Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R29/00—Arrangements for measuring or indicating electric quantities not covered by groups G01R19/00 - G01R27/00
  • G01R29/08—Measuring electromagnetic field characteristics
  • G01R29/10—Radiation diagrams of antennas

Definitions

• the present invention relates to a method and a device for measuring a radiation pattern of a radiative source in echogenic medium.
• a radiation pattern of a radiating source which can be of acoustic, electromagnetic or optical type
• the principle of reciprocity can be exploited, that is to say that the radiative source can be characterized as emission, but can also be used as a receiver on which a plane wave is sent.
• the radiative source can be characterized as emission, but can also be used as a receiver on which a plane wave is sent.
• anechoic chamber which, by definition, make it possible to avoid the presence of echoes.
• These devices consist of foams, often of pyramidal shape, whose purpose is to absorb the incident waves.
• foams are used whatever the nature of the wave type, for example for electromagnetic waves or acoustic waves.
• foams are expensive and need to be replaced regularly, which complicates maintenance.
• the present invention aims to overcome the aforementioned drawbacks and to make it possible to perform more quickly and more economically than known techniques, the measurement of a radiation pattern of a radiative source.
• the invention also aims more particularly at reducing the size of the installations in which the measurements of radiation patterns are made.
• the invention also aims to obtain these results by avoiding the need to use expensive and fragile materials such as absorbent foams or to perform many mechanical displacements.
• the radiative source having a maximum linear dimension a, characterized in that it comprises first and second parallel reflecting plates, oriented along a longitudinal axis Y, creating an echogenic medium, between which is disposed the radiative source, the distance between the source radiative and each of the first and second plates being greater than or equal to each of said wavelengths Ai; at least one probe sensitive to the amplitude and the phase of the radiation of the far-field radiative source, which is also arranged between the first and second plates at a distance D R of the radiative source, being shifted relative to the radiative source along a transverse axis X perpendicular to the longitudinal axis Y of a value e greater than or equal to ⁇ / 10, the distance D R being greater than or equal to 2a 2 / Ai; a vector network analyze
• the radiative source may be disposed centrally between the first and second parallel reflective plates.
• the measuring device may further comprise a device for moving in fixed or variable pitch the probe in the transverse direction X and in this case, the computing unit is adapted to control the device for moving the probe in a transverse direction .
• the device for stepwise movement of the probe may comprise a guide rail and an electric motor.
• the measuring device according to the invention may further comprise a device for rotating the radiative source on itself about an axis parallel to the longitudinal axis Y.
• the measuring device comprises a first probe sensitive to the amplitude and phase of the radiation of the far-field radiative source, which is arranged between the first and second plates at a distance DR from the source radiative in a first direction, being offset with respect to the radiative source along a transverse axis X perpendicular to the longitudinal axis Y of a value e greater than or equal to ⁇ / 10, the distance D R being greater than or equal to 2a 2 / Ai; a first device for moving in fixed or variable pitch the first probe in said transverse direction X; a second probe sensitive to the amplitude and phase of the radiation of the far-field radiative source, which is arranged between the first and second plates at a distance D R of the radiative source in a second direction opposite to the first direction, being offset with respect to the radiative source along a transverse axis X perpendicular to the longitudinal axis Y of a higher value e or equal to ⁇ / 10, the distance DR
• the first and second reflective plates may advantageously be made of a metal such as copper or aluminum.
• the radiative source may be acoustic, electromagnetic or optical type and in this case, the first and second plates themselves are respectively acoustically, electrically or optically reflective.
• the minimum frequency of the predetermined frequency range F1 may preferably be between 100 MHz and 60 GHz.
• the invention also relates to a method for measuring a radiation pattern of a radiative source emitting radiation in a predetermined frequency range Fi corresponding to a predetermined wavelength range Ai, the radiative source having a maximum linear dimension a, characterized in that a) installing first and second parallel reflecting plates, oriented along a longitudinal axis Y, creating an echogenic medium, between which the radiative source is arranged, the distance d between the radiative source and each of the first and second plates being greater than or equal to at each of said wavelengths Ai;
• a Green matrix is established which depends only on the distance between the first and second plates, the position of the radiative source and the position of the probe,
• the radiative source can be arranged centrally between the first and second parallel reflecting plates, oriented along a longitudinal axis Y.
• step f) measurements of the electric field E are obtained for the different measurement steps using a vector network analyzer.
• the method may further comprise the steps according to which: h) the probe is moved in steps along said transverse direction X, steps c) to g) are repeated with each step displacement and
• regression techniques are also applied which allow a more robust reversal of the problem with respect to the noise.
• the radiative source may be of the electromagnetic type and in this case the minimum frequency of the predetermined frequency range F1 is between 100 MHz and 60 GHz.
• the frequency variation pitch AF in the frequency range Fi can be between 1 and 10 MHz when the central frequency is of the order of 1 Gigahertz.
• FIG. 1 represents a schematic view of a portion of a device for measuring radiative source radiation pattern in echogenic medium, according to the invention
• FIG. 2 represents a more general schematic view of a radiative source radiation pattern measurement device in an echogenic medium, according to the invention, with the implementation of two measurement probes
• FIG. 3 is a diagram corresponding to that of FIG. 1, in which examples of waves reflected by the reflecting plates of the radiative source radiation pattern measuring device according to the invention are shown,
• FIG. 4 is a diagram corresponding to that of FIG. 3, in which virtual sources corresponding to the different reflected waves represented in FIG. 3 are shown,
• FIG. 4A is an example of a radiation diagram obtained with the radiative source of FIGS. 3 and 4,
• FIG. 5 is a diagram corresponding to that of FIG. 1, in which examples of waves reflected by the reflecting plates of the radiative source radiation pattern measuring device according to the invention are shown, but the radiative source having rotated on itself,
• FIG. 6 is a diagram corresponding to that of FIG. 5, in which virtual sources corresponding to the different reflected waves represented in FIG. 5 are shown,
• FIG. 6A is an example of a radiation diagram obtained with the radiative source of FIGS. 5 and 6,
• FIG. 7 is an example of a radiation diagram obtained by synthesizing the diagrams of FIGS. 4A and 6A,
• FIG. 8 is a block diagram illustrating the various steps of a method for measuring a radiative source radiation pattern in an echogenic medium, according to the invention.
• FIGS. 9 to 11 are curves showing the evolution of the number of conditioning of the Green matrix as a function of the frequency steps for different cases of implementation of radiative source placed between reflecting plates, and - Figures 12 and 13 are examples of radiation patterns obtained with a method according to the invention.
• a radiating or radiative source 103 which is schematically represented by a triangle in FIGS. 1 to 6, can be characterized in the far field by its radiation pattern illustrated by an outline 120 or 320 in the examples given below.
• the radiating source 103 may be of acoustic, electromagnetic or optical type.
• a radiative source 103 constituted by an electromagnetic radiation antenna will more specifically be taken into account without limitation.
• the source 103 is used in transmission and intentional echoes of the transmitted signal are generated in order to reconstruct the radiation pattern 120 or 320 of this source, from measurement points 321 to 327, 331 to 337 (see FIGS. Figures 4A, 6A and 7).
• the generation of intentional echoes is based on the use of plates 101, 102 of material with reflective properties, forming flat walls PI, P2 preferably parallel, on which the waves emitted 1 to 7 or the to 7 '(FIGS. 3 to 6) are reflected.
• the plates 101, 102 may thus be metallic and made of a material such as copper or aluminum.
• the The nature of the plate material 101, 102 is adapted to the nature of the radiative source 103, so that these plates 101, 102 are reflective for the radiation emitted by this radiative source 103.
• the echoes originate from signals emitted on the sides.
• the amplitudes of these signals are weighted by the radiation pattern of the source, subject to proper placement of the plates 101, 102 forming the reflecting walls PI, P2.
• the signal received to characterize the radiation pattern is derived from a receiver 104 placed at a far distance from the source 103.
• the receiver 104 is also placed between the plates 101, 102 ( Figures 1 and 2).
• the measurement principle consists in exploiting the echoes and in extracting the information useful for the reconstruction of the radiation diagram 120, 320.
• the extraction of the information requires a measurement with a frequency variation with a step of AF frequency, which can be fixed or variable depending on the conditioning of the Green matrix and a range of frequencies that are chosen according to the geometry of the problem and the good mathematical conditioning of the problem.
• the basic technique is electronic and allows a substantial gain in measurement time compared to conventional techniques based on mechanical movements.
• the transmitter constituted by the source 103, and the receiver 104 must not be aligned face to face otherwise the problem will be poorly conditioned and the problem can not be reversed to reconstruct the radiation pattern.
• the spacing D between the plates 101, 102 must be chosen as a function of the frequency range Fi (or of the corresponding range of lengths Ai) to which the characterization is performed and also depending on the size (largest linear dimension a) of the source 103 to be characterized.
• the measuring device thus comprises first and second parallel reflective plates 101, 102 oriented along a longitudinal axis Y, creating an echogenic medium, between which the radiative source 103 is centrally arranged.
• the distance d between the radiative source 103 and each of the plates 101, 102 is greater than or equal to each of the wavelengths Ai corresponding to the measurement frequency range Fi.
• the distance between the radiative source 103 and the plate 101 may be different from the distance between the radiative source 103 and the plate 102. However, according to a particular embodiment shown in the drawings, this distance may be the same and the radiative source 103 is then disposed centrally between the first and second parallel reflective plates.
• the receiving probe 104 must be sensitive to the amplitude and the phase of the radiation of the far-field radiative source 103.
• the probe 104 is disposed between the plates 101, 102 at a distance D R of the radiative source 103, being offset with respect to the radiative source along a transverse axis X perpendicular to the longitudinal axis Y of a higher value ⁇ or equal to Ai / 10, the distance D R (Rayleigh distance) being greater than or equal to 2a 2 / Ai, where a is the largest linear dimension of the source 103.
• a device 105, 106 is provided for moving stepwise, fixed or variable, the probe 104 in the transverse direction X.
• This device may comprise, for example, a guide rail 106 or a rack and an electric motor 105.
• the measuring device further comprises a vector network analyzer 111, to which the probe 104 is connected, and a calculation unit 110 adapted to receive data of the vector network analyzer 111, controlling the device 105, 106 to stepwise move the probe 104 in the transverse direction X and acquire at each step the data of the vector network analyzer 111 for several frequencies Fi with a no fixed frequency variation or AF variable.
• the measurement device comprises a measurement block 100 with, as in the case of the embodiment of FIG. 1, a first probe 104 sensitive to the amplitude and to the phase of the radiation of the far-field radiative source 103, which is arranged between the plates 101, 102 at a distance D R of the radiative source 103 in a first direction, being offset with respect to the radiative source along a transverse axis X perpendicular to the longitudinal axis Y of a value ⁇ greater than or equal to Ai / 10, the distance D R being greater than or equal to 2a 2 / Ai.
• a first device 105, 106 is provided for moving in fixed or variable pitch the first probe 104 in the transverse direction X.
• the measurement block 100 of the measuring device comprises a second probe 104 'sensitive to the amplitude and the phase of the radiation of the same far-field radiative source 103, which is arranged between the plates 101, 102 at a distance D R of the radiative source 103 in a second direction opposite to the first direction, being offset with respect to the radiative source along the transverse axis X perpendicular to the longitudinal axis Y of a value e greater than or equal to ⁇ / 10, the distance DR being greater than or equal to 2a 2 / Ai.
• a second device 105 ', 106' is provided for moving the second probe 104 'in the transverse direction X by fixed or variable pitch.
• the second probe 104' makes it possible to detect the rear part of the radiation pattern of the radiative source 103.
• the first and second probes 104, 104 'of the measurement block 100 are connected to the vector network analyzer 111 by lines 108, 108'.
• the computing unit 110 is adapted to receive data from the vector network analyzer 111, via the line 109, to control, by the lines 107, 107 ', the first and second devices 105, 106; 105 ', 106' for moving in steps respectively the first and second probes 104, 104 'in the transverse direction X and for acquiring at each step the data of the vector network analyzer 111 for several frequencies Fi with a pitch of variation of Fixed frequency or AF variable.
• the measuring device may comprise a device for rotating the radiative source 103 about itself about an axis parallel to the longitudinal axis Y.
• FIG. 3 schematically shows by way of example and in a simplified manner a radiative source 103 having a radiation pattern 320 placed between two parallel reflecting plates 101, 102, as well as a receiving probe 104 also placed, offset from the radiative source 103, between the plates 101, 102, as indicated above with reference to FIGS. 1 and 2.
• FIG. 3 shows four first radii 1 to 4 emitted by the radiative source 103 and reflected by the plates 101, 102 to reach the receiving probe 104.
• Other subsequent rays emitted by the source 103 are not shown in FIG. 3 for the sake of clarity. It is these rays reflected by the walls 101, 102 which constitute echoes operated in the context of the present invention.
• the receiving probe 104 is associated with a vector network analyzer 111 sensitive not only to the amplitude, but also at the phase of the signals.
• p 0.99
• the resolution of the linear system thus consists in performing a frequency sweep where the number of frequencies equals the number of useful images.
• the technique is limited in resolution by the number of images chosen, which can range from a few images to several hundred images, but the electronic character of the frequency sweep allows a substantial time saving compared to conventional techniques based exclusively on mechanical movements of the antenna (or source radiative any) under test. According to the invention, it is simply possible to combine certain mechanical displacements constituted by a rotation of the radiative source 103 on itself in order to improve the resolution, but most of the measurements are carried out electronically.
• each image or virtual source makes it possible to find a point 321 to 327 of the radiation diagram of the real source 103.
• the reconstitution of the radiation pattern 320 of the source 103, shown in FIG. 4A, will thus be all the more precise as the number of points 321 to 327 will be large and well distributed on the lobes of the radiation pattern.
• the radius 1 is a direct ray going from the source 103 to the probe 104
• the spoke 2 has undergone a single reflection on the plate 102
• the spoke 3 has undergone a first reflection on the plate 101 and a second reflection on the plate 102
• the spoke 4 has undergone a single reflection on the plate 101 and the spokes 5 to 7, not shown in Figure 3, correspond to other images or more distant virtual sources that allow to increase the resolution.
• Figure 5 is similar to Figure 3, but corresponds to a rotation of the source 103 on itself about an axis parallel to the plates 101, 102, to give it a position 103 ', which changes the position of its 320 'radiation pattern.
• the rays 7 ' (of which only the rays 1' to 4 'are shown in FIG. 5) emitted by the source 103' in its new position and received by the receiving probe 104 positioned as in the case of FIG. , after a greater or lesser number of reflections on the walls of plates 101, 102 remained in the same fixed position, can create images or virtual sources shown in Figure 6 with each time the definition of a point 331 to 337 of the radiation pattern 320 of the source 103, which allows to otherwise reconstructing this radiation pattern 320 from points 331 to 337 (see Figure 6A).
• FIGS. 3 to 7 show, by way of example, a radiation pattern 320 with a main lobe and two secondary lobes, but the invention applies to radiative sources 103 which may have other forms of radiation patterns.
• the first position of the antenna 103 makes it possible to have certain points 321 to 327 of the radiation diagram 320, but as can be seen in FIG. 4A, the sampling points are narrowed on the sides and, with the example shown with seven sampling points, only two points, namely the points 321 and 322 are on the main lobe of the radiation pattern 320.
• FIGS. 5, 6, 6A By rotating the antenna 103 on its phase center, and by renewing the measuring operation (FIGS. 5, 6, 6A), the same echoes are obtained as in the configuration of FIGS. 3, 4, 4A, that is to say that the images or virtual sources are in the same positions, but the weighting of the echoes changes due to the rotation of the antenna.
• the points that tightened on the sides better sample the useful area.
• Figure 6A shows the sampling of the radiation pattern 320 with points 331 to 337, including in particular, in this example, the points 333, 334, 336 are on the main lobe of the radiation pattern 320.
• an interlacing of the two sampling series of FIGS. 4A and 6A makes it possible to increase the number of points in the zone initially depleted.
• the rotation of the source 103 thus makes it possible to better distribute the points that sample the radiation pattern. This better distribution of points makes it possible to apply regression techniques which increase the robustness of the process.
• a distance DR is defined between the source 103 and a measurement probe 104, so that which the spatial distribution of far-field radiation energy is independent of this distance D R.
• this distance D R must be greater than or equal to the Rayleigh distance, namely 2a 2 / Ai.
• the radiative source to be tested 103 is considered as a point source and, in the case of an antenna, the electric field E emitted by this antenna is given by the following formula:
• F (9, cp) is the radiation pattern
• ⁇ and ⁇ are the angles in elevation and azimuth respectively
• G (r, o) is the Green's function of free space which is given in its three-dimensional general form by the following formula:
• the images corresponding to the echoes of the radiation of the radiative source 103 each give rise to a signal emitted by a virtual source, all virtual sources being aligned with the actual radiative source.
• Each image contributes to the field measured by the receiving probe 104, but the contribution decreases with the distance of the virtual source with respect to the probe 104. This is why truncation is performed considering only a limited number of images.
• the measurement of the field E by the probe 104 can be expressed by the following formula:
• N unknowns, namely the N, sampled images of the radiation pattern
• the system must be adjusted so as to have a number of equations at least equal to that of the unknowns.
• An effective way is to modify the phases of the different possible wavefronts using frequency variations. Since the phase is very sensitive to changing the working frequency, the frequency is varied so as to use N f frequencies.
• E p is the total field measured at N f frequencies
• F is the vector of the radiation pattern consisting of N, points forming the unknowns
• G is a matrix f XN, which contains the samples of the Green function of space free.
• the frequency range between the minimum working frequency and the maximum working frequency shall be chosen according to the type of radiative source because it influences the radiation pattern. In general, this range of frequencies is chosen as narrow as possible. It is thus necessary to carefully choose the frequency step AF, that is to say the difference between two consecutive working frequencies out of a total number N f of linearly spaced or variable pitch frequencies. For example, it is possible to adopt a constant frequency step model, the working frequency being located at the center of the frequency range, but this is only one possible embodiment.
• the matrix G is well conditioned, that is to say that this matrix G has a number of conditioning as low as possible.
• the positions of the source 103, the probe 104 and the plates 101, 102 determine the set of generated echoes and consequently the corresponding samples of the Green function of the free space constituting the matrix G.
• the source 103 and the probe 104 are not disposed face to face but offset along the X axis of Figure 1.
• FIG. 9 shows curves 51, 52, 53 giving the conditioning number of the Green matrix as a function of the frequency step for three different conditions of relative positioning of the source 103 and of the probe 104.
• Curve 53 shows an optimal case where source 103 and probe 104 are shifted horizontally along the X axis of FIG. 1. In this case, it can be seen that an optimum, ie weak, number of conditioning , is obtained for a frequency step AF of the order of 10 MHz.
• the curves 51 and 52 correspond to the cases where the source 103 and the probe 104 face each other, the curve 51 corresponding more particularly to the case where the source 103 and the probe 104 are equidistant from the plates 101 and 102. It can be seen that, even for a frequency step of the order of 10 MHz, the number of conditioning remains high.
• the conditioning of the matrix G also depends on the number of images N , which determines the total field to be taken into account as well as the number of frequencies (or corresponding wavelengths) to be used for the measurements.
• FIG. 10 shows curves 54 and 55 showing the evolution of the conditioning number of the Green matrix as a function of the frequency pitch AF respectively for a number N, equal to 18 and for a number N, equal to 180 It can be seen that the optimum conditioning number is obtained for lower frequency steps if the number of images increases.
• the curve 55 N, equal to 180
• an optimized conditioning number is obtained at a frequency step of 10 MHz.
• the number of conditioning can be improved if a number of frequencies strictly greater than the number of images is used and if the number of frequencies is much greater than the number of images (case illustrated on the curve 58 ), it is even possible to obtain an optimal conditioning number with a relatively low frequency step of 4 MHz.
• the upper limit for the number of frequencies depends on both the frequency step used and the maximum range of frequency values in which the radiative source 103 can operate without changing its properties.
• the frequency range Fi of the radiative source 103 to be used is identified which, in this example, consists of an antenna.
• a step 202 we deduce the wavelengths Ai corresponding to the frequencies f1.
• first and second parallel reflective plates 101, 102, oriented along a longitudinal axis Y, are created, creating an echogenic medium, between which the radiative source 103 is arranged, preferably centrally, the distance d between the radiative source 103 and each of the plates 101, 102 being greater than or equal to each of the wavelengths Ai, and at least one probe 104 sensitive to the amplitude and phase of the radiation of the radiative source 103 in the field is installed remote, also having this probe 104 between the first and second plates 101, 102 at a distance D R of the radiative source 103, the distance DR being greater than or equal to 2a 2 / Ai, where a is the maximum linear dimension of Antenna 103.
• the distance D between the two reflecting plates 101, 102 is also determined from the values d of the spacing between the antenna 103 and the plates 101, 102 and the width e of the antenna.
• the probe 104 is positioned in a position offset from the radiative source 103 along the transverse axis X by a value e greater than or equal to Ai / 10. This is initially a first position of the probe 104, then, after different iterations of new positions.
• a frequency variation step AF is determined in the frequency range Fi, the different frequencies being used so that the echoes have different delays.
• a Green matrix is established which depends only on the dimensions of the system, namely the distance D between the plates 101 and 102, the position of the radiative source 103 and the position of the probe 104.
• a step 207 measurements of the electric field E are made by the probe 104 with the frequency variation step AF.
• This frequency step is not necessarily fixed, that is to say that the useful frequencies are not necessarily equidistant.
• a step 208 the measured values of the electric field E are acquired with the aid of a vector network analyzer 111 for the different measurement steps.
• a radiation pattern F is deduced using the Green matrix, which corresponds to an inversion of the problem.
• a test is made to know if the spatial sampling is finished. If this is not the case, the probe 104 is moved in steps in the transverse direction X, and steps 204 to 210 are repeated and if the test of step 210 reveals that the spatial sampling is finally, we go to a final step 211.
• step 211 an interleaved radiation pattern of the solutions found at the end of each preceding step 209 is performed.
• regression techniques can be applied that allow for a more robust inversion of the problem with respect to noise.
• the minimum frequency of the predetermined frequency range Fi is a function of the type of radiative source 103 to be analyzed.
• this minimum frequency can be typically between 100 MHz and 60 GHz.
• the pitch of frequency variation AF in the frequency range Fi can be typically between 1 and 10 MHz when the center frequency is of the order of the gigahertz.
• the minimum frequency can go well beyond the values indicated in the case of a radiative source of electromagnetic type, which corresponds to smaller wavelengths and by suite allows to realize a device still smaller.
• the frequency range Fi can be in the kHz range, but the wavelengths are of the same order as in the microwave, hence a device size which can be of the same order and can thus be much smaller than in the devices of the prior art.
• FIGS. 12 and 13 show examples of radiation patterns 120 obtained by the method according to the invention.
• FIG. 12 corresponds to a case where a conditioning number cond (G) equal to 14.28 is obtained, with a frequency step of 6 MHz, a number of frequencies equal to 5 for frequencies Fi included in the range 0.64 GHz and 1.36 GHz.
• G conditioning number cond
• the uncertainty on the vertical position of the source 103 is 5 mm and the uncertainty on the position of the walls 101, 102 is 1 cm.
• Figure 13 shows a reference radiation pattern 120 and radiation patterns 120A, 120B and 120C obtained from point sampling using the method described above, but using different conditioning numbers.
• diagram 120C with the lowest number of conditioning is closest to the reference diagram 120, while the diagram 120A with the highest number of conditioning is furthest from the reference diagram 120.
• the diagram 120B is acceptable for some applications if the requested accuracy is limited.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• General Physics & Mathematics (AREA)
• Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
• Length-Measuring Devices Using Wave Or Particle Radiation (AREA)
• Radar Systems Or Details Thereof (AREA)

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• 2014
  • 2014-10-10 FR FR1459768A patent/FR3027113B1/fr not_active Expired - Fee Related
• 2015
  • 2015-10-08 WO PCT/FR2015/052704 patent/WO2016055739A2/fr active Application Filing
  • 2015-10-08 EP EP15788153.3A patent/EP3204781A2/de not_active Withdrawn

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