Improved device incorporating spiral antennas

invention relates to spiral antennas.

A spiral antenna comprises on a support two wires of identical length adjacent to coil together to form a spiral whose lower operating frequency value is first approximated to that of its outer diameter.

If the radiation is to be limited to the portion of space around the spiral, the other side of the support may be brought into contact with a cavity filled with electromagnetically absorbent material. An antenna of this type, properly fed with high frequency electrical signals, radiates in the desired space portion in a very high frequency band. I'm so wide.

It was intended to have such networked antennas. However, such a configuration raises, as will be seen in more detail below, malfunctions linked in particular to network properties, particularly when operating in a very wide frequency band.

The invention aims to provide a solution to this problem.

One purpose of the invention is to propose a device comprising a plurality of networked spiral antennas that can operate in a very wide frequency band without operating changes connected to the network structure.

According to a general feature of the invention, the proposed antenna device comprises on a substrate at least two radiant elements and a pair of high frequency electrical signal supply terminals for each of these elements; each of them comprises a spiral shaped zone and at least one of them has an extension of the wires of its spiral having different geometrical characteristics from said spiral.

Further advantages and features of the invention will be apparent from examination of the following detailed description and the

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-3additional drawings, in which:

Figures 1 and 2 very schematically illustrate an isolated classical spiral antenna;

- Figure 3 schematically illustrates three reassembled spiral antennas in a configuration with malfunctions,

Figure 4 is a partial schematic representation of an embodiment of a device according to the invention.

The drawings include the essential elements of definite character. In this regard, they form an integral part of the specification and may not only serve to better understand the following detailed description, but may also contribute, if necessary, to the definition of the invention.

As shown schematically in Figures 1 and 2, a printed spiral antenna comprises, on one side of a support (e.g. a dielectric) SU, two identical identical lengths of wire BI and B2 adjacent each other to form a spiral SP. In other words, except for the vicinity of the ends of the yarn, each portion of yarn is surrounded by two portions of the other yarn.

It should be noted that a spiral di is illustrated here. Archimedes, that is, a spiral in which each wire has a constant thickness and a constant spacing relative to the other wire. However, other types of coils are foreseeable, such as so-called logarithmic coils, in which an expansion rate for the widths of the strands is provided, as well as increasing spacing between them. In the context of the present description, the terms spiral or spiral antennae should be interpreted in a very broad sense, covering all types of spirals.

Such an antenna is capable of operating in a very wide frequency band such that the ratio between the upper frequency and the lower frequency is, for example, on the order of four. Its lower operating frequency is then given, in a first approximation, by the following formula:

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-4ρΐ.Ίλ · = c / ϊΊ = lambdal where pi denotes the real number roughly equal to 3.14,

D designates the outer diameter of the SP spiral, c designates the speed of light,

F1 denotes the lower operating frequency, and lambdal means the wavelength associated with frequency F1.

A spiral antenna also has the particularity of radiating both in the space portion in front of the spiral SP and in the space portion in front of the other face, or rear face, of the SU bracket. Also, if this radiation is to be limited to the portion of space in front of the front face of the support, the other face of the support may be brought into contact with an AC cavity filled with high frequency electromagnetic wave absorbing material in a broadband.

The two wires of such an antenna are fed by means of wires FI1 and F12 connected to the respective ends of the two wires located in the center of the spiral. The feeding of high frequency electrical signals is generally carried out with the aid of a CO coaxial cable which is by nature asymmetrical since it comprises a center core and a sheath. A well-functioning spiral antenna requires, due to its symmetrical geometric characteristics, a symmetrical type electrical signal feed, ie identical for both wires. And, equally, necessary to provide, in the back of the cavity. AC, a symmetric electronic element SY, which ensures this symmetrization function. It should be noted here that the two wires FI1 and FI2, which run through the cavity of absorbing material CA, do not disturb the radiation of the antenna since it is inhibited in the rear space portion.

In order, in particular, to benefit from the very wide band operating properties of the spiral antennas, they are to be grouped in a network. One solution could be to arrange these spirals side by side as illustrated very schematically in figure 3. However one such

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The solution is not satisfactory for the reasons given now.

Indeed, it is well known that the proper functioning of a network at a given frequency depends closely on the spacing step of the elementary antennas that make up this network. Thus, for a lambda wavelength, corresponding to a given operating frequency, it is necessary that the network step p is less than or equal to half the value of this wavelength. Indeed, if step p exceeds half of that value, the network radiation diagram may present a parasitic lobe or network lobe, out of phase with the useful main lobe of this network, disrupting the operation of the latter.

step p of such a network is minimal when the spirals are close to each other, such that their respective outside diameter D is substantially equal to step ρ. The low operating frequency, F1, corresponding to the lambdal wave length, step p, which is the same as diameter D, then takes, by applying the formula given above, the value (lambdal / pi). Therefore, there is no malfunction at this frequency since step p is less than (lambdal / 2).

However, if this network is to be operated in a very wide frequency band, going to a high operating frequency F2 equal to, for example, four times the low operating frequency F1, we realize that the step p is then equal to the product of the wavelength lambda2 corresponding to the frequency F2 by a factor equal to 4 / pi. 0 Grid operation is then changed at frequency F2, due to the presence of a grid lobe, since step p is greater than lambda2 and therefore, a fortiori a (lambda2 / 2).

invention brings a solution to this problem.

Indeed, the applicant has observed that in a device comprising a plurality of radiant elements (at least two) each having a spiral-shaped zone, at least one of them should have an extension of its spiral wires having characteristics different geometric from

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-6 of said spiral.

From this very general observation, we have conceived the invention in a particular embodiment illustrated in FIG. Figure 4.

In this figure, for the sake of simplicity, only the geometrical configurations of the wires of the different coils have been shown, and naturally a pair of high frequency electrical signal supply terminals is provided for each of the radiant elements of this network.

If this network has to operate from a low frequency F1, the length of the two wires of each radiant element of the network, identical length for all radiant elements, is determined such that an elemental spiral antenna, formed by these two wires, has an outside diameter D which permits operation at this low frequency F1.

In a network which has to operate in a very wide frequency band up to a high frequency F2 equal to, for example, four times the low frequency, a generally lower, preferably preferably half, network step p2 is chosen. wavelength lambda2. The two wires of each radiant mesh member are then wound adjacent to form a spiral shaped zone having an outer diameter D2 substantially equal to step p2. All of these spiral shaped zones SP1-SP7 are then aligned side by side on the substrate to form a row.

The excess length of the wires Bli and B2i of a radiant element is then disposed on the free surface of the substrate and forms an extension BBli and PB2i having different geometrical characteristics from the corresponding spiral SPi.

Thus, in this example, the two threads PBli and PB2i of the spiral extension SPi leave the latter at diametrically opposite points and circle around all zones SP1-SP7 of the radiant elements, in the same direction as that of the spirals. In other words, all the threads of all extensions run

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A method adjacent each other to form a peripheral crown that completely surrounds the spirals SP1-SP7.

Such a network then functions correctly at the high frequency F2, once the pitch has been determined for it. It works equally well at all other frequencies, up to low frequency F1, since step p2, calculated for high frequency F2, is necessarily less than half the value of the lambdal wavelength corresponding to this low operating frequency. .

It should also be emphasized that the radiation contribution of this antenna device is mainly provided by the SFi spirals with regard to the high operating frequency, while the peripheral crown CF contributes mainly to the low operating frequency. .

However, it may be advantageous for the lines of this CP peripheral crown to be partially or fully covered with a lossy material such as ferrite (Ferrite) loaded materials. In this case, the lines of this crown do not participate directly in the radiation at the bottom of the band, since they dampen the electromagnetic wave the entire length of its path over these lines. On the other hand, these lines make it possible to noticeably improve the behavior of the lower part of the shell, very largely avoiding the return propagation of the electromagnetic wave in the spiral, propagation generated by the reflection of the electromagnetic wave at the end of the wire.

It is well understood that this radiation in the lower part of the band can be controlled by proper location of the loss material, however it should be noted that in any case this low frequency radiation also occurs for a small part at the level of the SPi spirals. and this with virtually no disturbance.

The invention is not limited to the embodiment described above, encompassing all variants contained in the table of the following claims.

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Thus, the extension of the spiral wires may lie in the plane of the latter or outside that plane. Also, in one case and / or the other, the extension may or may not circle around said spirals.

Spirals have previously been described having all in their plane the same angular configuration. One skilled in the art knows that it is possible to vary the phase of a spiral antenna by acting on this angular configuration. Such consideration may apply to the present invention.

Of course, some of the means described above may be omitted in variants in which they are of no use.

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