. 9 shows that if the antenna is out of centre, e.g.

by 50 relative to the panel, there will be no substantial modification in the emission spectrum of the antenna near the main lobe, irrespective of whether the panel is passive (external curve) or active (internal curva). When, on the other hand, the panel Is active, the side-lobes of the antenna are almost completely abscrbr-d in it region of the panel between .D and 900 from the antenna axis. In the curve on rig. 9, this is shown by the shaded area, which represents tile energy of the waves absorbed in this region.

A panel of the aforementioned king have many direct applications. For exan?le, as illustrated in Fig. 8, it can be mounted in a radome 5 carried by an aircraft and disposed at the bottom as shown diagrammativally at 6 in ord.er to cut off interference from the ground, thus improving the operation of an antenna 7 engaged in target acquisition in the plane of sight, e.g. between the positions 7 and 7' of the flat antenna illustrated. The transmitted microfrequency wave is polarized in linear manner, the electric field vector # being in the plane of sight. During the aforementioned acquisition the panel is active and is supplied with the previously-described conjugate currents having a cjiven value. nor the purpose of acquisition on the ground, the panal is made passive by supplying the diode wires with h a large current (usually the saturation current of the diodes), making the panel transparent.

The panel may also be applied inter alia to ground radar installations in order to eliminate harmful interference e.g. from neighbouring radar installations or nearby metal constructions such as hangars which would otherwise give harmful interference.

Of course the invention is in no way limited to the illustrated and dascribed embodiments, which have been given by way of example only. The ivnention includes all technical equivalents of the described means and combinations thereof if made in accordance with the spirit of the invention and embodied in accordance with the following claims.

For example, although the invention has been described with reference to plane panels, the panels can ' curved, e.g. c-ylinerrcally or pherically, without modification, inter alia to match the curvature of the radome protecting the antenna.

Claims (10)

Claims

1. An electrically-controlled microwave spatial attenuator panel adapted to convey transmitted or received electromagnetic waves passing through it without substantial attenuation or deformation when it is in a first electrical state and to stop them and absorb them substantially totally When it is in a second electrical state, the panel being of the kind using at least one network of rows of parallel conductive Mires or wire portions stretched in a plane substanti & ly parallel to the electric field vector E of the waves, the wires being periodically nterrus?ted by variable controllable resistance components, more particularly diodes, the panel being characterised in that it comprises at least three networks of the aforementioned wires (101, 102,......... 401, 411........, 402, 412........) as aforementioned, disposed one behind the other at a distance (measured in free space, dielectric coefficient = 1) substantially equal to a quarter of the wavelength of the electromagnetic waves to be absorbed or conveyed, and the networks are connected to at least one switch (4) which, at least when the panel is absorbent, induces electric currents It, 12 having a value fixed by a function defined for each network, the value of the function being dependent on the constructional characteristics of the panel.

2. A panel according to claim 1, characterised in that metal tapes or tracks (20. 21,........, 60, 61, 62.....) are disposed at an angle to the networks of parallel wires and preferably substantially perpendicular thereto, the tracks being substantially continuous and forming wave guides and electromagnetically separating the aforementioned controllable resistance components (111, 112,....... 121, 122, ........, 501, 502,....., 511, 512.......) mounted on the aforementioned wires from the adjacent component.

3. A panel according to claim 2, characterised in that the wires and the associated controllable resistance components are mounted on one surface of a di-electric panel (1, 2) of appropriate quality and the tracks are mounted perpendicular to the aforementioned wires on one or the other side of the dielectric panel.

4. A panel according to claim 2 or claim 3, characterised in theft the tracks are in electric contact with the wires on one surface of the dielectric panel.

5. 6 panel according to claim 4, characterised in that the tracks (21, 22, 23), apart from the two outside tracks (20, 24) of a network which serve as input and output collectors respectively of the control current, are periodically interrupted, e.g. once between each pair of adjacent rows of wires.

6. A panel according to any of the.-preceding claims, characterised in that the controllable resistance components ere mounted in series in groups, e.g. of 10 to 20, and the groups are electrically energized in parallel.

7. A panel according to claim 6, characterised in that the groups are formed in rows between two adjcent parallel aforementioned tracks (60 - 61, 62 the diodes (5 1 502l...00055111 51210.0.00) are mounted alternately in one and in the other direction on the aforementioned wires, and each track is made up of separate successive portions (6001, 6023......., 60n 6112, 6134......) each in electrical contact with two adjacent diodes @@@@' 502) except for the outer portions (6001, 60n, 62011 62n*eer) which are in contact with the collector (70, 71) for energizing those wires which are in contact only with the end diode (501* 50n, 511, 51n....) in the row.

8. A panel according to claim 5 or claim 7, characterised in that short portions of track ensuring radioelectric continuity of the track are provided on the other side of the panel, opposite cuts ora2d on the tracks.

9. A method of using a microwave spatial attenuator panel according to any of the preceding claims, characterised in that the panel is associated with a transmitting arid receiving antenna and, in order to make the panel transparent to electromagnetic waves,a large current of e.g. a number of milliamperes is conveyed between the networks, whereas in order to make the panel absorbent, weak conjugate currents are conveyed through the two conjugate networks, the currents being defined in accordance with the construc tonal characteristics of the panel, which under these conditions cuts off most of the transmitted and/or received electromagnetic waves travelling through the panel without substantially disturbing or modifying the main lobe of the antenna when it is off-centre relative to the panel.

10. Application of a panel according to any of claims 1 to 8 to radomes protecting antennas for transmitting and/or receiving microwave electromagnetic waves, in order to attenuate the effects of reflection and interferellce coming from a region of space offcentre relative to the main lobe of the antenna, characterised in that the panel is disposed near the antenna in the radome in the direction of the region, the effects of which are to be suppressed.

li. Mierowave spatial attenuator panel substantially as hereinbefore described and as short in the accompanying drawings.

10. Application of a panel according to any of claims 1 to 8 to radomes protecting antennas for tran3- mitting and/or receiving microwave electromagnetic waves, in order to attenuate the effects of reflection and interference coming from a region of space off-centre relative to the main lobe of the antenna, characterised in that the panel is disposed near the antenna in the radome in the direction of the region, the effects of which are to be suppressed.

11. Microwave spatial attenuator panel substantially as hereinbefore described and as shown in the accompanying drawings.

Amendments to the claims have been filed as follows 1. An el electricallr-controlled microwave spatial attenuator panel adapted to convey transmitted or received electromagnetic waves passing through it without substantial attenuation or deformation when it is in a first electrical state and to stop them and absorb them substantially totally when it is in a second electrical state, the panel using rows of parallel conductive wires or wire portions stretched in a plane substantially parallel to the electric field vector E of the waves, the wires being periodically interrupted by variable controllable resistance components, the panel being characterised in that it comprises at least two networks of the aforementioned wires disposed one behind the other at a distance (measured in free space, dielectric coefficient = i) substantially equal to a quarter of the wavelength of the electromagnetic waves to be absorbed or conveyed, and the networks are connected to at least one switch which when the panel is absorbent, induces in each network respective electric currents Ii, I2, each having a reduced value fised by a function defined for each network, the value of the function being dependent on the constructional characteristics of the panel, and when the panel is passing induces currents of large value.

2. A panel according to Claim 1, characterised in that metal tapes or tracks are disposed at an angle to the networks of parallel wires and preferably substantially-perpendicular thereto, the tracks being substantially continuous and forming wave guides and electromagnetically separating the aforementioned controllable resistance components mounted on the aforementioned wires from the adjacent component.

3. A panel according to Claim 2, characterised in that the wires and the associated controllable resistance components are mounted on one surface of a di-electric panel of appropriate quality and the tracks are mounted perpendicular to the aforementicned wires on one or the other side of the dielectric panel.

4. A panel according to Claim 2 or Claim 3, characterised in that the tracks are in electric contact with the wires on on resurface of the dielectric panel.

5. A panel according to Claim 4, characterised in that the tracks, apart from the two outside tracks of a network which serve as input and output collectors respectively of the control current, are periodically interrupted.

6. A panel according to any of the preceding Claims, characterised in that the controllable resistance components are mounted in series in groups, and the groups are electrically energized in parallel.

7. A panel according to Claim 5, characterised in that the groups are formed in rows between two adjacent parallel aforementioned tracks, the diodes are mounted alternately in one and in the other direction on the aforementioned wires, and each track is made up of separate successive portions each in electrical contact with two adjacent diodes except for the outer portions which are in contact with the collector energizing those wires which are in contact only with the end diode in the row.

8. A panel according to Claim 5 or Claim 7, characterised in that short portions of track ensuring radioelectric continuity of the track are provided on the other side of the panel, opposite cuts formed on the tracks.

9. A method of using a microwave spatial attenuator panel according to any of the preceding claims, characterised in that the panel is associated with a transmittIng and receiving antenna and, in order to make the panel transparent to electromagnetic waves, a large current of a number of milliamperes is conveyed through the networks, whereas in order to make the panel absorbent, weak conjugate currents are conveyed through the two networks, the value of the currents being defined in accordance with the constructional chracteristics of the panel, which when supplied with such weak conjugate currents cuts off most of the transmitted and/or received electromagnetic waves travelling through the panel without substantially disturbing or modifying the main lobe of the antenna when it is off-centre relative to the panel.