WIDEBAND WIRE ANTENNA

Abstract

The disclosed antenna includes: a radiating element disposed in a radiating plane transverse to an axis of the antenna; a reflecting plane, which is transverse to the axis, the radiating plane being located at a predetermined height above the reflecting plane; and a substrate, interposed between the radiating plane and the reflecting plane, and having a constant thickness. This antenna is characterized by a local relative electrical permittivity of the substrate that is a function of the radius, i.e. the distance to the axis, and a height, i.e. a distance to the reflecting plane, the local relative electrical permittivity being, at constant height, increasing as a function of the radius, and, at constant radius, increasing as a function of the height at least for a portion of the substrate in the vicinity of the reflecting plane.

Claims

1. A wideband wire antenna comprising: a radiating element, the radiating element comprising at least one metal wire shaped around an axis of the antenna, in a transverse radiating plane; a reflecting plane, the reflecting plane being transverse to the axis, the radiating plane being located at a predetermined height above the reflecting plane; and, a substrate, the substrate being interposed between the radiating element and the reflecting plane, and having a constant thickness, wherein a local relative electrical permittivity and/or a local relative electrical permeability of the substrate is a function of the radius, measured as a distance to the axis, and a height, measured as a distance to the reflecting plane, the local relative electrical permittivity and/or a local relative electrical permeability being, at constant height, increasing as a function of the radius, and, at constant radius, increasing as a function of the height at least for a portion of the substrate in the vicinity of the reflecting plane.

2. The antenna according to claim 1, wherein the local relative electrical permittivity and/or the local relative electrical permeability is, at constant radius, decreasing with height at least for a portion of the substrate in the vicinity of the radiating element.

3. The antenna according to claim 2, wherein the local relative electrical permittivity and/or the local relative electrical permeability is, at constant radius, a cosine function of the height.

4. The antenna according to claim 1, wherein the local relative electrical permittivity and/or the local relative electrical permeability is a continuous function of the radius and the height.

5. The antenna according to claim 1, wherein the substrate results from the combination of at least a first material having a first relative electrical permittivity and/or a first relative electrical permeability, with a second material having a second relative electrical permittivity different from the first and/or a second relative electrical permeability different from the first, a relative concentration of the first and second materials being a function of the radius and height.

6. The antenna according to claim 5, wherein the combination of the first and second materials is achieved by using an additive manufacturing technology.

7. The antenna according to claim 5, wherein the first material has a plurality of first interstices, some of said first interstices being filled by the second material and/or the second material has a plurality of second interstices, some of said second interstices being filled by the first material.

8. The antenna according to claim 4, wherein the first interstices and/or the second interstices have a characteristic dimension which depends on the radius and/or on the height.

9. The antenna according to claim 7, wherein the first interstices and/or the second interstices have a parallelepipedal or spherical.

10. The antenna of claim 6, wherein the additive manufacturing technology is three-dimensional printing.

11. The antenna of claim 9, wherein the largest dimension of an interstice is less than λ/10.

12. The antenna according to claim 2, wherein the local relative electrical permittivity and/or the local relative electrical permeability is a continuous function of the radius and the height.

13. The antenna according to claim 3, wherein the local relative electrical permittivity and/or the local relative electrical permeability is a continuous function of the radius and the height.

14. The antenna according to claim 2, wherein the substrate results from the combination of at least a first material having a first relative electrical permittivity and/or a first relative electrical permeability, with a second material having a second relative electrical permittivity different from the first and/or a second relative electrical permeability different from the first, a relative concentration of the first and second materials being a function of the radius and height.

15. The antenna according to claim 3, wherein the substrate results from the combination of at least a first material having a first relative electrical permittivity and/or a first relative electrical permeability, with a second material having a second relative electrical permittivity different from the first and/or a second relative electrical permeability different from the first, a relative concentration of the first and second materials being a function of the radius and height.

16. The antenna according to claim 4, wherein the substrate results from the combination of at least a first material having a first relative electrical permittivity and/or a first relative electrical permeability, with a second material having a second relative electrical permittivity different from the first and/or a second relative electrical permeability different from the first, a relative concentration of the first and second materials being a function of the radius and height.

17. The antenna according to claim 6, wherein the first material has a plurality of first interstices, some of said first interstices being filled by the second material and/or the second material has a plurality of second interstices, some of said second interstices being filled by the first material.

18. The antenna according to claim 8, wherein the first interstices and/or the second interstices have a parallelepipedal or spherical shape.

19. The antenna according to claim 10, wherein the substrate results from the combination of at least a first material having a first relative electrical permittivity and/or a first relative electrical permeability, with a second material having a second relative electrical permittivity different from the first and/or a second relative electrical permeability different from the first, a relative concentration of the first and second materials being a function of the radius and height.

20. The antenna according to claim 11, wherein the substrate results from the combination of at least a first material having a first relative electrical permittivity and/or a first relative electrical permeability, with a second material having a second relative electrical permittivity different from the first and/or a second relative electrical permeability different from the first, a relative concentration of the first and second materials being a function of the radius and height.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The invention and its advantages will be better understood upon reading the following description of a particular embodiment, given only as an example, and with reference to the attached drawings, in which:

[0038] FIG. 1 is a schematic view of an antenna according to the invention;

[0039] FIG. 2 is a half-section along an axial plane of the antenna of FIG. 1;

[0040] FIG. 3 is a plot of the local relative electrical permittivity in the antenna substrate of FIG. 1 as a function of radius r (distance to the axis A) and height h (distance to the reflecting plane);

[0041] FIG. 4 illustrates a possible structure of the antenna substrate of FIG. 1 to achieve the local relative electrical permittivity distribution shown in FIG. 3; and,

[0042] FIG. 5 is a plot of the gain versus frequency of an antenna according to the prior art and an antenna according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] The figures show a preferred embodiment of the antenna according to the invention.

[0044] As shown in FIGS. 1 and 2, the wideband wire antenna 2 comprises, stacked along an axis A, a reflecting plane 8, a substrate 6 and a radiating element 4.

[0045] An origin O is chosen at the intersection of the axis A and the reflecting plane 8.

[0046] The coordinate along the axis A is called the height h. This is the distance to the reflecting plane 8.

[0047] A direction D is chosen extending radially to the axis A in the reflecting plane 8. The coordinate along the direction D is called the radius r. It is therefore the distance to the axis A.

[0048] The radiating element 4 is arranged in a radiating plane S, which is located at a height h.sub.0 from the reflecting plane 8.

[0049] The radiating element 4 is, for example, made by etching a metal layer on a support film 5.

[0050] The radiating element 4 comprises, for example, first and second metal wires 10 and 12 which are respectively shaped into a spiral, in particular an Archimedean spiral, around the axis A.

[0051] The reflecting plane 8 is for example a disc with axis A and radius r.sub.0. It is made of a metallic material. Its function is to reflect any incident wave regardless of its frequency.

[0052] The substrate 6 has the general external shape of a disc with axis A, radius r.sub.0, and constant thickness, equal to height h.sub.o.

[0053] The substrate 6 is in contact with the reflecting plane 8 via a lower surface 14. The substrate 6 is in contact with the radiating element 4, or more precisely with the support film 5 of the radiating element 4, via an upper surface 15.

[0054] A feeder (not shown in the figures) for the radiating element 4 is positioned below the reflecting plane 8. The reflecting plane 8 and the substrate 6 are advantageously provided with a passage (not shown), along the axis A, for the passage of the feed lines of the radiating element 4.

[0055] As the operating frequency F increases, the active zone Z of antenna 2 moves closer to the axis A. The peripheral part of antenna 2 therefore radiates at low operating frequencies and the central part of antenna 2 radiates at high operating frequencies.

[0056] According to the invention, the substrate 6 has a local relative electrical permittivity ε.sub.r at P(r,h) which is a function of both the radius r and the height h. It can therefore be written as: ε.sub.r(r,h).

[0057] FIG. 3 shows a possible example of this function. In FIG. 3, iso-permittivity curves have been plotted and the corresponding value of the local relative electrical permittivity .sub.Er has been indicated.

[0058] The dependence of the permittivity .sub.Er on h, for a given radius r, is such that for h close to 0, i.e. for points P(r,h) of the substrate in the immediate vicinity of the reflecting plane 8, the permittivity is minimal, preferably equal to one.

[0059] Thus, the material of the substrate 6 in contact with the reflecting plane 8 has a low permittivity so as to avoid the generating of creeping waves.

[0060] Advantageously, the dependence of the permittivity on h, for a given radius r, is such that for h close to h.sub.o, i.e. for points P(r,h) of the substrate 6 in the immediate vicinity of the radiating plane 4, the permittivity is minimal, preferably equal to one.

[0061] Thus, the material of the substrate 6 in contact with the radiating element 4 has a low permittivity so as to avoid coupling between two consecutive strands of the radiating element 4.

[0062] Furthermore, irrespective of either or both of these behaviours at the lower and upper boundaries of the substrate 6, the dependence of the local relative permittivity ε.sub.r(r, h) is advantageously continuous on h and r.

[0063] Thus, the substrate material does not interfere with wave propagation through the substrate.

[0064] It should be noted that in the prior art, the relative electrical permittivity considered is an effective permittivity, obtained by integration over the height h, at a given radius r.

[0065] FIG. 3 shows, in grey scale, an example of a substrate whose permittivity .sub.Er at a point P(r, h) depends on the radius r and the height h of that point.

[0066] The local relative electrical permittivity combines the three improvements identified above, namely a value close to one on the bottom surface 14, a value close to one on the top surface 15, and continuity at all points.

[0067] The local permittivity, for a given radius r, has a first minimum at zero height, then increases with height, reaching a maximum (e.g. at the middle of the substrate (h.sub.0/2), then decreases with height h, reaching a second minimum at height h.sub.o.

[0068] Preferably, the local relative electrical permittivity’s dependence on h and r is of the general form:

[00001]${\epsilon }_{\text{r}}\left(\text{r,h}\right)=\frac{\left[{\left(\frac{\pi }{2}\frac{\text{r}}{h_0}\right)}^2-{\epsilon }_{\min }\right]\ast \frac{\left(\text{n}+1\right)}{{\text{h}}_0^{\text{n}}}\ast {\text{h}}^{\text{n}}}{\text{y}}+{\epsilon }_{\min }$

where y is a parameter with a constant and predefined value, and n is a variable that can be an integer or a function depending on r and/or h

[0069] In the embodiment shown in FIG. 3, the permittivity takes the particular form:

[00002]${\epsilon }_{\text{r}}\left(\text{r,h}\right)=A\left(r\right)\cos \left(\frac{h-\frac{h_0}{2}}{\frac{h_0}{2}}\right)+{\epsilon }_{\min }$

[0070] In this example, the local relative electrical permittivity .sub.Er is a cosine function of the height h, at a given radius r.

[0071] The minimum value of this function is ε.sub.min, which is preferably 1.

[0072] The value of the maximum of this function for a given height h depends on the radius r.

[0073] As in the prior art, the effective permittivity at a given radius r, i.e. the integral according to the variable h of the local relative electrical permittivity ε.sub.r(r,h) between 0 and h.sub.o, is a function of the radius r adapted to allow the desired constructive interference, the principle on which this antenna technology is based.

[0074] As illustrated in FIG. 4, an additive manufacturing process, such as three-dimensional printing, is preferably used to produce the substrate 6.

[0075] The material of the substrate 6 is a combination of at least two materials, respectively a first material with a first low relative permittivity and a second material with a second high relative permittivity.

[0076] The relative concentration of the first and second materials at a point P(r,h) is a function of the coordinates h and r.

[0077] For instance, and preferably, the first material is deposited so as to have a plurality of first interstices, some of said first interstices being filled by the second material and/or the second material has a plurality of second interstices, some of said second interstices being filled by the first material.

[0078] For example, three-dimensional printing allows the substrate to be structured into cells.

[0079] To make the cell 21, the first material is deposited to form the walls 32 of the cell while leaving an interstice 31, which is left empty.

[0080] To make the cell 22, the first material is deposited to form the walls 34 of the cell, while leaving an interstice 33, which is then filled with the second material.

[0081] To make the cell 23, the second material is deposited to form the walls 36 of the cell, while leaving an interstice 35, which is then filled with the first material.

[0082] To make the cell 24, the second material is deposited to form the walls 37 of the cell, without leaving any interstices. The cell is full.

[0083] The thickness of the walls (and therefore the size of the interstices) is adjusted for each cell in order to obtain the required local relative electrical permittivity value, taking into account the properties of the materials used.

[0084] Advantageously, the first interstices and/or the second interstices have a characteristic dimension which depends on the distance to the axis and/or the distance to the radiating plane and/or to the reflecting plane.

[0085] The first interstices and/or the second interstices have a rectangular parallelepiped shape (as a first approximation). Alternatively, they have a spherical shape.

[0086] The largest dimension of an interstice is less than A/8, preferably less than A/10, more preferably less than A/15.

[0087] Because of this honeycomb structure, the substrate has good mechanical strength.

[0088] FIG. 5 is a plot showing the gain (in dB decibels) as a function of the operating frequency (in Hz hertz) of an antenna according to the prior art and of an antenna according to the invention. The gain is evaluated here along the axis of the antenna.

[0089] It can be seen, especially in the first half of the frequency spectrum, that the gain of the antenna according to the invention is much more stable in frequency with gain values often higher than those of an antenna according to the state of the art.

[0090] Alternatively, instead of characterizing the antenna by a local relative electrical permittivity as a function of r and h, it could be characterized by a local relative electrical permeability as a function of r and h.