System for determining radiation characteristics of an antenna

Abstract

A system (1) for determining radiation characteristics of an antenna comprises an azimuth positioner (50) comprising a device (52) for driving the rotation of an antenna (2) about a vertical axis of rotation (R), a measuring arm (10) comprising a free end (12) and a mounting end (11), a frame (20) on which the measuring arm is mounted and comprising means (21, 22) for driving the mounting end of the measuring arm in a plane (P1) tangential to a cylinder of revolution of which the axis is the vertical axis of rotation (R), and measuring probes (40) positioned on the free end of the arm, the measuring arm extending longitudinally towards the azimuth positioner in a horizontal direction perpendicular to the tangential plane, the means for driving the mounting end of the measuring arm driving all of the measuring probes in a measuring plane (P2) parallel to the tangential plane and extending at a distance from the vertical axis of rotation.

Description

DESCRIPTION TITLE: SYSTEM FOR DETERMINING THE RADIATION CHARACTERISTICS OF AN ANTENNA

[0001] This invention resulted from a contract entered into by the Ministry of Defence - which has certain rights to it. TECHNICAL FIELD OF THE INVENTION

[0002] The invention relates to the field of antenna characterization. In particular, the invention relates to a system for determining the radiation characteristics of an antenna. PREVIOUS STATE OF THE ART

[0003] Currently, commercially available solutions for determining the radiation characteristics of an antenna cover all or part of the UHF band (300-3000 MHz) and rely primarily on near-field spherical measurements. These measurements require complex mathematical processing to reconstruct virtual volumes around the antenna, such as parallelepiped Huygens boxes. A few methods have also been tested in the VHF band (30-300 MHz), but not down to 30 MHz. These tests have also highlighted the need for time windowing techniques or additional post-processing, particularly to abstract away the measurement environment, especially reflections from the metallic walls of the anechoic chambers used, as the absorbents covering them are only marginally effective in the lower part of the VHF band.

[0004] In a simple and common practice, determining the radioelectric characteristics of an antenna system usually involves characterizing the system in the far field. However, in the VHF frequency ranges, the infrastructure required for these measurements must be very large relative to the operating wavelengths. At the lower end of the VHF band, and for this type of measurement, the dimensions of anechoic chambers become prohibitive, and electromagnetic absorbers become either ineffective or... or of prohibitive dimensions as well. The more common outdoor bases, however, remain very imposing and the effects of reflections on the ground must be taken into account and / or compensated for so as not to significantly affect the measurements.

[0005] The other problem associated with far-field characterization in this frequency range lies in the fact that the immediate environment of the antennas under test (such as power cables, walls, supports, trees, etc.) often interacts strongly with them, and their measured characteristics can thus be significantly altered, even in operational situations. It is therefore necessary to characterize the antenna in the presence of its platform and in all possible deployment configurations, which can be very cumbersome, time-consuming, and sometimes impossible to implement in practice.

[0006] To mitigate some of these problems, one proposed solution involves characterizing the antennas not in the far field, but in the near field. This is then achieved using known near-field to far-field transformation techniques to recover radiation characteristics at long distances and according to the various scenarios considered. While this can significantly reduce the size of the measurement infrastructure, this solution also presents technical difficulties, requiring complex mathematical processing and post-processing that can compromise the accuracy of the measurements. Indoors, the issue of reflections off the walls of anechoic chambers remains an additional obstacle and also necessitates the implementation of time-windowing techniques to filter and "smooth out" the response of the measurement environment.

[0007] The preceding points are more fully documented in the following publication: V. Rodriguez, “Basic Rules for Indoor Anechoic Chamber Design [Measurements Corner],” in IEEE Antennas and Propagation Magazine, vol. 58, no. 6, pp. 82-93, Dec. 2016 DESCRIPTION OF THE INVENTION

[0008] One aim of the invention is to provide a system for determining the radiation characteristics of a simple antenna to implement and which partially addresses the disadvantages previously mentioned.

[0009] To this end, the invention provides a system for determining the radiation characteristics of an antenna, the system comprising an azimuthal positioner including a device for rotating an antenna around a vertical axis of rotation, a measuring arm having a free end and a mounting end, a frame on which the measuring arm is mounted and including means for driving the mounting end of the measuring arm in a plane tangential to a cylinder of revolution with axis, the vertical axis of rotation, and measuring probes positioned on the free end of the arm, in which the measuring arm extends longitudinally towards the azimuthal positioner in a horizontal direction perpendicular to the tangential plane,the means for driving the mounting end of the measuring arm, which drives the measuring probes in a measuring plane parallel to the tangential plane and extending at a distance from the vertical axis of rotation.

[0010] Advantageously, but optionally, the system according to the invention has at least one of the following technical characteristics: - the arm is made of dielectric material; - the means for driving the mounting end of the measuring arm include a first vertical sliding link between the measuring arm and the frame in which the mounting end of the measuring arm is slidably driven; - the means for driving the mounting end of the measuring arm include a second horizontal sliding joint, perpendicular to the first vertical sliding joint, between the frame and the first sliding joint; - the system comprising a base, the drive means for the mounting end of the measuring arm include a second sliding link horizontal, perpendicular to the first vertical sliding connection, between the frame and the base; - the system further includes means for moving the measuring probes along the horizontal direction perpendicular to the tangential plane; - the measurement probes are electro-optical probes; - the system also includes a set of optical / radio frequency converters positioned on the frame and connected to the probes by optical fiber links; - the azimuthal positioner includes a metal plate arranged so as to be positioned under the antenna to be measured; - that the system includes another measuring arm having a free end comprising means for measuring an electromagnetic field arranged so as to allow measurements according to hemispherical field sections; - the measuring probes include at least one electrical measuring probe and one magnetic measuring probe, the electrical measuring probe being configured to measure electrical components of an electromagnetic field, and the magnetic measuring probe being configured to measure magnetic components of an electromagnetic field. - the measuring probes include at least two electrical measuring probes and / or two magnetic measuring probes; - the system includes a vector network analyzer configured to acquire data from measurement probes; - the system is arranged to measure electromagnetic field components in the measurement plane by scanning along adjacent parallel lines spaced at a predetermined acquisition step Ad; and, - the acquisition step Ad is less than Àmin / 2 with Àmin a wavelength associated with a maximum frequency recorded during measurements. BRIEF DESCRIPTION OF THE FIGURES

[0011] Other features and advantages of the invention will become apparent from the following description of an embodiment of the invention. See the attached drawings: [Fig.1] is a schematic side view of a system for determining the radiation characteristics of an antenna according to the invention; [Fig.2] is a schematic top view of the system for determining the radiation characteristics of an antenna according to the invention of figure 1; [Fig. 3] is a schematic view of an acquisition circuit for the system for determining the radiation characteristics of an antenna according to the invention of Figures 1 and 2; and [Fig. 4] is a three-dimensional schematic view of a principle of acquisition by the system for determining the radiation characteristics of an antenna according to the invention of Figures 1 and 2; and, [Fig. 5] is a three-dimensional view of a virtual Huygens box acquired by the system for determining the radiation characteristics of an antenna according to the invention of Figures 1 and 2; and, [Fig.6] is a schematic top view of an alternative embodiment of a system for determining the radiation characteristics of an antenna according to the invention.

[0012] For clarity, identical or similar elements are identified by identical reference symbols across all figures. DETAILED DESCRIPTION OF A METHOD OF IMPLEMENTATION

[0013] The system for determining the radiation characteristics of an antenna according to the invention, which will be described in more detail below, will allow the characterization of an antenna or antenna system under test by using electro-optical probes at a very close distance from the antenna under test and by recovering tangential components of an electromagnetic field radiated by said antenna under test onto faces of a parallelepiped containing it, one lower face of which is completely closed by a metallic surface. The virtual parallelepiped surface thus formed delimits a volume of a virtual pad around the antenna under test, which is also called a "Huygens box".

[0014] Thus, the system for determining the radiation characteristics of an antenna according to the invention will allow the implementation of a method, the least invasive possible, in which electro-optical probes will be used. powered by optical fiber to collect information useful for reconstructing far-field radiation characteristics.

[0015] The operating principle of the Huygens box is based on the equivalence theorem, which demonstrates that any structure generating electromagnetic fields can be advantageously replaced by electric current densities J sand magnetic Ms on a closed surface surrounding said structure. These current densities are then directly deduced from the tangential components of the electric field Ê and magnetic field H since they are defined as the cross product of said fields by the external normal n to the closed surface considered:

[0016] s = n AH

[0017] ~M s = - n A Ê

[0018] Since the cross product of two collinear vectors is by definition zero, only the tangential components of the magnetic and electric fields are needed to evaluate the electromagnetic field at any point in space outside the closed surface under consideration.

[0019] A crucial condition for ensuring accurate prediction of electromagnetic fields outside the Huygens box is that the environment surrounding the measurement is completely unobstructed and that the measuring equipment does not interact with the components being measured. Failure to meet these conditions can lead to significant errors in both near-field and far-field predictions.

[0020] To meet this requirement, the metallic elements of the electro-optical probes used must be of negligible dimensions compared to the wavelengths of the signals to be measured, and optical fiber links should be preferred to avoid the presence of coaxial cables.

[0021] By default, and in the absence of specific information regarding the radiation of the antenna under test, the characterization must be performed on all of the magnetic and electrical components of all open faces of the Huygens box thus constituted (i.e. excluding the bottom face here).

[0022] An example of measurements taken on the faces of a Huygens box is shown, for illustrative purposes only, in figure 5.

[0023] With reference to Figures 1 to 3, we will describe an embodiment of a system for determining the radiation characteristics of an antenna 1 that will allow the measurement of all the tangential components of a virtual Huygens box 3 surrounding an antenna 2 or any antenna system placed on a metallic ground plane 51 and operating in all or part of the [30-400 MHz] band, without any intervention on the antenna 2 under test. Other test frequency bands can be used with the system for determining the radiation characteristics of an antenna 1 according to the invention; the [30-400 MHz] band is used here purely for illustrative purposes.

[0024] The system for determining the radiation characteristics of an antenna 1 according to the invention comprises a central buried azimuthal positioner 50 with a metal plate 51, forming a bearing platform, flush with the ground surface S. The azimuthal positioner 50 allows a complete 360° rotation around a vertical axis of rotation R by means of a rotation drive device 52. The rotation drive device 52 is positioned under the metal plate 51. The metal plate 51 is solid. The metal plate 51 is arranged to support the antenna 2 under test. Thus the metal plate 51 is arranged so as to be positioned under the antenna 2 under test. In addition, experimental tests have made it possible to highlight limitations regarding the electrical dimensions of the metal plate 51 which "closes" a lower face 36 of the Huygens box 3 containing the antenna 2 under test.To ensure that the shapes of the radiation patterns are preserved at low frequencies, the largest dimension of the metal plate 51 is preferably greater than or equal to one-tenth of the wavelength associated with the lowest acquisition frequency. At 30 MHz, this metal plate 51 can be a disk with a diameter greater than or equal to 1 m or a square centered on diagonals greater than or equal to 1 m. In one variant. During construction, the metal plate 51 is wholly or partially perforated. A mesh of perforations is then arranged to be sufficiently fine with respect to the wavelengths used to characterize the antenna 2 under test. For example, the mesh size is less than Åmin / 25, where Åmin is associated with the smallest wavelength in the characterized frequency range.

[0025] A radio feed line 25 connects the antenna 2 under test to a radio measurement bench 6, which is installed in an operating room for the system for determining the radiation characteristics of an antenna 1 according to the invention. This radio feed line 25 is underground so as to minimize any potential interference in the measurements performed by the system for determining the radiation characteristics of an antenna 1 according to the invention on the antenna 2 under test. The radio feed line 25 is, in this instance, integral with the metal plate 51. Alternatively, the radio feed line 25 passes through a thickness of the metal plate 51.

[0026] According to one embodiment, the radio feed line 25 is replaced by an optical fiber and an optical / radio frequency converter at one end and connected to the antenna 2 under test.

[0027] The system for determining the radiation characteristics of an antenna 1 comprises a measuring arm 10 including a mounting end 11 and a free end 12. The measuring arm 10 is mounted on the frame 20 by means of a first sliding joint 21 in which the mounting end 11 of the measuring arm 10 slides relative to the frame 20. The first sliding joint 21 is vertical and extends along one of the Z axes of the orthonormal XYZ coordinate system. The measuring arm 10 is made of a dielectric material to avoid interfering with the measurement of electromagnetic fields emitted by the antenna 2 under test.The composition, shape and structure of the dielectric measuring arm 10 are chosen according to the conditions and environment of the measurements carried out, in particular to reduce not only the possible influence of said measuring arm 10 on radiation from the antenna 2 under test, but also to minimize as much as possible any sags and dampings under. Vertical stress (mass of elements fixed at the free end 12) as well as horizontal stress (wind force) are considered. For example, once the measuring arm is fitted with elements fixed at the free end 12, the measuring arm 10 is arranged so that the vertical deflection remains less than 2 mm and the horizontal deflection less than 4 mm, with very short damping times to eliminate vibration problems, even for winds up to 30 km / h. This arrangement improves the accuracy of the radiation characteristics of the antenna under test 2.

[0028] Furthermore, the system for determining the radiation characteristics of an antenna 1 also includes a frame 20 positioned at a distance from the azimuthal positioner 50. The frame 20 is placed on the ground S via a base 22 of the system for determining the radiation characteristics of an antenna 1. According to one embodiment, the system for determining the radiation characteristics of an antenna 1 includes a second sliding link 22 connecting the frame 20 and the base 30, in which the frame 20 slides relative to the base 30. The second sliding link 22 is horizontal and extends along an X-axis of an orthonormal XYZ coordinate system as illustrated in Figures 1 and 2.

[0029] The system for determining the radiation characteristics of an antenna 1 thus includes drive means 21, 22 for the mounting end 11 of the measuring arm 10 in a plane P1 extending along the X and Z axes of the orthonormal coordinate system XYZ. Here, plane P1 is tangential to a cylinder of revolution C whose axis is the vertical axis of rotation R of the azimuthal positioner 50. The cylinder of revolution C has radius Rc, corresponding to the shortest distance between the vertical axis of rotation R and plane P1. The drive means 21, 22 are preferably motorized to automate or control the movements of the measuring arm 10.

[0030] On the other hand, the system for determining the radiation characteristics of an antenna 1 comprises a set of measuring probes 40 mounted on the free end 12 of the measuring arm 10. The set of measuring probes 40 includes an electric field measuring probe and a magnetic field measuring probe. For this purpose, the free end 12 of the measuring arm It includes a support, also made of dielectric material, for attaching the set of measuring probes 40 for magnetic and electric fields. This support, manually adjustable in depth, allows for fine adjustment of the distance between the measuring probes 40 and the surface to be scanned within a virtual volume 3 surrounding the antenna 2 under test.

[0031] According to an embodiment not shown, the set of measuring probes 40 comprises two electric field measuring probes. Such an arrangement optimizes acquisition time when certain characteristics of the antenna under consideration are known.

[0032] According to an embodiment not shown, the set of measuring probes 40 comprises two magnetic field measuring probes. Such an arrangement optimizes acquisition time when certain characteristics of the antenna under consideration are known.

[0033] Although this has a significant impact on the computational load, a set of 40 measuring probes, comprising two electrical and two magnetic probes, allows for the rapid and highly accurate determination of an antenna's radiation characteristics. In this configuration, the system includes a vector network analyzer designed to receive data from the 40 measuring probes. These probes are connected to the vector network analyzer, which measures transmission parameters between the antenna under test and each probe in the set. The vector network analyzer then acquires the various measurements from the probes. This arrangement enables a simultaneous and consistent analysis of the electrical and magnetic characteristics of the electromagnetic field emitted by the antenna.

[0034] In an alternative embodiment, the drive means 21, 22 further comprise means 121 for moving all the electro-optical measuring probes 40 in the horizontal direction perpendicular to plane P1, that is, in a direction parallel to the Y-axis of the orthonormal coordinate system XYZ. For example, the measuring probes 40 are mounted on the free end 12 of the measuring arm 10 via a third sliding link perpendicular to the first 21 and second 22 sliding links of the drive means of the system for determining the radiation characteristics of an antenna 1. In another variant, this third sliding link is provided between the measuring arm 10 and the frame 20, or between the frame 20 and the base 30.

[0035] The measuring probes 40 are connected via optical fibers 45 to remote optical fiber / radio frequency converters 4. There is one optical fiber / radio frequency converter 4 per measuring probe 40. The optical fiber / radio frequency converters 4 are, for example, positioned in the vicinity of the frame 20, such as, here, behind the frame 20, for example on a suitable support for said frame 20 or even in a dedicated remote room.

[0036] The 40 measurement probes should preferably meet a dual requirement: have an active tip occupying only a surface area of ​​a few mm 2 and the control logic part (a few tens of mm 2The measuring probe is positioned at the rear of the probe, for example, approximately 30 cm from the point to be measured. This prevents the measurement from being distorted by coupling and interaction between the measuring probes 40 and the antenna 2 under test. For example, the measuring probes 40 are two TDS-type probes (E and H) manufactured by SPEAG. Once mounted on the support at the free end 12 of the measuring arm 10, the measuring probes 40 are positioned so that their active ends are in close proximity to each other, separated by approximately less than 1 mm. Thus, the measuring probes 40 are said to be co-located, or considered to be located at the same measurement point of the virtual surface. This co-location of the measuring probes 40 is made possible by the intrinsic immunity of the electrical (E) and magnetic (H) measuring probes to each other.In addition, each active end of the measuring probes 40 is positioned according to two orientations of its active end at 90° to each other: one orientation to measure a component of the field associated with the measuring probe 40 considered and one orientation to measure a component orthogonal to the previous one of said associated field, the two components being in a plane perpendicular to a longitudinal or principal axis of the measuring probe 40 considered.

[0037] Once mounted on the frame 20, the measuring arm 10 extends longitudinally towards the azimuthal positioner 50 in a horizontal direction, here parallel to an axis Y of the orthonormal coordinate system XYZ and perpendicular to the tangential plane P1. The drive means 21, 22 of the mounting end 11 of the measuring arm 10 consequently drive the set of measuring probes 40 in a measuring plane P2 parallel to the tangential plane P1 and extending to an acquisition distance DM from the vertical axis of rotation R of the azimuthal positioner 50.

[0038] We will now describe the operation of the system for determining the radiation characteristics of an antenna 1.

[0039] The system for determining the radiation characteristics of an antenna 1 will allow for near-field measurements, controlling the measurement probes 40 according to planar scans applied to each of the lateral faces 31, 32, 33, 34, as well as to a top face 35 of a virtual rectangular parallelepiped, or cuboid, 3 called a "Huygens box" around the antenna 2 under test. This approach, by directly measuring the faces of the Huygens box 3, avoids complex mathematical processing that could introduce additional uncertainties in the measurements. The principle of the planar scan on a lateral face 31 of the virtual Huygens box 3 is illustrated in Figure 4.

[0040] The aforementioned planar scan is carried out according to a protocol described below, allowing recovery of a magnetic tangential component and an electrical tangential component at each pass over each of the lateral faces 31, 32, 33, 34 as well as the upper face 35 of the virtual Huygens box 3 surrounding the antenna 2 under test.

[0041] For the lateral faces, the entire face is scanned, for example, by successively scanning the X-axis for each height value of the Z-axis. Each face is scanned twice to allow the acquisition of all four components. Between these two scans, the probes are rotated manually, or automatically, by a quarter turn.

[0042] The four lateral faces 31, 32, 33, 34 to be measured are successively presented in front of the dielectric arm 10 thanks to the rotational movement of the Azimuth positioner 50 (positions 0°, 90°, 180° and 270°). Thus, the lateral faces 31, 32, 33, 34 are successively positioned in the measurement plane P2 in which the active ends of the measuring probes 40 will move.

[0043] For each of the lateral faces 31, 32, 33, 34 to be measured, the system for determining the radiation characteristics of an antenna 1 is driven so as to perform a displacement D applied to the active end of the probes along horizontal scanning bands 310 extending from a left lateral edge of the lateral face 31, 32, 33, 34 under consideration to a right lateral edge of said lateral face 31, 32, 33, 34 under consideration, as illustrated in Figure 4. In practice, the displacement D is alternating: a scanning band 310 is swept from right to left, then the next adjacent scanning band 310 is swept from left to right, and vice versa. Two adjacent scanning bands 310 are separated by a predetermined distance Ad, also called the "acquisition step".

[0044] To avoid aliasing artifacts during acquisitions, the acquisition step size Ad must always be less than Åmin / 2, where Åmin is the wavelength associated with the maximum frequency recorded during the acquisitions. Furthermore, in the case of acquisitions at very close range to the antenna (i.e., in a reactive field zone), this acquisition step size Ad is also correlated to the acquisition distance DM of the set of measuring probes 40 relative to the antenna 2 under test, according to the following formula:

[0045]

[0046] For example, for an acquisition distance of 10 cm, the spatial step should therefore be around 5 cm in all frequencies of the VHF range.

[0047] For planar scans of the lateral faces 31, 32, 33, 34, the measuring probes 40, E and H are positioned parallel to each other or with a very small angle, less than 5°, due to their size so that their active ends are close to each other to be considered colocalized as explained previously.

[0048] In the first series of passes, the active tips of the measuring probes 40 are oriented horizontally for probe E (acquisition of the horizontal components of the electric field) and vertically for probe H (acquisition of the vertical components of the magnetic field). Alternatively, both measuring probes 40 are oriented horizontally, both vertically, or vertically for probe E and horizontally for probe H.

[0049] Therefore, for each of the lateral faces 31, 32, 33, 34 of the virtual Huygens box 3, the system for determining the radiation characteristics of an antenna 1 performs sweeps from top to bottom and alternately from left to right and right to left with an acquisition step Ad. Alternatively, it is possible to perform the sweeps in different ways: from bottom to top, only from left to right, or only from right to left. It is also possible to perform the sweeps from left to right or right to left and alternately from top to bottom and bottom to top, or simply from top to bottom or bottom to top.

[0050] Once the four lateral faces 31, 32, 33, 34 have been scanned in the first series of passes, a second series of passes is performed. In this second series of passes, the active ends of the measuring probes 40 are oriented at 90° to their orientation for the first series of passes: for example, vertically for probe E (acquisition of the vertical components of the electric field) and horizontally for probe H (acquisition of the horizontal components of the magnetic field).

[0051] Therefore, for each of the lateral faces 31, 32, 33, 34 of the virtual Huygens box 3, the system for determining the radiation characteristics of an antenna 1 performs the sweeps in the same way as during the first series of passes previously described.

[0052] Regarding the upper face 35 of the virtual Huygens box 3, the measuring probes 40 are positioned at 90° to each other, with their active ends close together, so that they are always co-located. Again, the system for determining the radiation characteristics of a Antenna 1 will perform two series of passes over the upper face 35. The orientation of the active ends of the measuring probes 40 is then chosen so as to allow a measurement of the components of the electromagnetic fields which are in a plane of the upper face 35, therefore along the X and Y axes.

[0053] During the first series of passes, the active ends of the measuring probes 40 are oriented horizontally, in the direction of the scan for the active end of probe E (acquisition of the horizontal components of the electric field oriented in the direction of the scan) and perpendicular to the direction of the scan for the active end of probe H (acquisition of the horizontal components of the magnetic field oriented perpendicular to the scan).

[0054] Therefore, the system for determining the radiation characteristics of an antenna 1 performs scans on the upper face 35 in a manner similar to that described for the lateral faces 31-34: for example, alternately from right to left and from left to right according to the acquisition step Ad, and from front to back across the entire upper face 35. Alternatively, the scan is performed on a first half of the upper face 35, i.e., up to or from the vertical axis of rotation R, then the antenna 2 under test is rotated 180° by the azimuthal positioner 50, and a second half of the upper face 35 is scanned in a similar manner. As before, other scans are possible: alternately from front to back at the acquisition step and from left to right or right to left, or even in only one direction of the alternating sweep.

[0055] During the second series of passes, the measuring probes 40 are rotated 90° in the plane of the upper face 35 and their active end retains its previous orientation: horizontally, but perpendicular to the direction of the scan for the active end of probe E (acquisition of the horizontal components of the electric field oriented perpendicular to the direction of the scan) and in the direction of the scan for the active end of probe H (acquisition of the horizontal components of the magnetic field oriented in the direction of the scan).

[0056] Therefore, the system for determining the radiation characteristics of an antenna 1 performs the scans on the upper face 35 in a similar way.

[0057] As an alternative embodiment, the positioning and orientation of the measuring probes 40 can be automated and motorized. It is therefore important to use motors that do not disturb the measured electromagnetic field of the antenna 2 under test: for example, the actuating parts are made of a dielectric material and a hydraulic or pneumatic circuit is provided to operate them, for example, so as to relocate the motor itself at least to the frame 20.

[0058] It should be noted that the system for determining the radiation characteristics of an antenna 1 was described using 40 measurement probes from SPEAG. However, the principle of measurement using an electro-optical probe is possible with any other electro-optical sensor powered solely by optical fiber. This therefore includes: active probes operating on the principle of miniaturized active transducers, powered by photovoltaic converters whose collected signal modulates a VCSEL (Vertical-Cavity Surface-Emitting Laser) (the principle of the SPEAG probes); devices based on the Pockels effect, by measuring the phase shift experienced by a light beam passing through a miniature crystal according to the intensity of the electric field in which it is immersed; or even a combination of the two previous technologies.

[0059] During the various scans mentioned above, complex data collected by each of the two electro-optical measuring probes 40 are transmitted via two optical fiber links 45 to two optical / radio frequency converters 4. These converters are connected to a vector network analyzer 61, which is itself connected to the antenna 2 under test via the buried radio feed line 25, which emerges at the azimuthal positioner 50. The radio feed line 25 is preferably coaxial. If necessary, a power amplifier can also be inserted between the vector network analyzer 61 and The antenna 2 under test. The vector network analyzer 61 transmits, via a port, to the antenna 2 under test and receives a signal emitted by the antenna 2 under test via the measurement probes 4 and the optical / radio frequency converters 4 on two additional ports (for the simultaneous acquisition of two components (1E and 1H or 2E or 2H) depending on the configuration of the measurement probes 40). The vector network analyzer 61 is part of the radio frequency measurement bench 6 which is installed in the operating room of the system for determining the radiation characteristics of an antenna 1. The radio frequency measurement bench 6 also includes a computer 62 and a control bench 63 for the system for determining the radiation characteristics of an antenna 1. Acquisition software allows the control of the mechanical axes and the radio frequency devices, enabling the automated recording of a measurement sequence.

[0060] In order to fully exploit the data thus recovered, it is necessary to carry out two additional operations: a phase calibration of the two electro-optical measuring probes 40 and their associated coaxial cabling between the associated optical / radio frequency converter 4 and the vector network analyzer 61; an amplitude calibration of the system for determining the radiation characteristics of an antenna 1 (also including the insertion losses of the coaxial cabling).

[0061] Since the phase responses of the two 40 electro-optical measuring probes (magnetic and electric) are uncorrelated (but constant over time) and vary in frequency, it is essential to correct the unwanted phase shift observed at each measurement point. To achieve this, it is necessary to use a perfectly controlled configuration in which the phase relationship between the electric and magnetic components is precisely known. The simplest configuration to obtain generally involves far-field conditions under which the principal electric and magnetic components will be perfectly in phase. This configuration can be obtained in free space or in measurement cells adapted to this problem (transverse electromagnetic or TEM cell, parallel-plate cells, etc.).

[0062] Amplitude calibration of the system for determining the radiation characteristics of an antenna 1 is also essential for calculating the power radiated by the virtual Huygens box 3, which subsequently allows for accurate estimation of the gains achieved (for example, in electromagnetic simulation). To do this, it is first necessary to know precisely the power injected at an input connector of the antenna 2 under test. This characterization can be performed with a spectrum analyzer or a calibrated power probe, with power emission preferably carried out using a radio frequency generator, for example, of 50 Ω. Since the acquisition of the face components is performed in transmission via the vector network analyzer 61, radiated power information is not directly usable.To circumvent this problem, the proposed solution consists of characterizing, at a specific point on the previously measured virtual Huygens box 3, the power received on each electrical and magnetic measuring probe 40 in position. Knowing the antenna factors of each probe beforehand (generally provided by the manufacturer), it is therefore possible to determine the amplitude information of the electrical and magnetic components measured at this point for the characterized injected power. It is then also possible to normalize all the measured data to correspond to a reference transmission power.

[0063] Once all measurements have been carried out and calibrated according to the principles described above, it is then possible to convert these data into files compatible with the IEC / TR 61967 "Near-field scan data exchange" standard, for example, thus maximizing compatibility with commercial electromagnetic simulation software.

[0064] In Figure 6, we will describe an alternative embodiment of a system for determining the radiation characteristics of an antenna 100. This system differs from the embodiment of the system for determining the radiation characteristics of an antenna 1 described previously in that, instead of the measuring arm 10, it includes a second measuring arm 60 mounted at one end to rotate around the Y-axis with the frame 20. A pivot joint A motorized joint 25, optionally, is provided for this purpose. Here, the pivot joint 25 is mounted on the first sliding joint 21. The second measuring arm 60 comprises a beam 62 fixed to the pivot joint 25 at the first end of the second measuring arm 60 and a rod 63 slidably mounted in the beam 60 such that a second end of said second measuring arm 60 is located opposite and away from the vertical axis of rotation R of the azimuthal positioner 50. The second end of the second measuring arm 60 comprises measuring means 61 for an electromagnetic field arranged to allow measurements along hemispherical field cross-sections, the cross-sections lying in a plane parallel to plane P1 and passing through the vertical axis of rotation R. As with the measuring arm 10, the second measuring arm 60 is made of a dielectric material.

[0065] The system for determining the radiation characteristics of an antenna 100 allows for the taking of azimuthal and vertical diagrams of the antenna 2 under test (always placed at the center of the central azimuthal positioner) in near field or far field conditions, in the chosen band of [30 - 400 MHz]. The system for determining the radiation characteristics of an antenna 100 allows for the description of vertical sections passing through the vertical axis of rotation R of the azimuthal positioner 50.

[0066] It follows from the above that the use of the system for determining the radiation characteristics of an antenna 1 makes it possible, in particular, to: fully describe the lateral and upper surfaces of the virtual parallelepiped of the virtual Huygens box 3; identify all the useful electromagnetic components of the electromagnetic field emitted by the antenna 2 under test; and ensure the absence of modification and interference on the radiation of the antenna 2 under test (environment near the antenna under test devoid of metallic parts, fiber optic probe connection minimizing electromagnetic disturbances near the antenna 2 under test). The first above-ground metallic part is located approximately 5.10 m from the faces of a virtual Huygens box 3 with sides of 1 meter, for example.

[0067] On the other hand, if the system for determining the radiation characteristics of an antenna 1,100 has been described with regard to a virtual surface in the form of a Huygens box 3, the system for determining the radiation characteristics of an antenna 1,100 can be controlled to carry out measurements on the surface of any elongated virtual volume with axis the vertical rotation axis R having a regular or non-regular polygonal section, or even a cylindrical virtual volume of revolution with axis, the vertical rotation axis R.

[0068] Naturally, the invention is described above by way of example. It is understood that the person skilled in the art is able to carry out different variants of the invention without going out of the scope of the invention.

[0069] It is emphasized that all features, as they are apparent to a person skilled in the art from this description, the drawings and the attached claims, even if in practice they have only been described in relation to other specific features, both individually and in any combinations, may be combined with other features or groups of features disclosed herein, provided that this has not been expressly excluded or that technical circumstances render such combinations impossible or meaningless.

Claims

DEMANDS 1. System (1) for determining the radiation characteristics of an antenna, the system comprising an azimuthal positioner (50) including a device for rotating an antenna (2) about a vertical axis of rotation (R), a measuring arm (10) having a free end (12) and a mounting end (11), a frame (20), on which the measuring arm is mounted and including means for driving the mounting end of the measuring arm in a tangential plane (P1) to a cylinder of revolution (C) with axis, the vertical axis of rotation (R), and measuring probes (40) positioned on the free end of the arm, in which the measuring arm extends longitudinally towards the azimuthal positioner in a horizontal direction perpendicular to the tangential plane,the drive means for the mounting end of the measuring arm, driving the measuring probes in a measuring plane (P2) parallel to the tangential plane and extending at a distance from the vertical axis of rotation (R).

2. System according to claim 1, wherein the arm is made of dielectric material.

3. System according to any one of claims 1 to 2, wherein the means for driving the mounting end of the measuring arm comprise a first vertical sliding link (21) between the measuring arm and the frame in which the mounting end of the measuring arm is slidably driven.

4. System according to claim 3, wherein the drive means of the mounting end of the measuring arm comprise a second horizontal sliding linkage, perpendicular to the first vertical sliding linkage, between the frame and the first sliding linkage.

5. System according to claim 3, wherein the system comprising a base, the drive means for the mounting end of the measuring arm comprise a second horizontal sliding link (22), perpendicular to the first vertical sliding joint, between the frame and the base.

6. System according to any one of claims 1 to 5, wherein the system further comprises means for moving (121) the measuring probes (40) in the horizontal direction perpendicular to the tangential plane.

7. System according to any one of claims 1 to 6, wherein the measuring probes (40) are electro-optical probes.

8. System according to claim 7, wherein the system further comprises a set of optical / radio frequency converters (4) connected to the measuring probes (40) by optical fiber links.

9. System according to any one of claims 1 to 6, wherein the azimuthal positioner comprises a metal plate (51) arranged so as to be positioned under the antenna to be measured.

10. System according to any one of claims 1 to 9, wherein the system comprises another measuring arm (60) having a free end comprising means for measuring (61) an electromagnetic field arranged to allow measurements according to hemispherical field sections.

11. System according to any one of claims 1 to 10, wherein the measuring probes (40) comprise at least one electrical measuring probe and one magnetic measuring probe, the electrical measuring probe being configured to measure electrical components of an electromagnetic field, and the magnetic measuring probe being configured to measure magnetic components of an electromagnetic field.

12. System according to any one of claims 1 to 11, wherein the measuring probes (40) comprise at least two electrical measuring probes and / or two magnetic measuring probes.

13. A system according to any one of claims 1 to 10, wherein the system is arranged to measure electromagnetic field components in the measurement plane according to a following scan adjacent parallel lines spaced at a predetermined acquisition step Ad.

14. System according to claim 11, wherein the acquisition step Ad is less than Amin / 2 with Amin a wavelength associated with a maximum frequency recorded during measurements.

15. System according to any one of claims 1 to 12, wherein the system comprises a vector network analyzer configured to acquire data from the measuring probes (40).

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