EP1432073B1 - Coaxial collinear antenna - Google Patents

Abstract

The collinear antenna has three wire conductors, a central and two outer conductors. There are a number of alternating radiating zones, alternating between a first and second element. Each radiating zone is formed from an outer cylindrical conductor (46).

Description

The present invention relates to a collinear antenna of the alternating coaxial type.

Such antennas have already been described in particular in US Pat. No. 2,158,376, a figure of which has been reproduced as appended FIG. 1, or in US Pat. No. 5,600,338.

The antenna consists of a series of dipoles D1, D2, D3, etc. interconnected by DF1, DF2 phase shifters, etc. More specifically, each dipole D1 is constituted by a conductive tube element 10 and the antenna further comprises two parallel rectilinear conductive elements 12 and 14. The conductive cylinders 10, 12, 14, etc., constituting the dipoles D1, D2, D3 are alternately welded on one of the conductors 12 and 14 and surround the other conductor. For example, the dipole D1 is constituted by the cylindrical element 10 coaxial with the conductive element 14 and soldered on the conductive element 12. The phase shifter elements DF consist in the fact that the same conductive element 12, 14 passes from a position where it is welded to the cylindrical conductive member at a position in which it is disposed along the axis of the next cylindrical conductive member. This change of disposition corresponds substantially to a phase shift of λ / 2. Thus, overall, an addition is obtained of the currents flowing in the portions of the conductors 12 and 14 corresponding to the different dipoles. However, the alternating position of the conductive cylinders, with respect to the two conductive rectilinear elements, makes the radiation pattern of the whole of the antenna is not symmetrical, and the antenna is therefore not omnidirectional.

Another disadvantage of the antenna described in the aforementioned US patent lies in the fact that each dipole is constituted by the cylindrical conductive element and the linear conductor disposed along the axis of this cylinder. It follows from this configuration that the physical length of the cylindrical tube does not correspond to the radiating length thereof. The antenna is therefore not properly tuned to its working frequency.

An object of the present invention is to provide a collinear antenna of the alternating coaxial type which makes it possible to obtain a current distribution on the antenna such that the radiation pattern is effectively omnidirectional.

• trois éléments filaires conducteurs sensiblement rectilignes et parallèles entre eux, comprenant un conducteur central et deux conducteurs latéraux ; et
• 2N zones rayonnantes constituées par une alternance de premières zones rayonnantes et de deuxièmes zones rayonnantes :
  • .. chaque première zone rayonnante comprenant en outre un élément conducteur cylindrique dont l'axe est confondu avec ledit élément filaire central et qui est relié électriquement auxdits deux éléments filaires latéraux ;
  • .. chaque deuxième zone rayonnante comprenant en outre deux éléments conducteurs cylindriques dont les axes sont respectivement sensiblement confondus avec les éléments filaires latéraux, lesdits éléments cylindriques étant reliés électriquement audit élément filaire central ; un espace étant laissé entre deux zones rayonnantes consécutives.

To achieve this object according to the invention, an antenna of the collinear type is characterized in that it comprises a radiating part comprising:

• three wire elements substantially rectilinear conductors and parallel to each other, comprising a central conductor and two lateral conductors; and
• 2N radiating zones constituted by an alternation of first radiating zones and second radiating zones:
  • each first radiating zone further comprising a cylindrical conductive element whose axis coincides with said central wire element and which is electrically connected to said two lateral wire elements;
  • each second radiating zone further comprising two cylindrical conductive elements whose axes are respectively substantially merged with the lateral wire elements, said cylindrical elements being electrically connected to said central wire element; a space being left between two consecutive radiating zones.

It is understood that, thanks to the fact that the successive dipoles consist of radiating elements formed from a conductive cylindrical element and two conductive cylindrical elements and that, moreover, the antenna comprises three linear conducting elements, the The antenna structure is symmetrical and the radiated electric field is also symmetrical.

Each cylindrical element of length l internally comprises a disc made of a dielectric material of coefficient ε, orthogonal to the wire element, whose length in the direction of the wire element is such that: $$\mathrm{l}+\mathrm{\epsilon }{\mathrm{l}}^{\text{'}}=\mathrm{\lambda }/\mathrm{two}$$

Due to the presence of the disk of dielectric material inside each cylindrical conductive element, it is possible to compensate for the difference between the physical length of the cylindrical conductor and its electrical length as an antenna without thereby making the production more complex. of the antenna. We understand more that these disks made of dielectric material allow the mechanical maintenance of the cylindrical elements with respect to the rectilinear conductive wire elements.

Other characteristics and advantages of the invention will appear better on reading the following description of several embodiments of the invention given as non-limiting examples.

• la figure 1 déjà décrite montre une antenne colinéaire coaxiale alternée de type connu ;
• la figure 2 est une vue en perspective de l'ensemble de l'antenne conforme à l'invention ;
• la figure 3 est une vue en coupe verticale partielle de l'antenne selon l'invention ; et
• la figure 4 est une vue partielle montrant une zone rayonnante d'un type perfectionné.

The description refers to the appended figures, in which:

• FIG. 1 already described shows an alternating coaxial collinear antenna of known type;
• Figure 2 is a perspective view of the assembly of the antenna according to the invention;
• Figure 3 is a partial vertical sectional view of the antenna according to the invention; and
• Figure 4 is a partial view showing a radiating area of an improved type.

FIG. 2 shows the antenna 20 as a whole. Functionally, it is constituted by a radiating part 22, a blocking end 24 opposite to the connection zone of the antenna cable 26 and at its end close to its connection to the cable, the antenna preferably comprises two current traps referenced respectively 28 and 30.

The radiating part 20 of the antenna is constituted by a succession of radiating or radiating zones formed by first radiating zones 32 ₁ , 32 ₂ , etc., and by second radiating zones 34 ₁ , 34 ₂ , etc., the second radiating zones being arranged alternately with the first radiating zones.

From the point of view of its construction, the radiating part 22 of the antenna is made from three straight conductors 36, 38 and 40 parallel to each other. The conductor 38 will be called the central linear conductor and the other two conductors will be called lateral linear conductors. The latter are equidistant from the central conductor 38. The first radiating zones 32 ₁ , 32 ₂ , etc., are constituted by two cylindrical conductive surfaces respectively referenced 42 and 44. The second radiating zones 34 ₁ , 34 ₂ , etc., consist of by a single substantially cylindrical conductive surface 46.

Referring now to FIG. 3, the making of the first radiating zones 32 _i and the second radiating zones 34 _i will be described in more detail.

The second radiating zone 34 _i is, as already indicated, constituted by a conducting cylinder 46 whose diameter d is substantially equal to the distance which separates the rectilinear lateral conductors 36 and 40. The cylinders 46 constituting the second zones radiating, have a length L. The axis XX 'of the cylinder 46 is coincident with the central rectilinear conductor 38 while its outer face 36a is welded to the lateral conductors 36 and 40. This establishes an electrical connection between the cylinders 46 constituting the second radiating zones 34 _i and the lateral conductors 36 and 40.

The first radiating zones 32 _i are, as already indicated, constituted by two conductive cylinders 42 and 44 identical to each other and preferably identical to the cylinder 46 constituting the second radiating zone 34 _i . The cylinders 42 and 44 therefore also have a diameter d and a length L. Each cylinder 42, 44 has its axis respectively YY 'and ZZ' respectively coincident with the straight lateral conductors 36 and 40. The outer face respectively 44a and 42a of the cylinders conductors 42 and 44 is welded to the central conductor 38. An electrical connection is thus established between the pairs of cylinders 42 and 44 constituting the first radiating zones 32 _i and the central conductor 38. The length L of the cylinders 42, 44 and 46 corresponds to at the half-wavelength λ / 2.

It should be added that a space, which will be defined later 48 _i , is provided between the different radiating zones 32 _i and 34 _i , this space has a length e.

Since each passage from a first radiating zone 32 _i to a second radiating zone 34 _i , the various rectilinear conductors 36, 38 and 40 pass from a coaxial position to a connection position to the conductive cylinder, we obtain and substantially a phase shift of 180 ° between two successive radiating zones, which makes it possible to effectively obtain the sum of the currents flowing in each radiating zone in emission or reception.

The bandwidth of the antenna is improved if the diameter of conductive cylindrical surfaces 42, 44 and 46 is increased. suitable value of d is 0.08 λ. However, the phase shifts in the conductive cylindrical surfaces and in the straight conductors 36, 38 and 40 are different for the same physical length of conductor. To compensate for these different phase shifts, according to an improved embodiment of the antenna shown in FIG. 4, a dielectric disk 50 is mounted inside the conductive cylinder 42, 44 or 46, which may, for example, be made of Teflon . The introduction of this disk 50 makes it possible to compensate the electrical length in the conductive cylinder 42 and in the rectilinear conductor 40. The length 1e of the dielectric disk 50 in the direction of the straight conductor 40 can be determined in the following manner. If we call it the dielectric constant dielectric length ε and the length of the cylinder 42, we must have the relation. $$\mathrm{\lambda }/\mathrm{two}=\mathrm{l}+\mathrm{\epsilon }{\mathrm{l}}^{\text{'}}$$

As already indicated in connection with FIG. 2, the antenna 20 also preferably comprises, at its end 52 of connection to the coaxial antenna cable 26, two current traps 28 and 30. current 28, 30 is constituted by a conductive cylindrical surface 54, 56 coaxial with the cable 26 and whose length L 'corresponds to λ / 4, λ being the working wavelength of the antenna. The lower end 54a, 56a of the cylinders 54 and 56 is connected to the outer face 26a of the coaxial cable 26 by an annular portion 58 and 60 also conductive.

In a preferred embodiment, the antenna has N = 14 radiating zones. The radiating zones consist of one or two cylindrical conductive surfaces of ratio L / d, the ratio is of the order of 5.

With this antenna, for the working wavelength of 52 mm, a bandwidth of the order of 2.5% and a gain of 10 dBiso are obtained.

Due to the realization of the alternating radiating zones formed by a conductive cylindrical surface and two conductive cylindrical surfaces, the antenna generally has a geometric symmetry with respect to the central rectilinear conductor 38. thus a radiation pattern in the most omnidirectional azimuth possible. In addition, the realization of the antenna is simple since it consists in welding the conductive cylindrical surfaces 42, 44 and 46 on the rectilinear electrical conductors 36, 38 and 40. It should be added that, in the case where each conductive cylinder is equipped with a dielectric disk, this dielectric disk is at the same time a spacer for mechanically holding the conductive cylindrical surface relative to the rectilinear electrical conductor and centering the cylindrical tube / rod assemblies.

Claims (5)

1. An antenna of colinear type (20) characterised in that it comprises a radiating portion (22) comprising:

   - three substantially rectilinear conductive wire elements (36, 38, 40) that are mutually parallel, comprising a central conductor (38) and two lateral conductors (36, 40); and

   - 2N radiating zones (32₁,32₂,...,34₁,34₂,...) constituted by alternating first radiating zones (32₁,32₂,...) and second radiating zones (34₁,34₂,...):

   - each second radiating zone (34₁,34₂,...) further comprising a cylindrical conductive element (46) whose axis coincides with said central wire element (38) and which is electrically connected to both of said lateral wire elements (36, 40); and

   - each first radiating zone (32₁,32₂,...) further comprising two cylindrical conductive elements (42, 44) whose axes coincide substantially respectively with the lateral wire elements (36, 40), said cylindrical elements being electrically connected to said central wire element (38); a gap (48_i) being left between two consecutive radiating zones (32_i, 34_i).
2. An antenna according to claim 1, characterised in that each cylindrical element (42, 44, 46) resonates at half wavelengths.
3. An antenna according to claim 2, characterised in that each cylindrical element (42, 44, 46) is of length L and contains internally a disk of a dielectric material (50) having a coefficient ε, the disk extending orthogonally to the wire element (36, 38, 40) and being of length ℓ' in the direction of the wire element such that: $$\mathrm{L}+\mathrm{\epsilon }{\mathrm{l}}^{\prime }=\mathrm{\lambda }/2$$

   
4. An antenna according to any one of claims 1 to 3, characterised in that it comprises, at its end for connection (52) to an antenna cable (26), at least one current trap (28, 30) comprising at least one conductive element surrounding said cable and of length λ/4, being electrically connected to said cable (26).
5. An antenna according any one of claims 1 to 4, characterised in that the ratio between the length of a cylindrical conductive element (42, 44, 46) over its diameter is about 5.

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