Device for measuring electromagnetic radiation from an object under test

Abstract

The invention relates to a device for measuring electromagnetic radiation from an object under test. The device comprises a circular structure surrounding a test volume within which the object is located. The circular structure includes probes arranged at regular intervals along its circumference, each configured to receive or transmit one of the electromagnetic radiations and connected to each other by capacitive coupling elements. Figure for the abstract: Fig. 2

Description

Title of the invention: Device for measuring electromagnetic radiation from an object under test

[0001] The invention is in the field of measurement instrumentation. It relates more particularly to a device for measuring electromagnetic radiation from an object under test.

[0002] The principle of a spherical scanning radiometer (or "scanner" according to the commonly used Anglo-Saxon term) is to describe a sphere around the object under test in order to measure a radiation pattern in all directions.

[0003] It has already been proposed, for determining the radiation pattern of an object under test, to use devices comprising a set of probes distributed on an arc surrounding the object under test and directed towards said object. Each probe comprises one or more antennas, for example made of printed circuit boards (or "PCBs" according to the commonly used Anglo-Saxon term). Each antenna can operate in transmit and receive mode.

[0004] By rotating the arch or the object under test, it is thus possible to measure the radiation pattern of the object under test in successive slices to obtain a three-dimensional radiation pattern of the object under test.

[0005] As shown in [Fig. 1], the measurements are thus carried out on a sphere completely surrounding the object under test. In a spherical system, the angular measurement resolution depends mainly on the measurement frequency and the size of the object.

[0006] The resolution A 9 of the measurement can be calculated from the following formula:

[0007] A / (2 \

[0008] with R^n the radius of the minimal sphere surrounding the object under test and the most short wavelength of magnetic radiation that can be used to produce the radiation pattern of the object under test.

[0009] The minimum sphere surrounding the object under test depends on the object's dimensions. The number of sampling points N is a function of the radius Rmin of the minimum sphere surrounding the object under test and satisfies the following formula:

[0010] N = \ + wavecn “ 10 \ ''itan /

[0011] n is a constant used to determine the resolution required for the angular measurement. It is related to the number of spherical modes needed to describe a radiation pattern for a given antenna size.

[0012] The principle of producing a radiation pattern of an object under test using a spherical scanner comprising a set of measuring probes distributed over an arc is known from document CA2535927A1.

[0013] Known spherical scanners in the prior art have an additional limitation due to their sensitivity to coupling between the measuring probes, which limits their proximity. This coupling between measuring probes hinders or even prevents measurements from being taken. In order to maintain good angular resolution, it is necessary to space the probes apart within the arch to limit this coupling. This implies the use of arches with large diameters, ranging, for example, from 2 m to 6 m in diameter. Such devices are therefore relatively bulky and have a significant implementation cost.

[0014] Furthermore, since the probes used are small compared to the measured wavelength, they must be coupled with a transmit or receive amplifier to increase their sensitivity. The use of such an amplifier does not allow for simultaneous transmission and reception measurements, which leads to the loss of the reciprocity principle underlying antenna measurements.

[0015] There is therefore a need to reduce the size of the devices used to produce a three-dimensional radiation pattern of an object under test while maintaining the principle of reciprocity of measurements by antenna.

[0016] The invention addresses the technical problem posed by means of a device for measuring electromagnetic radiation from an object under test, comprising a circular structure surrounding a test volume within which said object is located, the circular structure comprising probes arranged at regular intervals along the circumference of said structure, each configured to receive or transmit one of the electromagnetic radiations and connected to each other by capacitive coupling elements.

[0017] The general idea behind the invention is to use the strong coupling existing between each probe to facilitate the measurement of electromagnetic radiation rather than seeking to eliminate it. By determining the intensity of the coupling between each probe and its first, second, third, ..., i-th neighbors, the different components of the measured electromagnetic radiation are calculated.

[0018] Advantageously, the device takes advantage of the strong coupling between the measuring probes to improve the accuracy and signal-to-noise ratio of the measurements performed. The strong coupling between the probes also allows for a reduction in the size of the device. Preferably, the device has a diameter less than or equal to one meter, for example, a diameter approximately equal to 720 mm. By approximately equal, it is understood that the diameter of the device is greater than or equal to 715 mm and less than or equal to 725 mm. The device is therefore more than two to six times smaller than the known state-of-the-art devices mentioned above. Advantageously, the device does not require amplification of the emitted or transmitted signals and therefore allows measurements to be taken in both transmission and reception.

[0019] Advantageously, the device makes it possible to obtain: a wide-aperture and stable radiation pattern, a low cross-polarization (20dB lower than the main polarization to ensure good discrimination between polarizations, a wideband behavior over at least one decade, the lowest possible angular resolution.

[0020] According to particular embodiments of such a device:

[0021] the intensity of the capacitive coupling between two adjacent probes is greater than or equal to at 0.1 pF considering the formula for a parallel-plate capacitor.

[0022] Each probe comprises: a first linear probe configured to receive or transmit the horizontal component of electromagnetic radiation, a second linear probe configured to receive or transmit the vertical component of electromagnetic radiation, in which the first linear probe and the second linear probe cross at the coupling elements.

[0023] The probes include dipole antennas.

[0024] The probes include Vivaldi antennas.

[0025] the device further includes an electrical resistor connecting each coupling element to ground.

[0026] The device further comprises a Wilkinson divider including one input port and two output ports: the first output port being electrically connected to the first linear probe, the second output port being electrically connected to the second linear probe.

[0027] a symmetrizer comprising: a first differential port electrically connected to the first linear probe, a second differential port electrically connected to the second linear probe.

[0028] The probes are arranged along the circumference of the circular structure at 15-degree intervals.

[0029] The probes are arranged along the circumference of the circular structure every 10 degrees.

[0030] The probes are arranged along the circumference of the circular structure every 5 degrees.

[0031] The device includes, in addition to a support element configured to accommodate the object under test, said support element comprising fixing elements fixed to the sides of the circular structure and a counter-rotation module.

[0032] Other features, details and advantages of the invention will become apparent from the description given with reference to the accompanying drawings provided by way of example, which represent, respectively:

[0033] Fig. 1 is an illustration of the principle of spherical measurements of an object under test;

[0034] Figure [Fig. 2] is a functional diagram of a radiation measurement device electromagnetic of an object under test according to an embodiment of the invention;

[0035] Fig. 3 is a functional diagram of part of the measuring device of Fig. 2, comprising several probes;

[0036] Figure 4 is a functional diagram of a probe according to a first mode of realization ;

[0037] The [Fig.5] is a functional diagram of a probe according to a second embodiment;

[0038] The [Fig.6] is a graph illustrating the gain achieved for each linear probe of a probe according to the second embodiment;

[0039] Figure 7 is a functional diagram of a Wilkinson divider connected to measuring device of the [Fig.2].

[0040] Fig. 8 is a functional diagram of a probe according to the second embodiment of Fig. 5 of a measuring device comprising a probe arranged every 10 degrees.

[0041] Figure 9 is a functional diagram of a probe according to the second mode of realization of [Fig.5] a measuring device comprising a probe placed every 5 degrees.

[0042] The [Fig. 10] is a functional diagram of a measuring device according to the [Fig.2] comprising a support element for the object under test.

[0043] The [Fig. 11] is a working diagram of a measuring device according to the [Fig.2] and comprising a switching system.

[0044] Figure 2 is a functional diagram of a device for measuring the electromagnetic radiation of an object under test. The measuring device comprises a circular structure 10 surrounding a test volume. The test volume is configured to contain the object under test. The test volume defines a theoretical spherical object of maximum volume Vmax that can be measured with said measuring device. The circular structure 10 is made of a dielectric material. Advantageously, this prevents interference with the measurement.

[0045] The circular structure 10 comprises probes 12 arranged at regular intervals along the circumference of the circular structure 10. The probes 12 are arranged along the circumference of the circular structure 10 every 15 degrees. Alternatively, the probes 12 are arranged along the circumference of the circular structure 10 every 10 degrees. Alternatively, the probes 12 are arranged along the circumference of the circular structure 10 every 5 degrees. For a probe 12 arranged every 15 degrees, the circular structure 10 comprises 24 probes 12. For a probe 12 arranged every 10 degrees, the circular structure 10 comprises 36 probes 12. For a probe 12 arranged every 5 degrees, the circular structure 10 comprises 72 probes 12.

[0046] Preferably, the circular structure 10 has a diameter less than or equal to one meter, for example, a diameter approximately equal to 720 mm. By approximately equal, it is understood that the diameter of the device is greater than or equal to 715 mm and less than or equal to 725 mm. Preferably, the circular structure 10 is made in a modular fashion. By modular, it is understood that the diameter of the circular structure 10 and the number of probes 12 can be adjusted so as to adapt to the dimensions of the object under test.

[0047] Each of the probes 12 is configured to receive or transmit one of the electromagnetic radiations from the object under test. Each of the probes 12 is connected to the probes 12 adjacent to it by capacitive coupling elements 14. Each probe 12 is strongly coupled to the adjacent probes 12.

[0048] Preferably, the intensity of the capacitive coupling between two adjacent probes is greater than or equal to 0.1 pF considering the formula of the parallel plate capacitor.

[0049] Each probe 12 comprises at least one linear probe 12i, where i is the number of the i-th linear probe of probe 12. Each linear probe 12i comprises an alternating unit antenna and coupling element 14. The unit antennas and coupling elements 14 are made of PCB material. Each linear probe 12i is configured to receive or transmit a spatial component of the electric field polarization of the electromagnetic radiation. The electric field polarization includes the direction and magnitude of the electric field.

[0050] Preferably, each probe 12 comprises a first linear probe 12a configured to receive or transmit the horizontal component of the electric field of the electromagnetic radiation and a second linear probe 12b configured to receive or transmit the vertical component of the electric field. The first plane containing the first linear probe 12a is oriented at 90 degrees to the second plane containing the second linear probe 12b, the first linear probe 12a being connected to the second linear probe 12b by the capacitive coupling element 14 as as shown in [Fig.3]. The two linear probes 12a, 12b intersect at a 90-degree angle as shown in [Fig.3].

[0051] In a first embodiment, the unit antennas comprise dipole antennas 30 as shown in [Fig.4].

[0052] Advantageously, the use of dipole antennas 30 makes it possible to carry out electromagnetic radiation measurements with a bandwidth of -6 dB from 700 MHz to 3 GHz with a minimum gain in the direction of the object under test of -3 dBi from 700 MHz to 3 GHz.

[0053] In a second embodiment, the unit antennas comprise Vivaldi 32 antennas as shown in [Fig.5].

[0054] The outer elements of a Vivaldi 32 antenna define a flared slot. These flared slots are strongly coupled to the adjacent elements. Advantageously, a Vivaldi 32 antenna exhibits a strongly coupled dipole mode at low frequencies and a directional antenna mode at high frequencies.

[0055] Advantageously, the Vivaldi 32 antennas improve high-frequency performance to allow optimal operation over a wider bandwidth. The bandwidth is thus significantly expanded, enabling radiation compatible with a measuring probe over more than a decade.

[0056] Advantageously, the use of Vivaldi 32 antennas makes it possible to carry out measurements of electromagnetic radiation with a bandwidth of -6 dB from 400 MHz to 6 GHz with a minimum gain in the direction of the object under test of -6 dBi from 400 MHz to 8 GHz.

[0057] Measurements carried out with a device according to the second embodiment show effective operation over a frequency band from 400 MHz to 6 GHz. The gain oscillates between -3 and 7 dBi with a high polarization purity (difference between vertical and horizontal polarization) of more than 20 dB as shown in [Fig. 6].

[0058] Preferably, each capacitive coupling element 14 is connected to the ground of the measuring device by an electrical resistance 16. Advantageously, the electrical resistances 16 make it possible to eliminate parasitic resonances which affect the stability of the probe 12 on all frequency bands.

[0059] The value of the resistors 16 is greater than or equal to 50 Ohms and less than or equal to 100 Ohms. Measurements show that the absorption of parasitic resonances is optimal for a resistance value of the electrical resistor 16 approximately equal to 70 Ohms. By "approximately equal to," it is understood that a resistance value greater than or equal to 69 Ohms and less than or equal to 71 Ohms is understood.

[0060] The resistors 16 slightly reduce the efficiency of the unit antenna but this does not have a significant impact on the performance of the probes 12.

[0061] Preferably, the measuring device further comprises a two-stage Wilkinson divider 20. As shown in [Fig. 7], the Wilkinson divider 20 comprises a first output port 22a electrically connected to the first linear probe 12a and a second output port 22b electrically connected to the second linear probe 12b. The Wilkinson divider 20 also comprises an input port 24.

[0062] The Wilkinson divider 20 comprises two stages and provides phase-in-phase input to the first linear probe 12a and the second linear probe 12b over a wide frequency band. Wide frequency band means that the Wilkinson divider 20 provides phase-in-phase input to the first linear probe 12a and the second linear probe 12b over the interval [400 MHz; 6 GHz]. The architecture and operating principle of a two-stage Wilkinson divider are described by (Saxena et al. 2021).

[0063] Fig. 8 shows how the Wilkinson divider 20 is connected to two adjacent probes 12.

[0064] Preferably, when the measuring device includes a probe 12 arranged every 5 degrees, the measuring device further includes a switch 26, for example an SPDT switch (or "Single Pole Double Throw switch" according to the commonly used Anglo-Saxon term). The switch 26 allows selection of one probe 12 from among two adjacent probes 12 connected to the same switch 26 to perform the measurement as shown in [Fig. 9].

[0065] Alternatively, the device further comprises a symmetrizer including a first differential port electrically connected to the first linear probe 12a and a second differential port electrically connected to the second linear probe 12b. The symmetrizer replaces the Wilkinson divider 20.

[0066] Advantageously, the symmetrizer allows for a more symmetrical measuring device and therefore a lower cross-polarization.

[0067] The circular structure 10 is configured to rotate about a vertical axis A1 connecting two opposite edges of the circular structure 10. The rotation is achieved by a dedicated mechanical system comprising a dedicated gear driven by a stepper motor. Alternatively, the circular structure 10 is configured to rotate about several different axes A1, each axis A1 connecting two different opposite edges of the circular structure 10.

[0068] By rotating the circular structure 10, it is thus possible to measure the radiation pattern of the object under test in successive slices to obtain a three-dimensional radiation pattern of said object.

[0069] Preferably, the measuring device further comprises a support element 40. The support element 40 comprises a support plate 42 and elements of The support plate 44 is configured to hold the object under test, as shown in [Fig. 10]. The support plate 42 is configured to hold the object under test. The support elements 44 are attached at one end to the support plate 42 and at the other end to the sides of the circular structure 10. The support elements 44 allow the support plate 42 to be positioned within the circular structure 10. Alternatively, the support plate 42 rests on an external support structure. Preferably, the support plate 42 is positioned within the circular structure 10 so that the object under test is at the center of the circular structure 10. Additional support elements, for example, rigid foam support elements, can be added to allow the object under test to be positioned at the center of the arch.Advantageously, the fastening elements 44 allow the dedicated mechanical system described above to rotate the circular structure 10 around the axis Al without the circular structure 10 being blocked by the fastening elements 44 during its rotation. The support platform 42 includes a counter-rotating device 46 configured to rotate the object under test about the axis Al and in the opposite direction to that of the circular structure 10, such that the rotation of the object under test about the axis Al by the counter-rotating device 46 completely compensates for the rotation of the circular structure 10 about the axis AL. Advantageously, the object under test thus remains stationary during the rotation of the circular structure 10, which makes it possible to obtain the three-dimensional radiation pattern of said object. Alternatively, the counter-rotation module 44 is configured to rotate the object under test around the axes Ai defined above and in the opposite direction to that of the circular structure 10 so that the rotation of the object under test around the axis Ai by the counter-rotation module 44 totally compensates for the rotation of the circular structure 10 around the axis Ai.

[0070] In the prior art, the support element comprises a support plate and a support structure connecting the lower edge of the circular structure to the center of the circular structure along axis AL. The portion of the support structure located at the center of the circular structure terminates in the support plate configured to accommodate the object under test. The circular structure is thus not obstructed by the support element during its rotation. However, such a configuration necessitates sacrificing a space for a measuring probe within the circular structure in order to install the support structure.

[0071] Advantageously, the support element 40 does not require the sacrifice of a probe 12 location within the circular structure 10. The regularity of the arrangement of the probes 12 within the circular structure 10 is thus not compromised, which makes it possible to increase the accuracy and the signal / noise ratio of the measurements made by the measuring device.

[0072] In order to access the various probes 12, the measuring device also includes a switching system 50. The switching system comprises a main switch 52 and secondary switches 54 as shown in [Fig. 11]. The main switch 52 is configured to control the secondary switches 54. Each secondary switch 54 is configured to individually control a set of several adjacent probes 12. Coaxial cables are used to connect the switches to the probes 12, with one coaxial cable per linear probe 12i for each probe 12. For a probe 12 arranged every 15 degrees and comprising a first linear probe 12a and a second linear probe 12b, the switching system 50 comprises 3 secondary switches, each connected to 8 adjacent probes 12, for a total of 24 probes 12 and 48 connection ports as shown in [Fig. 10].For a probe 12 arranged every 10 degrees and comprising a first linear probe 12a and a second linear probe 12b, the switching system 50 includes 3 secondary switches, each connected to 12 adjacent probes 12, for a total of 36 probes 12 and 72 connection ports. For a probe 12 arranged every 5 degrees and comprising a first linear probe 12a and a second linear probe 12b, the switching system 50 includes 3 secondary switches, each connected to 24 adjacent probes 12, for a total of 72 probes 12 and 144 connection ports. In the embodiment comprising a probe every 5 degrees, the Wilkinson divider is replaced by a switch that allows switching between the first linear probe 12a and the second linear probe 12b.

[0073] The invention has been described with reference to particular embodiments, but variations are possible. For example:

[0074] The probes 12 are arranged along the circumference of the circular structure 10 at 20-degree intervals.

[0075] The antennas used within the measuring device are chip antennas. References

[0076] (Saxena et al. 2021): A. Saxena, M. Hashlu, D. Banerjee, MA Chaudhary, Theory and Design of a Flexible Two-Stage Wideband Wilkinson Power Divider, Electronics, 2021, Volume 10, Issue 17, 2168.

Claims

Demands

1. Device for measuring electromagnetic radiation from an object under test, comprising a circular structure (10) surrounding a test volume within which said object is located, the circular structure (10) comprising probes (12) arranged at regular intervals along the circumference of the circular structure (10), each configured to receive or transmit one of the electromagnetic radiations and connected to each other by capacitive coupling elements (14).

2. Device according to claim 1, the intensity of the capacitive coupling between two adjacent probes (12) being greater than or equal to 0.1 pF, considering the formula for a parallel-plate capacitor

3. Device according to claim 1 or 2, wherein each probe (12) comprises a first linear probe (12a) configured to receive or transmit the horizontal component of electromagnetic radiation, a second linear probe (12b) configured to receive or transmit the vertical component of electromagnetic radiation, wherein the first linear probe (12a) and the second linear probe (12b) intersect at the coupling elements (14).

4. Device according to any one of claims 1 to 3, wherein the probes (12) comprise dipole antennas (30).

5. Device according to any one of claims 1 to 3, wherein the probes (12) comprise Vivaldi antennas (32).

6. Device according to any one of claims 1 to 5, further comprising an electrical resistance (16) connecting each capacitive coupling element (14) to the ground of the measuring device.

7. Device according to any one of claims 3 to 6, further comprising a Wilkinson divider (20) comprising: a first output port (20a) electrically connected to the first linear probe (12a), a second output port (20b) electrically connected to the second linear probe (12b).

8. A device according to any one of claims 3 to 6, further comprising a symmetrizer comprising: a first differential port electrically connected to the first linear probe (12a), a second differential port electrically connected to the second linear probe (12b).

9. Device according to any one of claims 1 to 8, wherein the probes (12) are arranged along the circumference of the circular structure (10) every 15 degrees.

10. Device according to any one of claims 1 to 8, wherein the probes (12) are arranged along the circumference of the circular structure (10) every 10 degrees.

11. Device according to any one of claims 1 to 8, wherein the probes (12) are arranged along the circumference of the circular structure (10) every 5 degrees.

12. Device according to any one of claims 1 to 11 further comprising a support element (40) configured to accommodate the object under test, said support element (40) comprising a support plate (42) and fastening elements (44).

13. Device according to claim 12, the support plate (42) further comprising a counter-rotation module (46).