CA1324657C - Omnidirectional antenna, particularly for the transmission of radiobroadcast or television signals in the uhf band, and radiating system made of several such antennas - Google Patents

Abstract

This antenna, in particular intended for the transmission of radio or television signals in the decimetric-wave range, comprises: - a vertical, central support tube (100), - a plurality of identical radiating arrays (200), preferably three in number, uniformly distributed around the central tube and each formed from a vertical bifilar line (210, 210') supporting, coupling and supplying in a symmetrical manner, a plurality of horizontal dipoles (220, 220') uniformly distributed along this bifilar line, and - an equipower, equiphase power distribution system, preferably housed entirely inside the central support tube, identically and simultaneously supplying the three radiating arrays from a single coaxial supply line. The antenna lacks a reflector, this significantly reducing its weight and its wind resistance relative to conventional panel antennas generally used in this range. Advantageously, these antennas are superimposed and enclosed in a sealed, essentially cylindrical, self-supporting and superimposable radome. This antenna achieves an omnidirectional pattern at 0.9 dB between 460 and 860 MHz, and can radiate 5 to 7 kW per antenna element. <IMAGE>

Description

...
Antenna omnidirectio elle, in particular for the emission of signals of radio or television broadcasting in the ~ decimeter ~ wave band, and radiating system formed from a grouping of these antennas ~
The present invention relates to an omnidirectional antenna.
This antenna is particularly applicable to the emission of signaw ~ from broadcasting or television in the UHF band (so-called UHF band), where we will see that it provides advantages 10 particularly interesting.
The invention is however not limited to this application or to this frequency band, and might as well be suitable for a very large diversity of different situations.
For radio or television antennas, (with some exceptions) of a radiating system with the most diagram omnidirectional possible (by "omnidirectional diagram", we will hear a diagram with no dips below 3 dB on 360) ao This system which must also have mechanical characteristics compactness and lightness allowing it to be placed on top of a pylon minimizing both the static load (self-weight of the system radiant) than dynamic (taken in the wind) supported by it Most often, an antenna system called "antenna" is used for this purpose.
with panels ", made up of radiant elements each formed a dipole placed in front of a reflector, the dipole being oriented vertically or horizontally depending on the desired polarization As such a radiating element is a gain element, therefore directive, it is necessary to group four, arranged 90 from each other, to get the desired omni-directional diagram To increase the admissible power, we generally superimpose a plurality of these radiating elements (most often two, four or eight radiating elements) so as to form panels ~
radiant, the reflector being most often common Each panel is supplied separately with the same phase and even power than everyone else (unless you want to play on the form of the diagram by introducing phase shifts or variations of power) by means of a distributor assembly This configuration, although operating satisfactorily on a very large number of current transmitting stations, presents a number of drawbacks First of all, it is necessary to provide, at the top of the pylon 46 proper, a pylonet for properly arranging the ~
q ~,. .
,.

2 1 324657 radius elements ~ overlapping lants forming the four radiating faces of the configuration.
This pylonet must satisfy two anonymous conditions:
- firstly, it must be sufficiently dimensioned in order to allow the installation of power supplies for each panel and the passage of a man in the center of the configuration to be able maintain it: we have seen that each element radiant was powered by a clean supply coaxial and, as this coaxial must necessarily be placed behind the reflective panel of the radiating element so as not to disturb the operation of it, the coaxial cable bundle should pass inside the pylonet, which should therefore have a size 1 ~ sufficient (for faces with eight superimposed radiating elements, there are thus 32 coaxials to pass through this pylonet).
For this convenience of installation, and also for good mechanical rigidity, so it is desirable that the structure of the pylonet is as wide as possible.
- secondly, from a radioelectric point of view, the troughs of the diagram will become more accentuated as the centers of phase of the radiating elements will go away.
To obtain the most regular diagram there is, it is therefore desirable to bring the elements as close as possible radiant from each group, so provide a section of pylonet as small as possible (limited however by the minimum dimension of 3 reflectors).
To minimize static and charge dynamics mentioned above, it is also desirable to minimize the cross section of the p ~ lonet, especially as the radiating unit must be protected by a radome whose size, taking into account the size of the radiating elements, will present a very large wind catchment area and will therefore require all the more the pylon.
Another drawback of this type of antenna results from the complexity of its supply system (each of the radiating elements to be powered by a clean coaxial, as indicated above), which requires 40 provide a large number of secondary supply coaxials and connection boxes; the cost price of such an antenna system goes thus grow very quickly with the number of radiating elements.
.
In addition, losses will increase rapidly, both due to the 46 more connection boxes than longer elongation , ..

::
r, ~ c. ~.

3 1 324657:
secondary supply coaxials; typically for a system radiating with panels of eight superimposed radiating elements sized for the band 470-860 MHz, the height of the pylonet, and therefore longest coaxial, is around 12 meters, which creates 5 significant losses in such a frequency range.
This typically leads to sections of pylon and of the order of 0.8 ~ 0.8 m and radome diameters of the order of one meter for transmissions in the 470-860 MHz band, a group of four panels ~
with its radome having a specific mass of 350 to 400 kg and having a windward area of the order of 1.3 m2.
Another type of antenna suitable for the above use, although less used, is the antenna known as "supertourniquet".
In this type of antenna, to obtain the omnidirectional diagram desired, we use the rotating field principle, the radiating element then being made up of two flat, vertical "bat wings" and perpendicular to each other, crossing at their center and 90 ° out of phase one in relation to the other.
2D We thus superimpose a high number of radiating elements, each radiant element being powered separately by a system common distributor, and the two dipoles formed by the "bald wings"
mouse "of each radiating element being fed in quadrature of aperiodically via a 3 dB coupler.
This type of antenna, although it has a large overall diameter smaller than an antenna panel system due to the absence of reflector, thereby significantly reducing the sizing of the pylonet, however presents a number disadvantages:
.... '' - first of all, the need to carry out aperiodic feeding in quadrature between the dipoles results in the use of 3 dB couplers placed in the radiation field, the balancing charge of the 36 coupler to be sized according to the power at issue, - then the coaxial cables for supplying the dipoles are located in the radiation field of the antenna and therefore disturb the radiation of this by creating hollows in the diagram, - moreover, for equal gain, the total antenna height is greater than that of an antenna with radiant panels, causing in addition correlatively problems of compensation of the diagram in site in the case of antennas with a large number of elements radiant, - finally, the cost price is high due to the complexity mechanical, presence of 3 dB couplers and multiplication

4 l 324657 coaxial power cables.
As we can see, the two types of antennas used up to present for radio or television transmitters in the g, ~ even decimeter waves are not entirely satisfactory because they do not allow performance to be achieved simultaneously mechanical (compactness to limit wind resistance, reduced weight, structure simple to manufacture) than radioelectric (omnidirectionality of the diagram, possibility of accepting a significant power) desirable.
The present invention proposes to resolve these drawbacks, by offering a new type of antenna which, while presenting excellent radio-electric properties, being compact, light and achievable at a cost low thanks to both its simple mechanical structure (absence of -pylonet, in particular) and to the reduction to a minimum of connections in coaxial cables. ~ ~ -To this end, according to the invention, the antenna comprises:
aQ '"''~:' --a central, vertical support tube, - a plurality of identical radiating networks, regularly distributed around the central tube and each formed by a line:
vertical two-wire supporting, coupling and supplying in a manner ,? 5 symmetrical a plurality of horizontawc dipoles, regularly distributed along this bifilar line, and - a power distribution system with equiphase and power supplying the networks identically and simultaneously radiating from a single coaxial supply line.
3 ~,:
According to a number of advantageous features: ~
. . .
- there are three radiating networks;
--each radiating network has four horizontal dipoles ~
--the dipoles are of the shortened half-wave type, calculated on the central operating frequency of the antenna with a shortening coefficient of about 0.9, the distance between two consecutive superimposed dipoles is a shortened half-wave, calculated for the central operating frequency of the antenna 4 ~ with a shortening coefficient of around 0.85, and the - -distance from the dipoles to the central axis of the system is a quarter wave not shortened, calculated for the central operating frequency the antenna;
- the power distribution system is fully housed at 46 inside the central support tube; ~:
':. . ' ::.
. .
- .. ~. . . -.
- ':: -': '..

- the two-wire line has a lower half and a half upper, each of these halves being excited at a point located mid-height by a coaxial line passing inside one of the conductors of the two-wire line, this line itself being connected to the power distribution system located in the support tube central approximately at the connection of the two halves of each two-wire line;
- each branch of the dipole has a curvature substantially circular whose center of curvature is approximately on the central axis of the antenna.
The invention also relates to a radiating system formed of a plurality of antennas of this type, these antennas being superimposed and distinctly supplied by clean coaxials connected to a distributor 15 common Preferably, each antenna is then enclosed in a radome waterproof, substantially cylindrical, self-supporting and stackable.
aD Other characteristics and advantages of the invention will become apparent on reading of the detailed description below, made with reference to annexed drawings in which:
- Figure 1 is a perspective view of a radiating assembly constituting the antenna according to the invention, FIG. 2 shows a plurality of reS radiating assemblies, superimposed and coupled so as to increase the radiated power, the whole being protected by an external radome, FIG. 3 is a section along line III-III of FIG. 2, showing the radiant assembly of the present invention seen from above, - Figure 4 is an elevational view, partially in section, of the radiating assembly of FIG. 1, - Figure 5 is a front view, taken in the direction VV of the Figure 4, of one of the three radiating networks that this radiant together, - Figure 6 is a top view, in section along line VI-VI of the ffgure 4, showing the detail of the first section of the coaxial supplying the radiating network, 4 ~ - Figure 7 is a front view, in section, corresponding to the region marked VII in FIG. 5, showing one of the two in more detail branches constituting the second section of this coaxial feed, - Figure 8 is an azimuth diagram noted for an antenna 46 according to the invention, showing the omnidirectional nature of the diagram of it, . ::
,,, ', ~' - Figure 9 and the diagram in site corresponding to this same antenna, and - Figure 10 is a comparison of the azirnut diagrams that we would have for two similar antennas, one of which would include three radiating networks at 120 (as in FIGS. 1 to 7), and the other four radiating networks at 90. -The same reference numerals refer, in all the figures, to similar elements.
'"` `~''' Figure 1 shows the general structure of a radiating assembly constituting the antenna according to the invention: this comprises essentially a central support tube 100, vertical, partly provided lower and upper part of fixing plates, respectively 110 and 120, allowing to assemble end to end several support tubes superimposed - and therefore a plurality of identical radiating assemblies-- - ~
in order to increase the total radiated power. -Around this support tube are arranged 120 from each other three identical radiating networks 200, each comprising a two-wire line 2 ~ vertical with two parallel conductors 210,210 'supporting a plurality of 220,220 'horizontal dipoles (four in the example shown) regularly distributed along this two-wire line.
The radio power supply, which is brought to 310 by a cable coaxial arriving at the base of the antenna - so in an area that will slightly disturb the radiation pattern--, pass (staying in coaxial) inside the support tube 120, then is distributed (still in coaxial) to each of the three radiating networks passing inside a horizontal tube 340, mounted halfway up the central tube 100, which as ~ ure also the mechanical maintenance of these radiating networks in combined with the bra ~ eupports 130,140 in the upper part and in part low. .
As we can see, energy supply and distribution are entirely internal to the antenna structure, this which eliminates any possibility of disturbance of the diagram due to the physical presence of power lines in the field of radiation, as in the case of antennas of the prior art.
Typically, the antenna has no panel reflector. - -To increase the radiated power, we can superimpose (figure 2) ~:
a plurality of modules 10 each formed from a radiating assembly 11; :
similar to that illustrated in Figure 1 and powered by a coa ~ ial 12 connected a distributor in the lower part of the antenna, and a cylindrical radome 4 ~ protection 13. The assembly is placed at the top of a pylon 14, the -.
,.:, ''"' ....:.:

7 l 324657 ~
upper module being closed by a cover 5 and possibly surmounted by a lightning rod (not shown), as is good known. :
The radome 13 (Figures 2 and 3) is a reinforced polyester cylinder provided with

5 each of its ends of flanges 16,17 intended for the assembly of dif ~ erent superimposed modules, thus making a radome self-supporting, which greatly simplifies its mechanical production.
The entire system is of course leak-proof.

Figures 4 to 6 describe in more detail the structure of the assembly radiating according to the invention, in particular from the supply of the three dipole arrays.
The radio power supply, connected at 310, is brought to mid-height of the central tube 100, inside of it, by a line coaxial 320 (the return conductor being formed by the very wall of the support tube) comprising a plurality of sections 321 to 325 of diameters crescents forming a quarter-wave impedance transformer, and held centrally inside the support tube 1 00 by spacers 326,327.
aD The power is then distributed between the three radiating networks by distribution equiphase equipupower, always by a link coaxial.
The 330,340 coaxial link supplying each of the radiating networks consists (Figure 6) of a conductor 332, maintained inside a tube 341 by spacers 333, and one of the ends 331 of which is connected to the central common line 320.
This tube 341 constitutes both the line return conductor coaxial and a mechanical support connecting the radiating network to the tube central support; for this purpose, this tube 341 is provided with one of its 3 ~) ends of a link 342 to a part 150 secured to the central tube, and its other end of a part 343 supporting the two conductors 210,210 'of the two-wire line, which extend on either side of this part 343 (Figure 7), and consist of hollow tubes of conductive material, for example fixed by brazing.
The core 332 of the coaxial line is then connected to an element distributor 334 which supplies the branch symmetrically upper and lower branch of one of the conductors (on the drawings, the conductor 210 ') of the two-wire line, the other conductor (the conductor 210) being connected to the common ground.
For this, the core of the coaxial extends inside the conductor 210 to a point 339 located approximately halfway up each of the two upper and lower branches (this point 339, which will be the point excitation of the two-wire line, is identified at P in Figures 4 and 5).
To this end, provision is made, between this point 339 and the distributor 334, for a conductor, produced in two sections 335,336 of increasing diameters of so as to act as an impedance transformer, these two sections . . .
:. ,.

., - ... .

~. ,., .., ..., ... s ~

being held inside the conductor 210 by spacers 337.
The end of the supply line then crosses the conductor 210 in 211 to come e ~ quote the driver 210 'in 339 through a transverse connection piece 338.

6 So, as we can see, the power supply is entirely coaxial from the input connector 310 to the excitation point P, this system coaxial power supply being furthermore entirely contained within the supporting structure of the antenna (which therefore plays a dual role mechanical and electrical).

The two-wire line carries a plurality of dipoles 220, 220 'which thus go be fed symmetrically and constitute the radiating organs the antenna itself.
The 220,220 'dipoles used are of the shortened half-wave type, calculated on the central operating frequency of the antenna with a shortening coefficient of about 0.9.
The distance between two consecutive overlapping dipoles is half - - -shortened wave, calculated for the central operating frequency of the antenna with a shortening coefficient of around 0.85.
~) The distance from the dipoles to the central axis of the system is a quarter wave, not shortened, calculated for the central operating frequency of the antenna.
The impedance brought back to the level of the excitation point P, that is to say of the connection of two-wire lines supplying the dipoles is 50 n, power is supplied by the coaxial lines for which maintains a constant impedance of 60 n thanks to the transformers with quarter-wave lines exposed above.
~ 30 Note that the ends of the two-wire line correspond to intensity nodes, and can therefore be grounded directly by Ies spacers 130,140, which also provide mechanical maintenance of ~ -The whole. -:
The assembly can be made of copper or copper alloy tube and ~ -assembled by brazing, which makes it mechanical particularly simple. - ... ~.
From the electric we point, the antenna thus constituted therefore consists of four superimposed crowns (such as those visible in FIG. 3 ~, each formed of three dipoles placed horizontally at 120 one of the other on the three sides of an equilateral triangle, and fed in phase with equal power.
Such a configuration provides, without the aid of any reflector, a quasi-omnidirectional diagram, as can be seen in the figure . .-.
.:.

9 l 324657 8, which represents an azimuth diagram recorded for an antenna comprising an element such as that illustrated in FIGS. 4 to 7 and that we have just described, calculated for a central frequency of 520 MHz operation: as we can see, the diagram 5 is omnidirectional to within 0.9 dB.
Figure 9 shows the diagram of the site diagram, whose form very suitable for a radio or television antenna.

Regarding electrical performance, we have seen that the antenna makes it possible to radiate without damage a power of the order of ~ at 7 kW, this power can of course be multiplied by superimposing several identical radiating assemblies.
The impedance, as indicated above, is 50 Q, the gain of 15 ~ dB is the average standing wave ratio of 1.15.
Regarding mechanical performance, for antennas operating in the band 460-860 MHz, the radiating units are enclosed in radomes 0.54 m in diameter and 1.16 m high 20 with a wind surface of 0.63 m2 (to be compared to a surface of wind resistance of around 1.35 m2 for an antenna operating in the same range, but made from antenna panels, such as described in the introduction to this description), and a module complete (radome plus radiant assemblies) at a mass of approximately 40 kg (against 375 kg in the case of a panel antenna).
The choice consisting in grouping dipole networks three in number is not limiting, but it is particularly advantageous.
Indeed, if we increase the number of networks, the ends 30 adjacent 3 dipoles of the same crown will be found more and more closer together, which will increase their mutual coupling and accentuate the troughs in the diagram.
Figure 10 illustrates this phenomenon: there is shown the diagram in azimuth D4 raised for a system with 4 networks, to compare with the diagram 35 D 3 for the three network system which is the subject of this description: we see that the maximum troughs are now at minus 2 dB instead of 0.9 dB in the other case.
The solution to three networks is therefore that which gives the diagram the more homogeneous.

Finally, as a variant, the dipoles can be optimized by modifying their shape: instead of providing them straight and forming the three sides of a equilateral triangle exinscribed to the circle passing through the centers of the three two-wire lines (configuration of figure 3), one can deform or bend 46 dipoles so as to bring them closer to the outline of this circle, or even make them marry this outline (shape illustrated in broken lines on the - lo t 324657 ::
figure 3). :
This improvement reduces radiation phase shifts between the different points of the dipole and thus make it even more: -:
omnidirectional the azimuth diagram.

:

~ ..: ....
:: ...
,,.;, . ~., ~ ...

:. ..:

;,, ',:.
..
:. "'. ~' ~ ", ', ~

:. . '' : - :: ::
'..' .. ';' ~ ' :.
, - ~
'.:, ~ ,,' - ''.,, -:. . , ~:
'~.,'".,:.,'::
"''''' "',"', '', '. "',', -"''

Claims (11)

1. An omnidirectional antenna, in particular for the emission of radio broadcasting signals or UHF television, characterized by:
- a central, vertical support tube, - a plurality of radiating networks identical, regularly distributed around the central tube and each formed of a vertical two-wire line symmetrically supporting, coupling and supplying a plurality of horizontal dipoles regularly distributed along this two-wire line, and - a power distribution system equiphase equipuence supplying identically and simultaneously radiating networks from a line single coaxial feed. 2. The antenna of claim 1, in which the radiating networks are three in number. 3. The antenna of one of claims 1 and 2, in which each radiating network comprises four horizontal dipoles. 4. The antenna of one of claims 1 and 2, in which the dipoles are of the half-wave type shortened, calculated on the center frequency of antenna operation with a coefficient of shortening of about 0.9. 5. The antenna of one of claims 1 and 2, in which the distance between two dipoles consecutive overlays is a shortened half-wave, calculated for the central operating frequency of the antenna with a shortening coefficient of 0.85 about. 6. The antenna of one of claims 1 and 2, in which the distance from the dipoles to the central axis of the system is a quarter wave not shortened, calculated for the central operating frequency of the antenna. 7. The antenna of one of claims 1 and 2, in which the power distribution system is fully housed inside the support tube central. 8. The antenna of one of claims 1 and 2, in which the two-wire line has one half lower and upper half, each of these halves being excited at a point halfway up by a coaxial line passing inside one of conductors of the two-wire line, this line being itself connected to the power distribution system located in the central support tube approximately at level of connection of the two halves of each line two-wire. 9. The antenna of one of claims 1 and 2, in which each branch of the dipole has a substantially circular curvature, the center of which curvature is approximately on the central axis of the antenna. 10. A radiating system formed by a plurality antennas according to one of claims 1 and 2, these antennas being superimposed and supplied separately by own coaxials connected to a common distributor. 11. The radiant system of the claim 10, in which each antenna is enclosed in a waterproof radome, substantially cylindrical, self-supporting and stackable.