WO2017029122A1

WO2017029122A1 - Multifunctional broadband sector antenna

Info

Publication number: WO2017029122A1
Application number: PCT/EP2016/068664
Authority: WO
Inventors: William HUBERT; David SAINTIER; Cyrille Le Meins
Original assignee: Thales
Priority date: 2015-08-14
Filing date: 2016-08-04
Publication date: 2017-02-23
Also published as: FR3040110A1; SG11201803953SA; FR3040110B1; EP3335277A1; EP3335277B1

Abstract

The invention relates to a broadband or ultra-broadband sector antenna (1) having a height H, a depth D and a width W, including a first ground plane (2) acting as reflective plane, at least one antenna assembly comprising at least one first strand (101) and at least one second strand (102), the antenna operating in a frequency range [f1, f2], characterised in that: one strand (101, 102) has a folded shape, an inner curve F₁ starting at a point A positioned towards the centre of the antenna O, and an outer curve F₂ forming an extension of the first inner curve F₁; the inner curve F₁ is determined so as to guarantee the stability of the radiation pattern at the maximum operating frequency of the antenna; the outer curve F₂ is determined so as to guarantee the stability of the impedance of the antenna at the supply terminals thereof, at the minimum operating frequency; and the first strand (101) and the second strand (102) are supplied in opposite phase.

Description

MULTIFUNCTION WIDE BAND SECTORAL ANTENNA

The invention particularly relates to a very high frequency / ultra high frequency antenna, VHF / UHF, broadband or ultra wideband sectorial radiation. It relates more generally, the field of antennas and antenna systems by networking, for remission with powers of a few tens to a few hundred Watts, for example, and the reception in the VHF / UHF bands of waves electromagnetically polarized linearly.

For some applications, the use of antennas must meet the needs of integration on a carrier structure and the possibility of making antennas and antenna networks that can be used for several functions. The first axis assumes a maintenance of the radiation and impedance performance of the antennas after integration on complex carrier structures. These structures may be surface vessels (naval application), land vehicles or aircraft. Moreover, this performance maintenance must take place over a very large bandwidth (half a decade or even a decade). The second axis is related to the multifunction aspect requested by the users. The ever-increasing number of integrated carrier functions is accompanied by an increase in the number of antennas to be integrated into their structure. This difficult integration with regard to mechanical constraints, performance and electromagnetic compatibility can be solved by pooling the radiating elements. On the other hand, this pooling raises the problem of the unification of the requirements inherited from the various systems to which the antennas and the antenna networks participate.

Many articles dealing with ultra wide band dipole antennas can be cited. When it comes to modifying this simple architecture to integrate it close to a ground plane (the structure) while maintaining satisfactory radiation properties and impedance matching allowing use on a very wide band of frequency, the available corpus is already more limited. In this respect, patent application FR 301 1685 describes a dipole-loop antenna. With overall dimensions of 1 x1 m for a height of 0.25m, it can be used over a band from 100 MHz to 500 MHz, via an impedance matching circuit. It can also be placed in a circular network.

The Rhode and Schwartz antenna referenced AD066FW also describes a broadband antenna array structure usable between 1 18 MHz and 453 MHz for enhanced communications functions through a beamforming system.

Another form of antenna is described in the publication entitled

The Self-Grounded Bow-Tie Antenna by J. Yang and A. Kishk, IEEE AP-S / URSI 201 1. Designed to operate between 2 GHz and 15 GHz, it advantageously takes advantage of a short-circuiting of the dipole strands to:

- Extend the frequency band of use,

- Wear an antenna profile better known as the "Vivaldi" antenna which limits the phenomena of lamination when the antenna is electrically large.

However, with a minimum frequency of 2 GHz for dimensions 54 (L) × 58 (1) × 24 (h) mm, a transposition in frequency from 100 MHz shows that this solution is not suitable for applications envisaged for the present invention. invention.

Despite all the advantages offered by the solutions of the prior art, the latter have certain drawbacks because of their design and their size that adversely affect the integration and networking capabilities. When the congestion is contained, the stationary wave ratio better known under the abbreviation ROS and the resulting gains no longer meet the quality of service requirements. When the congestion is too important, the network association to obtain an omnidirectional path is not obvious. Moreover, the dipole-loop antenna of the aforementioned patent requires an adaptation circuit additional impedance that can limit power handling for certain applications.

In summary, the solutions described in the prior art and known to the applicant do not allow in particular to have simultaneously:

"An ROS less than 3 and a gain greater than 2 dBi, in the main transmit / receive direction, over the entire desired frequency band for the antenna alone,

• stability of the radiation pattern, without lamination phenomenon,

· Optimized height (less than or equal to 1 meter) and reduced width (less than or equal to 40 cm) to facilitate integration and networking (circular or otherwise),

• A restricted depth (less than or equal to 25 cm) to integrate easily into the structure,

· A self-adapted nature on a given impedance, for example 50Ω, not requiring a reported impedance matching circuit.

The object of the present invention is to propose a networkable antenna adapted to operate in a broadband or ultra wideband domain, which notably makes it possible to be easily integrated in a given location and which has a stability in the field. operating diagram.

The invention relates to a sectoral antenna, broadband or ultra wideband, having a height H, a depth D, a width W, comprising a ground plane acting as a reflective plane, at least one antennal assembly comprising at least a first strand and at least a second strand, the antenna operating in a frequency range [f-ι, f ₂ ], characterized in that:

• A strand has a folded shape, an internal curvature Fi, F'i starting from a point A, A 'positioned towards the center of the antenna O, an outer curvature F ₂ , F' _2, located in the extension of the first internal curvature Fi, F'-i, • The shape of the internal curvature Fi, F '-i, is determined in order to guarantee the stability of the radiation pattern at the maximum operating frequency of the antenna,

• The shape of the external curvature F ₂ , F ' _2, is determined in order to guarantee the stability of the impedance that the antenna presents at its supply terminals, at the minimum operating frequency,

• The first strand and the second strand are energized in phase opposition.

The shape of a strand is, for example, characterized in the following manner:

• Let the Cartesian coordinates of three points A, B and C, AB belonging to the internal curvature Fi, BC belonging to the external curvature F ₂ , the origin point 0 of the Cartesian coordinate system corresponding to the center of the ground plane,

• The inner curve Fi of a strand is defined by:

ezc ₁ _ _e z _B c ₁

(J: X = x _B + (x _A - x _B ) _{e¾Cl_} _eZgCl , Vz G [z _A , z _B ],

• The outer curve F ₂ of a strand is defined by:

g ^zc 2 - Q ^Z B ^C 2

(F ₂ ): X = X _B + (x _c - _B ) _eZcC ₂ - _e z _B c ₂ ' ^{V e}

XA, XB, XC, Z _A , Z _B , Z _c , are the coordinates of the points A, B and C in a Cartesian coordinate system and Ci and c ₂ are two curvature parameters.

According to an alternative embodiment, the shape of a strand seen from the front corresponds to the intersection of a first ellipse Ei having a first radius Ri corresponding to the major axis and a second radius R ₂ corresponding to the minor axis, with a second ellipse E ₂ having a first radius R ₂ corresponding to the major axis substantially identical to the radius of the minor axis of the first ellipse, and a second radius R ₃ , the value of R ₂ is chosen as a function of the width of the antenna, the ratio R - | / R ₃ is chosen to optimize the transitions at the antenna power supply and at the terminal foldback of the strand.

The parameters of an antenna are defined such that, for an operating frequency range [f-ι, f ₂ ] and a center frequency f ₀ : D is in the range [λ _0/5 , λ _0/3 ]

H is substantially equal to λ ₀ ,

W is in the range [λ _0/3 , λ _0/2 ],

R ₃ is between 0.6 ^* ^ and 0.8 ^* R _1;

R ₂ - W / 2.

According to an alternative embodiment, the depth of the antenna D is chosen to be substantially equal to a quarter of the wavelength λ ₀ , the height H of the antenna is substantially equal to the wavelength λ ₀ , the width W of the antenna is substantially equal to 2 ^* λ _0/5 .

The sectoral antenna is for example characterized in that: "The ground plane comprises two folds forming two capacitive roofs,

• The first elliptical strand and the second elliptical strand are folded in the center of the antenna towards the ground plane,

A first end of the first strand is at a first point A close to the ground plane and a first end of the second strand is at a second point A 'near the ground plane,

A second end of the first strand and a second end of the second strand are respectively positioned at two points C, C corresponding to a point whose dimension is such that z _c is substantially equal to 0.48 λ ₀ ,

• R1 + R3 is equal to z _c -z _A ,

• R ₂ is substantially equal to W / 2.

The sectoral antenna according to the invention may comprise several sets each composed of two strands having an elliptical shape. The antenna power supply is, for example, carried out via connection means supplied in phase opposition thanks to a Balun or a 0/180 ° hybrid coupler.

The antenna may comprise at least two RF connectors selected according to the operating frequency range of the antenna and the desired power handling, the connectors are energized in phase opposition.

The sectoral antenna operates at a frequency belonging to the VHF / UHF domain with the transmission of power from a few tens to a few hundred Watts and a reception in the bands

VHF / UHF linearly polarized electromagnetic waves.

According to an alternative embodiment, the sectoral antenna according to the invention is suitable for integration into mobile equipment or fixed infrastructure.

Other features and advantages of the present invention will appear better on reading the following description of an attached exemplary embodiment of the figures which represent:

FIG. 1, a 3D view of an example of an antenna according to the invention,

FIG. 2, a profile view of the antenna of FIG.

FIG. 3, a diagram for explaining the specific shape of the antenna strands,

• Figure 4, radiation patterns in the vertical plane of the antenna at different frequencies,

FIG. 5, a representation of a gain of the antenna in the main direction of emission as a function of frequency, and

• Figure 6, an ROS of the antenna as a function of frequency.

Before explaining an exemplary embodiment of an antenna according to the invention, the applicant sets the following definitions:

•: the minimum frequency of operation in Hz,

· F ₂ : the maximum operating frequency in Hz, F ₀ : the central frequency of operation in Hz and such that f ₀ = (fi + f ₂ ) / 2,

• or λ _χ the wavelength (in meters) associated with the frequency f _x and such that λ _χ = c / f _x with c the speed of propagation of the waves (in m / s), x being a corresponding generic index to the indices 0, 1, 2 of the frequencies,

• The points A, B and C (figure 2) that will make it possible to define the profile of a strand are identified by a Cartesian coordinate system in the direct orthonormal coordinate system X, Y and Z such that the origin is in the center of the antenna, X points towards the front of the antenna (ie the main direction of emission) and Z towards the top.

The general ratings of the antenna are as follows:

• The first parameter D determined is the depth of the chosen antenna such that D is in the interval [λ _0/5 , λ _0/3 ], preferably D = λ _0/4 . This parameter defines at the same time xB (the abscissa of point B according to FIG. 2), ie XB = D,

The second fixed parameter H is the height of the chosen antenna such that H is substantially equal to or equal to λ ₀ ,

Finally, in order to achieve the operating requirements at the minimum frequency, the width W of the antenna is chosen such that W is between λ _0/3 and λ _0/2 , with preferably W = 2 * λ _0/5 .

FIG. 1 schematizes a three-dimensional view of an example of a broadband or ultra wideband antenna 1 according to the invention which will be detailed using FIG. 2. The antenna 1 is composed of a first elliptical strand. 1 01 and a second elliptical strand 1 02, the two elliptical strands being folded to a ground plane 2 at the center O of the antenna 1, a first end 1 01 a (Figure 2) of the first strand being at the a first point A (ΧΑ, ΖΑ) located near the ground plane and a first end 1 02a of the second strand 1 02 being at a second point Α '(Χ'Α, ΖΆ) located near the ground plane 2. A second end 101b of the first strand and a second end 1 02b of the second strand is position at two points points C, C whose dimensions are given relative to the ground plane as it will be explained a little further. The antenna 1 is enclosed by a first perpendicular folding and second folding of the ground plane, better known under the term "pseudo capacitive roofs", 31, 32.

The two strands 101, 102 have in this example an elliptical shape and are arranged symmetrically with respect to an axis Ox. The two strands are supplied in phase opposition by two connection means 30, 30 'thanks to a Balun or hybrid coupler 0 ° / 180 ° known to those skilled in the art. The connection means 30, 30 'may be RF connectors or any other type of suitable connection known to those skilled in the art depending on the frequency and power handling.

Figure 2 and Figure 3 illustrate the definition and shape of the strands using an ellipse representation. The front view of the strands is generated by the intersection of a first ellipse Ei which has a first radius R-ι for the major axis and a second radius R ₂ for the minor axis, with a second ellipse E ₂ having a same radius R ₂ for the major axis and the radius R ₃ for the minor axis. The intersection I of the two ellipses E ₁ and E ₂ is shown in thicker lines in FIG.

FIG. 2 represents, in a Cartesian coordinate system where the origin point O corresponds to the midpoint of the antenna, the profile of the strands. Each strand has a shape consisting of a first curve Fi (AB), F'-ι (Α'-Β '), called inner curvature with respect to the center O of the antenna, followed by a second curve F ₂ ( BC), F ' ₂ (B'-C) or outer curvature. The two strands have a substantially identical shape and symmetrical with respect to the axis OX, more generally with respect to an axis perpendicular to the antenna and passing through the center O.

The different parameters for generating the antenna strands are defined in FIG. 2 and FIG. 3:

· Seen from front or projected in the yOz plane, a radiating strand is generated by the intersection of two ellipses sharing the same radius transverse R ₂ , the latter fixing the total width of the antenna. Then, the ratio R-1 / R3 is chosen to optimize the transitions at the level of the feed and the terminal folding of the strand.

• Seen in profile, the curvature of the strand towards the ground plane is defined by the points A, B, C and by the equations of the curves F-ι and F ₂ . The lower part of the intersection of the two ellipses is then fixed at A (feeding point of the strand) then goes through B and C.

Let the Cartesian coordinates of points A, B and C, such as:

The equations of the curves are given by two additional curvature parameters: Ci and c ₂ . The equation of F-ι is such that:

ezc ₁ _ _e z _B c ₁

(J: X = x _B + (x _A - X _B ), Vz G [z _A , z _B ].

Similarly, the equation of F ₂ is such that:

e ^zc 2 _ _e ^z B ^c 2

(F _2): X = x _B + (x _c - ¾) _e _ z _cC2 _e¾C2) Vz G _[B z, z _c].

The second strand is then generated by X-axis symmetry, the preceding formulas apply for the points referenced A ', B' and C in FIG.

To define the pattern of strands seen from the front we will, for example, use the following parameters:

First, the coordinates of the points A, A 'are adjusted by means of electromagnetic simulations and according to the integration constraints of the connection means 30, 30'. For example, for the band 100-500 MHz, the abscissa XA, XA \ is approximately equal to 5 mm and the dimension z _A , z _A \ is approximately equal to 5 mm similarly. However, for higher frequency applications, these coordinates can be reduced. The values of the dimensions will be chosen in particular according to the frequency band of operation, • To improve the impedance matching, the antenna structure is made up of two folds of the ground plane, at the top and bottom when considering the antenna in a vertical position as shown in FIG. figure 1 . The proximity of the end of the strands with these capacitive roofs 31, 32 is determined by the dimension of the point C, ie z _c such that z _c = γ * λ ₀ ~ 0.48 ^* λ ₀ ,

• From previous definitions, we deduce that R1 + R3 = z _c - z _A ,

• Following an optimization in electromagnetic simulation,

also determines R ₃ in the range [0.6 ^* Ri, 0.8 ^* Ri] with R ₃ ~ 0.7 ^* Ri,

• Finally, R ₂ "W / 2.

One way of obtaining the curvature of the strands is described below and in relation with FIG. 2:

• The strands are bent in the plane containing the vectors X and Z (axis OX, OZ) according to two exponential functions Fi (F-) and F ₂ (F ₂ '),

• The junction between these two functions is parameterized by the point B (point B ') dimension determined by optimization in electromagnetic simulation, ie z _B approximately equal to 1/3 λ ₀ ,

• The inner curvature of the strands corresponding to the part of the curve going from A to B (A 'to B') is generated by the function of exponential type Fi, (F'i) which receives as parameters the coordinates of the points A and B and a curvature parameter ci, such that Ci varies from -20 / λ ₀ to -15 / λ ₀ , preferably Ci ~ -18 / λ ₀ , for example. This curvature serves to guarantee the stability of the radiation pattern at the maximum frequency,

• The outer curvature of the strands corresponding to the BC (B'-C) part is generated by the exponential type function F ₂ , (F ' ₂ ) which receives as parameters the coordinates of the points B and C (B' and C) and a curvature parameter c ₂ , such as c ₂ ~ 30 / λ ₀ , for example. This curvature serves to guarantee the stability of the impedance that the antenna presents at its terminals at the minimum frequency.

The curvature parameters Ci and c ₂ are defined by electromagnetic simulation using simulation tools known to those skilled in the art, for example a rigorous method of electromagnetic simulation known as the "full-wave method". All parameters can be adjusted to optimize performance.

In fine, the proposed antenna thus sports a bandwidth (or operating range) in frequency of 5: 1 with a standing wave ratio

(ROS) less than 3.

The following example is a given encrypted example for an antenna

Ultra Wide Band, for use band from 100 MHz to 500

MHz the dimensions of the antenna are:

· Height (H): 1 meter,

• Width (W): 0.4 meters,

• Depth (D): 0.25 meters,

• The spacing between the two feed points A-A 'is 1 cm.

The refolding towards the center makes it possible to give a Vivaldi antenna profile which channels the radio frequency radiation to minimize the phenomena of lamination on the radiation in the vertical plane of the antenna as illustrated in FIG. use ranging from 100 MHz to 500 MHz.

The addition of perpendicular folds to the strands minimizes bulk while maintaining a gain in the main direction of transmission greater than 2 dBi over the entire band, as shown in Figure 5 plotting the gain of the antenna in the main direction of transmission according to the working frequency.

Figure 6 shows the ROS of the antenna as a function of frequency with respect to a characteristic impedance of 50Ω. With the two-point power supply to reduce the impedance that presents the antenna at its terminals, the proposed solution avoids the use of an impedance matching circuit. The antenna is then self-adapted with an ROS of less than 2.5 with respect to a characteristic impedance of 50Ω.

By its sectoral influence, the proposed solution allows to privilege a direction of the space and thus strengthens its gain compared to a solution based on omnidirectional antennas. The network association of this solution allows to wrap the carrier structure to better disregard it. Overall, this feature allows use for V / UHF communications. Finally, its network-associated Ultra Wide Band character makes it possible to envisage a use of the direction-finding type.

In general, the antenna can be made of conductive metal (copper, aluminum, ...) or composite material (carbon, ...).

The antenna according to the invention can easily be integrated on mobile equipment, such as a ship, on the surface of a wall or at a mast fitted to a vehicle or a terrestrial infrastructure. A single powered antenna sports a sectoral radiation while minimizing the impact of the structure on the operation of the antenna.

Without departing from the scope of the invention, the description of the steps for defining a shape of antenna strands applies for non-elliptical strands such as other Ultra Wide Band shapes known to those skilled in the art.

The shape of the antenna according to the invention makes it possible to optimize the occupation of the available space to improve the gain and the impedance matching. Indeed, the elliptical shape of the strands makes it possible to contribute to the ultra-broadband character of the antenna.

The antennas according to the invention notably allow integration of antennas and antenna arrays on a carrier structure, the use in several functions.

The advantages of the proposed solution are: Frequency-stable sectoral radiation pattern, for wide or ultra-wide frequency bands, a self-adapted design, i.e. without impedance matching circuit,

structure integration facilitated by its narrow profile (reduced width and thickness),

easy circular networking for omni-directional azimuth coverage,

an operation for communications (transmission and reception), direction-finding or spectrum control functions thanks to its performance,

A simple form allowing a transposition in other frequency bands (VHF, UHF and SHF) and which can be conformed.

Claims

1 - Antenna sector (1), broadband or ultra wideband, having a height H, a depth D, a width W, having a first ground plane (2) acting as a reflective plane, at least one antennal assembly comprising at least a first strand (101) and at least one second strand (102), the antenna operating in a frequency range [f-ι, f ₂ ], characterized in that:

• A strand (101, 102) has a folded shape, an internal curvature Fi, F'-i from a point A, A 'positioned towards the center of the antenna O, an outer curvature F ₂ , F' ₂ located in the extension of the first internal curvature Fi, F'-i _,

• The internal curvature F-i, F'i is determined in order to guarantee the stability of the radiation pattern at the maximum operating frequency of the antenna,

• The external curvature F ₂ , F ' ₂ is determined in order to guarantee the stability of the impedance that the antenna presents at its supply terminals, at the minimum operating frequency,

• The first strand (101) and the second strand (102) are energized in phase opposition.

2 - Sectorial antenna according to claim 1, wherein the curvature of a strand is characterized as follows:

Let the Cartesian coordinates of three points A, B and C, AB belonging to the inner curvature Fi, F'-ι, BC belonging to the external curvature F ₂ , F ' ₂ , the origin point 0 of the Cartesian coordinate system corresponding to the center of the plan of my

The inner curve Fi of a strand is defined by: (FJ = = X _B + (x _A - X _{B eZAC1} _ _eZBC1 , Vz [¾ ¾],

The outer curve F ₂ of a strand is defined by:

g ^zc 2 g ^z B ^c 2

(F ₂ ): X = x _B + (XC - XB) _eZcC _{2 -} _eZB c ₂ > _V z e [z _B , z _c ]

XA, XB, XC, Z _A, ZB, Z _c are the coordinates of points A, B and C in a Cartesian coordinate system, and this curvature c ₂ are two parameters. 3 - Sectoral antenna according to one of the preceding claims characterized in that the folded shape of a strand (101, 102) front view corresponds to the intersection of a first ellipse Ei having a first radius Ri corresponding to the major axis and a second radius R ₂ corresponding to the minor axis, with a second ellipse E ₂ having a first radius R ₂ corresponding to the major axis substantially identical to the radius of the minor axis of the first ellipse, and a second radius R ₃ , the value of R ₂ is chosen as a function of the width of the antenna, the ratio R- | / R ₃ is chosen in order to optimize the transitions at the level of the antenna supply and the terminal folding of the strand.

4 - sectorial antenna according to one of claims 2 or 3 characterized in that the parameters of an antenna are such that for an operating frequency range [f-ι, f ₂ ] and a central frequency f ₀ :

D is in the range [λ _0/5 , λ _0/3 ],

H is substantially equal to λ ₀ ,

W is in the range [λ _0/3 , λ _0/2 ],

R ₃ is between 0.6 ^* R ₁ and 0.8 ^* R _1,

R ₂ "W / 2 _,

d -20 / λ ₀ to -15 / λ ₀ and c ₂ "30 / λ ₀ .

5 - sector antenna according to claim 4 characterized in that the depth of the antenna D is substantially equal to a quarter of the length wavelength λ ₀ , the height H of the antenna is substantially equal to the wavelength λ ₀ , the width W of the antenna is substantially equal to 2 ^* λ _0/5 .

6 - sectorial antenna according to one of claims 3 to 5 characterized in that:

• The ground plane comprises two folds forming two capacitive roofs (31, 32),

• The two elliptical strands (101), (102) are folded towards the ground plane (2) in the center of the antenna (1),

· A first end (101 a) of the first strand (101) at a first point A near the ground plane (2) and a first end (102a) of the second strand (102) are at the level of a second point A 'near the ground plane (2),

A second end (101b) of the first strand (101) and a second end (102b) of the second strand (102) are respectively positioned at two points C, C corresponding to a point whose dimension is such that z _c is substantially equal to 0.48 λ ₀ ,

• R1 + R3 is equal to z _c -z _A ,

• R ₂ is substantially equal to W / 2.

7 - Sectorial antenna according to one of the preceding claims characterized in that it comprises several sets consisting of two strands having an elliptical shape. 8 - sectoral antenna according to one of claims 2 to 7 characterized in that the supply is performed via connection means (30) supplied in phase opposition by means of a balun or 0/180 ° hybrid coupler. 9 - sector antenna according to claim 8 characterized in that it comprises at least two RF connectors (30) chosen according to the range frequency of operation of the antenna and the desired power handling, the connectors are energized in phase opposition.

10 - Sectoral antenna according to one of the preceding claims characterized in that the operating frequency belongs to the VHF / UHF range with the emission of power from a few tens to a few hundred Watts and a reception in the VHF / UHF bands d linearly polarized electromagnetic waves. 1 1 - Sectorial antenna according to one of the preceding claims characterized in that it is suitable for integration into a mobile equipment or a fixed infrastructure.