US 2285669 A
Description (OCR text may contain errors)
June 9, 1942..
G. LEHMANN -ANTENNA Filed June 4, 19:53.
wllltvwl'rilwnl W E: .F v. W n 6 n0 A A a a "n. i f Fw? c u A 5 Z J3 Patented June 9, 1942 UNITED STATES PATENT OFFICE ANTENNA ration of France Application June 4, 1938, Serial No. 211,860 In France June 10, 1937 12 Claims.
The present invention relates to antennas or systems of antennas for emitting or receiving radio-electric waves. It is applicable both to receiving antennas and to emitting antennas and it is more especially concerned with antennas utilized in the case of short or very short waves.
It is known that, in the case of very short wave-lengths, there is considerable advantage in choosing the length of the antenna in accordance with the wave-length that is radiated or received. There are half-wave antennas, quarter-wave antennas and so on. Theory and experience teach that the radiating (or receiving) power of such an antenna decreases considerably as soon as it is used in connection with a wave-length different from that to which it is tuned. Furthermore, in the case of an emitting antenna, the feed is then rendered very difficult because of the considerable variation of the impedance of utilization of the antenna.
On the other hand, antennas are generally located at places where access is practically impossible (top of a mast or of a, building) and anyway it is very difiicult to modify their lengths once they have been fitted. However, it is highly desirable to be able to utilize such an antenna for a whole range of wave-lengths while preserving inside said range substantially the same radiating properties and the same characteristics from the point of view of the emitting (or receiving) apparatus with which it is coupled.
The object of the present invention is to provide an antenna system which complies with this condition without requiring any modification of the mechanical and geometrical properties of the aerial when mounted in position.
In the following description, the invention will be set forth by referring more specifically to the case of a bipolar antenna, but of course the invention is not in any way limited to this particular case and it applies'to all kinds of aerials constituted either by combinations of bipolar antennas or, more generally, to systems of conductors in which stationary waves are produced.
It is known that a bipolar antenna which J emits on the wave-length for which it has been studied is the seat of stationary waves, and on the other hand it is also known that stationary waves are equivalent to two progressive waves, of
the same amplitude and moving in opposite directions.
On the other hand, the elementary study of progressive or travelling waves shows that when The essential feature of the present invention consists in replacing the conductor, or a conductor element, of an aerial system. by two wires located at a short distance from each other and forming a circuit closed through an impedance intended to absorb the progressive waves without reflecting them. In the case of a bipolar antenna element, the two elementary conductors are directly connected together at their ends and in their middle parts there are inserted, respectively, the current feed system for one of them, and this impedance for the other one. The value of this impedance, determined experimentally, is substantially equal to the characteristic impedance of the line equivalent to this pair of conductors.
With this arrangement, only progressive waves flow through. this antenna system, in opposite directions for the respective wire elements thereof, so that the field produced at great distance by this system of two wires is equal to that of a corresponding bipolar antenna of the usual type, since the radiations of the respective wires are combined so as to produce a composite radiation equivalent to that of such an antenna of the usual type.
On the contrary, this system of two wire elements may be considered, from the point of view of the current feed, as equivalent to a conductor closed through' its characteristic impedance, so that the feed characteristics remain constant when the wave-length varies.
This assimilation of two separate conductors located at a short distance from each other with a single antenna conductor is supported by, ex-
Antennas of the di-pole type, employed with short wave lengths have characteristics (especially the impedance) which are very readily influenced by objects located near them, and especially by metallic bodies. This is above all due to the fact that the lines of force of the fields produced and passing from one portion to the other of the wire constituting the antenna spread out greatly around thelatter and consequently are modified by the adjacent dielectrics or conductors; these are antennas which may for this reason he called open antennas. The antenna of the present invention is in this sense a closed antenna since the lines of force passing from one portion ofthe wire to the other remain in the immediate neighborhood of the antenna, and hence it is insensitive to local objects, an insensitivity that is completely proved by experience.
Other features of the present invention vin'll result from the following detailed description of some specific embodiments thereof.
Preferred embodiments of the present invention will be hereinafter described, with reference to the accompanying drawing, given merely by way of example, and in which:
Fig. 1 shows an aerial constituted, in the known manner, by a bipolar conductor;
Fig. 2 diagrammatically shows an aerial of equivalent construction, made according to the present invention;
Fig. 3 is a similar view, with indications thereon for the explanation of the operation of this system;
Fig. 4 diagrammatically shows another embodiment of the invention.
The known structure illustrated by Fig. l ineludes: at I the emitting winding for the feed of current to the aerial, at 2 the feed conductors, at 3 the coupling system, at 4 the two branches of the bi-polar conductor, the length of each branch being equal, in the case illustrated by this figure, to one fourth of the wave length that is emitted.
Fig. 2 shows an embodiment of the system according to the invention, reference character I still designating the emitting means and 2 the feeding conductors. According to the principle of the invention, the aerial includes two elementary wires, to wit CABD on the one hand, and CEFD on the other hand, these rectilinear wire elements being parallel and located at a small distance from each other as compared to the wave length that is emitted. The elementary wires are connected together at their ends and D by regular loops the size of which (the diameter in the case of a circular loop) is small with respect to the diameter of the wires. Between points E and F there is inserted an impedance 6 the value of which is substantially equal to the characteristic impedance of the double conductor ACE, BDF. On the other side, points A and B are connected to the feeding system through wires 2. This arrangement has been shown by way of example as it is the simplest one. But other coupling means, for instance one including a transformer, might be used according to the invention.
The operation of this aerial may be explained as follows:
As the line circuit ACE, BDF is closed through an impedance equal to its characteristic impedance, only progressive waves moving in the direction of arrows (Fig. 3) 'flow through this circuit. The same applies to the conductors of the feeding system, which is also closed on its characteristic impedance.
The radiation produced by the feeding conductors in themselves is zero since, at each point of a transverse section thereof, the currents, at any time, are equal and of opposed directions so that the equivalent current, from the point of view of the radiations, is "zero.
On the contrary, considering two points M, N
of the wires of the aerial located at the same height X above point D, the values of the currents I1, 12 at these points are given by the following equations (at least approximately) These equations are true subject to the only condition that the bend at C does not modify the propagation of the waves and this is supported by experience.
It will be noted that the form of these equations is the same for both, with the difference of the sign of the term which was obvious since, starting from C, X increases in the direction of propagation of the waves in one of the branches and it decreases in the other branch.
From the point of View of the field produced at great distance and since the distance between the two branches is small as compared with the wave-length, the radiation obtained is identical to that produced by a single conductor the intensity of which would be the sum of the two above indicated intensities. Now, this algebraic sum has the following value:
I =I -I =2A sin 21% cos 21% It will be noted that this equivalent current is equal to that of a bipolar antenna tuned to the wave-length, the intensity at the loop points of the current being equal to twice the intensity of each progressive wave.
This calculation clearly shows the existence of the radiating power of this aerial and its results are fully substantiated by experience.
On the contrary, concerning its feed, this aerial, through which only progressive Waves flow, has the particularly important advantages above pointed out.
For practical purposes, experience teaches that the wave-length can vary within a relatively wide range. As an approximate indication, the ratio in which L is the distance CD, should be greater than 0.8 and smaller than 3.
The upper limit is determined chiefly by the admissible loss of energy produced by the ohmic resistance of impedance 6, and the lower limit is determined by the drop of the radiating power.
Within these limits, the impedance of the aerial remains substantially fixed, which involves that the impedance of the feeder also remains fixed and the radiating power keeps a high value.
Fig. 4 illustrates the application of the invention in the case of an aerial having a single branch of conductors and of the quarter-wave type. In this case also:
I is the emitting means 2 the feeder conductors;
the aerial is constituted y the elements AC and CE of parallel rectilinear Wires.
The end E closes on the feeder generally by being earthed, through the intermediate of impedance I the value of which is equal to the characteristic impedance.
It will be noted that the examples above set forth concern aerials which, being arranged vertically, have no directive effect in the horizontal plane.
However, the invention is not limited to these examples and it is applicable to all aerials including bipolar systems (provided that these systems do not include inert reflecting bipolar antenna elements) which may be devised especially with a view to obtaining directive efiects.
' The present invention therefor permits of replacing tuned bipolar antenna elements by aperiodic systems which can be used within wide ranges of wave-lengths.
As a matter of fact, the present invention permits, in any aerial system including conductors in which stationary waves are formed, of replacing each of these conductors by two wires through which flow progressive waves moving in opposite directions, which permits, while keeping the radiating power of the aerials, of utilizing them within a very wide range of wave-length.
In a general manner, while I have, in the above description, disclosed what I deem to be practical and eflicient embodiments of the pres ent invention, it should be well understood that I do not wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of the present invention as comprehended within the scope of the appended claims.
What I claim is:
1. An omni-directional aerial element constituted by two similar conductors connected together at one of their ends and arranged parallel to each other and spaced apart to an extent which is very small with respect to the shortest wave to be handled by said element, an impedance substantially equal to the characteristic impedance of said two conductors for terminating the end of one of said conductors remote from the connected end whereby said conductors are traversed by progressive waves, a feeder connected to the other of said two conductors remote from the connected end, said two conductors being so close together that the aerial element is characterized by its substantially constant radiation characteristics over a wide range of wavelengths,
2. A bipolar antenna element, comprising: in combination, two wire elements directly connected together at their respective ends, said wire elements being rectilinear, parallel to each other and located close to each other compared to the shortest wavelength employed, one of said elements being adapted to be fed with current in its middle part, and an impedance of a value substantially equal to the characteristic impedanceof the line formed by said two wire elements, said impedance being connected in series with the middle part of the other of said wire elements, said impedance being calculated to let progressive waves moving in opposed directions to flow through said wire elements, said antenna element being characterized by its substantially constant radiation characteristics over a wide range of wave-lengths.
3. In an antenna system including current feed means, an antenna element for said system which comprises, in combination, two elementary wires directly connected together at at least one of their respective ends, said elementary wires being rectilinear, parallel to each other and located close to each other compared to the shortest wavelength employed, means for connecting said current feed means in series with an intermediate part of one of said elementary wires, and an impedance inserted in the other elementary wire of a value equal to the characteristic impedance of the line formed by these two elementary wires, so as to let progressive Waves moving in opposed directions to flow through said elementary wires, said antenna element being characterized by its substantially constant radiation characteristics over a wide range of wave-lengths.
4. An antenna element according to claim 3 in which said impedance and the corresponding end of the other wire are both grounded.
5. An antenna system adapted for use over a wide range of high frequencies, comprising: a plurality of antenna conducting elements; leadin conductors connected to a pair of said antenna elements; a second pair of said antenna elements disposed adjacent and substantially parallel to corresponding elements of said first pair of antenna elements and connected to respective ends of said first pair of antenna elements; the spacing between each of said first pair of elements and the adjacent and parallel one of said second pair of elements being small compared to the shortest wavelength employed whereby these elements per se are substantially non-directive; and an impedance equal substantially to the characteristic impedance of said antenna elements conductors connected between said second pair of antenna elements whereby progressive waves moving in opposite directions flow through adjacent ones of said antenna conducting elements.
6. An antenna system adapted for use over a wide range of high radio frequencies, comprising: a pair of antenna conductors arranged substantially as a di-pole; lead-in conductors for either feeding current to or receiving current from said antenna conductors; a second pair of antenna conductors positioned side by side to and only a small distance, compared to the shortest wavelength employed, away from said first pair of antenna conductors; an impedance bearing a predetermined impedance ratio to the characteristic impedance of said pair of antenna conductors and being connected to adjacent ends of said second pair of antenna conductors; and connections between the opposite ends of said second pair of antenna conductors and the respective ends of said first pair of antenna conductors.
'7. An antenna system, comprising: a substantially non-directive element having two parallel conductors spaced only a short distance from each other compared to the shortest wavelength employed; said conductors being connected to each other at one end; lead-in conductors; means for connecting one of said lead-in conductors to one of said parallel wires; an impedance of a value substantially equal to the characteristic impedance of the line formed by said two conductors, said impedance being connected to the other one of said parallel wires; and means for connecting said impedance to another one of said lead-in conductors, said impedance being of a magnitude such that progressive waves moving in opposite directions are permitted to flow through said parallel antenna conductors, said parallel conductors being positioned so close to each other that the antenna element may be used over a wide range of wave-lengths with substantially constant radiation characteristics.
8. An omni-directional aerial element as set forth in claim 1 including, a second feeder and a grounding connection between said impedance and said second feeder.
9. An antenna system comprising a conductor having a pair of separated arms, another conductor arranged parallel to said first conductor and closely spaced therefrom, a transmission line directly connected-to the adjacent ends of said pair of arms, and means for connecting said arms to said other conductor at points removed from said adjacent ends, said other conductor having a lumped resistor located substantially in the center thereof connected electrically in series relation thereto to provide a traveling wave effect for Waves traveling along said conductors,
10. An antenna system comprising a conductor having a pair of separated arms, another conductor arranged parallel to said first conductor and closely spaced therefrom,-a transmission line directly connected to the adjacent ends of said pair of arms, and means for connecting said arms to said other conductor at points removed from said adjacent ends, said other conductor having a lumped impedance located substantially in the center thereof connected electrically in series relation thereto to provide a traveling wave effect for waves traveling along said conductors 11. An antenna system operative over a wide range of frequencies comprising an aerial conductor having a pair of separated arms arranged end to end and providing terminals at the adjacent ends of said arms, another aerial conductor arranged parallel to said first conductor and spaced very close thereto relative to the length of the operating wave, connections between the ends of said last conductor and points on said arms removed from the adjacent ends of said arms,
whereby the impedance of said antenna system at said terminals is increased over that of a single conductor dipole, and a two-wire open feeder line having a predetermined impedance directly connected to said terminals, an impedance connected into said other aerial conductor, said last impedance being of the order of the characteristic impedance of said aerial conductors whereby said antenna system has an extremely flat i-rnpedance versus frequency characteristic over said range of frequencies.
12. An antenna system comprising a conductor having a pair of separated arms, another conductor arranged parallel to said first conductor and closely spaced therefrom, a transmission line directly connected to the adjacent ends 'of said pair of arms, and means for connecting said arms to said other conductor at points removed from said adjacent ends, said other conductor having an impedance located substantially in the center thereof connected electrically in series relation thereto of such value as to produce a traveling wave effect for waves traveling along said conductors.