US2977595A - Directional slot antenna - Google Patents

Description

March 23, 1961 s. ZISLER ETAL 2,977,595

DIRECTIONAL SLOT ANTENNA Filed July 16, 1956 2 Sheets-Sheet 1 March 28, 1961 s. ZISLER EI'AL 2,977,595

Fi llllllllllll 56 DIRECTIONAL SLOT ANTENNA Siegfried Zisler, Bievres, and Sigmund von Welser, Paris, France, asslgnors t Societe Frangaise Sadir-Carpentier, Paris, France, a corporation of'France Filed July '16, 1956, Ser. No. 598,012 Claims priority, application France July 28, 1955 8 Claims. (Cl. 343-769) Our invention has for its object a directional aerial of the slotted type. According to our invention we resort to circular or rectangular slots and the directional properties are obtained firstly by feeding the slot with a high frequency voltage applied between two points located to either side of said slot and on the other hand by inserting between two further points facing each other a connection constituted by a resistahce'or a short-circuit or else by providing the slot with a variable breadth along its periphery. These two last manners of obtaining a suitable directivity may in fact be applied simultaneously. A third method consists in feeding the slot not only between two points facing each other but across a plurality of such pairs of points. The high frequency voltages applied to these different pairs of points are adjusted both as to amplitude and as to phaseso as to produce the desired directional diagram.

According to a further feature of our. invention, the radiation produced by one of the surfaces of the metal foil in which the slot provided is cut through a cavity of a predetermined shape located on the side of the foil the radiation from which is to be cut out.

According to a further feature of our invention, we

use the same slot for'producing selectively as desired embodiments thereof, given by way of examples and byv no'meansin a limiting sense. In the drawings illustrating said embodiments:

Fig. 1 shows a slot constituted by an annular slot of constant breadth.

Fig. 2 is a vertical cross-section of the slotted foil associated with a cavity in registry with the slot.

Figs. 3 and 4 show two modifications of the. slot.

Fig. 5 is an. explanatory graph.

Fig. 6' is a modification. of Fig. 2.

Figs. 7, 8 and 9 relate to further modifications.

Fig. 10 is a wiring diagram.

As already explained, the slot is fed with high frequency current between two-points 1 and 2 facing each other to either side of the annular slot shown in Fig. 1, said points being located on a common radius of the concentric edges of the slot; preferably the point 1 on the outer edge of the slot is grounded for instance through connection with the sheath of a coaxial cable while the point 2 is connected with the core of said cable. I

The radiation is somewhat dissymmetrical, it is true, as a consequence ofthe application of the high frequency voltage between the points 1 and 2, but in many applica- .tions, the diagramobtained is not sufliciently directional.

{Patented Mar. 28, 1961 In order to increase the directivity, we provide according to our invention between two further points 3 and 4 facing each other to either side of the slot a metal strip forming a short-circuit or a resistance of a suitable value.

We have shown in Fig. 1 points 3 and 4 located on the same diameter as the points 1 and 2 and on the other side of the center of the slot. This arrangement is of advantage, but it is not essential audit is even possible to resort 'to a plurality of short-circuits or of resistances across the slot.

The desired directivity may also be obtained by feeding the slot not only across a single pair of points 1 and 2 but across a plurality of pairs, say three pairs of points such as 1-2, 5-6 and 7-8 as illustrated in Fig. 1. In such an embodiment, the same coaxial cable may feed the three pairs of points and the control of the phase and of the amplitude of the voltages applied between the points 5-6 and between the points 7-8 is provided by inserting, in elements fed by the coaxial cable for feeding said supplementary pairs of points 5-6 and 7-8, suitable attenuators and phase-shifters.

In the embodiment illustrated in- Fig. 1, a simple substantially fiat metal sheet is used, which sheet is provided with the slot so that consequently the radiations are identi* cal on either side of the sheet.

However, it may be of interest to cut out the radiation produced by one of said sides if such a radiation appears to be unnecessary. We reach this result byresorting to a well-known arrangement, to wit theassociation of a cavity with the side, the radiation from which is to be cut out. Such a cavity is shown in Fig. 2 in which are illustrated across-sectionally a first sheet with the points 1-2 and 3-4 thereon and the cavity constituted by a box 2t? of a suitable size.

The directivity pattern may be modified by resorting to a variable breadth slot. Fig. 3 shows such an arrangement which is obtained by using as a slot the empty space comprised between two non-concentric circles of which one forms the inner circle having its center at C.

1 and 2 designate again the feeding points for the slot and 3 and =4 the points between which is inserted the shortcircuit or the resistance. In this arrangement, the slot has its maximum breadth'in correspondence with the feedingpoints 1 and 2 and its minimum breadth. in registry with the points. 3 and 4. Obviously, the reverse arrangernent is also possible.

The slotted aerial according to our invention may also serve for executing two radiation patterns which are symmetrical with reference to an axis. This may be obtained very simply by feeding two different pairs of points and by changing the location of the short-circuit or of the resistance. across the slot. This isillustrated in Fig. 4 showing a slotted aerial of the type illustrated in Fig; 1. In order to obtain the first pattern we feed voltage across the points 1 and 2 and we insert a short circuit or resistance between the points 3 and 4, while the other pattern is obtained throughthe use of the feeding points 11-12 and of a short-circuit or a resistance at 13-14. The system of points 1, 2, 3, 4. is symmetrical of the system of points 11, 12, 13, 14 with reference to the axis A-A.- Fig. 5 illustrates as a solid line the pattern corresponding to the pairs 1-2 and 3-4, while it shows as a dotted line the pattern corresponding to the other pairs 11-12 and 13-14. Obviously, said two patterns are symmetrical with reference to the electrical axis of symmetry A-A of Fig. 4. g

It should be remarked thatthe size of the slot i.e. its developed length and its breadth isby no means critical for a predetermined wave length to be used. .In. other words, these two parameters may vary to alarge extent without any substantial modification in the directional pattern. a I

The aerial described radiates a field, the major part of which is polarized in a plane perpendicular to the plane of the aerial. In certain cases it is of interest to modify this polarization, or speaking more generally, to set the plane of polarization in any desired direction.

This result may be achieved in conformity with a further feature of our invention by adopting for the metal section located inside the slot a shape which is no longer fiat, but curved. This is illustrated in Fig. 6 which is a cross-sectional view similar to that illustrated in Fig. 2 including to one side of the metal sheet a cavity 20 enclosing the slot. The inner metal disc bounded by the slot is given for instance a convex shape as illustrated in solid lines or a concave shape as illustrated in dotted lines.

Experience shows that the fact of using such a concave or convex shape provides for a modification in the polarization of the radiation.

It is furthermore not necessary, when executing the invention, for the inner disc defining the slot inwardly to be solid and it is in fact possible to cut it in the manner shown in Fig. 7 in which said disc is given an annular shape while the slot is provided as precedingly with feeding points at 1 and 2 and with a short-circuit or resistance at 3 or 4. Now, in the case illustrated in Fig. 7, the inner disc on which the points 2 and 4 lie is cut so as to form a metal ring and experience shows that this removal of the central section of the disc does not modify in practice the properties of the aerial.

In this modification, it is also possible to adjust the direction of polarization by retaining the flat ring provided with the points 2 and 4 and by locating inside the open central section of said ring, a suitably sized auxiliary aerial having a predetermined direction of operation.

We have described, hereinabove, circular aerials, but our invention is, by no means, limited to such an embodiment. The shape of the slot may be modified within broad limits while retaining the results sought for. By way of example, Fig. 8 shows an aerial the slot in which is rectangular. Here again the central section of the rectangle limiting the slot inwardly may be removed: for instance the section bounded by the dotted line may be removed.

It'has also been assumed hitherto that the points feeding the aerial were located on the actual edges of the Slots. This arrangement is not essential and Fig. 9 shows that it is possible to feed the slot between a point 1 located on its outer edge and a point 2 located on the same radius as the point 1 and well inside the inner disc.

We have mentioned hereinabove that there was provided between points such as 3-4 of Fig. 1, a connectigln forming a short-circuit or a resistance of a suitable v ue.

The modification in the value of said resistance and the change of location of the short-circuit may be performed without any mechanical switching by resorting, in accordance with a further feature of the invention, to rectifiers, the biasing of which is modified through purely electrical means.

By way of example, we will disclose with reference to Fig. 10 an embodiment of this type applicable to the aerial illustrated in Fig. 4. Thus, the feeding is performed alternatingly across the points 1 and 2 and 11 and 12 and a connection such as a short-circuit or resistance of a suitable value may be inserted as required selectively across the points 3-4 and 13--14.

According to the last feature referred to, the points 11 and 1 are permanently connected with the outer sheath of the coaxial cable 30 feeding the high frequency energy. p y g The core of said cable 30 is connected onthe other hand through a condenser 21 forming a short-circuit for the frequencies to be considered with the two points 2 and 12 through the rectifiers 22 and 23 which are connected in opposite directions with the inner disc of the aerial at said points 2 and 12 respectively.

Between the points 3 and 4 are inserted in series a resistance 24 and a rectifier 25 adapted to provide for the passage of current towards the point 3. Similarly, between the points 13 and 14 are inserted in series a resistance 26 and a rectifier 27 allowing the current to flow towards the point 14; thus the two rectifiers 25 and 27 are connected in opposite directions with reference to the inner disc of the aerial.

Lastly a variable biasing may be applied to the inner core of the coaxial high frequency cable at a point between the condenser 21 and the parallel rectifiers 22 and 23. To this end, the cable core is connected through a choke coil 28 with the supply of biasing current 29.

The polarizing voltage supplied by 29 is clearly higher than the maximum amplitude of the high frequency voltag and the polarity of the supply 29 may be reversed as desired.

This alternately positive and negative polarizing voltage may be obtained in any of a number of ways known to the man familiar with the art. For example, any electronic generator supplying square waves or even a sinusoidal voltage having alternate positive and negative values will suit the purpose. Where it is desired to use a battery, a conventional polarity reversing vibrator system, Where the vibrator is actuated electromagnetically or by means of motor may also be employed.

It is immediately apparent that with such a wiring diagram the rectifiers 23 and 27 are blocked when the supply 29 feeds with positive voltage the coil 28. On the other hand, the rectifiers 22 and 25 oppose then only a low resistance against the passage of high frequency waves. Under such conditions, the arrangement is such that its operation is the same as if there were no connec= tion between the high frequency cable and the point 12 and as if the points 13 and 14 were insulated with reference to each other. We provide thus for the feeding across the points 1 and 2 with the insertion of the resistance 24 between the points 3 and 4. This produces the first radiation pattern illustrated in Fig. 5.

In contradistinction, when the supply 29 feeds the system with negative voltage, the rectifiers 22 and 25 are blocked while the rectifiers 23 and 27 become conductive. We obtain thus the second manner of feeding and connecting the aerial which leads to the second pattern of Fig. 5.

Obviously, many detail modifications may be brought to the embodiments described without widening the scope of the invention as defined in the accompanying claims. For instance it is obviously possible to associate at least partly the different modifications described with one another.

Obviously it is possible to form our improved aerials not only by means of metal sheets, but also by providing a suitable metal coat on insulating parts made of wood, plastic material or the like.

What we claim is:

1. A directional aerial comprising a sheet of metal in which a continuous slot is provided along a closed line dividing said sheet into inner and outer members, means for feeding high frequency energy between two points on opposite sides of said slot, shorting means for connecting the two sides of the slot electrically at a distance from said first mentioned points at two further points on opposite sides of the slot and an empty cavity surrounding the slot on one side of the metal sheet to cut off the radiation on the corresponding side of said sheet said members being electrically connected solely by said shorting means.

2. A directional aerial including a metal sheet member provided with an opening having a closed outline, a perforated metal annulus member lying inside said opening, the inner and outer edges of said annulus member substantiallyhomothetical with the outline of said opening and the outer edge of the annulus member forming a slot with the outline of the opening, means for feeding high frequency energy between two points on opposite sides of said slot and shorting means for connecting the two sides of the slot electrically at a distance from said first mentioned points at two further points on opposite sides of the slot said members being electrically connected solely by said shorting means.

3. A directional aerial comprising a sheet member of metal provided with an opening, an inner metal member lying inside said opening to form a slot with the edge of the metal sheet member, two pairs of points opposite sides of the slot, two further pairs of points on opposite sides of the slot, a high frequency supply and switching means selectively connecting said high frequency supply with one of the two first pairs of points and simultaneously electrically interconnecting a corresponding pair of the further pairs of points said members being electrically connected solely by said simultaneously electrically interconnecting means.

4. A directional aerial comprising a sheet of metal provided with a circular opening, an inner circular metal member lying inside said opening to form a slot with the edge of the first metal sheet, two pairs of points facing each other being provided to either side of the slot, two further pairs of points facing each other being provided to either side of the slot, a high frequency supply and switching means connecting selectively said high frequency supply with either of the two first pairs of points and simultaneously electrically interconnecting a corresponding pair of the further pairs of points.

5. A directional aerial comprising a sheet of metal provided with an opening, an inner metal member fitted inside said opening to form a slot with the edge of the first metal sheet, two pairs of points on opposite sides of the slot, two further pairs of points on opposite sides of the slot, a coaxial cable adapted to feed high frequency voltages and including an outer grounded sheath and an inner core, means for connecting the outer sheath with the points of the first two pairs lying on the one side of the slot, a condenser connected with the core and connected in parallel with the points of the first two pairs lying on the other side of the slot, oppositely poled rectifiers coupled to the said points of the first pairs on said other side of the slot between these points and the condenser, a connection between the points forming each of the further pairs of points, further rectifiers in said connections and providing for the flow of current from the point on the inside of the slot towards a point on the outside in one further pair and from the point on the outside of the slot towards a point on the inside of the slot in the second further pair, means feeding selectively a positive and a negative voltage higher than the maximum high frequency voltage supplied by the cable core through the condenser to the first mentioned rectifiers to provide, according to the polarity of said voltage, a flow of current through one of the first pair of points and through the connection between the points of the further pair of points for which the corresponding further rectifier allows current to pass.

6. A directional aerial comprising a sheet of metal provided with a circular opening, an inner circular metal member lying concentrically inside said opening to form a slot with the edge of the metal sheet, two pairs of points along difierent radii on opposite sides of the slot, two further pairs of points on opposite sides of the slot, a coaxial cable adapted to feed high frequency voltages and including an outer grounded sheath and an inner core, means for connecting the outer sheath with the points of the first two pairs on one side of the slot, a condenser connected with the core and connected in parallel with the points of the first two pairs lying on the other side of the slot, oppositely poled rectifiers coupled to the said points of the first pairs on said other side of the slot between these points and the condenser, a connection between the points of the further pairs of points, further rectifiers inserted in said connections and providing for the flow of current from the point on the inside of the slot towards the point on the outside in one further pair and from the point on the outside of the slot towards the point on the inside of the slot in the second further pair, means feeding selectively a positive and a negative voltage higher than the maximum high frequency voltage supplied by the cable core through the condenser to the first mentioned rectifiers to provide, according to the polarity of said voltage, a flow of current through one of the first pair of points and through the connection between the points of the further pair of points for which the corresponding further rectifier allows current to pass.

7. An aerial as claimed in claim 1, wherein said inner and outer members are respectively bound by circles, said circles being eccentric with respect to each other.

8. An aerial as claimed in claim 1, wherein said inner member has a bulged shape.

References Cited in the file of this patent UNITED STATES PATENTS

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