EP0814537B1 - Method and device with lower backwards and under horizon radiations in a group of antennas - Google Patents

Description

The invention relates to a method and a device for decrease the rear radiation of an antenna while lowering this weakened radiation to a selected area below the horizon. She applies more particularly to aerials made up of at least two elementary antennas including the phases are opposite in pairs on the back of said air.

Such a system mainly allows a diffusion linear or not of a plurality of transmitters operating on the same frequency, synchronized or no. This is particularly the case of a chain of transmitters isofrequencies along a highway, the weak radiation of the antennas on their rear reducing considerably the length of the interference zone with the previous transmitter.

In French patent application n ° 88 15254, the Applicant describes a method and a device in which, along the route, there are transmitters, or repeaters, hereinafter called relays, placed between transmitting and receiving antennas, and fixed on the same frequency, said relays being directional and two consecutive relays being run approximately in the same direction. According to this request, we use directional groupings of elementary antennas spatially offset, horizontally by λ / 4 and about 2 m vertically, and supplied with such so that the fields emitted are added in the direction of the show and evade to cancel in the opposite direction.

Thanks to this arrangement of antennas, the system allows to reduce to a few hundred meters the interference zone between relays.

However, canceling backward fields is not really effective only on the horizon. In the case where the receiving antenna is located at another height than those of the transmitter, the rear radiation of each of the antennas, located at a different level, arrives from a different angle at the receiving antenna in the interference zone with the radiation of the previous transmitter, zone of almost equal field for two consecutive relays. In particular, the antennas vehicles placed on a height much lower than those of the antennas of the transmitter. The radiation arrives under a certain angle, certainly small but whose effects are not negligible in a system where you want to get a null field. Added to this is the radiation reflected by the ground which does not arrive at the same angle to the antenna receptor. This reflected radiation is theoretically 180 ° out of phase with direct radiation. However, due to the Brewster effect, the angle of reflection is not absolutely equal to the angle incidence and phase shift is not exactly 180 °. Despite this, we can neglect the Brewster effect thereafter.

Due to these unavoidable conditions, the effect backward radiation cancellation of the antenna array is disturbed. For example, the upper antenna being located at 34 m, and the antenna less than 2 m below, there is a difference of a few dB between the two radiations in the area interference. It is therefore necessary to compensate for these side effects so that a minimum of energy reaches the interference zone.

The object of the invention is therefore to reduce the rear radiation of an array of antennas emission while lowering this attenuation towards a selected area under the horizon.

• on sélectionne l'endroit où le champ résultant doit être minimal en ajustant les phases de chacune des antennes élémentaires de telle façon que la valeur minimale du champ soit obtenue dans une zone déterminée à l'arrière du groupe d'antennes et vue de celui-ci sous un angle déterminé. Les antennes étant situées à des hauteurs différentes, les niveaux reçus sur la route de chacune d'entre elles sont différents. Ce phénomène est dû à ce que les zones de réflexion n'étant pas situées au même endroit, la sommation du trajet direct et du trajet réfléchi pour chaque antenne donne une valeur différente. On égalise les amplitudes des antennes élémentaires en répartissant la puissance de façon que le champ reçu résultant soit minimal dans la zone choisie.

This object is achieved according to the invention, in that:

• the location where the resulting field must be minimum is selected by adjusting the phases of each of the elementary antennas so that the minimum value of the field is obtained in a determined area at the rear of the group of antennas and seen from it. ci from a determined angle. The antennas being located at different heights, the levels received on the road of each of them are different. This phenomenon is due to the fact that the reflection zones are not located in the same place, the summation of the direct path and the reflected path for each antenna gives a different value. The amplitudes of the elementary antennas are equalized by distributing the power so that the resulting received field is minimal in the chosen area.

According to the invention, the vertical interval between the elementary antennas of a couple is related to the wavelength and the intrinsic structure of the antenna. According to a particular form of the invention, this interval is about 2 m.

The device for implementing the invention is characterized in that it includes a distributor of variable power to adjust the amplitude of the field radiated by each of the elementary antennas of so as to obtain identical result fields in a specific area behind the group of antennas and a phase correction device on each of the elementary antennas in order to obtain an opposition of perfect phase.

According to a particular form of the invention, the power distributor consists of a volume conductor of length λ / 4, of a fixed line and of two moving lines moving relative to the previous in order to increase the level of the low antenna and reduce that of the high antenna. To avoid having contact turning the lines mobiles are supplied by serial lines open to their ends (intangible short circuit between the beginning of the serial line and that of the mobile line).

The phase correction device is consisting of an adjustable line

La figure 1 représente schématiquement la propagation du rayonnement des antennes élémentaires d'un système aérien d'antennes vers l'arrière de celui-ci ;

La figure 2 représente, dans un repaire X Y, l'addition vectorielle des champs avec un champ résultant non minimalisé ;

La figure 3 représente schématiquement le montage d'alimentation des antennes élémentaires selon l'invention ;

La figure 4 représente schématiquement le répartiteur de puissance variable utilisé dans un exemple de réalisation de l'invention.

The invention will be better understood by means of a nonlimiting exemplary embodiment described below and shown in the accompanying drawing in the case of a radio transmitter of a chain of isofrequency transmitters located on the edge of a highway. .

FIG. 1 schematically represents the propagation of the radiation of the elementary antennas of an aerial system of antennas towards the rear thereof;

FIG. 2 represents, in an XY coordinate system, the vector addition of the fields with a non-minimized resulting field;

FIG. 3 schematically represents the supply arrangement of the elementary antennas according to the invention;

FIG. 4 schematically represents the variable power distributor used in an exemplary embodiment of the invention.

As seen in Figure 1, the antennas elementary 1 and 2 of the aerial radiation system 3 radio transmitter are arranged one above the other and shifted horizontally.

According to the embodiment, the height H1 of the upper antenna 2 is 34 m. and the antenna lower 1 is located below at an interval ΔH about 2 m. The receiving antenna 4 of a vehicle traveling on the highway culminates at a height H2 about 2 m. Each antenna radiates a V field. makes the horizontal shift of λ / 4 of the antennas the field V1 of antenna 1 and field V2 of antenna 2 are added forward, so that we have forward from the transmitter a resulting field equal to V1 + V2, and retreat backwards, so that the field resulting back from the transmitter is V2 - V1. When the amplitude of the fields received from the antennas is the same, we have behind the aerial a field resulting null at the height of transmitting antennas: V2 - V1 = 0, for as long as the conditions are those of space free. On the other hand, at the height H2 of the antenna receiver 4, the radiation from each antenna makes a angle with the horizontal and the Fresnel ellipsoid is more or less masked.

Due to the difference in height ΔH between the two elementary antennas, these angles are different and the resulting field V2 - V1 will not be zero.

On the other hand, the radiation is reflected on the floor. One neglects the Brewster effect which can however be corrected by the invention. For the same reasons that previously the reflection of the two radiation is not done in the same place and reflected fields, therefore not having the same amplitude therefore do not cancel each other out. The receiving antenna also captures the resulting reflected field and this disrupts reception.

In Figure 2, we see the composition of the vectors field in the case of an uncorrected system.

The receiving antenna 4 receives from the transmitting antenna 1 a direct field V1 (X1, Y1) and a reflected field VR1 (X2, Y2); from antenna 2 a direct field V2 (X3, Y3) and a reflected field VR2 (X4, Y4). Y1 and Y3 are neighbors of 0.

The value of the resulting field is equal to: R = ΣX 2 + ΣY 2

The object of the invention is to lower the value of R.

The device according to the invention is shown in the figure 3.

The signal from the transmitter 5 is transmitted to the dispatcher variable power 6 which adjusts the amplitude of signals to elementary antennas to compensate the difference in levels received by the receiver since each of the antennas due to their difference altitude so as to obtain a minimum field R in a area given behind the antennas.

As shown very schematically in Figure 4, this power distributor consists of a cylinder comprising a central line coupled to two lines to variable coupling by rotation. The mobile lines are excited by an open serial line connection for make a non-contact rotating joint. The rotation two lines with variable coupling around the line central allows to distribute the power

Each of the adjusted outputs of the distributor is connected to an adjustable phase correction line 7 for the antenna signal 1 and 8 for the antenna signal 2.

So in a given area, the phase differences from different radiation paths, direct and reflected, and center variations of phase from one antenna to another, are compensated by the adjustable lines 7 and 8. By proper adjustment, can therefore choose the area where these phase differences are compensated. Since the amplitudes of the signals have been adjusted in order to obtain a zero field in a given area, we can create a null field in a chosen area. In the embodiment, this area is the interference zone between the rear radiation of the transmitter and the front radiation of the transmitter previous in a linear broadcasting chain simulcast.

Claims (5)

1. A process for reducing the rear field of a group of directional antennae comprising at least a pair of elementary antennae offset vertically from one another by a certain interval and horizontally by λ/4, characterised in that:

   the place at which the resultant field must be at a minimum is selected by adjusting the phases of each of the elementary antennae such that the value of the field is reduced within a given zone to the rear of the group of antennae and viewed therefrom at a given angle below the horizon,

   the amplitudes of the signals received from the elementary antennae are equalised by distributing the power such that the resulting radiated field is minimal in the selected zone.
2. A device for transmitting a radio emission, comprising an overhead system of antennae formed of at least one pair of elementary antennae offset vertically by a certain height and horizontally by λ/4, characterised in that it further comprises a variable power distributor which makes it possible to adjust the amplitude of the fields received from each of the elementary antennae and a phase correction device on each of the elementary antennae, so as to obtain a null resultant field in a given zone to the rear of the group of antennae and viewed therefrom at a given angle below the horizon.
3. A device according to Claim 2, characterised in that the power distributor is formed by a conductor volume of a length equal to λ/4, of a fixed line and two mobile lines, which are excited by an open-line connection, moving relative to said line so as to increase the level of the lower antenna and to reduce that of the upper antenna.
4. A device according to Claim 2, characterised in that the phase correction device is formed of an adjustable line.
5. The application of the process according to Claim 1 to a chain of isofrequency emitters along a traffic lane.

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