Log-periodic antenna and associated vehicles

Abstract

TITLE: Log-periodic Antenna and Associated Vehicle The present invention relates to a log-periodic antenna (10) comprising a material (12) extending in a plane along an elongation axis (E), the material (12) carrying successive radiating elements (14) arranged along the elongation axis (E), the radiating elements (14) extending along an elevation axis (Z), wherein, over at least a portion of the material (12), the ratio of the distance separating a radiating element (14) from an immediately successive radiating element (14) to the distance separating the radiating element (14) from the immediately preceding radiating element (14) is constant, characterized in that at least a plurality of successive radiating elements (14) are arranged alternately on either side of a plane defined by the elongation axis (E) and the axis elevation (Z) and at a non-zero distance from this plane. Figure for the abbreviation: Figure 2

Description

Title of the invention: Log-periodic antenna and associated vehicle

[0001] The present invention relates to a log-periodic type antenna comprising a material extending in a plane along an elongation axis, the material carrying successive radiating elements arranged along the elongation axis, the radiating elements extending along an elevation axis, in which, over at least a part of the material, the quotient of the distance separating a radiating element from an immediately successive radiating element by the distance separating the radiating element from the immediately preceding radiating element is constant.

[0002] Among directional antennas, log-periodic antennas allow for a wide bandwidth thanks to the large number of radiating elements they contain. A log-periodic antenna is a directional radiation antenna comprising an array of radiating elements, in which the distance between successive radiating elements and / or the length of successive radiating elements follows a geometric ratio. Due to the mathematical relationship between their distances, widening the bandwidth of such an antenna requires, for matching purposes, increasing the number of radiating elements it contains. When a wide bandwidth is desired, the number of radiating elements in such an antenna and their spacing can become so large that the antenna has a wingspan and length that make it impractical to use.

[0003] In particular, when such an antenna is intended to be mounted on a vehicle, the dimensions of the broadband log-periodic antenna may be prohibitive.

[0004] It is known in the prior art to equip a log-periodic antenna with a folding system. However, this requires one or more users to operate the antenna directly to fold it, which can be cumbersome and dangerous, or the antenna incorporates an automatic deployment system. In the latter case, the antenna is more expensive and heavier.

[0005] The aim of the invention is then to propose a log-periodic antenna whose span and length are less than those of prior art antennas, for similar performance in terms of matching and radiated power over the bandwidth in particular.

[0006] For this purpose, the invention relates to an antenna of the aforementioned type characterized in that at least a plurality of successive radiating elements are arranged alternately on either side of a plane defined by the elongation axis and the elevation axis and at a non-zero distance from this plane.

[0007] According to other advantageous aspects of the invention, the log-periodic antenna comprises one or more of the following features, taken individually or in any technically possible combination:

[0008] - the distances between two successive radiating elements and the elongation axis form a strictly increasing sequence for at least three successive radiating elements;

[0009] - each radiating element consists of a pair of monopoles;

[0010] - the value of the quotient of the distance separating a radiating element from an element radiating immediately successive by the distance separating the radiating element from the immediately preceding radiating element on there at least a part of the material is between 0.8 and 0.98;

[0011] - the successive radiating elements extend alternately in directions opposite the axis of elevation;

[0012] - the monopolies of each pair of monopolies extend in opposite directions of the elevation axis;

[0013] - the monopolies of each pair of monopolies are substantially identical;

[0014] - at least one radiating element has several folds, and is included in a plane which contains the elevation axis, so as to have a fractal shape;

[0015] - the quotient of the lengths of at least two successive radiating elements is constant.

[0016] The invention also relates to a vehicle comprising a log-periodic antenna as defined above.

[0017] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0018] - [Fig. 1] [Fig. 1] is a perspective representation of a portion of an antenna log-periodic according to the invention,

[0019] - [Fig.2] [Fig.2] is a top view of the log-periodic antenna of [Fig.1],

[0020] - [Fig.3] [Fig.3] is a representation similar to that of [Fig.1], of an antenna according to another embodiment, and

[0021] - [Fig.4] [Fig.4] is a schematic cross-sectional view of radiating elements according to the invention.

[0022] The log-periodic antenna 10 comprises a material 12 on which a plurality of radiating elements 14 are mounted. The material 12 is in particular intended to be supported by a support in order to raise the log-periodic antenna 10. The support is for example mounted on the roof of a vehicle such as a truck.

[0023] The log-periodic antenna 10 is particularly intended to operate in transmission and / or reception in the frequency band [20; 600] MHz, which corresponds to a wavelength between 0.5 and 15 meters.

[0024] The material 12 extends along an elongation axis E, and the radiating elements 14 extend along a direction parallel to an elevation axis Z perpendicular to the elongation axis E. The plane of the antenna P is defined as the plane generated by the elevation axis Z and the elongation axis E.

[0025] With reference to [Fig. 1], the material 12 comprises two electrically conductive lines 16 arranged side by side. A spacing is defined between the lines 16 to ensure a specific impedance to the electromagnetic wave propagating along them. The two lines 16 form the framework of the antenna and support the radiating elements 14. An excitation source, not shown, is used to circulate an electromagnetic wave through the material 12, so as to distribute the electromagnetic wave among the radiating elements 14 forming the antenna 10.

[0026] In the embodiment shown, the radiating elements 14 consist of a pair of monopoles 17A, 17B which are linear monopoles. A linear monopole is formed of a straight rod of constant cross-section.

[0027] The monopoles 17A, 17B of each pair are connected respectively to lines 16A, 16B.

[0028] For a particular radiating element 14, the monopole 17A extends along the elevation axis Z in a direction opposite to that of the monopole 17B substantially in the continuation of one another, being offset by the gap between the two lines 16A, 16B.

[0029] The successive monopoles 17A, 17B along the elongation direction of the same line 16 extend alternately in opposite directions of the elevation axis Z.

[0030] Advantageously, the monopoles 17A, 17B constituting a radiating element 14 are identical.

[0031] A monopole 17A, 17B extends continuously between a connecting end 20 and a free end 22. The monopoles 17A, 17B are connected to the material 12 at their connecting end 20.

[0032] The portion of the material 12 not parallel to the elongation axis E is called the folded portion 24 and the part of the material 12 parallel to the elongation axis E is called the straight portion 26.

[0033] As shown in [Fig. 1], each line 16 has a polygonal line shape made up of coplanar segments. Line 16 consists of a segment parallel to the elongation axis E on the straight part 26, and a plurality of angularly offset segments connecting the connecting ends 20 of the different monopoles 17A, 17B on the folded portion 24.

[0034] The segments constituting the polygonal line on the folded portion 24 intersect at a single point with the elongation axis E, which gives the line 16 a zig-zag shape. In the same direction of angle measurement, for example in the trigonometric direction, the angles formed by successive segments of the plurality of segments that constitute the line 16 are alternately salient and re-entrant angles.

[0035] The two lines 16A, 16B of the material 12 are offset from each other along the direction orthogonal to the plane P of the antenna.

[0036] Lines 16A, 16B for example have a tubular shape, and are in particular assembled by welding a plurality of metal tubes, which makes it possible to achieve the characteristic polygonal line shape of lines 16A, 16B from tubes.

[0037] With reference to [Fig.2], the radiating elements 14 located on the folded portion 24 extend between a first radiating element 28 numbered 0 and a last radiating element 30 numbered n+1, the set of radiating elements 14 of the folded portion 24 being located between the first radiating element 28 and the last radiating element 30 along the elongation axis E.

[0038] The radiating elements 14 strictly included between the first radiating element 28 numbered 0 and the last radiating element 30 numbered n+1 have their connection point located on either side and at a non-zero distance from the plane of the antenna P.

[0039] For a radiating element i+1, with i between 0 and n-1, we denote by d^j+i the distance between the radiating element i+1 and the immediately preceding radiating element i. Similarly, we denote by dj+1j+2 the distance between the radiating element 14 numbered i+1 and the immediately following radiating element 14 numbered i+2.

[0040] The quotient of dj by dj+i j+2 is equal to a coefficient r which is a strictly positive real number, for at least one value of i between 0 and n-1.

[0041] Alternatively, the quotient of dj by dj+i j+2 is r for any value of i between 0 and n-1.

[0042] In another variant, for any radiating element 14 belonging to the folded portion 24 or to the straight portion 26, the quotient of the distance between the radiating element 14 and the immediately successive radiating element by the distance between the radiating element 14 and the immediately preceding radiating element is equal to r.

[0043] Advantageously, the value of the coefficient r is between 0.8 and 0.98.

[0044] The curve length of a monopole 17A, 17B is defined as the distance obtained by traversing the monopole 17A, 17B from its connecting end 20 to its free end 22. The curve length of a radiating element 14 consisting of a pair of monopoles 17A, 17B is defined as equal to the sum curve lengths of the two monopoles 17A, 17B. For a radiating element 14 numbered i, its curve length is denoted Lj.

[0045] The quotient of the curve length Lj of the radiating element 14 numbered i by the curve length Lj+^ of the next radiating element is equal to r.

[0046] Alternatively, for a radiating element 14 belonging to the folded portion 24 or to the straight portion 26 and having a successive radiating element 14, the quotient of the curve length of the radiating element 14 by the curve length of the immediately following radiating element 14 is equal to r.

[0047] In the embodiment shown, the connection end 20 of a radiating element 14 on the material 12 is considered to be located in the middle of the segment defined between the connection ends 20A, 20B of the monopoles 17A, 17B of the radiating element 14.

[0048] In particular, the orthogonal projection of the connecting end 20A of a monopole 17A of a radiating element 14 on the elongation axis E is equal to the orthogonal projection of the connecting end 20B of the other monopole 17B of the radiating element 14 on the elongation axis E.

[0049] The distance to the axis, denoted ai, is the distance between the connecting end 20 of the radiating element 14 numbered i+1 and its orthogonal projection onto the elongation axis E, for i G [2; n-1].

[0050] The sequence of distances to the axis ai is a strictly increasing sequence, the material 12 of the log-periodic antenna 10 has, on its folded portion 24, a span increasing along the elongation axis E, from the first radiating element 28 to the last radiating element 30. The span of the antenna is defined as the height of the antenna taken along the elevation axis Z.

[0051] In particular, in the embodiment shown, the distance ai satisfies, for i in the interval [2; n-1], the following relation:

[0052] = (i-lj^+So

[0053] And, for i = 1 and i = n:

[0054] a x = a0+C0

[0055] a n = a n .1+C2

[0056] with Co, Cp and C2 being positive and non-zero dimensioning constants, whose physical quantity is homogeneous to a length.

[0057] Preferably the size Co is less than the size Cp and the size Cj is less than the size C2, for example Co, Cp and C2 have respective values ​​of 20 cm, 30 cm, and 40 cm.

[0058] The value of n, which represents the number of segments of each of the lines 16A, 16B not parallel to the elongation axis E, is notably between 5 and 40, for example equal to 9.

[0059] The distance dj j+i between a radiating element 14 numbered i and the next element numbered i+1 along the elongation axis E is noted Y* and the same distance taken along the axis orthogonal to the plane of the antenna P is noted Xj, for i going from 1 to n-1.

[0060] The distances Xj and Yj for i ranging from 1 to n-1 are equal to:

[0061] = Si+Si-i 100621 \

[0063] Because the sequence of distances to the axis ai is a strictly increasing sequence, the sequence of distances Xj is also a strictly increasing sequence.

[0064] The first radiating element 28 numbered 0 of the log-periodic antenna 10 is arranged on the elongation axis E, and is located at the junction between the straight portion 26 and the folded portion 24.

[0065] The distance dg j between the first radiating element 28 and the immediately following radiating element 14 is chosen, when dimensioning the log-periodic antenna 10, taking into account a wavelength X of use of the log-periodic antenna 10, preferably such that:

[0066] 0.03*X < d01< ort*A

[0067] with °t a dimensioning parameter being defined by the following formula:

[0068] <j t = 0.243*t-0.051

[0069] The distance dg along the axis orthogonal to the plane in the antenna P is denoted ao, and this distance is denoted Yo along the elongation axis E, the following relation is therefore verified: 100701 Y o ^(d^)

[0071] The last radiating element 30 numbered n+1 of the log-periodic antenna 10 is arranged on the elongation axis E, and is located at a junction between the straight portion 26 and the folded portion 24.

[0072] Let dn n+j be the distance between the last radiating element 30 and the immediately preceding radiating element 14. Let an be the projection of dn n+j onto the axis orthogonal to the plane of the antenna P and Yn the projection of dn n+i onto the elongation axis E, which satisfy the relation:

[0073] Y / 7^ y vdn,n+l /

[0074] The length Yj taken along the elongation axis between two consecutive radiating elements 14 belonging to the folded portion 24 is less than the distance dj j+i between two consecutive radiating elements 14. The length of the folded portion 24 of the log-periodic antenna 10 is equal to the sum of the lengths Yj for i ranging from 0 to n. A log-periodic antenna 10 according to the invention therefore has a material length 12, taken along the elongation direction E, that is less than the material length 12 of a prior art log-periodic antenna.

[0075] The log-periodic antenna 10 illustrated in [Fig.3] has a first zone 32, similar to the portion of the antenna shown in [Fig.1], in which the radiating elements 14 consist of a pair of linear monopoles 17A, 17B, and a second zone 34 in which the radiating elements 14 consist of a pair of folded monopoles 36A, 36B.

[0076] Each folded monopole 36A, 36B is contained in a plane, in which the elevation axis Z is included, and has several folds, which give it a fractal shape.

[0077] For the same curve length, the length taken along the elevation axis Z of a folded monopole 36A, 36B is less than that of a linear monopole 17A, 17B. The folding implemented on the folded monopoles 36A, 36B reduces the span of the log-periodic antenna 10 along the elevation axis Z.

[0078] In the embodiment shown in [Fig.3], a folded monopole 36A, 36B of the first radiating element 38 of the second zone 34 has fewer folds than a folded monopole 36A, 36B of the immediately following radiating element 40 of the second zone 34.

[0079] In this embodiment, the sequence of curve lengths Lj of the radiating elements 14 is a strictly increasing sequence. In particular, when the sequence of curve lengths of the radiating elements 14 is strictly increasing, there exists an index i from which it is particularly advantageous to reduce the length, taken along the elevation direction Z, of the radiating elements 14.

[0080] Fig. 4 illustrates radiating elements 14 according to different embodiments, shown in cross-section along a plane including the elevation axis E.

[0081] The radiating elements 14 have two folded monopoles 36A, 36B which extend on either side of the material 12, shown schematically in cross-section, in which the electric current from the excitation source flows.

[0082] A first pair of radiating elements 42 is shown, in which the folded monopoles 36A, 36B include portions parallel to or perpendicular to the elevation axis E.

[0083] A second pair of radiating elements 44 represents folded monopoles 36A, 36B comprising a plurality of portions not parallel to the elevation axis E and not perpendicular to the elevation axis E.

[0084] The folded monopoles 36A, 36B of the same radiating element 14 are advantageously arranged symmetrically with respect to the material 12.

[0085] The log-periodic antenna 10 according to the invention is particularly suitable for integration on a vehicle, in particular the roof of a land vehicle, due to its reduced dimensions in wingspan and length compared to a log-periodic antenna according to the prior art.

Claims

Demands

1. A log-periodic antenna (10) comprising a material (12) extending in a plane along an elongation axis (E), the material (12) carrying successive radiating elements (14) arranged along the elongation axis (E), the radiating elements (14) extending along an elevation axis (Z), wherein, over at least a portion of the material (12), the ratio of the distance separating a radiating element (14) from an immediately successive radiating element (14) to the distance separating the radiating element (14) from the immediately preceding radiating element (14) is constant, characterized in that at least a plurality of successive radiating elements (14) are arranged alternately on either side of a plane defined by the elongation axis (E) and the elevation axis (Z) and at a non-zero distance of this plan.

2. Log-periodic antenna (10) according to claim 1, wherein the distances between two successive radiating elements (14) and the elongation axis (E) form a strictly increasing sequence for at least three successive radiating elements (14).

3. Log-periodic antenna (10) according to any one of the preceding claims, wherein each radiating element (14) consists of a pair of monopoles (17A, 17B; 36A, 36B).

4. Log-periodic antenna (10) according to any one of the preceding claims, wherein the value of the quotient of the distance separating a radiating element (14) from an immediately successive radiating element (14) by the distance separating the radiating element (14) from the immediately preceding radiating element (14) on at least a part of the material (12) is between 0.8 and 0.

98.

5. Log-periodic antenna (10) according to any one of the preceding claims, wherein the successive radiating elements (14) extend alternately in opposite directions of the elevation axis (Z).

6. Log-periodic antenna (10) according to claim 4, wherein the monopoles (17A, 17B; 36A, 36B) of each pair of monopoles (17A, 17B; 36A, 36B) extend in opposite directions of the elevation axis (Z).

7. Log-periodic antenna (10) according to claims 3 to 6, wherein the monopoles (17A, 17B; 36A, 36B) of each pair of monopoles (17A, 17B; 36A, 36B) are substantially identical.

8. Log-periodic antenna (10) according to any one of the preceding claims, wherein at least one radiating element (14) has several folds, and is contained in a plane which contains the elevation axis (Z), so as to have a fractal shape.

9. Log-periodic antenna (10) according to any one of the preceding claims, wherein the ratio of the lengths of at least two successive radiating elements (14) is constant.

10. Vehicle comprising a log-periodic antenna (10) according to any one of the preceding claims.

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