Method And Device For Radiating Megametric Radio Waves

Abstract

1. A process for radiating megametric radio waves which consists in generating an alternating voltage at extremely low frequency ranging from 1 cycle to 100 cycles per second, applying said voltage to two points which are immersed within a conductive liquid mass close to the free surface thereof and distant from each other by several kilometers in order to create in said liquid mass between said points and close to said free surface current streams parallel to said free surface and capable of generating by radiation electromagnetic waves propagating far off at said extremely low frequency, and rendering negligible the perturbations of said waves under the action of the induction effects produced by the application of said current to said points.

Description

The present invention relates to a method and a device the purpose of which is to radiate radio waves in the megametric frequency and which are particularly directed towards long-distance overland and deep-sea telecommunications.

It is well known that radio waves of comparatively low frequency comprised, say, between 10 kilocycles and 100 kilocycles per second will enable considerable transmission ranges to be achieved overland or underwater. Antennae used to radiate the fields required to obtain such waves are disposed above ground and customarily comprise a vertical element the height of which may often attain 250 meters and an antenna spreader of considerable area the purpose of which is to produce a capacitance effect with the ground in order to increase antenna efficiency.

On the other hand, when it is desired to use such waves to communicate with a submerged receiver unit, depth limitations soon arise by reason of the fact that sea-water considerably attenuates such waves. Thus, for a frequency of 100 kilocycles per second, the attenuation is 11 decibels per meter of water depth, while for a frequency of 10 kilocycles the attenuation is still 3.5 decibels per meter of depth.

In order therefore to achieve communication with receivers submerged at great depth or located at great distance from the transmitting station, it becomes necessary to use very low frequencies, included, for example, between 1 cycle and 100 cycles. For waves of this frequency, the attenuation sustained in sea-water is 0.35 decibel per meter at a frequency of 100 cycles and only 0.035 decibel per meter at a frequency of 1 cycle per second. The difficulty consequently resides in building an antenna capable of radiating electromagnetic energy on such low frequencies. As an example, and by way of comparison, an antenna which for a frequency of 10 kilocycles has a vertical arm 250 meters high and a wire spreader stretching over 25 acres would require for operation at a frequency of 100 cycles per second a height of 25,000 meters and a wire spreader stretching over 2,500 acres. These figures are enough to show that it would be virtually impossible to build such an antenna.

With a view to permitting telecommunication with radio receivers submerged at great depth or located at a great distance from the transmitting station above ground, or else situated at very great altitude above the earth, the present invention has for its main object a method for radiating megametric radio waves, which consists in producing alternating currents at ultra-low frequency included between 1 cycle and 100 cycles per second, and causing the horizontal flow, in sea-water and as close as possible to the surface of the water and over distances of several kilometres, of said alternating currents, in order to obtain, by radiation of the ultra-low-frequency radio energy supplied by said currents, megametric Zenneck waves having an electrical field vector slightly inclined in the direction of propagation, the vertical and horizontal components of said vector respectively enabling receiver stations which are located at great overland distances and submerged at great depth to be reached.

It is a further object of the invention to provide a submerged antenna whereby the aforementioned method may be put into practice, characterized by the fact that it comprises two metal floats distant from each other by several kilometers and supporting fully-immersed electrodes of large size, one of which is connected by an insulated surface cable to the secondary winding of a transformer the primary winding of which is connected to a source of current generating in said secondary winding a difference in potential across said electrodes which alternates therebetween at the extremely low frequency to be used, ranging from 1 c/s to 100 c/s, the secondary winding of said transformer being connected to the other electrode through the medium of an insulated cable immersed at great depth or lying on the sea-bed, the said primary and secondary windings being designed to fully match the load represented by the impedance across said electrodes and said source of current.

The electrodes preferably consist of metal grids, conducting plates or wires connected in parallel. The source of current may conveniently be a mains supply, or be an alternator or a conventional valve-type oscillator. In cases where a mains supply is used, the latter may be chopped in order to obtain coded language. The valve oscillator may be susceptible of modulation or not.

The description which follows, with reference to the accompanying drawings given by way of example only and not in any limiting sense, will give a clear understanding of how the invention may be performed and will bring out further particularities thereof.

In the drawings,

FIG. 1 is an explanatory diagram showing how the Zenneck waves are propagated above ground and under the sea.

FIG. 2 is a schematic illustration of a first embodiment of a submerged megametric-wave antenna according to the invention equipped with electrodes consisting of metal grids.

FIG. 3 is an explanatory diagram showing how the use of the submerged antenna according to the invention leads to the generation and propagation of Zenneck waves.

FIG. 4 is a schematic illustration of a second embodiment of a submerged megametric-wave antenna according to the invention.

FIG. 5 is a schematic illustration of a third embodiment of a submerged megametric-wave antenna according to the invention.

FIG. 6 is a schematic illustration of the manner of propagation of Zenneck megametric waves up to an immersed receiver unit.

FIG. 7 is a schematic illustration of a method of exciting a submerged megametric-wave antenna according to the invention by means of an alternator.

FIGS. 8 and 9 schematically illustrate two other embodiments of the electrodes equipping the antenna according to the invention and respectively consisting of conducting plates in FIG. 8 and of parallel-connected metallic wires in FIG. 9.

FIG. 10 is a schematic illustration of a method of exciting a submerged megametric-wave antenna according to the invention by a mains supply which is chopped to obtain a coded language.

FIG. 11 is a schematic illustration of a method of exciting a submerged megametric-wave antenna according to the invention by a conventional valve oscillator.

FIG. 12 is a schematic illustration of a method of exciting a submerged megametric-wave antenna according to the invention by a valve oscillator associated to a modulator.

Low frequency electromagnetic waves cannot be propagated over large distances above ground unless the "electrical field" vector of the waves is vertical. In fact however, and as shown in FIG. 1, the electrical field vector E of such low frequency waves is always slightly inclined towards the direction F of propagation above the surface of the earth. This vector may be resolved into a horizontal component Ex and a vertical component Ez. The type of wave which generates this electrical field E is known as a Zenneck wave. The vertical component Ez of this electrical field E, travels great distances in the direction F above ground and becomes attenuated as the distance increases; this component enables reception stations located very far from the transmitting station to be reached. The horizontal component Ex of this electrical field E will travel perpendicularly to the surface of the earth in the direction f and, if the wave be travelling over the sea, attain with sufficient amplitude and relatively low attenuation a receiver set submerged at great depth. In FIG. 1 these attenuations are represented, for depths of z.sub.1, z.sub.2 and z.sub.3, by the vectors E.sub.1 x, E.sub.2 x and E.sub.3 x.

FIGS. 2 to 5 show various possible embodiments of submerged antennae which enable an ultra-low-frequency radiation of radio energy generating such Zenneck waves but which retain a size compatible with practical possibilities.

Referring now to FIG. 2, positioned on the surface of the sea are two floats 1, 2 distant by L kilometers from each other and respectively supporting fully immersed large-size electrodes consisting, say, of grids 3 and 4. There is established, across said grids 3 and 4 and alternatingly therebetween at an extremely low frequency ranging for example from 1 c/s to 100 c/s, a difference in potential obtained by means of a transformer 5 disposed in the proximity of the sea and the primary and secondary windings 6 and 7 of which are designed to fully match the load represented by the impedance existing across said grids 3, 4 and the source of alternating current at said extremely low frequency. Said source of current may consist of a mains supply which may be chopped by a chopper 30 (FIG. 10) to provide coded language, or alternatively of an alternator (when the utilization frequency is different from the mains supply frequency) or of a conventional valve oscillator 31 (FIG. 11) which may be modulated or not by means of a modulator 32 (FIG. 12).

Under the effect of the electromotive force developed in the secondary winding 7, an alternating current said extremely low frequency is established in the sea across the grids 3 and 4 in the form of streams parallel to the surface, such as i1, i2, i3. These current streams are channelled by insulated cables 9, 10, of which one, the cable 9 connected to the grid 3 which is nearest to the transformer 5, runs above the surface of the sea and has a relatively small length, while the other, the cable 10 connected to the grid 4, runs along the sea-bed and has a length of several kilometers. Under such conditions the current streams i become comparable to the streams of current circulating in an antenna and generate at said extremely low frequency electromagnetic waves propagating far off. If the perturbation of said waves under the induction of the current flowing through surface cable 9 is negligible, for rendering negligible that of said wave under the action of the current flowing through immersed cable 10, it is most important that said cable 10 should run along the sea-bed at as great a distance P as possible from the surface current streams. In fact, the direction of the current flowing through cable 10 being opposite to that of the streams i referred to, the opposing effect generated by said current is markedly attenuated owing to the losses due to the conductivity of the sea-water for the fields which are propagated across the water depth P. Therefore the energy radiation produced by said current streams i will not be attenuated by the oppositely directed radiation produced by the immersed cable 10. In practice, this depth P will be of the order of some tens of meters.

Since the length of the current streams i (a few kilometers) is always very small in comparison with the wavelength used (several megameters), the radiation resistance of such an antenna is low yet nevertheless sufficient to give rise to considerable radiated power in response to currents of high intensity, and, when the antenna is made to operate with long pulses, this radiated power may substantially exceed the emitted powers which are customarily radiated by radio-telegraphy stations, for frequencies comprised between 10 and 30 kc/s, and which are limited by the corona effect or by insulation faults.

FIG. 3 shows how, whereas the current streams are horizontal, a vertical electrical field may be formed with this type of antenna. The streams i parallel to the surface of the sea set up an electrical field E parallel thereto and parallel to a magnetic field H which is perpendicular to the plane of the figure and likewise parallel to the water surface. The lines of force l1, l2, l3, of the electrical field E curve across the two ends of the antenna since, due to the fact that the wavelength is much greater than the length of the antenna, the lines of force of said electrical field E form into semi-circles above the current streams, as is well known to radio engineers. Thus the line of force l1 produces two electrical fields E'.sub.1 and E".sub.1, the line of force l2 two fields E'.sub.2, E".sub.2, the line of force l3 two fields E'.sub.3, E".sub.3, and so on. The fields E' and E", which are opposite to each other, travel only outwardly from the antenna, along F' and F" respectively, and do not interfere with each other any more than do the magnetic fields H' and H".

As stated precedingly, the electrical fields E'.sub.1, E".sub.2, E'.sub.3 and E".sub.1, E".sub.2, E".sub.3 have horizontal components capable of travelling through the sea and vertical components which travel along the surface of the sea and of the ground. These components thus allow receiver sets submerged at great depth beneath the sea or located at great distances on land to be reached. The semi-circular lines of force of the electrical field E, located above the current streams, ensure propagation of the electrical fields E.sub.1, E.sub.2 and E.sub.3 in the atmosphere, thereby permitting extra-terrestrial communication with space vehicles.

The radiation capacity of this type of antenna can be improved by reducing the difference between the characteristic impedance

Z.sub.o = .sqroot..mu..sub.o /.SIGMA..sub.0

of free space and the characteristic impedance

Z.sub.1 = .sqroot..mu..sub.1 /.SIGMA..sub.1

of sea-water, where .mu..sub.o and .mu..sub.1 are the permeabilities of air and sea-water respectively and .SIGMA..sub.o and .SIGMA..sub.1 their respective permittivities or specific inductive capacities. Thus, should there be disposed above the sea a medium of permeability .mu..sub.2 and permittivity .SIGMA..sub.2, in sufficient thickness and in such a way that the characteristic impedance

Z.sub.2 =.sqroot..mu..sub.2 1.SIGMA..sub.2

of this second medium should be comprised between the characteristic impedance Z.sub.o of free space and the characteristic impedance Z.sub.1 of sea-water, then efficiency will be improved to an extent which be all the greater as the medium of characteristic impedance Z.sub.2 is thicker. Similarly, if there be added above said medium of characteristic impedance Z.sub.2 a further medium of permeability .mu..sub.3 and permittivity .SIGMA..sub.3 having a characteristic impedance

Z.sub.3 = .sqroot..mu..sub.3 /.SIGMA..sub.3

included between that Z.sub.o of air and that Z.sub.2 of the first medium, then the efficiency of such an antenna will be further improved to a marked extent.

FIG. 4 shows a possible embodiment of a submerged antenna of this type. This particular antenna model features a vast basin bounded by walls 11 and 12 of sufficient height to prevent waves from breaking over them onto the antenna even when heavy seas are running. The grids 3a and 4a which serve as electrodes are placed along the length of two opposite walls 11 and 12 and are prolonged by equal-sized grids 3b and 4b arranged outside the basin bounded by those walls. By reason of the shorter path to be followed, current streams such as i1, i2, i3 occur mainly between said walls 11 and 12 rather than outside them. The transformer 5 feeds said grids 3a and 4a through the medium of the insulated cables 9a and 10a.

The supply cable 10a is carefully disposed along the bottom of the basin, whereby its natural radiation is caused to be attenuated by the depth P of sea-water to be crossed. This type of antenna operates in two media. The first medium 13, consisting of sea-water, is at the bottom, whilst the second medium 14, the constants .mu..sub.2 and .SIGMA..sub.2 of which are such that its characteristic impedance

Z.sub.2 = .sqroot..mu..sub.2 /.SIGMA..sub.2

is included between those Z.sub.o and Z.sub.1 of air and sea-water, is above it. The second medium 14 may consist, for example, of petroleum or mineral oil, or any other chemical product which will not react in contact with sea-water and the characteristic impedance of which is included between that of air, namely 377 ohms, and that of sea-water, which is very low. The characteristic impedance of a mineral oil could be 263 ohms, for example.

In the embodiment of a submerged antenna shown in FIG. 5, this antenna, which is of the mobile type, takes the form of a metal ship 15 carrying the transmission equipment 8, 5 and towing a metal buoy 2a through the medium of an insulating tow-line 16. To this buoy is fixed a grid 4c which acts as the second antenna electrode, the first being the metal hull of the ship 15. The transformer 5 is bonded to the ship at 17 and connected to said grid 4c via the insulated cable 10b. Said cable 10b is lone enough to ensure that its average depth below the surface of the water is great. Horizontal current streams such as il, i2, i3 are set up between the hull of ship 15 and the grid 4c as soon as a voltage is established across the terminals of the primary winding of transformer 5.

FIG. 6 shows how a signal from the transmitter is received by a receiver 18 located on the sea-bed and equipped with an appropriate receiving antenna 19. The horizontal component Ex of the electrical field E and the magnetic field H perpendicular thereto, both of which are parallel to the water surface, are propagated towards the bottom of the sea and reach the antenna 19 of receiver 18 after a degree of attenuation resulting from passage through a depth of water P. Concurrently, the vertical component Ez of the electrical field E is propagated through the air in the direction of arrow F.

FIG. 7 shows an embodiment of the transmitting device according to the invention operating in conjunction with an alternator and disposed on the shore. An alternator 20 connected to the primary winding 6 of the transformer 5 is driven by a motor 21 powered off a three-phase main supply 22. The said alternator is excited in long pulses through the medium of its exciter winding 23 connected to a pulse-generating electronic device 24 of any type whatsoever. In the particular embodiment illustrated in FIG. 7, this pulse generator 24 is operated in response to a tape 25 bearing a program recorded thereon in accordance with any principles well-known per se.

It is manifest that many modifications suggested by technology or practical considerations may be made to the embodiments described hereinbefore. By way of example, instead of consisting of grids, the electrodes could be constituted by parallel-connected conducting plates 28, 29 (FIG. 8) or wires 28, 29 (FIG. 9).

Similarly, and in accordance with the well-known principles of reciprocity, the antenna described as a radiation emitter may likewise be used as a receiver. When such is the case, matching between the antenna and the receiver proper is achieved by known means such as a booster transformer.

Claims

What we claimed is:

1. A process for radiating megametric radio waves which consists in generating an alternating voltage at extremely low frequency ranging from 1 cycle to 100 cycles per second, applying said voltage to two points which are immersed within a conductive liquid mass close to the free surface thereof and distant from each other by several kilometers in order to create in said liquid mass between said points and close to said free surface current streams parallel to said free surface and capable of generating by radiation electromagnetic waves propagating far off at said extremely low frequency, and rendering negligible the perturbations of said waves under the action of the induction effects produced by the application of said current to said points.

2. A process according to claim 1, wherein the liquid mass is recovered by at least one liquid substance floating thereon, each liquid substance having a specific impedance comprised between those of said liquid mass and of the material filling up the space above said free surface, the impedance of each liquid substance increasing according to a reverse relation to the distance of said liquid substance from said free surface, whereby the radiating properties of the current streams flowing at said extremely low frequency through said mass between said points close to said surface are improved.

3. A device for radiating megametric radio waves comprising, in combination, a source of alternating voltage at an extremely low frequency ranging from 1 c/s to 100 c/s, a transformer including a primary winding connected to said source and a secondary winding, said source and said transformer being disposed close to a greatly extended liquid mass, two metal floats at the surface of said mass spaced from each other by several kilometers, two fully immersed electrodes of large size respectively supported by said floats, an insulated cable of relatively small length disposed on the free surface of said liquid mass and interconnecting the first electrode which is nearest to the transformer and one end of said secondary winding, and an insulated cable, having a length equal to several kilometers, interconnecting the second electrode and the other end of said secondary winding and immersed within said liquid mass at such a depth that the induction effects resulting from the flowing of said current through said immersed cable are negligible in the superficial portion of said mass existing between said electrodes, said primary and secondary windings being designed to fully match the load represented by the impedance across said electrodes and said source of current, whereby the current streams parallel to the free surface of said liquid mass which are set up between said electrodes on said free surface and through said liquid mass give rise to megametric radio waves generating on the free surface of said liquid mass a plurality of electric fields slightly inclined in their propagation direction and the horizontal component of which vertically propagates inwardly and outwardly of said liquid mass with a slight attenuation while their vertical component propagates at great distance over said free surface and over land with an attenuation varying in terms of distance.

4. A device according to claim 3, wherein each electrode consists of a metal grid.

5. A device according to claim 3, wherein each electrode consists of a conducting plate.

6. A device according to claim 3, wherein each electrode consists of parallel-connected metallic wires.

7. A device according to claim 3, wherein the source of current is constituted by the mains supply.

8. A device according to claim 7, wherein the mains supply are chopped to obtain coded language.

9. A device according to claim 3, wherein the source of current is constituted by an alternator.

10. A device according to claim 9, wherein the alternator has an exciter winding, and further comprising a tape having a program recorded thereon, and an electronic pulse-generating device operated in response to said tape and connected to said exciter winding for exciting said alternator in long pulses.

11. A device according to claim 3, wherein the source of current is constituted by a conventional valve oscillator.

12. A device according to claim 11, wherein the valve oscillator is capable of modulation.

13. A device according to claim 3, wherein the source of alternating current and the transformer are disposed on land in the vicinity of a shore bordering the sea which forms the liquid mass, and wherein the first electrode is immersed at a relatively small distance from said shore, whereby the radiating device is stationary.

14. A device according to claim 13, wherein the immersed insulated cable lies upon the sea-bed.

15. A movable device for radiating megametric radio waves, of the naval type, comprising in combination, a ship having a metal hull, a source of alternating current at an extremely low frequency ranging from 1 c/s to 100 c/s disposed on board, a transformer disposed on board and including a primary winding connected to said source and a secondary winding one end of which is connected to said hull, a metal buoy distant from said ship by several kilometers, an insulating tow-line interconnecting said ship and said buoy, a fully immersed electrode of large size supported by said buoy, and an insulated cable, having a length equal to several kilometers, interconnecting said electrode and other end of said secondary winding and immersed at such a depth that the induction effects resulting from the flowing of said current through said immersed cable are negligible in the superficial portion of the sea existing between said ship and said electrode, said primary and secondary windings being designed to fully match the load represented by the impedance across, on the one hand, said ship and said electrode and, on the other hand, said source of current, whereby the current streams parallel to the surface of the sea which are set up through the sea between said ship and said electrode give rise to megametric radio waves generating on the sea surface a plurality of electric fields slightly inclined in their propagation direction and the horizontal component of which vertically propagates inwardly and outwardly of the sea with a slight attenuation while their vertical component propagates at great distance over the sea and over land with an attenuation varying in terms of distance.

16. A device for radiating megametric radio waves comprising, in combination, a source of alternating current at an extremely low frequency ranging from 1 c/s to 100 c/s, a transformer including a primary winding connected to said source and a secondary winding, said source and said transformer being disposed close to a greatly extended liquid mass, two fully immersed electrodes of large size distant from each other by several kilometers, means for supporting said electrodes in immersed condition, an insulated cable of relatively small length disposed on the free surface of said liquid mass and interconnecting the first electrode which is nearest to the transformer and one end of said secondary winding, and an insulated cable, having a length equal to several kilometers, interconnecting the second electrode and the other end of said secondary winding and immersed within said liquid mass at such a depth that the induction effects resulting from the flowing of said current through said immersed cable are negligible in the superficial portion of said mass existing between said electrodes, said primary and secondary windings being designed to fully match the load represented by the impedance across said electrodes and said source of current; between said electrodes, at least a layer of a liquid substance which floats on said liquid mass, the substance constituting each layer having natural permeability and permittivity characteristics such that their natural impedance is comprised between those of air and liquid of said liquid mass, the impedance of each layer increasing according to a reverse relation to the distance of said layer from the free surface of said liquid mass, and means for keeping each layer between said electrodes.

17. A device according to claim 16, wherein the substance forming each layer is an insulating substance.

18. A device according to claim 16, wherein the substance forming each layer is selected from the group consisting of petroleum and mineral oil.

19. A device according to claim 16, wherein the means for keeping each layer between the electrodes comprises a basin having bounding walls of sufficient height to prevent waves from breaking over them when storm conditions exist over the liquid mass and two of which are distant from each other by several kilometers, and wherein each electrode consists of two parallel elementary electrodes of equal size which are electrically connected at their top, said electrodes straddling the two walls of said basin distant from each other by several kilometers, which two walls act as a means for supporting said electrodes.

20. A submerged antenna usable for emission and reception of megametric radio waves comprising, in combination, two metal floats disposed on a greatly extended liquid mass and distant from each other by several kilometers, two fully immersed electrodes of large size respectively supported by said floats, a first insulated cable of relatively small length disposed on the free surface of said liquid mass and connected to the first electrode, and a second insulated cable, having a length equal to several kilometers, immersed within said liquid mass and connected to the second electrode, said cables being connected, in the case of emission, to a device for generating high power electrical energy at an extremely low frequency ranging from 1 c/s to 100 c/s disposed in the vicinity of the first electrode and, in the case of reception, to a receiver close to said first electrode and matching with the antenna, the depth at which said second insulated cable is immersed, being such that the induction effects resulting from the flowing of a current at extremely low frequency through said second cable are negligible in the superficial portion of said mass existing between said electrodes.