EP0205393A1 - Omnidirectional cylindrical antenna - Google Patents

Abstract

The array antenna with rotational symmetry consists of an array of elementary antennas in a cylindrically shaped printed circuit. …<??>It is made up of small-sized radiating sources which are arranged on a cylindrical surface in overlying circles. The sources are distributed angularly over the circles with a constant angular pitch. There is weak coupling between them. For each circle of sources, all the sources are supplied in phase and with the same amplitude. …<??>An angular shift may be provided between the set of sources of one circle and that of the sources of the next circle. The antenna can be supplied via a three-wafer printed circuit line. It can consist of an array of doublets bent into wafers. The transmitter (24), to which is applied the video signal to be transmitted and which supplies the modulated carrier to the array of radiating sources, is installed inside the cylinder. …<IMAGE>…

Description

The present invention relates to an array antenna with symmetry of revolution consisting of an array of elementary antennae in a printed circuit of cylindrical shape and intended more particularly for the transmission of terrestrial broadcasting signals in the 12 GHz band.

Terrestrial broadcasting antennas must have a very wide omni-directional or sectoral radiation pattern in azimuth and a much narrower diagram in elevation. In addition, in a given direction, the radiated power must be constant as a function of the frequency in the operating band of the antenna. To obtain these diagrams, several technologies have so far been used with more or less success: reflector antennas, slot antennas, dipole arrays, arrays of sources in microstrip printed circuit.

Antennas using technology other than that of the printed circuit are too bulky to be installed on most sites. In the state of the art, the basic idea was to bring the pseudo-center of phase to the center of the structure to have an omnidirectional radiation. This was done with multi-source reflector antennas at the cost of heavy and large structures.

The planar printed circuit antennas have a directional radiation pattern. Grouping them to obtain an omnidirectional diagram is very difficult at 12 GHz. Indeed, it is necessary to carry out distributions towards the various antennas with severe conditions on the phases to avoid unfavorable recombinations of diagrams of the various elementary antennas. These elementary diagrams must be broad and have a radiated phase as constant as possible; otherwise, the number of elementary antennas must be multiplied, which complicates the power distribution.

In an article entitled "Large-bandwidth flat cylindrical array with circular polarization and omnidirectional radiation" by G. Dubost, J. Samson and R. Frin, published in the journal "Electronics Letter" in 1979, a network of four sources is described. radiant in microstrip circular polarization technology which are plated on a cylinder, the power distribution being carried out by means of coaxial cables and couplers of trade. Such a radiating source with circular polarization is described in patent FR-A-2 429 504.

An object of the invention is to provide an array antenna consisting of an array of elementary antennas in a printed circuit plated on a cylinder which is compact and which has a less wavy azimuth radiation pattern than those of known antennas. According to a characteristic of the invention, omnidirection _- nality is not obtained by reducing the phase centers of the elementary antennas to the center of the structure, but by placing these elementary antennas periodically on a circumference centered on an axis of revolution and in sufficient number to have weak undulations of the radiated diagram.

According to a characteristic of the invention, there is provided such an array antenna formed of radiating sources of small dimensions which are arranged on a cylindrical surface in superimposed circles, said sources being angularly distributed with a constant angular pitch on the circles, little coupled between them and, by circle of sources, all supplied in phase and with the same amplitude.

According to another characteristic, an angular offset is provided between all of the sources of a circle and that of the sources of the next circle.

According to another characteristic, the offset is a fraction equal to the angular step divided by the number of circles.

According to another characteristic, the array antenna is supplied by a line on a three-plate printed circuit applied to a cylinder.

The use of a triplate line creates inside the cylinder an armored space. The supply conductors, located under the external ground plane, are also fully shielded.

Furthermore, in the article entitled "Network of symmetrical folded doublets in broadband plates around 12 GHz" by G. Dubost and C. Vinatier published in the review "L'onde électrique", 1981, vol. 61, n ° 4, pp. 34-41, a planar radiating source is described, the radiating elements of which are folded doublets and which is supplied by a triplate line. This network is also described in documents FR-A-2 487 588 and EP-A-0 044 779. This network leads, among other things, to directional diagrams when it is planar.

Another object of the invention consists in using this type of network to produce a network antenna with symmetry of revolution having practically omnidirectional radiation, that is to say whose undulations in the plane perpendicular to the axis of symmetry are significantly reduced compared to those obtained with the antennas forming part of the state of the art.

According to a characteristic of the invention, there is provided such an antenna consisting of a network of doublets folded into plates of the type described in the document FR-A-2 487 588 mentioned above, said doublets being aligned along circles, the gap between them. centers of adjacent doublets being of the order of 0.9 o, where o is the wavelength in vacuum of the carrier emitted by the antenna.

According to another characteristic, inside the cylinder is installed the transmitter to which the video signal to be transmitted is applied. and which supplies the network of radiating sources with the modulated carrier.

This structure has the advantage of minimizing the lengths of the conductors traversed by the very high frequency signal, which limits losses and increases the radiation of the transmitter.

According to another characteristic, the network of radiating sources is divided into sub-networks, each sub-network covering an angular sector, the output of the transmitter being connected to a power and equiamplitude power divider having as many outputs as there are networks and whose outputs are respectively connected to the attack points of the sub-networks.

• la Fig. 1 est une vue en plan d'un doublet replié en plaques connu,
• la Fig. 2 est une vue en coupe du doublet de la Fig. 1, suivant la ligne II-II,
• la Fig. 3 est une vue en coupe du doublet de Fig. 1, suivant la ligne III-III,
• la Fig. 4 est une vue en perspective d'une antenne cylindrique à axe vertical, suivant l'invention,
• la Fig. 5 est une vue en coupe transversale de l'antenne de la Fig. 4,
• la Fig. 6 est une vue schématique illustrant une variante de la Fig. 4,
• la Fig. 7 est une vue développée d'un sous-réseau de distribution alimentant un sous-réseau de sources rayonnantes,
• les Figs. 8 à 10 sont des vues en coupe verticale partielle de plusieurs structures de répartition de l'antenne des Figs. 4 et 5,
• la Fig. 11 est une vue d'une variante du réseau de distribution de la Fig. 10, et
• la Fig. 12 est une vue à plus grande échelle d'un détail du réseau de la Fig. 11.

The characteristics of the invention mentioned above, as well as others, will appear more clearly on reading the following description of exemplary embodiments, said description being made in relation to the accompanying drawings, among which:

• Fig. 1 is a plan view of a known doublet folded into plates,
• Fig. 2 is a sectional view of the doublet of FIG. 1, along line II-II,
• Fig. 3 is a sectional view of the doublet of FIG. 1, along line III-III,
• Fig. 4 is a perspective view of a cylindrical antenna with a vertical axis, according to the invention,
• Fig. 5 is a cross-sectional view of the antenna of FIG. 4,
• Fig. 6 is a schematic view illustrating a variant of FIG. 4,
• Fig. 7 is a developed view of a distribution sub-network supplying a sub-network of radiating sources,
• Figs. 8 to 10 are views in partial vertical section of several distribution structures of the antenna of Figs. 4 and 5,
• Fig. 11 is a view of a variant of the distribution network of FIG. 10, and
• Fig. 12 is an enlarged view of a detail of the network of FIG. 11.

An elementary antenna usable in the array antenna of the invention can be the folded doublet which is shown in FIG. 1 and which, when it is planar, forms part of the state of the art. As we will see below, we use this elementary antenna giving it a cylindrical shape. The doublet of FIG. 1 comprises a supplied strand formed by two half-plates 1 and 2 separated by a cut 3, and a folded strand formed by a long continuous plate 4 and two symmetrical portions 5 and 6 connecting, on the one hand, 1 and 4 and, on the other hand, 2 and 4.

The plate 4 is connected, in its central part, to a ground plate 7, perpendicular to 4 and symmetrical, with respect to the axis of symmetry of the dipole, of the central conductor 8 of a three-ply line. The central conductor 8 is indicated in FIG. 1, by dashed lines because it passes successively under 7, 4, 5 and 1, each of the metal surfaces 7, 4, 5 and 1 serving as ground surfaces on one side of the conductor 8. In particular, under the half plate 1, line 8 is equidistant from the sides of 1.

In addition, the doublet in FIG. 1 comprises a second continuous long plate 9, symmetrical with the plate 4 with respect to the axis of symmetry 10 of the two half-plates 1 and 2, and two symmetrical portions 11 and 12 connecting, on the one hand, 1 and 9 and , on the other hand, 2 and 9. The portions 11 and 12 are symmetrical with the portions 5 and 6 with respect to the axis 10.

The plate 9 is connected, in its central part, to a plate 13 perpendicular to 9 and symmetrical by 7 with respect to the axis 10. The plates 7 and 13 are part of the same large plate 14 which surrounds the doublet proper , with openings 15 and 16 separating the doublet from the plate 14. Of course, the openings 15 and 16 are symmetrical relative to the center of the doublet.

As shown in the section of FIG. 2, the central conductor 8 forms with the plate 7, on the one hand, and a ground plate 17, on the other hand, a three-plate supply line. In practice, the metal elements 1, 2, 4, 5, 6, 7, 9, 11, 12, 13 and 14 form one side of a first printed circuit 18 while the central conductor 8 forms the other side of this printed circuit board. Against the face of 18 carrying the conductor 8, the bare face of a second circuit is applied printed 19 whose other side is uniformly coated with the metal plate 17.

The recesses 15 and 16 must be large enough to avoid an exaggerated coupling between the radiating doublet and the ground plate 14 of the triplate line.

From the plate 7, the central conductor 8 is successively extended under one half of the plate 4 (towards the portion 5), then under the portion 5, then under the half-plate 1 and, finally, after passing under the cut 3, under a part of the half-plate 2. Of course, each of the different segments constituting the central conductor is always under the axis of symmetry of the plate which covers it.

où c est la vitesse des ondes électromagnétiques dans le vide.The distance between the end 20 of the conductor 8 and the middle of the cutoff 3 is equal to a quarter of a wavelength, that is to say / 4, where denotes the wavelength in the insulating medium of the printed circuits 18, 19, with:

where c is the speed of electromagnetic waves in a vacuum.

Thus, the quarter-wave line under the half-plate 2 is open, which brings a short circuit under the edge of the half-plate 2 adjacent to the cutoff 3. It therefore appears that the quarter-wave line allows avoid passage through circuit 18 and soldering.

The detailed description which has just been given is only intended to illustrate an exemplary embodiment of an elementary radiating source and should not be interpreted as limiting the scope of the invention to this kind of radiating source. Indeed, it is possible with a triplate line to use open slits in the external ground plate of the line. However, it should also be noted that the doublet in Figs. 1 to 3 constitutes a radiating source with wide bandwidth.

The antenna 21 of FIG. 4 consists of a hollow support cylinder 22, which is obtained, for example, by rolling and machining, and antenna sub-arrays 23 which are pressed against the external face of the cylinder 22 by suitable means, not shown, such as screws which are screwed into tapped holes provided in the wall of the cylinder 22. The elementary radiating sources of the sub-arrays 23 are, in the example described, doublets identical to that of FIGS. 1 to 3. On the half of the cylinder 22 is placed a sub-network of four horizontal rows of sixteen doublets each.

The interior of the cylinder 22 makes it possible to house the active part of the antenna, that is to say the transmitter 24, which conventionally comprises a video input, a DC power supply and a microwave output. Optionally, a radiator 25 can be added to cool the transmitter. The emitter and the radiator are supported by horizontal plates which are themselves fixed at various points on the internal face of the cylinder 22. These plates are notched as much as possible to allow the air to circulate from bottom upwards around the transmitter and radiator, as well as holes for the passage of the video cable and the power supply.

The horizontal section of Fig. 5 shows wound around the cylinder 22, the two layers of printed circuits 26 and 27 carrying the radiating sources with, on the internal face of the layer 26, the ground plane 28, on the internal face of the layer 27, the central conductor of the power distribution network 29 and, on the external surface of the layer 27, the second ground plane 30 in which cutouts reveal the strands of the doublets which constitute the network 23.

In practice, the structure of the assembly 26 to 30 constitutes a three-ply structure identical to that which has been described in relation to FIGS. 1 to 3, with all the advantages which it entails with regard to the shielding of power distribution lines, that is to say of network 29.

In addition, it should be noted that the ground plane 28 prevents parasitic radiation coming directly from the transmitter from being transmitted to the outside.

In Fig. 7, the developed representation of the central conductor of a distribution sub-network 29 usable with the sub-network 23 has been shown. For reasons of convenience of presentation, instead of considering the elementary sources grouped in four circular rows, it will be considered that the network of FIG. 7 comprises sixteen groups of four radiating sources, only one of which is symbolized in S1 by an H in dashed lines, with their supply conductors L1.1 to L4.16, similar to 8, Fig. 3. Each group i comprises four conductors Ll.i to L4.i. It will be recalled, as shown in FIG. 1, that each supply conductor 8 has a terminal segment parallel to the strands of the doublet and a starting segment which is directed perpendicular to the terminal segment towards the middle of the latter, the two segments being joined by an elbow.

The feeder segments of conductors Ll.i and L2.i are connected to a power divider by two Dl.i directed parallel to the terminal segments. The starting segments of the conductors L3.i and L4.i are connected to a power divider by two D2.i aligned with the divider Dl.i, but directed in the opposite direction. The inputs of the dividers Dl.i and D2.i are respectively connected to the two outputs of a power divider by two D3.i which is parallel to the starting segments. The assembly of four conductors Ll.i to L4.i and of the three dividers Dl.i to D3.i forms the supply group of a group of four radiating sources. In such a group, the centers of the individual sources are at the four corners of a square and the terminal segments are all directed in the same direction.

The groups of radiating sources are grouped by four as follows. Assuming that J is a multiple of four, plus one, the centers of the squares of the groups J. to j + 3 are themselves at the four corners of a square, with their divisors D3.j and D3 (j + 1) aligned, but directed towards each other, and their dividers D3. (j + 2) and D3. (j + 3) aligned, but directed towards each other. The inputs of the dividers D3.j and D3. (J + 1) are connected to the outputs of a power divider by two D4.j while the inputs of the dividers D3. (J + 2) and D3. (J + 3 ) are connected to the outputs of a power divider by two D4 (j + 2). The dividers D4.j and D4. (J + 2) are aligned parallel to the terminal segments, but with their inputs directed towards each other and connected to the outputs of a power divider by two D5.j.

Since there are sixteen groups themselves assembled four by four, there are four dividers D5.1, D5.5, D5.9 and D5.13 which are all orthogonal to the terminal strands. The inputs of the dividers D5.1 and D5.5 are connected, by two conductors of the same length, bent twice, to a power divider by two D6.1. Likewise, the inputs of the dividers D5.9 and D5.13 are connected to a power divider by two D6.9. The dividers D6.1 and D6.9 are orthogonal to the terminal segments, directed in the same direction, and their inputs are connected to the inputs of a power divider by two D7 which is parallel to them, oriented in the same direction and in the vertical axis of symmetry of the network when it is developed on a plane. The input of the D7 divider is extended vertically to a point of connection to a connector.

In the exemplary embodiment of FIG. 7, a distribution network has been considered for four times sixteen radiating sources. To switch to a network of four times thirty two antennas, one could juxtapose two 4x16 networks by planning to combine the inputs of the divider D7 and its corresponding to a divider D8.

In an exemplary embodiment of the invention, the pitch of the sub-network 23 was, in both directions, horizontal and vertical, equal to 0.9 times the wavelength in a vacuum corresponding to a frequency of 12 GHz for the carrier transmitted, and two sub-arrays were plated on a cylinder 22 cm in diameter. A network comprising four rows of sources requires then to provide a cylinder with a height of about 13 cm.

As shown in Figs. 4 and 8 to 10, provision has been made for the antenna to be provided with two diametrically opposite antenna connectors 31 and 32.

In Fig. 8, a single coaxial connection 33 has been provided between the emitter 24 and the connector 31. Above the connector 31, a network 23 has been pressed, the distribution network of which was identical to that of FIG. 7, with the input conductor of the divider D7 extended vertically downwards to the connector 31. The transmitter 24 is modulated by the video transmitted by the cable V and supplied by the power supply cable A.

In Fig. 9, the source 24 is connected, by a coaxial link, to the input of a power divider by two 35 whose outputs are respectively connected, by equipaxial coaxial links and equiamplitudes 36 and 37, to the connectors 31 and 32. In this case, each connector 31 or 32 is connected to a distribution network identical to that of FIG. 7. The two subnets overlap together around the cylinder and allow 360 ° coverage.

The configuration of FIG. 10 is a variant of that of FIG. 9, in which the divider 35, which can be a commercial 3 dB divider, has been replaced by a custom power divider 38 with equiphase and equiamplitude outputs by construction.

With the assembly of FIG. 8, the diameter of the cylinder 22 being 22 cm, the measurements carried out showed that a satisfactory horizontal coverage of 165 ° was obtained, undulations of the horizontal radiation diagram of the order of - 3 dB, a width of 3 dB of the vertical radiation pattern corresponding to an angle of 16 ° and a horizontal polarization.

With the assembly of FIG. 9 and the same cylinder, these results become: - 3 dB, omnidirectional, 16 ° and a horizontal polarization.

In Fig. 6, there is shown schematically a variant of the network shown in FIG. 4. In this network, where the elementary radiating sources are represented by crosses, these are distributed on four horizontal circles C1 to C4. On all the circles, the sources are equal in number N and the angular pitch between adjacent sources is 360 ° / N. The distribution of the sources on the circle C2, below C1, is angularly offset by 360 ° / (4xN) and so on until the distribution of the circle C4. With 16 sources over 180 °, as in FIG. 3, the angular step is equal to 11 ° 15 '. The undulations in the diagram therefore have an undulation of period 11 ° 15 '. With the antenna of FIG. 6, the period of the undulations is reduced to less than 3 °. It should be observed that, when the period of the ripple is reduced, so is the amplitude thereof.

The distribution network of FIG. 11 is suitable for such an antenna. Experience has shown that the amplitudes of the ripples are reduced below - 1.5 dB.

In the network of FIG. 11, the power dividers by two successive are no longer dividers by simply widening the input conductor and branching on two conductors without change of direction, but T-dividers as shown in FIG. 12.

The T-divider in Fig. 12 includes an input conductor 39 extended by a quarter-wave transformer, then extended by two quarter-wave transformers 40 and 41, perpendicular to the direction of the conductor 39.

More particularly, the distribution network of FIG. It is intended to supply a sub-network of 4x4 sources. In a group of sources such as group G1, the sources hl and h2, on two different circles, are shifted by a quarter of a step. As a result, the input segments of their supply conductors L'l.1 and L'2.1 are not aligned. In the exemplary embodiment, they are respectively joined to the output conductors of a divider by two at T D'1 whose direction of the output conductor makes an angle of + 45 °. Likewise, the conductors L'3.1 of h3 and L'4.1 of h4 are combined with a T-divider D'2.1 whose input conductor is oriented at -135 °. Note that the dividers D'1.1 and D'2.1 are, to respect the lengths of the course, on the same horizontal circle. So their input conductors are not aligned. These are therefore extended by turning the first by -90 ° then by + 90 °, and the other by + 90 °, then by -90 ° in order to join the output conductors of a T-divider D'3.1 whose input conductor is oriented at -45 °.

For sources in group G2, the conductors L'1.2 and L'2.2, as well as L'3.2 and L'4.2, are not aligned respectively. They are joined to a T-divider D'3.2 by two dividers, similar to those which have been described. The input conductor of the D'3.2 divider is oriented at + 135 °. The input conductors of D'3.1 and D'3.2 are connected by conductors respectively bent at -45 ° and + 45 °, then at -45 ° and + 45 °, to the output conductors of a divider D'4.1 . The output conductor of the divider D'4.1 is oriented at + 45 °. In groups G3 and G4, we also find the divider D'4.2 whose input conductor is oriented at -135 °.

The input conductors of D'4.1 and D'4.2 are respectively extended by bends at -90 °, then + 45 ° and finally -45 °, to be connected to the output conductors of a divider D'5 whose the input conductor is at -45 °.

The input conductor of D'5 is connected, by a suitably bent conductor, to an input connector such as 31 or 32, or to a cascade of dividers, not shown, the input of the latter of which is connected to a connector.

As mentioned above, a satisfactory omni-directional antenna can be constituted by a printed circuit board plated on a cylinder 22 cm in diameter and 13 cm in height, the transmitter being contained inside the cylinder. It is quite possible to superimpose several of these antennas, each containing a transmitter operating with a different carrier and modulated by a different video to transmit as many programs. This solution is particularly advantageous because it avoids the multiplexing of programs as well as the power limitations imposed to reduce the effects of intermodulations.

Note also that by using as elementary radiating source doublets such as that of Figs. 1 to 3 which have a large bandwidth, the superimposed antennas can be constituted by identical arrays.

Claims (9)

1) Network antenna with symmetry of revolution consisting of a network of elementary antennas in printed circuit arranged on a cylindrical surface (22) characterized in that it is formed of a plurality (N) of radiating sources of small dimensions by relative to the circumference of said cylindrical surface and arranged in superimposed circular rows (C1 to C4), said sources being, in each circular row, angularly distributed with a constant angular pitch (360 ° / N) and all supplied in phase and with the same amplitude by a line in triplate printed circuit (28-26-29-27-30) applied to said cylindrical surface (22). 2) Network antenna according to claim 1, characterized in that each radiating source is a doublet folded in plates (1-2-4-5-6-9-11-12). 3) network antenna according to claim 2, characterized in that the difference between the centers of the adjacent dipoles is of the order of 0.9 ao, where λo is the wavelength in the vacuum of the carrier emitted by l 'antenna. 4) network antenna according to one of claims 1 to 3, characterized in that inside the cylinder is installed the transmitter (24) to which is applied the video signal to be transmitted and which supplies the network of radiating sources with modulated carrier. 5) network antenna according to one of claims 1 to 4, characterized in that the network of radiating sources is divided into sub-networks, each sub-network covering an angular sector, the output of the transmitter being connected to a divider Equiphase power (35 or 38) having as many outputs as there are sub-networks and whose outputs are respectively connected to the attack points of the sub-networks. 6) network antenna according to one of claims 1 to 5, characterized in that an angular offset (360 ° / 4N) is provided between all of the radiating sources of a circular row and that of the radiating sources of the row following circular. 7) Antenna according to claim 6, characterized in that the offset is a fraction equal to the angular pitch divided by the number of circular rows. 8) Network antenna according to one of claims 1 to 7, characterized in that several of them are superimposed with the same vertical axis, each comprising, inside its cylinder, its transmitter modulated by the video to be transmitted. 9) Antenna according to one of claims 2 to 8 and intended to operate around 12 GHz, characterized in that, on a circular row, are provided thirty-two radiating sources, the diameter of the cylindrical surface being 22 cm.

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