System for determining the radiation characteristics of an antenna

Abstract

A system (1) for determining the radiation characteristics of an antenna includes an azimuthal positioner (50) comprising 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 comprising means for driving the mounting end of the measuring arm in a tangential plane (P1) to a cylinder of revolution with axis, 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 azimuthal positioner in a horizontal direction perpendicular to the tangential plane,the drive means of the mounting end of the measuring arm driving the entire set of measuring probes in a measuring plane (P2) parallel to the tangential plane and extending at a distance from the vertical axis of rotation. Figure for the abbreviation: [Fig.1] ,

Description

Title of the invention: System for determining the radiation characteristics of an antenna. Technical field of the invention

[0001] 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. Prior art

[0002] Currently, commercially available solutions for determining the radiation characteristics of an antenna cover all or part of the UHF band (300-3000 MHz) and are essentially based on spherical measurements in the near field, requiring complex mathematical processing to reconstruct virtual volumes around the antenna, such as parallelepiped-shaped Huygens boxes. A few methods have also been tested in the VHF band (30-300 MHz), but without going down to 30 MHz. These tests have also highlighted the need to implement time windowing techniques or additional post-processing, particularly to abstract from the measurement environment, and especially from reflections from the metallic walls of the anechoic chambers used, as the absorbers covering them are very weakly effective in the lower part of the VHF band.

[0003] In a simple and common practice, determining the radioelectric characteristics of an antenna system usually involves characterizing said 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 prohibitively large. Outdoor bases, which are more common, are still very large, and the effects of reflections from the ground must be taken into account and / or compensated for to avoid significantly affecting the measurements.

[0004] The other problem related to far-field characterization in this frequency range lies in the fact that, very often, the environment near the antennas under test (such as power cables, walls, supports, trees, etc.) 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 carrier and in all the envisaged implementation configurations, which can prove to be very cumbersome, time-consuming and sometimes impossible to implement in practice.

[0005] To mitigate some of these problems, one proposed solution involves characterizing the antennas not in the far field, but in the near field, then using known near-field to far-field transformation techniques to recover the radiation characteristics at long distances and according to the various scenarios considered. While the dimensions of the measurement infrastructure can be significantly reduced, this solution also presents technical difficulties, requiring complex mathematical processing and post-processing that can compromise the accuracy of the measurements. Indoors, the problem of reflections on 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.

[0006] The preceding elements 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

[0007] An object 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.

[0008] To this end, according to the invention, a system for determining the radiation characteristics of an antenna is provided, 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 drive means for 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.

[0009] 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 horizontal sliding link, perpendicular to the first vertical sliding link, 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 fiber optic links; the azimuthal positioner includes a metal plate arranged so as to be positioned under the antenna to be measured; which 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 measurement probes include at least one electrical measurement probe and one magnetic measurement probe, the electrical measurement probe being configured to measure electrical components of an electromagnetic field, and the magnetic measurement 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 Xmin / 2, where Xmin is a wavelength associated with a maximum frequency recorded during measurements. Brief description of the figures

[0010] Other features and advantages of the invention will become apparent from the following description of an embodiment of the invention. See the accompanying drawings:

[0011] [Fig-1] is a schematic side view of a system for determining the radiation characteristics of an antenna according to the invention;

[0012] [Fig.2] is a schematic top view of the system for determining the radiation characteristics of an antenna according to the invention of [Fig.1];

[0013] [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

[0014] [Fig. 4] is a three-dimensional schematic view of an acquisition principle by the system for determining the radiation characteristics of an antenna according to the invention of Figures 1 and 2; and,

[0015] [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,

[0016] [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.

[0017] For clarity, identical or similar elements are identified by identical reference signs throughout the figures. DETAILED description of a method of implementation

[0018] The system for determining the radiation characteristics of an antenna according to the invention, which will be described in more detail below, will make it possible to characterize an antenna or an 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 on 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".

[0019] 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 powered by optical fiber will be used to collect information useful for a reconstruction of the radiation characteristics in the far field.

[0020] 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 Js and magnetic current densities Ms on a closed surface surrounding said structure. These current densities are then directly deduced from the tangential components of the electric and magnetic fields, since they are defined as the cross product of said fields with the external normal to the closed surface considered: Js = -n AH / MAE

[0021] Since the cross product of two collinear vectors is by definition zero, only the tangential components of the magnetic and electric fields are therefore necessary to evaluate the electromagnetic field at any point in space outside the closed surface considered.

[0022] A key condition for ensuring accurate prediction of electromagnetic fields outside the Huygens box is to ensure that the environment near the measurement is completely unobstructed and that the measuring equipment does not interact with the measured components. If these conditions are not met, significant errors can be introduced into both the near-field and far-field predictions.

[0023] In order 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 are preferred to avoid the presence of coaxial cables.

[0024] By default and in the absence of specific information regarding the radiation of the antenna under test, the characterization must be carried out on all the magnetic and electrical components of all the open faces of the Huygens box thus constituted (i.e. excluding the lower face here).

[0025] An example of measurements on the faces of a Huygens box is illustrated, for illustrative purposes only, in [Fig.5].

[0026] 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.

[0027] The system for determining the radiation characteristics of an antenna 1 according to the invention comprises a central buried azimuthal positioner 50 having a metal plate 51, forming here 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, in this case, 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 embodiment, the metal plate 51 is wholly or partially perforated. A mesh of perforations is then arranged so as to be sufficiently fine with regard to the wavelengths used to characterize the antenna 2 under test. For example, the mesh size is less than Xmin / 25, where / .min is associated with the smallest wavelength in the characterized frequency range.

[0028] A radio feed line 25 allows the antenna 2 to be connected under The test is performed on a radio measurement bench 6 installed in an operating room of 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 carried out 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 case, integral with the metal plate 51. Alternatively, the radio feed line 25 passes through a thickness of the metal plate 51.

[0029] 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.

[0030] 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, in this case, a first sliding link 21 in which the end of Mounting 11 of the measuring arm 10 relative to the frame 20. The first sliding joint 21 is vertical and extends along one of the Z axes of the orthonormal coordinate system XYZ. 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 performed, in particular to reduce not only the potential influence of said measuring arm 10 on radiation from the antenna 2 under test, but also to minimize as much as possible any deflection and damping under both vertical (mass of elements fixed at the free end 12) and horizontal (wind force) stress.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 low damping times allowing the elimination of vibration problems, and this for winds up to 30 km / h. Such an arrangement makes it possible to improve the accuracy of the radiation characteristics of the antenna under test 2.

[0031] 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.

[0032] The system for determining the radiation characteristics of an antenna 1 thus comprises drive means 21, 22 for the mounting end 11 of the measuring arm 10 in a plane PI extending along the X and Z axes of the orthonormal coordinate system XYZ. The plane PI is tangential, here, to a cylinder of revolution C with axis, 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 the plane PL. The drive means 21, 22 are preferably motorized in order to automate or control movements of the measuring arm 10.

[0033] 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. To this end, the free end 12 of the measuring arm includes a The support, also made of dielectric material, allows for the attachment of the entire set of magnetic and electric field measuring probes 40. 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.

[0034] According to an embodiment not shown, the set of measuring probes 40 comprises two electric field measuring probes. Such an arrangement makes it possible to optimize the acquisition time when certain characteristics of the antenna under consideration are known.

[0035] According to an embodiment not shown, the set of measuring probes 40 comprises two magnetic field measuring probes. Such an arrangement makes it possible to optimize the acquisition time when certain characteristics of the antenna under consideration are known.

[0036] Although this has a significant impact on the computational load, a set of measuring probes 40, comprising two electrical and two magnetic probes, makes it possible to obtain the radiation characteristics of an antenna with high precision and speed. In this case, the system includes a vector network analyzer configured to receive data from the measuring probes 40. The measuring probes 40 are connected to the vector network analyzer, which measures transmission parameters between the antenna under test and each probe in the set of measuring probes. The vector network analyzer then acquires the various measurements from the measuring probes. This arrangement allows for a simultaneous and consistent analysis of the electrical and magnetic characteristics of the electromagnetic field emanating from the antenna under consideration.

[0037] 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 the plane PI, 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 alternative embodiment, this third sliding link is provided between the measuring arm 10 and the frame 20, or between the frame 20 and the base 30.

[0038] 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 4 are, for example, positioned in the vicinity of the frame 20, as, here, behind the frame 20, for example on a suitable support of said frame 20 or in a remote dedicated room.

[0039] The measuring probes 40 should preferably meet two requirements: their active end should occupy a surface area of ​​only a few mm², and the control logic section (a few tens of mm²) should be located 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 of 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 40 measurement probes are said to be co-located or considered to be located at the same point of measurement 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 in two orientations, with its active end at 90° to each other: one orientation to measure a component of the field associated with the measuring probe 40 in question, and one orientation to measure a component orthogonal to the former associated field, the two components lying in a plane perpendicular to a longitudinal or principal axis of the measuring probe 40 in question.

[0040] 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 PI. 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 PI and extending to an acquisition distance DM from the vertical axis of rotation R of the azimuthal positioner 50.

[0041] We will now describe the operation of the system for determining the radiation characteristics of an antenna 1.

[0042] The system for determining the radiation characteristics of an antenna 1 will allow for near-field measurements to be performed by 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 direct measurement of 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 [Fig.4].

[0043] 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.

[0044] For the lateral faces, the entire face is, for example, acquired by successively scanning the X-axis for each height value of the Z-axis. Each face is scanned twice to allow the acquisition of the 4 components. Between these two scans, the probes are rotated manually, or automatically, by a quarter turn.

[0045] The four lateral faces 31, 32, 33, 34 to be measured are successively presented in front of the dielectric arm 10 by means of the rotational movement of the azimuthal 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.

[0046] 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 [Fig. 4]. In practice, the displacement D is alternating: a scanning band 310 is scanned from right to left, then the next adjacent scanning band 310 is scanned from left to right, and vice versa. Two adjacent scanning bands 310 are separated by a predetermined distance Ad, also called the "acquisition step".

[0047] In order to avoid aliasing artifacts during acquisitions, the acquisition step size Ad must always be less than Xmin / 2, where Xmin 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:

[0048]

[0049] For example, for an acquisition distance of 10 cm, the spatial step should therefore be on the order of 5 cm in all frequencies of the VHF range.

[0050] 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 co-located as explained previously.

[0051] In a first series of passes, the active ends 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.

[0052] 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 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.

[0053] 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).

[0054] 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 scans in the same way as during the first series of passes previously described.

[0055] 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 to each other, so that they are always co-located. Again, the system for determining the radiation characteristics of an 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 measurement of the components of the electromagnetic fields that are in a plane of the upper face 35, i.e., along the X and Y axes.

[0056] 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).

[0057] Therefore, the system for determining the radiation characteristics of an antenna 1 performs the 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 over 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 from right to left, or even in only one direction of the alternating sweep.

[0058] 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).

[0059] Therefore, the system for determining the radiation characteristics of an antenna 1 performs the scans on the upper face 35 in a similar manner.

[0060] In an alternative embodiment, the positioning and orientation of the measuring probes 40 can be automated and motorized. It is then important to have motors that do not disturb the measured electromagnetic field of the antenna 2 under test: for example, the actuating parts are made of 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.

[0061] It should be noted that the system for determining the radiation characteristics of an antenna 1 has been described using measurement probes 40 from the company SPEAG. However, the principle of measurement by 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 Lasers) (principle of the probes of the company SPEAG); devices based on the Pockels effect, by measuring the phase delay suffered 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 mix of the two previous technologies.

[0062] 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, which are connected to a vector network analyzer 61. This analyzer 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.

[0063] In order to be able 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).

[0064] Since the phase responses of the two electro-optical measuring probes 40 (magnetic and electric) are uncorrelated with each other (but constant over time) and variable in frequency, it is essential to correct the unwanted phase difference observed at each measurement point. To achieve this, it is necessary to use a perfectly controlled configuration in which the phase relationship between the The electrical and magnetic components are perfectly known. The simplest configuration to obtain generally involves far-field conditions under which the main electrical 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.).

[0065] 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 Q. 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 beforehand the antenna factors of each probe (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.

[0066] 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 standard "Near-field scan data exchange", for example, thus maximizing compatibility with commercial electromagnetic simulation software.

[0067] In [Fig. 6], we will describe an alternative embodiment of a system for determining the radiation characteristics of an antenna 100. This system for determining the radiation characteristics of an antenna 100 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 comprises a second measuring arm 60 mounted at one end to rotate around the Y-axis with the frame 20. A pivot joint 25, optionally motorized, is provided for this purpose. Here, the pivot joint 25 is mounted on the first sliding joint. 21. The second measuring arm 60 comprises, here, 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 the plane PI 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.

[0068] The system for determining the radiation characteristics of an antenna 100 allows for the recording of azimuthal and vertical diagrams of the antenna 2 under test (always placed at the center of the central azimuthal positioner) under 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 cross-sections passing through the vertical axis of rotation R of the azimuthal positioner 50.

[0069] 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.

[0070] 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.

[0071] Naturally, the invention is described above by way of example. It is understood that a person skilled in the art is able to carry out different embodiments of the invention without departing from the scope of the invention.

[0072] It is emphasized that all features, as they are apparent to a person skilled in the art from the present description, drawings and 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 make 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 (PI) 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 of the mounting end of the measuring arm comprise a second horizontal sliding link (22), perpendicular to the first vertical sliding link, between the frame and the base.

6. A system according to any one of claims 1 to 5, wherein the system further comprises means for moving (121) the probes measure (40) along 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. A 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. System according to any one of claims 1 to 10, wherein 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.

14. System according to claim 11, wherein the acquisition step Ad is less than Xmin / 2 with / .min 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 measurement probes (40).

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