WO2011000703A1

WO2011000703A1 - Omnidirectional, broadband compact antenna system comprising two highly decoupled separate transmission and reception access lines

Info

Publication number: WO2011000703A1
Application number: PCT/EP2010/058494
Authority: WO
Inventors: Sébastien PALUD; Cyrille Le Meins; Thierry Guignard; Franck Colombel; Mohamed Himdi
Original assignee: Thales; Centre National De La Recherche Scientifique; Universite De Rennes 1
Priority date: 2009-06-30
Filing date: 2010-06-16
Publication date: 2011-01-06
Also published as: FR2947391B1; FR2947391A1; EP2449629A1; EP2449629B1

Abstract

The invention relates to a very broadband omnidirectional antenna system operating in a selected frequency range, to be positioned on a carrier and comprising: A first antenna element (1) operating in a transmission mode and comprising: a first conductive plate (6) with a length L1, a width l1, and a surface area S1, and a second conductive plate (5) with a length L2, a width l2, and a surface area S2, the two plates (5, 6) being separated by a gap E; a broadband excitation means (4) having an outer surface and a surface profile suitable for generating an electric field with linear vertical polarisation created between the two plates (5, 6), said broadband excitation means being pseudo-conical in shape; at least one conductive link (7) arranged between the first conductive plate (6) and the second conductive plate (5), said link or links (7) being connected to said plates via a matching circuit (8); and a second spiral antenna element (2) operating in a receiving mode, placed on a metal plane (12) covered with a ferrite material (11), the assembly being interlocked in said first antenna element (1). The antenna system is to be used for the frequency range of 30 MHz to 3000 MHz.

Description

OMNIDIRECTIONAL AND LARGE COMPACT ANTENNA SYSTEM

BAND COMPRISING TWO ACCESS TRANSMISSION AND RECEPTION

The subject of the invention relates to an omnidirectional compact and very broadband antennal system having a separate access access and reception access and very strongly decoupled, that is to say, an antennal element having a function of emission and an antenna element having a reception function.

The invention lies in the field of antennas or antenna systems dedicated to electromagnetic wave emission / reception applications in a very wide band, for example 30-3000 MHz.

The concept implemented in the invention can be integrated on all types of carrier (ground, naval or airborne). It is particularly suitable for integration on the roof of a mobile carrier (civilian and military vehicles). It can be exploited in other frequency bands than the one mentioned above.

For antennal transmission and reception systems on board a mobile carrier, especially those dedicated to scrambling or convoy protection applications, various technical problems must be solved, including the following:

• decoupling between reception or interception antennas and transmitting or jamming antennas located on the same carrier,

• obtain the frequency bandwidth to cover,

• obtain impedance matching on the covered frequency band,

• respect a certain compactness (height, for example) of the antenna,

• ensure a gain and coverage of radio (radio) antenna,

• take into account the carrier on which the antenna is arranged in order to obtain the performances mentioned above,

• provide power handling for the transmitting or jamming antenna, • achieve a compactness and discretion of the radiating elements compared to the covered band.

Different antennal structures are known to the Applicant, such as monopole type antennas, saber antennas, dipole type antennas, biconical or discone antennas, or antennas loaded with a resistor or a resistor. box of agreement.

These antennas have certain disadvantages, for example:

• A limited bandwidth requiring the use of two antennas to cover the above-mentioned frequency band. Such an architecture is likely to accentuate the phenomena of coupling and masking between antennas when they are installed close to one another,

• A generally large footprint for low frequencies that does not meet the criterion of discretion and road gauge such as, for example, for jamming applications dedicated to the protection of convoys,

• Weak gains on the horizon and un-optimized electromagnetic radiation, which usually changes with the wearer.

The antenna structure according to the invention solves at least one or more of the aforementioned problems.

The object of the present invention relates to a very broadband omnidirectional antennal system working in a selected frequency range intended to be positioned on a carrier and characterized in that it comprises at least in combination the following elements:

A first antenna element operating in transmission and comprising:

A first conductive plate having a length L1 and a width 11, of surface S1,

A second conductive plate having a length L2 and a width 12, of surface S2,

• The two plates being separated by a gap E,

Broadband excitation means having an outer surface and a surface profile adapted to generate or capture a biased electric field vertical line created between the two plates under the effect of a signal applied at a point of excitation of said first antennal element, said electric field propagating within a guide structure formed by the first plate, the second plate and the broadband excitation means, said excitation means has a pseudoconic form.

At least one conductive link disposed between the first conductive plate and the second conductive plate, the one or more metal links being connected to said plates via at least one matching circuit,

A second antennal element of square spiral type operating in reception placed on a metallic plane covered with a ferrite type material suitable for trapping the currents, the assembly being embedded in said first antennal element.

The second antennal element is, for example, nested in a conical portion itself integrated in the high pseudo-conical portion of said broadband excitation means.

The second antennal element may consist of a first element adapted to operate at low frequencies, said first element being constituted by volumic turns of constant diameter and pitch per spiral side, a second element having a logarithmic square spiral profile. planar plane placed in continuity and in the same plane as said first element, a third element adapted for high frequencies and made by conformation on a pyramid with four sides of a logarithmic spiral with a square profile.

The four-sided pyramid as well as the support of the elements can be made of relative permittivity foam close to 1.

Said conductive plates are provided with orifices for fixing the metal links and adaptation circuits.

Said matching circuits or antenna load circuits are constituted by one or more of the elements selected from the following list: resistance, capacitance and / or power choke.

The matching circuit consists of one or more power resistors. In this way, the first antennal element has an optimized radiation towards the ground and the horizon. The second antennal element associated with the metallic plane covered with the ferrite tiles has an optimized radiation upwards and the horizon, ie. in a hemispherical way.

The antennal system has a strong decoupling between the first antennal emission element and the antennal receiving element. It operates according to an electric field component in vertical polarization. The presence of the plane of ferrite tiles accentuates the decoupling between the antennal emission element and the antennal receiving element by trapping the currents at the level of the metal plane. The first antennal element supports strong powers.

Other features and advantages of the device according to the invention will appear better on reading the description which follows of an example of embodiment given by way of illustration and in no way limiting attached to the figures which represent:

FIG. 1A, a perspective view of the transmission-reception system according to a possible embodiment configuration,

• Figure 1B, a side view of Figure 1A,

FIG. 1C, a detail of the constitution of the antenna 1 or first antennal element,

FIG. 1D an example of positioning of the antenna system according to the invention on a carrier,

FIG. 2, a detailed view of the reception (or interception) antenna,

FIG. 3A, a view from above of the profile of the spiral arms that can be envisaged,

FIG. 4, the decoupling obtained in measurement between the transmission part and the interception part of the system for a given configuration,

• Figure 5, the standing wave ratio obtained in measurement for the transmission part and the receiving part (or interception) of the system for a given configuration, without the carrier. In order to better understand the principle of the antennal system according to the invention, the following description aims at a use for the emission of electromagnetic waves on the horizon and below the horizon (that is to say towards the bottom) in the vertical plane and 360 ° azimuth in the horizontal plane, and for the interception of electromagnetic waves on the horizon and above the horizon in the vertical plane and on 360 ° of azimuth in the horizontal plane, for operation in a frequency range from 30 MHz to 3000 MHz.

FIG. 1A represents a perspective view of an exemplary embodiment of the antenna system according to the invention.

The antenna 1 used in the present description for illustrative purposes is detailed in the applicant's patent application FR 08 07230.

The antenna 1 consists, for example, of a lower plate 6 made of a conductive material such as a metal material having, for example, a length L1 of 2000mm and a width 11 of 1700 mm. This plate may be a planar or substantially planar metallic part independent or any of a carrier V (Figure 1 D). A second conductive plate which in this example corresponds to the upper plate 5 and has a length L2 in this example of 2000 mm and a width 12 of 1700 mm (Figure 1 B) forms the upper plane of the antennal system according to the invention. The plate 6 forming the lower plane and the plate 5 forming the upper plane, may have an identical surface respectively S1, S2. The two plates can be made of the same metallic material adapted to microwave frequencies.

The lower plate 6 and the upper plate 5 are spaced apart by a distance or gap E. The value of the spacing E between the two plates is chosen according to the minimum frequency of use. Thus, the spacing E may be less than the wavelength, corresponding to the minimum operating frequency, divided by 8. As a rule, the larger the dimensions of the plates, the smaller the spacing of the plates may be.

The antennal system according to the invention comprises a second antenna or antenna element 2 placed, for example, above the first antenna 1. Depending on the depth of the conical bowl 3 made inside the broadband exciter 4 of the antenna 1, it is possible to adjust the integration of the antenna 2 in the antenna 1. For a cavity depth greater than or equal to the vertical size of the antenna 2, and in the case of a pseudo-conical or conical cavity, it is then possible to completely integrate the second antennal element in a conical part, it itself integrated in the high pseudo-conical portion of said broadband excitation means. The metal cavity may be of any shape, nevertheless the use of a conical or pseudoconic type of cavity makes it possible to improve the radiation performance of the antenna 2 for reception or interception on the horizon.

The transmitting or scrambling antenna 1 is constituted by a broadband exciter 4 positioned between the metal planes 5 and 6 in which a matrix of holes Ti is formed in order to receive metal links 7 loaded by power resistors 8 or of adaptation circuits. The metal links 7 have the particular function of allowing electrical conduction between the various elements. The dielectric spacers 9 and 10 have the particular function of ensuring a mechanical rigidity of the system. The power resistors 8 may be arranged either in the upper part of the metal link 7 at the level of the upper plate 6, or as mentioned in FIGS. 1A, 1B in the lower part of the metal link 7 at the level of the lower plate. 6 of the antenna. Without departing from the scope of the invention, instead of the power resistance, it is possible to use a charging circuit or adaptation circuit composed of one or more of the elements chosen from the following list: resistance, inductance, and / or capacity, the elements mentioned being used alone or in combination, knowing that the final function will be to ensure the adaptation of the antennal system. For example, the resistance values chosen to illustrate the invention provide an adaptation of the antenna 1 to a characteristic impedance 50 ohms, and accept high power on the transmission path.

The conductive metal bonds 7 may be made of any type of material having conductive properties adapted to microwave frequencies.

The receiving antenna 2 is placed above a metal plane 12 covered almost completely by ferrite tiles 1 1 (Figure 1 B). These tiles can have a shape, a thickness and characteristics of permittivity and variable permeability insofar as they retain absorption properties for the frequency bands 30 MHz -1000 MHz, in this example. They must remain attached to each other as much as possible. It is therefore appropriate to fix them, to stick them or to reduce their freedom of movement by an appropriate device. They make it possible to reduce to a few cm the thickness of the antenna 2 by absorption of the currents reflected on the metallic plane 12. They also make it possible to reduce the coupling between the transmitting antenna 1 and the receiving antenna 2 and of to make possible the radiation of the receiving antenna 2 in vertical polarization on the horizon, while not disturbing the radio performance of the transmitting antenna 1.

The radiation of the transmitting antenna 1 is specifically oriented towards the horizon or towards the ground while the receiving antenna 2 equipped with these ferrite tiles proposes a radiation directed towards the horizon or toward the upper hemisphere. . This decorrelation of the radiation patterns greatly favors the decoupling between the two antennas. The direction of the radiation arrows is symbolized in FIG.

The receiving antenna 2 (or interception) and the transmitting antenna 1 (or scrambling) according to the invention provide by construction an electromagnetic wave with a predominantly vertical polarization on the horizon.

The broadband exciter has the particular function of establishing an electric field E guided between the two planes (5, 6) and its outer wall S ₃ . The exciter may consist of several conductive facets (metal, for example) 2Oi whose profile of their outer wall has been optimized to operate on the bandwidth of the antenna. The assembly of the different facets 20i (for example, with symmetry of revolution), as well as their profile are chosen to ensure a progressive and omnidirectional transition of the electric field between an excitation point 21 disposed at the level of the lower plane 6 and the plane The excitation point 21 is, for example, a conductive cylinder formed for example in a machined metal material, providing the mechanical and electrical interface between the core of the connector 22 and the broadband exciter. The facets 20i may be metal plates, metal fabric or formed of metal rods. The facets 20i are, for example, connected to each other and to the upper plate 5 with metal screws (or conductive). Any other fastener allowing electrical continuity between the two parts may be considered. It is also possible to use a mechanically welded technique. The various metal parts are, for example, screwed or nested with each other so as to ensure good mechanical strength and electrical continuity from the core of the connector 22 to the exciter junction - upper plate. Any other technique allowing an assembly ensuring, on the one hand, a mechanical strength and on the other hand an electrical continuity can be used. The combination of elements 20 and 23 forms the broadband exciter. The assembly has an outer surface Se and a surface profile Ps adapted to generate a linear vertical polarization electric field created between the two plates 5, 6, under the effect of a signal applied at an excitation point 21 of the antenna, said electric field propagating within a guiding structure formed by the upper plate, the lower plate and the excitation means. The metal cone 23 makes it possible to ensure the mechanical and electrical interface between the facets 20i and the excitation point 21.

The exciter can take different forms and consist of one or more parts as long as this gradual transition is ensured between the two planes or the two plates. The progressive transition is defined in the context of the invention as a transition or mechanical profile progressive symmetry of revolution between the excitation point 21 and the upper plate 5 for very broadband impedance matching.

The broadband excitation means generates, for example, a vertically polarized electric field.

The broadband excitation means is, for example, adapted to create an electric field propagating between the two plates said antenna generating an omnidirectional radio radiation in azimuth oriented towards the ground and the horizon.

The use of facets to form the outer wall of the exciter offers advantages such as facilitating the assembly and manufacture of the system. The excitation of the facets 20i is provided by a conical metal cylinder 23 at the top of which is placed the excitation point 21 and at the base of which are fixed the metal facets 20i. This part 23 of the system is not necessarily conical, but may be cylindrical, hemispherical, exponential or logarithmic, according to shapes and profiles known to those skilled in the art.

The dimensions above are given for illustrative purposes. Indeed, the dimensions of the upper plane may be greater, smaller or equal to the dimensions of the lower plane according to the desired orientation of the radiation, to the ground, the horizon or the sky. The shape of the plates can be rectangular, circular, square, ovoid or polygonal complex depending on the surface acceptable by the wearer and the specification relating to the omnidirectionality of the radiation patterns.

Figure 2 shows a detailed view of the receiving antenna having in this example an interception role. It is constituted by the ferrite plane 1 1 placed on the metal plane 12 on the one hand, and by a logarithmic spiral discretized (ie whose logarithmic evolution is not done continuously but by piece) two-armed, B1, B2, square profile formed by the elements 13, 14 and 15, respectively adapted for low frequencies, medium frequencies and high frequencies.

In order to improve the radiation performance of the high frequency antenna, the ferrite tiles present in the center of the plane 11 can be removed. Element 13 is constituted by volume turns of constant diameter and pitch per spiral side, that is, each spiral side will see a constant pitch that will be different from another spiral side. A logarithmic progression, for example, makes it possible to change the pitch of the turns between two consecutive sides of the square spiral. These turns make it possible to inductively charge the profile of the spiral and thus reduce its surface bulk. The portion 14 is a planar logarithmic square spiral profile placed in continuity and in the same plane as the element 13. The portion 15 is made by conformation of a logarithmic spiral square profile on a pyramid with four faces. The conformation of 15 allows an improvement of the radiation performance at the high frequency horizon. The four-sided pyramid as the support 16 of the elements 13 and 14 is made, for example, of relative permittivity foam close to 1.

Ferrite tiles contribute to the reduction of the height of the receiving antenna but also to the absorption of currents This last point also favors the optimization of the decoupling between the reception and the emission, corresponding in the context of the application to the interception and to the jamming.

FIGS. 3A and 3B give a more detailed view of the elements 13, 14 and 15. The pitch used between each turn constituting the element 13 is chosen constant here by side of the antenna to facilitate the industrial realization of the element 13. The progression of this step can follow different quasi-logarithmic laws. However, care should be taken to use profiles with an important step on the first turns in order to minimize the phenomena of mismatch induced by overly pronounced reflection phenomena on these inductive elements. The excitation of the arms of the complete spiral forming the antenna 2 is in the center of 15 via a broadband impedance transformer with its outputs in phase opposition. The impedance ratio to be established is a function of the diameter of the wires constituting the arms of the spiral at level 15 and to a lesser extent of 13 and 14. Conductive elements 17 provide the electrical connections between elements 14 and 15.

FIG. 4 shows the measured decoupling obtained between the transmitting antenna 1 and the receiving antenna 2 on the frequency band

30 MHz - 3000 MHz for a configuration established according to the principle described above. The decoupling is very high over the entire frequency band despite the quasi-collocation of the radiating elements.

FIG. 5 represents the measured standing wave ratios obtained for the transmitting antenna 1 and the intercepting antenna 2 on the 30 MHz-3000 MHz frequency band for a configuration established according to the principle described above. For the transmitting antenna, this ratio remains lower than 6 over the whole band and less than 2: 1 from 100 MHz. The use of this antenna system in the presence of a small 4x4 type carrier vehicle reduces this ratio to 3: 1 over the entire band 30 MHz - 3000 MHz. For the interceptor antenna, the standing wave ratio is less than 4: 1 on 95% of the band, with an interceptor antenna 2 of 500 mm x 500 mm on a plane 11 of 700 mm x 700 mm . The use of a larger spiral would result in a lower ROS of 4: 1 over the entire 30 MHz - 3000 MHz band. In the field of antennas dedicated to the protection of convoys in the frequency band varying from 30 MHz to 3000 MHz, the antenna according to the invention notably has the following advantages:

A significant decoupling between the transmitting antenna and the receiving antenna is obtained on the one hand, thanks to the decorrelation of the radiation patterns of each of the antennas and on the other hand, by the absorbing action of the currents by the ferrites placed between the modified spiral antenna and the transmitting antenna,

The wide bandwidth adaptation of the receiving (or interception) antenna is obtained based on an antenna concept that is almost independent of the modified spiral type frequency.

This modified spiral antenna is square. She has two arms inductively loaded on the last laps. This inductive load is carried out using volumic turns. The structure has a logarithmic progression both in the spiral pitch and the progression of its generator. To facilitate the realization of the antenna, the diameter and the pitch of each side of the spiral are for example constant.

The optimization of the radiation on the horizon of the receiving antenna, is obtained in particular thanks to the shape of the central part of the antenna, relative to the upper part of the bandwidth, which is shaped on a pyramid to four sides.

The gain of the receiving antenna is directly related to the impedance matching of the antenna. The gain realized will be even better than the antenna will be well adapted.

The receiving (or interception) antenna is particularly compact. Its interweaving at the heart of the transmitting (or jamming) antenna favors this aspect. On the other hand, the fact that the modified spiral is disposed on a ferrite plane or an equivalent goes in the same direction.

The transmission and reception accesses are directly adapted to a characteristic impedance of 50 Ohms.

Claims

1 - An omnidirectional antennal system very wide band working in a chosen frequency range, intended to be positioned on a carrier and characterized comprising:

A first antenna element (1) operating in transmission and comprising:

a first conductive plate (6) having a length L1 and a width 11, of surface S1,

a second conductive plate (5) having a length L2 and a width 12, of surface S2,

the two plates (5, 6) being separated by a spacing E, a broadband excitation means (4) having an outer surface and a surface profile adapted to generate or pick up a linear vertical polarization electric field created between the two plates (5, 6) under the effect of a signal applied at an excitation point (21) of said antenna (1), said electric field propagating within a guiding structure formed by the first plate (6), the second plate (5) and the broadband excitation means (4), said broadband excitation means (4) has a pseudoconic form,

at least one conductive link (7) disposed between the first conductive plate (6) and the second conductive plate (5), the one or more links (7) being connected to said plates via at least one matching circuit (8),

A second antennal element (2) of square spiral type operating in reception placed on a metal plane (12) covered with a ferrite-type material (1 1) adapted to trap currents, the assembly being embedded in said first element; antennal (1).

2 - antennal system according to claim 1 characterized in that the second antenna element (2) is embedded in a conical portion itself integrated in the upper pseudo-conical portion of said broadband excitation means. 3 - Antenna system according to claim 2 characterized in that said second antenna element (2) consists of a first element (13) adapted to operate in the low frequencies, said element (13) being constituted by volumic turns of diameter and constant steps by spiral side, a second element (14) having a planar logarithmic square spiral profile placed in continuity and in the same plane as the element 13, a third element (15) adapted for the high frequencies and made by conformation on a four-sided pyramid of a logarithmic spiral with a square profile.

4 - Antenna system according to claim 3 characterized in that the four-sided pyramid as the support (16) of the elements (13) and (14) is made of relative permittivity foam close to 1. 5 - antennal system according to the claim 1 characterized in that said conductive plates (5, 6) are provided with orifices for fixing the metal links (7) and adaptation circuits (8).

6 - Antenna system according to claim 1 characterized in that said antenna matching circuits (8) are constituted by one or more of the elements selected from the following list: resistance, capacitance and / or power self.

7 - antennal system according to the preceding claims characterized in that the matching circuit consists of one or more power resistors.

8 - Antenna system according to one of claims 1 to 7 characterized in that the frequency range is in the range 30 MHz - 3000 MHz.