EP0403341A1 - Rotary dipole antenna for decametric waves - Google Patents

Abstract

The antenna has a support with a metal structure (1, P1-P8, Q3-Q8) and cables (H, K1-K3, L1, L2). In order to give the antenna good wind resistance, it was made using rigid half-wave (D) dipoles and these dipoles were mounted directly on the metal structure.Application to HF transmitting antennas.

Description

The present invention relates to antennas comprising a rotary support on which is mounted at least one vertical array of radiating dipoles and at least one vertical reflector formed of wires.

Such antennas are known and are used in HF. In the case of two dipole networks, these antennas most often have only one supply line which generally passes through the support and supplies one or the other of the two networks by means of a switching assembly.

The firing angle in azimuth of the known antennas is easily adjustable, in any direction, by rotation of the support; the firing angle in elevation and the antenna configuration can be adjustable by means of switching devices making it possible to connect, as desired, all or part of the dipoles of the same dipole network.

In these known antennas, the dipole arrays are formed of whole-wave wire dipoles made of conductive wires held between beams of the support by arrangements of cables, insulators, counterweights, pulleys, etc. Thus the dipoles are arranged in a sort of curtain stretched, in a vertical plane, between beams of the support.

This curtain, which comprises the dipoles of a network, has a bulk greater than the overall dimensions of all the dipoles of the network. Under the effect of the wind, the curtain deforms, causing, in particular, variations in the input impedance of the antenna and mechanical problems; it follows that the known rotary antennas are unusable from wind speeds always much lower than the maximum speed for which the stability of the antenna is ensured. This curtain which is used for positioning dipoles also have other drawbacks: it is highly stressed by the loads formed by frost deposits; it makes delicate the operations which consist in hoisting or lowering the rotary antenna as well as the interventions in the curtain.

As for the reflective curtain or curtains of known rotary antennas, they generally consist of a single ply formed of horizontal wires and overhead lines, and this ply is held only from above and from below. Again, the climatic conditions cause deformations which can affect the functioning of the antenna.

The object of the present invention is to avoid or at least reduce these drawbacks. This is obtained, in particular, by a different choice of the type of dipoles used and by a different way of positioning these dipoles.

According to the invention there is provided a rotary dipole antenna for HF waves, having a rotary support which comprises a metallic structure and cables, n, where n is a positive integer, networks of dipoles carried by the support and at most n reflectors vertical planes, made up of horizontal wires, each associated with at least one of the n networks, characterized in that the dipoles are rigid half-wave dipoles and in that the dipoles are fixed directly to the structure.

• - la figure 1, une vue partielle, de face, d'une antenne rotative selon l'invention,
• - la figure 2, une vue de côté de l'antenne rotative selon la figure 1,
• - la figure 3, une vue partielle plus détaillée de l'antenne rotative selon les figures 1 et 2.

The present invention will be better understood and other characteristics will appear with the aid of the description below and of the figures relating thereto which represent:

• FIG. 1, a partial front view of a rotary antenna according to the invention,
• FIG. 2, a side view of the rotary antenna according to FIG. 1,
• - Figure 3, a more detailed partial view of the rotary antenna according to Figures 1 and 2.

In the various figures, the corresponding elements are designated by the same references.

The rotary antenna which will be described below comprises two arrays of half-wave dipoles, that is to say of dipoles formed by two quarter-wave strands, and a set of switches for connecting one or the other of the two networks supplying the antenna. Depending on the network connected, the antenna is a low range antenna 4/4 / 0.5 - 6/7/9/11 MHz or a high range antenna 4/4 / 0.75 - 13/15/17/21 / 26 MHz; it is recalled that, according to the international electrical definition of antennas, for example the designation 4/4 / 0.5 - 6/7/9/11 MHz corresponds to an antenna intended to operate in the bands of 6, 7, 9 and 11 MHz (which gives about half a wavelength of 18 m at the central operating frequency of 7.7 MHz) and having 4 groups of 4 superimposed half-wave dipoles, the difference between two groups being equal to the half wavelength at the center frequency and the lowest group being at a distance from the ground equal to 0.5 times this wavelength.

The rotary antenna which is shown in Figures 1 and 2 comprises a central mast, 1, with a base 10; the mast rises 81 meters above the ground. In FIG. 1, only the part of the antenna situated to the left of the mast 1 has been fully represented for problems of space in the drawing and above all to allow the appearance, on the right of the mast, of the appearance of certain elements of the antenna.

On either side of the mast, in the plane of Figure 1 and perpendicular to the plane of Figure 2, horizontal beams P1-P8, Q3-Q8 are arranged in pairs. At one of their ends, these beams are articulated around a horizontal axis, such as A, integral with the mast 1; they are, in addition, guyed at mast 1 by guy wires such as H. The beams P1-P8 concern the network of half-wave dipoles of the low range antenna and the heights above the ground are 72, 54, 36 and 18 meters respectively for beams P1-P2, P3-P4, P5-P6 and P7-P8. It should be noted that the beams P5-P6 also relate to the half-wave dipole network of the high range antenna and that the beams P5 -P6, Q3-Q4, Q5-Q6, Q7-Q8 relating to the range antenna high are respectively 36, 28, 20 and 12 meters from the ground.

On each of the beams P1-P8, Q3-Q8, two rigid half-wave dipoles, such as the dipoles D or E, of the low and / or high range antenna concerned by the beam are fixed; the difference between the four dipoles of the same network located on the same pair of beams is equal to half the wavelength at the central frequency of use of the antenna considered, that is to say equal 18 meters for the low range antenna and 8 meters for the high range antenna; moreover, these four dipoles are arranged symmetrically with respect to the mast 1.

As appears from the front view according to FIG. 1 and from the side view according to FIG. 2, the half-wave dipoles are arranged at one end of a horizontal metal arm such as the arm Bd for the dipole. D and the Be arm for the dipole E; the other end of the arm is integral with the beam like the arm Bd with the beam P7 and the arm Be with the beam Q5; the length of the metal arms was taken a little more than a quarter of the wavelength, at the central working frequency of the dipole carried by the arm in question.

The rotary antenna according to FIGS. 1 and 2 further comprises two reflective planes, Rb, Rh, made of horizontal conducting wires of which only a part has been shown in FIG. 1; in FIG. 2, the planes Rb and Rh have been symbolized by two lines in dashed lines which correspond to the trace of these reflective planes in the plane of the figure. The wires of these reflecting planes are fixed at one of their ends to the mast 1. Between the beams P1, P2 and P7, P8 on the one hand and P3, P4 and Q7, Q8 on the other hand, the wires of the reflective planes are fixed, at their other end, to a lateral catenary, that is to say to a lateral cable such cables K2 and L1; this catenary is coupled to the ends of several beams, this is how the catenary K2 is fixed to the end of the beam P1, slides in an opening made in the ends of the beams P3, P5, P7 and is tensioned by a weight such as the weight Kp; similarly the catenary L1 is coupled to the beams P3, P5, Q3, Q5, Q7. Substantially parallel to these overhead lines, vertical conductive cables, such as K4, mounted in the same way as overhead lines, complete the maintenance of the wires of the reflector plane. On either side of the beams of the low range antenna and below the beams of the high range antenna, the wires of the reflective planes are fixed, at their opposite end to the mast, on a cable, such as cables K1, K3, L2, which is held on the mast and, at its end opposite to the mast, on the end of a beam, such as the beam P7 for the cable K3 spacers formed of vertical metal bars, such as the bar K5 associated with the cable K3 and the bar L3 associated with the cable L2, make it possible to separate the cable from the beam which is associated with it. This way of making the reflecting planes differs from the conventional way of making them in that the ply of wires is maintained not only at its high and low ends but also at intermediate levels thanks to beams such as P3 and P5, as it appears in figure 1.

In FIGS. 1 and 2 also appear holding bars, such as Md and Ne, which are conventional vertical supports making it possible to maintain the system of two-wire lines intended to supply the dipoles.

In FIG. 2, moreover, appear two switching devices C1, C2 mounted on the mast 1 and intended respectively to control the supply of the half-wave dipoles of the low range antenna and of the high range antenna, this supply being provided by a line, not visible in the figures, which passes inside the mast 1.

Figure 3 is a partial view, more detailed than Figure 2, which is located at the beams Q5, P7. In this view, the geometrical axis of the mast has been shown in center lines and the reflecting curtains, Rb and Rh, have been shown in broken lines. In this view also appear:
- arms Bd, Be
- bars Md, Ne
- steps S, S ′ and T which respectively line the beam P7, the arm Bd and the beam Q5 and which allow a technician to intervene in the antenna
- U and V guardrails which ensure the safety of the technician working on the antenna
- two-wire lines, such as Jd and Je, maintained by insulators on the vertical uprights of the guardrails.

By way of comparison, antenna characteristics are given below which correspond, the first, to the rotary antenna with rigid half-wave dipoles which has just been described and, the second, to a conventional rotary antenna designed and produced at using full-wave wire dipoles to be switched, like the rotary antenna described, either as a 4/4 / 0.5 - 6/7/9/11 MHz antenna or as a 4/4 / 0.75 - 13 antenna / 14/17/21/26 MHz:
- extreme longitudinal wind speed (within the meaning of the French "snow and wind" rules of June 1980) at 10 m from the ground: 184 km / h for the two rotary antennas
- maximum wind speed at 10 m from the ground, at which the antenna can operate: 100 km / h instead of 80 km / h with the conventional antenna,
- maximum wind speed at 80 m from the ground, at which the antenna can still operate: 131 km / h instead of 105 km / h
- total weight of the rotating antenna: 2000 kN, 1800 kN,
- overturning moment: 35,000 kN.m, 50,000 kN.m,
- dimensions (width x height in meters): 74 x 81, 76 x 88,
- illuminated width (in working wavelength): 1.96, 1.55
- gain in decibels: (G + 1) dB, GdB, i.e. a ratio of 1.26 - transverse deformation under the effect of a wind of 80 km / h at 10 m from the ground: none for rigid dipoles and negligible for their reflective curtain while, in the conventional antenna, the wire dipoles undergo significant deformations and displacements and that the deformations of the curtains reach several meters.

The present invention is not limited to the example described, thus it also applies to the case where the rotary antenna is not a double antenna but a single antenna, that is to say to a single network of rigid half-wave dipoles. It also applies to the case where the rotary antenna comprises three and more dipole arrays, distributed, for example, in the case of three arrays, around a support with horizontal section in the shape of an equilateral triangle with each side affected. to a network of rigid dipoles and to a reflector but, in this case the networks would no longer be supported by horizontal beams mechanically coupled to a central mast. It is also possible to produce, within the framework of the invention, rotary antennas not comprising devices for switching rigid dipoles and, when these devices exist, they can be arranged differently than in the example described, by example at the foot of the mast.

And it should be noted that it is possible to produce a rotary antenna with two arrays of half-wave rigid dipoles, comprising only one reflective curtain; in the case of the example described, this amounts to having only the curtain Rb but by increasing the number of conducting wires for this curtain where it acts as a reflector for the dipoles in the high range. It should also be noted that an interesting case is the case where the rotary antenna to be produced has a central mast and an odd number of dipoles per horizontal line of dipoles, indeed, in this case, the dipole in the middle of the line will be fixed not on one of the beams but directly on the central mast.

The present invention relates more particularly to rotary antennas intended for transmitting in HF.

Claims (5)

1. Rotary antenna with dipoles for HF waves, having a rotary support which comprises a metallic structure and cables, n, where n is a positive integer, networks of dipoles carried by the support and at most n vertical plane reflectors (Rb, Rh ), made up of horizontal wires, each associated with at least one of the n networks, characterized in that the dipoles (D, E) are rigid half-wave dipoles and in that the dipoles are fixed directly to the structure (1, P1-P8, Q3-Q8, Bd, Be). 2. Antenna according to claim 1, characterized in that the structure comprises a vertical central mast (1), lateral beams (P1 -P8, Q3-Q8) at least substantially horizontal, mechanically coupled to the central mast and metallic arms ( Bd, Be) substantially horizontal, perpendicular to the beams and in that these arms are fixed at one of their ends to one of the beams and each carry one of the dipoles (D, E) at their other end. 3. Antenna according to claim 2, in which at least one of the dipole arrays comprises horizontal lines of dipoles with an odd number of dipoles per line, characterized in that, in these lines with an odd number of dipoles, the middle dipole of the line is carried by the mast (1). 4. Antenna according to any one of claims 2 and 3, characterized in that the beams (P1-P8, Q3-Q8) are mounted in rotation, at one of their ends, around a horizontal axis (A ), integral with the mast (1) and are guyed by a guy (H) arranged obliquely between the beam in question and the mast. 5. Antenna according to any one of claims 2 to 4, characterized in that the planar reflectors (Rb, Rh) are mechanically coupled to the ends of at least part of the beams (P1-P8, Q3-Q8).

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