EP1523062B1 - Omnidirectional antenna for transmitting and receiving audio/video signals - Google Patents

Abstract

The antenna has a set of biquad antenna units (1), spaced uniformly in a same plane. Main radiation lobe of each unit is separated from an adjacent lobe to maximum by a wave-length in the direction of wave propagation. Each unit has a reflector (2) and a biquad connected to a coupler (4) by a coaxial cable (5). Feed centers of the units are separated by a length, where points are situated at their respective centers. The antenna units are in vertical rectilinear polarization and are fed wirelessly by currents of same phase and of same amplitude.

Description

The present invention relates generally to an omnidirectional antenna for transmitting and / or receiving audio and / or video signals.

More specifically, the invention relates to an omnidirectional antenna for the transmission and / or reception of audio and / or video signals, of the type comprising four antenna elements powered electrically by currents of substantially the same phase and of the same amplitude. each antenna element comprising a biquad-type radiating element, a feed center and a reflector associated with this radiating element and each of the feeding centers lying on a common circle and at the intersection points of two diameters orthogonal with this circle.

The 2.4 Ghz video electromagnetic signal receiving system usually includes a high gain omnidirectional antenna behind which a pre-amplifier is placed to improve the noise factor and receiver dynamics.

At sea, a system of this type provides excellent results for distances of the order of 1 to 5 km, however in calm sea. When the trough becomes large, the received signal picks up and vanishes, which takes about 3 seconds to return to its original value.

US Pat. No. 4,479,127 describes a horizontally polarized antenna formed of four antenna elements arranged in a first pair respectively. of parallel elements and a second pair of parallel elements, these first and second pair of elements being perpendicular to each other and the elements of each pair being equidistant from the axis of the assembly.

Each of these elements is formed of two square loops joined by a common vertex having feeding centers at the level thereof.

This antenna has a VSWR of less than 2: 1 and a four-leaf clover pattern.

Such an antenna can be used in long range transmission / reception applications.

The object of the present invention is to propose an antenna of the type indicated previously that can be used for example at frequencies of the order of 500 Mhz or 2.4 Ghz and which makes it possible to overcome the drawbacks of the state of the art.

To achieve this goal, the antenna according to the invention is characterized in that each antenna element is in vertical rectilinear polarization, in that the main radiation lobe of each antenna element has an opening substantially of 90 ° in the vertical and horizontal planes and that the feed centers of two adjacent antenna elements are separated by a working wavelength λ.

On the other hand, according to an additional and preferred feature, the feeding centers of two adjacent antenna elements are separated by a length equal to λ.

Each antenna element comprises a radiating element or radiator consisting of a continuous loop taking the geometric shape of two squares located in the same plane having a common vertex and perimeter substantially equal to 2 λ, and an associated reflector.

In the present description as well as in the claims, the radiating element thus described by the name "biquad" and an antenna element equipped with a biquad by "biquad antenna element" will be designated.

The biquad antenna element constitutes a particularly advantageous antenna element in the context of the invention because of the 90 ° opening of its main lobe and its appreciable gain of 10 dbi.

Thus, according to an advantageous characteristic of the invention, each main lobe of radiation has an opening substantially of 90 ° in the vertical and horizontal planes.

Similarly, according to a further feature of the invention, the antenna elements are connected to a coupler via a coaxial power supply cable.

• la figure 1 est une vue schématique en plan d'une antenne selon l'invention comprenant 4 éléments d'antenne biquad fixés à des supports d'éléments d'antenne et un coupleur
• la figure 2 est une vue frontale d'un élément d'antenne biquad à la figure 1 fixé à des supports d'éléments d'antenne
• la figure 3 est une vue en coupe longitudinale d'un coupleur à 5 voies
• la figure 4 représente la courbe définissant la longueur du conducteur cylindrique d'un coupleur en fonction de la fréquence de travail
• la figure 5 est une vue schématique en plan d'un autre mode de réalisation d'une antenne selon l'invention comprenant 4 éléments d'antenne biquad
• la figure 6 est une vue frontale d'un élément d'antenne biquad à la figure 5.

The invention will be better understood and other objects, features and advantages thereof will appear more clearly in the following explanatory description with reference to the accompanying drawings given solely as examples illustrating various embodiments of the invention. invention and in which:

• FIG. 1 is a schematic plan view of an antenna according to the invention comprising 4 biquad antenna elements fixed to antenna element supports and a coupler
• FIG. 2 is a front view of a biquad antenna element in FIG. 1 attached to antenna element supports.
• FIG. 3 is a longitudinal sectional view of a 5-way coupler
• FIG. 4 represents the curve defining the length of the cylindrical conductor of a coupler as a function of the working frequency
• FIG. 5 is a schematic plan view of another embodiment of an antenna according to the invention comprising 4 biquad antenna elements;
• Figure 6 is a front view of a biquad antenna element in Figure 5.

As represented in FIGS. 1 and 2, the antenna according to the invention comprises a set of four biquad antenna elements 1, each comprising the reflector 2 and the biquad 3 proper connected to a 5-way coupler, indicated in 4. This connection is provided by means of a coaxial power supply cable.

On the other hand, the feed centers 6 of these biquad antenna elements are on a common circle and at the points of intersection of two orthogonal diameters with this circle so that the rope which subtends the arc between two adjacent feeding centers equal to λ. In addition, each biquad 3 is tangent to the common circle.

Figure 1 also shows the 90 ° opening angle of the main lobe of each antenna element, two adjacent lobes being spaced from each other by a length λ. Consequently, the four biquad antenna elements 1 completely cover an angle of 360 °.

As represented in FIG. 2, the biquad 3 is configured in closed loop forming two squares in the same plane, united by a common vertex and each side of which is substantially equal to λ / 4. This biquad consists of a bare copper wire welded to the coaxial cable 5, the two ends of the copper wire being themselves secured, if necessary, to the reflector 2 by any means so as to stiffen the assembly.

The reflector 2, meanwhile, is formed of a metal plate generally made of copper. Steel, especially stainless steel or polychlorinated biphenyl ("PCB") can be used as well. In this case, it may be advantageous to solder, for example copper, to the passage opening of the coaxial cable 5 formed in this reflector, so as to ensure a good physical and electrical connection. Such an assembly is known having been described for example in "Biquad Antenna Construction", Martybugs.net, Wireless Networking Info (http: // Martybugs net / wireless / biquad) (date of making available to the public: 02 May 2003 and 20 July 2003).

FIG. 2 also shows that each antenna element 1, via its reflector 2, is secured to a support 7 which can take the form of four angled profiles. Usually this support is made of stainless steel. However, other materials including insulating materials such as polymethyl methacrylate may be used.

As for the coupler 4, this can be seen in FIG. 3, which shows the four female N connectors 8 to the chassis 9, the input N female connector. 10 as well as the linear conductors 11 and cylindrical 12.

In another embodiment, in accordance with FIGS. 5 and 6, the antenna according to the invention is devoid of antenna element support but comprises a set of four biquad antenna elements 1 each comprising the reflector 2 and the antenna. biquad 3 connected to the coupler 4 via the coaxial cable 5. In such an embodiment, the reflector 2 is also configured as an antenna element support.

The different measurements necessary for the development of each of the above biquad antenna elements can be easily determined from the values of the parameters expressed in the description above and this, as a function of the working wavelength λ in the air, a shortening coefficient K, being applied in the case where the antenna elements are embedded in an electrically insulating medium.

The following nonlimiting examples illustrate various embodiments of an omnidirectional antenna according to the invention:

EXAMPLE 1 ANTENNA at 2.4 Ghz

In a preferred embodiment of a 2.4 Ghz antenna, as shown in FIGS. 1 to 3, each of the four biquads 3 having its feed center at 6, is connected to a 2.4 Ghz coupler indicated 4 and shown in Figure 3. This connection is made via a coaxial cable 5 of an impedance 50 Ω, semi-rigid power supply cable covered with an electrically insulating material.

Each feeding center being distant from a length λ of an adjacent feeding center, the diameter of the circle connecting these four centers is, therefore, 174 mm.

The biquads 3 each consist of a continuous copper wire having a diameter of about 1.5 to 2.5 mm, preferably 2.5 mm, configured in two equal squares with a common apex and each side having a length of 36 mm (1/4 of wave = 31 mm). The length of each biquad, that is to say the distance separating the two farthest vertices, is 90 mm, each of these biquads being 17 mm distant from the associated reflector 2. Each reflector consists of a copper plate 100 mm x 100 mm and a thickness of 1.5 mm fixed on a support 7 of antenna element, two opposite reflectors being separated by 140 mm.

With regard to the coupler 4 shown in FIG. 3, the length of its linear conductors 11 is 19 mm each, the cylindrical conductor 12, formed of a copper or brass bar, having a diameter of 8.73 mm and a length of 65 mm determined by the curve in FIG.

EXAMPLE 2 ANTENNA at 500 Mhz

In another preferred embodiment of a 500 Mhz antenna, as shown in FIGS. 5 and 6, each of the four biquads 3 has its feed center at 6 and is connected to a 500 Mhz coupler indicated at 4 and shown in Figure 3 and this, by via a coaxial power cable 5 (impedance: 50 Ω).

As each feeding center is distant from a length λ of an adjacent feeding center, the diameter of the circle connecting these four centers is 850 mm.

On the other hand, the biquads 3, each consisting of a continuous copper wire, are configured in two equal squares, with a common vertex, each side of which has a length of about 150 mm (1/4 of a wave). . The length of each biquad (distance separating the two furthest vertices) is 420 mm and each of these biquads is 85 mm distant from the associated reflector 2. In addition, each reflector 2 consists of a stainless steel plate 680 mm long and about 600 mm high so that two opposing reflectors are separated by 680 mm. Similarly, each reflector is provided with a passage 13 for the coaxial cable 5, the orifice around which copper is soldered.

Coupler 4, for its part, is identical to that of Example 1 with the exception of the length of the cylindrical conductor which is 320 mm as determined by the curve in FIG.

The antenna according to the invention is particularly interesting for combating the typical swell phenomenon at sea. In fact, the video image received at 2.4 Ghz is of perfectly exploitable quality and without stall even by 4 m swell. between two boats about 6 km apart.

In addition, this antenna can be adapted to frequencies other than 2.4 Ghz and in particular at frequencies of the order of 500 MHz for the radio (telephone and "data") where it has been equally effective.

In addition, this antenna can be used both at the reception and the broadcast and can also find other applications such as 2Mbit transmission between ships.

Claims (6)

1. Omnidirectional antenna for transmission and/or reception of audio and/or video signals of the type including four identical antenna elements (1) radio-electrically supplied by currents with approximately the same phase and the same amplitude, each antenna element comprising a biquad type radiating element (3), a power supply centre (6) and a reflector (2) associated with this radiating element and each of the power supply centres is located on a common circle at the intersection points of two diameters orthogonal with this circle, characterised in that each antenna element is in straight vertical polarisation, in that the main radiation lobe of each antenna element has an aperture of approximately 90° in the vertical and horizontal planes and in that the power supply centres of two adjacent antenna elements are separated by a working wavelength λ.
2. Antenna according to claim 1, characterised in that the four antenna elements cover a total angle of 360°.
3. Antenna according to claim 1 or 2, characterised in that the antenna elements are connected to a coupler (4) through a coaxial cable (5) through which energy is supplied.
4. Antenna according to one of claims 1 to 3, characterised in that each antenna element comprises a radiating element (3) composed of a continuous loop with a geometric shape consisting of two squares located in the same plane with a common vertex and a perimeter equal to approximately 2 λ.
5. Antenna according to one of claims 1 to 4 for the use of frequencies of the order of 2.4 GHz.
6. Antenna according to one of claims 1 to 4 for the use of frequencies of the order of 500 MHz.

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