FR3136600A1 - Method for producing an array antenna whose radiating elements are mounted on a curved support surface - Google Patents

Abstract

Method for producing an array antenna whose radiating elements are mounted on a curved support surface. The antenna comprises a plurality of real elements (ERij) mounted on a support surface (S) of non-zero curvature. The method (100) comprises: defining (120, 130) a direction and a reference plane; define (140) an equivalent antenna in the reference plane, as a planar antenna comprising a plurality of equivalent elements (EEij); for each equivalent element, project (150) a center (CEij) of the equivalent element onto the support surface, to obtain an implantation point (CRij) of a real element; define (160) an inclined plane (Pij) at the implantation point; project (170) a contour of the equivalent element into the inclined plane, to obtain a contour of the real element; evaluate (180) a distance (dij) between the implantation point and the center of the equivalent element and calculate a phase shift to be applied to the signals transmitted/received by the real element, and production (210) of the antenna. Figure for abstract: Figure 1

Description

Method for producing an array antenna whose radiating elements are mounted on a curved support surface

The present invention relates to electronically scanned array antennas, in particular array antennas for aeronautics or telecommunications.

Today, array antennas are planar, the radiating elements of which they are made being arranged in a regular pattern in a plane.

For example, the forward radar of a fighter plane transmits and receives on a front antenna consisting of a plate of radiating elements, which is arranged transversely to the longitudinal axis of the aircraft. This front-facing antenna allows observation of an area located at the front of the aircraft.

This front antenna is topped with a radome of a substantially conical or ogival shape for aerodynamic reasons, the axis of the radome being substantially aligned with the longitudinal axis of the aircraft.

To increase the exploration of the space around the aircraft, it is known to carry additional antennas on board the aircraft, the plates of which are arranged perpendicular to the front antenna.

We would like to increase the capacities of an array antenna by using the external surfaces of the transport platform, such as the fuselage of an airplane, whatever their shape to carry the radiating elements of the array antenna. The radiating elements would therefore no longer be arranged in a plane.

There is therefore a need for a production method making it possible to dimension and then manufacture an array antenna whose radiating elements are carried by a support surface having at least one non-zero curvature.

The aim of the present invention is to meet this need.

For this, the subject of the invention is a method of manufacturing an electronically scanned array antenna comprising a plurality of real radiating elements, each real radiating element being mounted on a support surface, characterized in that, the support surface having a non-zero curvature and a real radiating element being positioned at an implantation point of the support surface so as to rest in an inclined plane, said inclined plane being inclined relative to a plane locally tangent to the support surface at installation point, the method comprises, in a sizing phase, the steps of: definition of a reference direction around which the pointing direction of the array antenna can be modified by electronic phase shift; definition of a reference plane normal to the reference direction; definition of an equivalent array antenna in the reference plane, the equivalent array antenna being a planar antenna comprising a plurality of equivalent radiating elements forming a regular pattern in the reference plane; for each equivalent radiating element: projection of a center of the equivalent radiating element, according to the reference direction, on the support surface, so as to obtain an implantation point of a center of a corresponding real radiating element ; definition of an inclined plane at the installation point on the support surface; projection of a contour of the equivalent radiating element, according to the reference direction, in the inclined plane, to obtain a contour of the corresponding real radiating element; evaluation of a distance between the point of installation of the real radiating element and the center of the equivalent radiating element and calculation, as a function of said distance, of a geometric phase shift to be applied to the signals transmitted or received by the real radiating element during operation of the array antenna, and in that the method comprises, in a manufacturing phase, the steps of producing the array antenna in accordance with the results of the sizing phase.

According to particular embodiments, this process comprises one or more of the following characteristics, taken individually or in all technically possible combinations:

- the evaluation step consists of determining a gain of each real radiating element in order to adjust a radiation power, evaluated in the reference plane, that this real radiating element produces.

- the evaluation step consists of determining an adjustment of a polarization of each real radiating element as a function of its installation position and/or its inclination on the support surface relative to the reference plane.

- the inclined plane is chosen parallel to the reference plane.

- the method begins with a step of delimiting at least one elementary support surface on the support surface, the elementary support surface grouping the real radiating elements to be activated to allow the array antenna to observe a domain around the reference direction.

- the support surface is a cone, an ogive, or a surface generated by rotation of a curve around an axis.

The invention also relates to a computer program product comprising software instructions which, when executed by a computer, implement the steps of the sizing phase of the manufacturing process.

The invention also relates to an array antenna resulting from the implementation of the preceding manufacturing process.

The invention and its advantages will be better understood on reading the detailed description which follows of a particular embodiment, given solely by way of non-limiting example, this description being made with reference to the appended drawings in which:

There is a schematic representation of an embodiment of the production method according to the invention;

There is a schematic representation in an axial plane of a first embodiment of an array antenna resulting from the implementation of the method of for a conical support surface;

There is a schematic representation in a transverse plane of the antenna of the ; And,

There is a schematic representation in a transverse plane of a second embodiment of an array antenna resulting from the implementation of the method of for a conical support surface.

General presentation of the process

From a general point of view, the method according to the invention relates to the placement of radiating elements on a support surface of any curvature in order to produce a functional electronically scanned array antenna.

A preferred embodiment of the method will be presented in relation to the block diagram of the and for the case of producing an array antenna carried by a conical support surface S, this antenna being illustrated in Figures 2 and 3.

The support surface S is a cone with axis A, vertex S0, and half-angle at the vertex σ.

The production process 100 comprises a first dimensioning phase 105, followed by a manufacturing phase 205.

The first step 110 of the sizing phase 105 consists of delimiting one or more elementary support surface(s) Sk on the support surface S of the carrier. A two-dimensional surface immersed in a three-dimensional space is characterized locally by two curvatures, respectively evaluated in two directions tangent to the surface and orthogonal to each other. The elementary support surface carries the radiating elements activated simultaneously for the observation of a domain located on one side of the axis A. In the embodiment of Figures 2 and 3, the support surface S is subdivided into four elementary support surfaces, S1, S2, S3 and S4 by axial planes P1 and P2 at right angles to each other. Alternatively, the support surface could be subdivided into a different number of elementary support surfaces, possibly so that two neighboring elementary surfaces partially overlap.

In what follows, we are more particularly interested in the first elementary support surface S1.

Then, in a step 120, a reference direction V1 is defined for the elementary support surface S1. The reference direction V1 makes an angle α with the axis A. The reference direction corresponds to the axis of the antenna beam “at rest”, that is to say without introducing an electronic phase shift between the signals emitted or received by the active radiating elements of the antenna to defocus the beam in a defocusing direction D (making an angle relative to the reference direction V1).

In a step 130, a reference plane PRef1 is defined as the plane normal to the reference direction V1.

In a step 140, an equivalent array antenna is defined in the reference plane PRef1. This virtual antenna is a planar antenna. It is composed of a plurality of equivalent radiating elements EEij. The equivalent radiating elements are arranged in the reference plane PRef1 in a regular pattern.

For example and preferably, this regular pattern is a rectangular matrix composed of rows and columns of equivalent radiating elements.

The equivalent radiating elements EEij are indexed by the integers i and j, respectively between 1 and Ni and 1 and Nj, Ni being the number of maximum equivalent radiating elements in a first direction of the reference plane and Nj being the number of elements maximum radiators in the other direction of the reference plane.

Equivalent radiating elements are identical to each other. Each equivalent radiating element preferably has a square shape, of side a. Alternatively, the radiating element can have another shape, for example that of a disk.

The edge of an equivalent radiating element is separated from the opposite edge of the neighboring equivalent radiating element by an interval e. Thus, the pitch between equivalent radiating elements along the rows or columns of the regular pattern is equal to the sum of a and e.

The method 100 continues by carrying out the following steps to correspond to each equivalent radiating element EEij, a real radiating element ERij constituting the network antenna to be manufactured.

In step 150, the center, CEij, of the current equivalent radiating element is projected, according to the reference direction V1, onto the support surface, in order to determine the location, on this support surface, of the point of implantation CRij of the corresponding real radiating element ERij.

Step 160 consists of defining an inclined plane Pij passing through the implantation point CRij of the real radiating element ERij. A priori, the inclination of the inclined plane Pij is quantified by two angles, for example evaluated from the main directions of the elementary support surface S1 in the vicinity of the implantation point CRij of the real radiating element ERij.

Step 170 consists of projecting, according to the reference direction V1, the exterior contour of the current equivalent radiating element EEij onto the inclined plane Pij to obtain the exterior contour of the corresponding real radiating element ERij.

Finally, step 180 consists of evaluating a difference in path dij between the implantation point CRij of the real radiating element ERij and the center CEij of the equivalent radiating element EEij of the reference plane PRef1.

The introduction of a “geometric” phase shift φij, proportional to the path difference dij, to the signals emitted or received by the real radiating element ERij, has the effect that the behavior of the array antenna, evaluated in the plane of reference PRef1, corresponds to that of the equivalent planar array antenna.

Optionally, an adjustment of the gain Gij of the real radiating element ERij is calculated so that the power it radiates, evaluated in the reference plane, corresponds to the power that the equivalent radiating element EEij would radiate. This gain makes it possible to take into account the difference in surface area between the real element and the equivalent element, but also the distortion of the radiation diagram in the event of a strong inclination of the inclined plane Pij of implantation of the real element ERij by relation to the reference plane.

Steps 150 to 180 are iterated for each equivalent radiating element EEij.

Finally in step 210 of phase 205, the real network antenna is produced in accordance with the dimensioning obtained at the end of phase 105.

Remarks and embodiment variants

When the support surface considered has strong curvatures, as is the case for the cabin of an aircraft, it must first be subdivided to define a plurality of elementary support surfaces. The process then applies to each elementary support surface successively. For example, as shown in Figures 2 and 3, when the support surface is a cone and the reference direction makes an angle of inclination with the axis of the cone, the maximum elementary support surface that can be considered is a half-cone resulting from the section of the cone by an axial plane, which includes the axis A and the vector product of the directions A and V.

The inclination of each inclined plane Pij can be chosen so that all the inclined planes are parallel to each other. For example, according to a first approach, each inclined plane is defined so as to be parallel to the reference plane as illustrated in Figures 2 and 3. It is then a question of compensating the curvatures of the support surface by mounting each real radiating element so that it is arranged parallel to the reference plane. In operation, we then introduce, for each radiating element, a geometric phase shift, which depends on the distance between the real radiating element considered and the reference plane. In this way, the signals evaluated in the reference plane are in phase for all the real radiating elements arranged on the support surface. From there, an electronic phase shift can be added to shift the array antenna beam away from the reference direction, so that it points in the shift direction D.

But, more generally, the inclination of an inclined plane is independent of that of the other inclined planes and only depends on the installation position on the support surface considered. For example, according to a second approach, each inclined plane is tangent to the support surface. The dimensions of each real radiating element and the differences between two neighboring real radiating elements are adapted during step 170 of projecting the contours of the equivalent radiating elements of the equivalent array antenna. In operation, a geometric phase shift is introduced which depends on the distance between the implantation point of the real radiating element and the center of the equivalent radiating element, so that the signals evaluated in the reference plane are in phase for all real radiating elements.

Advantageously, the gain Gij of the real radiating element ERij is adjusted so that the intensity of the radiation that it produces, evaluated in the reference plane, is equal to the intensity of the radiation of the equivalent radiating element EEij.

Advantageously, it is necessary to ensure that all the real radiating elements emit with an identical polarization relative to a trihedron associated with the reference plane. To do this, it is necessary to adjust the polarizations of each real radiating element according to their position and their orientation on the support surface.

Theoretically, a radiating element can be mounted on the support surface so as to be inclined by 90° relative to the reference plane. But, the radiation diagram would then be impacted by the angle of inclination of the real radiating element, especially since to this angle of inclination it is necessary to add the angle of depointing of the beam. In fact, the radiated surface decreases with the consequence of a loss of gain and a larger beam opening. The center frequency for which the antenna is calculated shifts upwards since the projections of the actual radiating elements and their spacings are smaller. This has the effect, in particular, of increasing the levels of the secondary and diffuse lobes. There is therefore a limit on the tilt angle to keep radiation patterns within acceptable use limits. For example, the angle of inclination must not lead to an angle relative to the reference plane greater than +/-60°.

Application example for a conical support surface

The process of will now be illustrated by an implementation on a conical surface with reference to Figures 2 and 3.

The process 100 begins with a phase 105 of sizing the antenna to be manufactured.

Step 110: the support surface S is here the surface of a conical-shaped radome. Such a radome is typically fitted to the nose of a fighter plane. A cone is a simple shape for which it is easier to explain the invention in detail, possibly by performing explicit calculations. A cone is characterized by zero curvature along a generator of the cone and a constant curvature in a plane transverse to the X axis.

On this surface, several elementary support surfaces are delimited. For example, four elementary support surfaces are delimited, each elementary support surface extending between axial planes P1 and P2. For reasons of symmetry of this embodiment, the planes P1 and P2 are at right angles.

In what follows, we consider the first elementary support surface S1.

Step 120: we define the reference direction V1 for the support surface S1. The reference direction must allow, by electronic phase shift, observation within an extended domain covering not only the front of the cone (i.e. in the direction of the axis A of the cone) , but also on the side of the cone.

Knowing that the depointing by electronic control of a beam is limited due to the degradations impacting the radiation pattern, this “electronic” depointing is arbitrarily limited to a maximum value , worth for example approximately +/-60°.

Thus, in the plane of Figure 2, if we still want to be able to observe along the axis A of the cone, the reference direction V1 must have an angle of inclination α less than or equal to with the axis A of the cone. α is for example chosen equal to 60°.

In the axial plane containing the reference direction V1, electronic depointing then allows observation in a range between 0 and 120° relative to the axis A of the cone.

In the plan of the , the reference direction V1 is taken according to the bisector of the angle between the planes P1 and P2 (β=45°).

The angle β being less than and considering the four reference directions V1, V2, V3 and V4 around the axis A, the antenna according to the invention allows observation in an extended domain between 0° and +120 over 360° around the axis A. This is to be compared to an antenna according to the state of the art (platter arranged perpendicular to axis A) which allows observation in a range between 0° and +60° over 360° around axis A .

Step 130: we define a reference plane PRef1 as the plane normal to the reference direction V1.

Step 140: the equivalent array antenna is composed of a plurality of equivalent radiating elements EEij. The equivalent array antenna is advantageously oriented in the reference plane so that the columns indexed by the index i of the pattern formed by the equivalent radiating elements are arranged parallel to the plane defined by the direction A and the direction V ( ) and that the lines, indexed by the index j, are arranged in a plane transverse to the direction A ( ).

The process continues by carrying out steps 150 to 180 for each equivalent radiating element EEij.

Step 150: we project, according to the reference direction V1, the center CEij of the equivalent radiating element EEij onto the support surface in order to determine the location of the implantation point CRij of the real radiating element ERij.

Step 160: we choose, in the present embodiment, to place each real radiating element ERij in an inclined plane Pij which is parallel to the reference plane whatever i and j.

Step 170: we project, according to the reference direction V1, the exterior shape of the equivalent radiating element EEij onto the inclined plane Pij to obtain the exterior shape of the corresponding real radiating element ERij. The projection here being orthogonal, there is no deformation of the contour of the radiating element.

Step 180: This step makes it possible to define the electrical path difference between each radiating element and the reference plane.

The path difference (or “geometric” phase shift ) for the real radiating element ERij is a function of the distance dij between the implantation point CRij of the real radiating element ERij and the center CEij of the equivalent radiating element EEij is evaluated.

The geometric phase shift to be introduced is then given by:

with λ the wavelength of the electromagnetic signal emitted or received.

The previous steps are repeated for another support surface delimited on the cone, for example the other half-cone.

In this embodiment, the real radiating elements being positioned in inclined planes parallel to the reference plane, there is no radiation power compensation to be calculated.

The method 100 continues with a phase 205 of manufacturing the antenna as such according to the dimensioning determined at the end of the implementation of the steps of phase 105. Each real radiating element ERij is therefore produced, in implanting it at the point CRij of the elementary support surface, and inclining it suitably relative to this support surface to obtain the antenna 100.

Second embodiment

There illustrates a second embodiment of an antenna 200 obtained by implementing the method according to the invention.

In an axial plane, this second embodiment is identical to the first embodiment shown on the , the real radiating elements ERij being arranged along inclined planes Pij parallel to each other and to the reference plane.

But, in a transverse plane, the real radiating elements ERij are now arranged along inclined planes Pij tangent to the support surface S, i.e. to the circle of radius R resulting from the intersection of the support surface with the transverse plane considered.

This second embodiment has the advantage of symmetry by rotation around the axis A, so that the reference direction V can be chosen, at a given instant of operation of the array antenna, in any which direction around axis A. Once the reference direction V has been chosen, the radiating elements to be activated are those located between the axial planes P1 and P2.

The implementation of the method according to the invention, however, leads to a strong geometric deformation between equivalent radiating elements on the reference plane and real radiating elements on the support surface.

This deformation cannot be compensated by an adjustment of the radiated power (or by an adjustment of the shape of the equivalent radiating elements and/or the pattern that they form), especially since the radiating elements located near the planes P1 and P2, which are strongly inclined relative to the reference plane, risk degrading the radiation pattern in the reference direction V. Under these conditions, the planes P1 and P2 are chosen so that they make an angle β relative to the reference plane. to the reference direction V less than or equal to . Thus, only the radiating elements located on the support surface between the planes P1 and P2 are activated for transmission (respectively reception) according to the associated reference direction V.

Benefits

Alternatively, instead of considering radiating elements of the radiating plane type, other technologies are possible such as a Vivaldi antenna, a dipole antenna, etc.

The method according to the invention applies to any support surface, whatever its curvatures. For a complex surface, we can use computer tools to define an optimal reference direction, simulate the geometry of the antenna, and calculate the geometric phase shifts to introduce and possibly the gain adjustments to obtain the desired behavior.

By antenna geometry, we mean the curvatures of the support surface at each point thereof, the chosen reference direction, and, for each radiating element, its installation point, the inclination of the radiating element in relation to the support surface and the shape of its contour.

In particular, the process can be iterated by modifying the parameter values (extension of the support surface, reference direction, pattern of the equivalent array antenna, or even inclination of the real radiating elements) to optimize the array antenna produced.

Preferably, the support surface is a cone, an ogive, or more generally any surface generated by the rotation of a curve around an axis.

Claims (8)

Method for producing (100) an electronically scanned array antenna comprising a plurality of real radiating elements (ERij), each real radiating element being mounted on a support surface (S), characterized in that, the support surface having a non-zero curvature and a real radiating element being positioned at an implantation point (CRij) of the support surface so as to rest in an inclined plane (Pij), said inclined plane being inclined relative to a locally tangent plane to the support surface at the point of implantation, the method comprises, in a dimensioning phase (105), the steps of:
- definition (120) of a reference direction (V1) around which the pointing direction (D) of the array antenna can be modified by electronic phase shift;
- definition (130) of a reference plane (PRef1) normal to the reference direction;
- definition (140) of an equivalent array antenna in the reference plane, the equivalent array antenna being a planar antenna comprising a plurality of equivalent radiating elements (EEij) forming a regular pattern in the reference plane;
- for each equivalent radiating element,
- projection (150) of a center (CEij) of the equivalent radiating element, according to the reference direction, on the support surface, so as to obtain an implantation point of a center (CRij) of a corresponding real radiating element;
- definition (160) of an inclined plane (Pij) at the installation point on the support surface;
- projection (170) of a contour of the equivalent radiating element, according to the reference direction, in the inclined plane, to obtain a contour of the corresponding real radiating element;
- evaluation (180) of a distance (dij) between the location point of the real radiating element and the center of the equivalent radiating element and calculation, as a function of said distance, of a geometric phase shift to be applied to the signals emitted or received by the real radiating element during operation of the array antenna,
and in that the method comprises, in a manufacturing phase (205), the steps of producing the array antenna in accordance with the results of the sizing phase. Production method (100) according to claim 1, in which the evaluation step (180) consists of determining a gain (Gij) of each real radiating element in order to adjust a radiation power, evaluated in the reference plane , that this real radiating element produces. Production method (100) according to claim 1 or claim 2, in which the evaluation step (180) consists of determining an adjustment of a polarization of each real radiating element as a function of its installation position and/ or its inclination on the support surface relative to the reference plane. Production method (100) according to any one of claims 1 to 3, in which the inclined plane is chosen parallel to the reference plane. Production method (100) according to any one of claims 1 to 4, in which the method begins with a step (110) of delimiting at least one elementary support surface on the support surface, the elementary support surface grouping the real radiating elements to be activated to allow the array antenna to observe a domain around the reference direction. Production method (100) according to any one of claims 1 to 5, in which the support surface is a cone, an ogive, or a surface generated by rotation of a curve around an axis. Computer program product comprising software instructions which, when executed by a computer, implement the steps of the sizing phase of the production process according to any one of the preceding claims. Network antenna resulting from the implementation of a production method in accordance with any one of the preceding claims.