WO2011000702A1

WO2011000702A1 - Modular band extension device for a very-wide-band omnidirectional antenna

Info

Publication number: WO2011000702A1
Application number: PCT/EP2010/058492
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: EP2449623B1; FR2947389B1; EP2449623A1; FR2947389A1

Abstract

The invention relates to a modular device that can be used to widen the usage band of a very-wide-band omnidirectional antenna, said antenna (1) being disposed on a carrier vehicle V. The invention is characterised in that it comprises at least the following elements: a first upper conductive plate (5) provided with one or more slots (8) that can be used to support metal links (2), said metal links (2) being equipped with a matching circuit (3); and a second lower conductive plate (6) also provided with one or more slots (8) that can be used to form electrical contacts between the power resistors (3) and the plate by means of wire ties (4). The antenna (1) includes a wide-band exciter (7) disposed between the first conductive plate (5) and the second conductive plate (6). The invention is suitable for switching from the 100 MHz-3 GHz band to the 30 MHz-3GHz band.

Description

MODULAR BAND EXTENSION DEVICE FOR WIDE BAND OMNIDIRECTIONAL ANTENNA

The object of the invention relates to a device with adjustable positions depending on the carrier vehicle to expand the band of use of a very broadband omnidirectional antenna, for example to expand the band 100 MHz-3GHz to the band 30 MHz-3GHz.

By the expression "adjustable positions", the description refers to elements of the device whose position and / or disposition may change depending on the antenna used and the carrier on which it is located.

The invention lies in the field of antennas or antenna systems dedicated to electromagnetic wave emission / reception applications in a very wide band.

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:

• obtain the frequency bandwidth to cover,

• guarantee impedance matching and power handling over the frequency band covered,

• respect a certain compactness (height, for example) of the antenna and the discretion of the radiating elements with respect to the covered band,

• ensure sufficient decoupling with respect to receiving or interception antennas located on the carrier,

• take into account the carrier on which the antenna is arranged to obtain the final performances expected.

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

These antennas have certain disadvantages, for example:

• Generally large footprint for low frequencies that do not meet the criterion of discretion and road size,

• 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,

• Weak gains on the horizon and un-optimized electromagnetic radiation; this one evolves according to the carrier,

• Use of impedance matching cells limiting the radiation efficiency of antenna structures and their power handling.

In the case of tuned or tunable antennas, the instantaneous bandwidth is limited.

The antenna structure according to the invention makes it possible to solve one or more of the aforementioned problems.

The invention relates to a modular device for widening the band of use of a very broadband omnidirectional antenna, said antenna being arranged on a carrier vehicle V, characterized in that it comprises at least the following elements:

A first upper conductive plate provided with one or more locations making it possible to maintain metal links, said metal links being loaded with an adaptation circuit, consisting of the power resistor,

A second lower conductive plate also provided with one or more locations for making the electrical contacts between the power resistors and said plate by metal links,

Said antenna (1) comprises a broadband exciter (7) having an external surface and a surface profile adapted to generate or capture a linear vertical polarization electric field created between the two plates (5, 6), said electric field propagating within a guide structure formed by the first plate (5), the second plate (6) and the means for broadband excitation (7), said broadband exciter being of "pseudo-conical" shape and consisting of conductive facets, metal fabric or metal rods.

The lower conductive plate of the antenna may be an independent plate attached to the carrier vehicle.

Said locations provided on the plates are holes or orifices allowing adjustment or easy movement of the metal links of the matching circuit consisting of power resistors.

The hole matrices or locations are extended around the metal planes and to near the junction of the upper metal plane and the upper part of the broadband exciter.

The said metal links are inclined or perpendicular to the planes.

The number and arrangement of the metal links provided with the matching circuit consisting of power resistors are defined taking into account the carrier on which the antenna is arranged.

The value of the power resistors vary and are adapted according to their number and the carrier on which the antenna is arranged.

The characteristics of the power resistors are chosen to allow the antenna to be used for high power applications also in the extended frequency band.

The frequency operating band is between 30 MHz and 3 GHz.

The matching circuit consists of, for example, one or more elements selected from the following list: resistance, capacitance and / or power choke.

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 side view of an example of antenna structure on which the invention is applied,

FIG. 1B, a view from above of FIG. 1A, FIG. 1C, a bottom view of FIG. 1A, FIG. 1D a detail of the antenna illustrated in FIG. 1A,

FIGS. 2A and 2B, seen in profile and seen from above, an example of integration of an antenna on a 4x4 carrier vehicle,

FIGS. 3A and 3B, two examples of potential vehicle-type carrier integration of the antenna on which the invention is applied,

FIG. 4, the standing wave ratio obtained with an antenna described in FIGS. 1A to 1D in the presence or absence of the device according to the invention and in the presence or absence of a carrier vehicle of small dimension as specified in FIG. figure 2,

FIG. 5, the gain realized on the horizon in vertical polarization with an antenna described in FIGS. 1A to 1D in the presence of the device according to the invention and in the presence or absence of a carrier vehicle of small dimension as specified in Figure 2. In order to better understand the architecture of the device with adjustable positions according to the invention, this depending on the carrier vehicle for receiving the antenna, the following description is a use of the antenna for transmission electromagnetic waves on the horizon and below the horizon, that is to say, downwards and over 360 ° azimuth for a frequency band between 30 MHz and 3 GHz.

The basic idea of the device according to the invention is to absorb a portion of the currents flowing on the reference antenna plates and to promote the excitation of the carrier vehicle which, given these dimensions radiate an electromagnetic field directed mainly towards the horizon in the low bands (30-100 MHz) of the transmitting antenna. The omnidirectional antenna operating in the frequency band (100-3000 MHz) sees its operating band very widely extended since it can then operate from 30 MHz to 3000 MHz. FIG. 1A represents a side view of an example of an antenna structure arranged by means of the modular device according to the invention on a carrier vehicle V (FIG. 2A).

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

An antenna 1 intended to be mounted on the support consists, for example, of a lower conductive plate 6 designed with 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 2A). 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 forms the upper plane of the antenna 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. 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 antenna 1 is constituted by a broadband exciter 7 positioned between the metal planes 5 and 6 in which a matrix of holes 8 (FIGS. 1B and 1C) is made in order to receive several metal links 2 loaded by power resistors. 3. The function of the metallic links is to enable electrical conduction between the different elements. The power resistors 3 are preferably situated on the lower plate 6. These power resistors 3 are, on the one hand, connected to the metal links 2 connected to the upper plane 5 and, on the other hand, to the connected metal links 4 6. In fact, the metal planes 5 and 6 are connected to each other via the elements 2, 3 and 4. The number of metal links can vary depending on the need. These links, according to their number, their placement and the value of the power resistance 3, allow optimization of the adaptation of the low frequency structure by absorbing undesirable currents. They also make it easier to excite the carrier vehicle that participates in the radiation in the frequency band 30MHz-100MHz.

By judiciously choosing the position of the metal links 2,4 as well as the power resistors 3, it is also possible to modify the radiation of the antenna, for example, to improve the radiation of the antenna in the presence of the carrier or to avoid radiation in one direction in the frequency bands of a few percent. The power resistors may have different values or not.

Figures 1 B and 1 C respectively show a top view and a bottom view of an embodiment of the antenna. On the upper metal plane 5 and the lower plane 6, a matrix of holes 8 is formed in order to easily adjust the location of the elements 2, 3 and 4 and allow the latter to play their role of conductor between the planes 5 and 6. Depending on the intended use or application, the metal links 2, 4 resistively charged by the power resistors 3 can be moved to all the positions 8 or holes Ti of the matrix. The dies will preferably be extended around the planes 5 and 6 and to the vicinity of the junction of the metal plane 5 and the upper part 9 of the broadband exciter 7 present between the two planes 5, 6.

The metal links can be inclined or perpendicular to the planes 5, 6. These links can be straight, bent or meandering. In the case where the metal plane 6 is directly made by a part of the carrier, for example when it corresponds to the roof of the vehicle (gallery or other), then the matrix of the missing plane 6 may not be realized and the elements 3, 4 directly attached to the carrier by means known to those skilled in the art or means that allow the conduction to be done.

The conduction metal bonds can be made of any type of material having properties conductors from the moment when this material is adapted to operate in the microwave.

The spacing between plates, the number and the arrangement of the metal links are, for example, determined according to the widening of the band of use to be obtained by using electromagnetic simulation tools.

The omnidirectional antenna 1 provided with metal links loaded with power resistors 3, for example, is adapted to a characteristic impedance of 50 Ohms. The fact of using power resistors 3 allows this antenna 1 modified according to the invention to be used for high power applications on the band 30-3000 MHz. This antenna also has radio coverage mainly directed to the horizon and to the ground over the entire frequency band.

The dielectric spacers 10 and 1 1 have the particular function of ensuring a mechanical rigidity of the system.

Without departing from the scope of the invention, instead of the power resistance, it is possible to use a more complex matching or charging circuit composed of one or more elements chosen from the following list: resistance, inductance, capacitance, the elements mentioned being used alone or in combination, knowing that the final function will be to ensure the impedance matching and the radiation of the antennal system on any carrier.

The broadband exciter 7 has the particular function of establishing an electric field E guided between the two planes 5, 6 and its outer wall S _θ

(FIG. 1 D). The exciter can consist of several conductive facets

(Metallic, 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. Facets 2Oi can be metal plates, metal fabric or formed of metal rods.

The facets 20i are, for example, connected to each other and to the upper plane 5 by means of 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 form the broadband exciter. The assembly has an external surface S _θ and a surface profile P _s 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 guide 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 facets 2Oi is ensured 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.

FIGS. 2A and 2B show a proposal for integrating the antenna 1 provided with the elements 2, 3, 4 according to the invention onto a vehicle V of the 4x4 type. The elements 2, 3, 4 are placed so as to compensate for example the dissymmetry of the vehicle which influences the omnidirectionality.

FIGS. 3A and 3B show a proposal for integrating the antenna 1 provided with resistively charged metal links on a vehicle 1 1 of the Avant Armored Vehicle type. The elements 2, 3, 4 are placed so as to compensate, for example, the dissymmetry of the vehicle and the positioning of the antenna which influences the omnidirectionality.

FIG. 4 represents the standing wave ratio obtained for a configuration of the antenna 1, with and without the resisitively charged metal links and with and without a carrier vehicle. The invention allows a significant improvement of the low frequency adaptation without degrading the adaptation to the rest of the band. The invention also allows the carrier vehicle to contribute to the adaptation of the antenna 1. The curve I corresponds to the ROS as a function of the frequency for an antenna alone (without a vehicle and without a metal link resistively charged), the curve II corresponds to an antenna without a vehicle and with resistively loaded metal links, the curve III corresponds to an antenna mounted on a vehicle and with resistively charged links.

FIG. 5 represents, in dB, the gain achieved on the horizon in vertical polarization over the frequency band 30-3000 MHz. The use of the invention in the presence of a carrier vehicle V allows a significant increase of the gain in low frequency and a stabilization of the latter on the intermediate frequencies by a judicious choice of the positioning of the elements 2, 3, 4. The gain in high frequency is not degraded by the presence of these elements. Curve IV represents the curve obtained without a vehicle with resistively charged metal links, curve V, a vehicle-mounted antenna and resistively charged metal links.

In the field of interception dedicated to the protection of convoys in the frequency band varying from 30 MHz to 3000 MHz, the antenna according to the invention has notably the following advantages:

• The low frequency band extension (30-100 MHz) is obtained thanks to the metal links loaded by power resistors. The links between the two plates of the reference antenna to excite the carrier vehicle may radiate at low frequencies. The modularity of the metal links allows an arrangement adapted to each carrier vehicle by reducing the omnidirectionality defects specific to each vehicle.

• The adaptation in the extension band (30-100 MHz) is obtained by the choice of the position of the metal links loaded by power resistors and by the values of these resistors. The metallic links disturb only very modestly the adaptation of the reference antenna in the upper band (100-30000 MHz).

• The compactness is obtained in the extension band thanks to the excitation of the vehicle which then participates in the radiation,

Claims

1 - Modular device for expanding the band of use of a very wideband omnidirectional antenna said antenna (1) being arranged on a carrier vehicle V, characterized in that it comprises at least the following elements:

A first upper conductive plate (5) provided with one or more locations (8) for holding metal links (2), said metal links (2) said metal links (2) being loaded with an adaptation circuit constituted by power resistance (3),

• A second lower conductive plate (6) also provided with one or more locations (8) for making the electrical contacts between the power resistors (3) and said plate by metal links (4),

Said antenna (1) comprises a broadband exciter (7) having an external surface and a surface profile adapted to generate or capture a linear vertical polarization electric field created between the two plates (5, 6), said electric field being propagating within a guiding structure formed by the first plate (5), the second plate (6) and the broadband excitation means (7), said broadband exciter being of "pseudo-conical" shape and constituted conductive facets, metal fabric or metal rods. 2 - Device according to claim 1 characterized in that the lower conductive plate (6) of the antenna (1) is an independent plate attached to the carrier vehicle V or a conductive portion of the carrier vehicle. 3 - Device according to claim 1 characterized in that said locations (8) provided on the plates (5, 6) are holes or orifices for adjustment or easy movement of the metal links (2,4) and a circuit of adaptation consisting of power resistors (3). 4 - Device according to one of claims 1 or 3 characterized in that the matrix of holes or locations (8) are extended on the periphery of the metal planes (5, 6) and up to the junction of the upper metal plane (5) and the upper part (9) of the broadband exciter (7).

5 - Device according to one of claims 1 to 4 characterized in that said metal links (2) are inclined or perpendicular to the planes (5, 6).

6 - Device according to one of claims 1 to 5 characterized in that the number and arrangement of metal links (2,4) provided with the matching circuit consisting of power resistors (3) are defined taking into account the carrier on which the antenna (1) is arranged.

7 - Device according to claim 6 characterized in that the value of the power resistors (3) are adapted according to their number and the carrier on which is disposed the antenna (1). 8 - Device according to one of claims 1 to 7 characterized in that the characteristics of the power resistors (3) are chosen so that the antenna (1) is used for high power applications also in the extended frequency band . 9 - Device according to one of the preceding claims characterized in that the matching circuit consists of one or more elements selected from the following list: resistance, capacitance and / or power self. 10 - Device according to one of claims 1 to 9 characterized in that the frequency operating band is between 30MHz and 3 GHz.