Technical field

[ 0001 ] The present disclosure relates generally to a device and method for imaging stochastic fields , and in particular to a device and method using correlation functions in multilevel 3D conformal arrays .

Background art

[ 0002 ] High-resolution scanning and imaging solutions for RF or mm-wave fields are employed in various fields such in test systems for antenna characteri zation . However, such scanning and imaging solutions are generally very costly due to the need to provide a dense antenna array and costly noi se reduction solutions .

[ 0003 ] There is thus a need for a high-resolution imaging solution having a relatively low cost .

Summary of Invention

[ 0004 ] According to one aspect , there is provided a transmitter and/or receiver comprising : a first annular or tubular, or part-annular or part-tubular , structure on which a first antenna array is mounted, the first antenna array being formed of a plurality of inward-pointing antennas and/or a plurality of outward-pointing antennas , each of the antennas of the first antenna array being configured to transmit and/or receive electromagnetic waves ; and a correlator coupled to each of the antennas of the first antenna array and configured to generate time and frequency domain correlations between : signals generated by a time and frequency waveform generator for transmission via any selected pair of the antennas ; and/or signals received via any selected pair of the antennas . [ 0005 ] According to one embodiment , the first antenna array comprises at least six antennas positioned at equal distance to an axis of the first annular or tubular, or part-annular or part-tubular , structure .

[ 0006 ] According to one embodiment , the first annular or tubular, or part-annular or part-tubular , structure is made of metal .

[ 0007 ] According to one embodiment , the antennas of the first antenna array are Vivaldi antennas comprising first and second lobes separated by a gap across which a feeding line is positioned, wherein the first or second lobe of each antenna is common with the first or second lobe of a neighboring one of the antennas .

[ 0008 ] According to one embodiment , the antennas of the first antenna array are configured to receive and/or transmit electromagnetic waves within a range of frequencies within the frequency range 1 to 100 GHz , wherein the range of frequencies has a central frequency of wavelength .

[ 0009 ] According to one embodiment , the annular or tubular, or part-annular or part-tubular , structure has a diameter of between 2 and 50 , and for example between 4 and 10 .

[ 0010 ] According to one embodiment , the annular or tubular, or part-annular or part-tubular , structure has a length of at least 10 .

[ 0011 ] According to one embodiment , the transmitter and/or receiver further comprises one or more thermal sensors mounted on the first annular or tubular, or part-annular or parttubular, structure .

[ 0012 ] According to one embodiment , the transmitter and/or receiver further comprises a signal processing circuit configured to receive one or more first temperature readings captured by the one or more thermal sensors , and to make one or more second temperature readings using a selected pair of antennas of the first antenna array and based on interferometer radiometry, the first and second temperature readings being time-synchroni zed .

[ 0013 ] According to one embodiment , the selection of the pair of antennas involves the selection, as a reference antenna, of an antenna having a highest signal to noise ratio among the antennas of the first antenna array .

[ 0014 ] According to one embodiment , the one or more thermal sensors spin-cross-over sensors comprising a layer of spincross-over material comprising for example [ Fe (HB ( 1 , 2 , 4- triazol- l-yl ) 3 ) 2 ] bis [hydrotris ( 1 , 2 , 4-triazol- l- yl ) borate ] Fe ( I I ) .

[ 0015 ] According to one embodiment , the transmitter and/or receiver further comprises one or more visual sensors mounted on the first annular or tubular, or part-annular or parttubular, structure .

[ 0016 ] According to one embodiment , the transmitter and/or receiver further comprises one or more second annular or tubular, or part-annular or part-tubular , structures on which a second antenna array is mounted, the second antenna array being formed of a plurality of inward-pointing antennas and/or a plurality of outward-pointing antennas , each of the antennas of the second antenna array being configured to transmit and/or receive electromagnetic waves , wherein the correlator is further coupled to each of the antennas of the second antenna array and configured to generate time and frequency domain correlations between : signals generated by the time and frequency waveform generator for transmission via any selected antenna of the first antenna array and any selected antenna of the second antenna array; and/or signals received at any selected antenna of the first antenna array and at any selected antenna of the second antenna array .

[ 0017 ] According to one embodiment , the first and one or more second annular or tubular, or part-annular or part-tubular , structures are arranged such that their axes are aligned .

[ 0018 ] According to one embodiment , a diameter of the first annular or tubular, or part-annular or part-tubular , structure is di f ferent from a diameter of at one of the one or more second annular or tubular, or part-annular or parttubular, structures .

[ 0019 ] According to one embodiment , the transmitter and/or receiver further comprises : a DUT support passing through the first annular or tubular, or part-annular or part-tubular , structure ; and a mechanism for rotating, around the axis of the first annular or tubular, or part-annular or part-tubular , structure , the DUT support with respect to the first annular or tubular, or part-annular or part-tubular , structure .

[ 0020 ] According to one embodiment , the first annular or tubular, or part-annular or part-tubular , structure is a tubular or part-tubular metasurface , and wherein the antennas of the first antenna array are excitation or detection points on the metasurface .

[ 0021 ] According to one embodiment , the first annular or tubular, or part-annular or part-tubular , structure is formed of flexible materials , such as a flexible coated polymer substrate on a first side of the structure , and/or flexible electronics on a second side of the structure opposite to the first side .

[ 0022 ] According to a further aspect , there is provided a device for applying as a skin to a part of a human or animal body for medical imaging and/or environment sensing, comprising the above transmitter and/or receiver .

[ 0023 ] According to a further aspect , there is provided a method of OTA ( over the air ) testing of a DUT comprising receiving, by the antennas of the first antenna array of the above receiver, signals emitted by the DUT , and determining a cross-correlation in the frequency and time domains between signals received via pairs of the antennas of the first antenna array .

[ 0024 ] One wants to build near- field and far- field scanning and imaging systems based on modular approach aggregating 3D circular array [ 1-5 ] ( references in square brackets herein designate technical references cited below) slices combined with full-crossover correlator modules supporting distributed dual-polari zation systems . The circular topology of the 3D circular array slices , in providing low power computationally ef ficient processing for fast scanning and imaging, of fers large bandwidth and small dimensions for well controlled pulse generation with high angular resolution . Beyond practical applications relative to near- field and far field sensing of electronic circuits and systems , the resulting ultra-wideband imaging capabilities are suitable for various short-range applications , such as medical imaging, security detectors , high accuracy Electromagnetic-Thermal sensing ( see technical references [ 6- 11 ] cited below) .

[ 0025 ] The use of a uni form circular array, with inward- looking antennas , can provide 360 ° azimuthal coverage and estimate source position and source radiation pattern within the tunnel formed by the array . In view of the cyclical symmetry of the array, the embedded element patterns are identical , without rotation, with low invasiveness resulting from active-impedance tuning, and with fast correlation measurements. The proposed novel 3D circular array leads to low-cost fabrication, low power, and very fast data acquisition (comfort for the patient and helps to get accurate tumor locations) . Near fields in E and H planes in the area of radiation exposure exhibit smooth spreading over the whole field of view enabling power-density and energy density extractions .

[0026] The simplicity of the ultra-broadband circular array together with its low complexity enables efficient computational processing of the full crossover correlation matrix, supported by numerical simulations, e.g. based on Method of Moment formulations specific to discrete bodies of revolution. This feature enables association [12] of measurement system with a modeling tool for building a Digital-Twin platform backed-up by accurate calibration procedures. Holistic [6] Electromagnetic-Thermal formulations using the Method of Moments [7] using of higher-order (Cumulants) correlation [6] technologies will create unifying bridges between partially [9] coherent stochastic Electromagnetic fields and Thermal heat exchanges between bodies at multiscale levels (down to nanometric resolutions [6] beyond [10] the classical [11] heat mechanisms) . When thermal and electric flows are coupled through Seebeck/Peltier/Onsager [13-14] coefficients and Joule heating new functionalities [15-17] in link with energyharvesting, heat flow cloaking, focusing, invisibility and reversal .

[0027] Combination of interferometric radiometry [13-18] (with embedded reference thermal sensors) combined with the near-field scanning system provides hybrid Electromagnetic- Thermal [6] imaging solution for emerging applications where simultaneous knowledge of heat transfer and electromagnetic radiations are needed. Such hybrid Electromagnetic-Thermal formulations will benefit from emerging Spintronic sensing technologies [6] , [24-25] .

[0028] Fully sampled cylindrical arrays will be able to absorb all incident power, i.e. acting as anechoic chambers, despite the structures being covered with metallic elements. Absorption in that case is enabled by matching at the level of all ports. Beyond that, the full information about radiated fields can be gathered from the whole collection of ports. Beyond the concept of "Active-Impedance" [27-29] or "Scanning-Impedance" [30] well known from the published literature, we propose new "Correlation-Tuners" integrated close to radiator elements for dynamically absorbing incident waves based on specific criteria.

[0029] The generalization of the proposed circular arrays to 3D conf ormal/cylindrical radiating/receiving surfaces will create new paradigms for eliminating the concept of "elements" in arrays and replacing it by the vision of "radiating current flows" over a textured surface (metasurface or metavolume, see for example [26] describing multi-beam scanning with modulated metasurfaces) that is fed by a limited number of emitting-receiving points. The radiating metasurfaces or metavolumes are fed by a limited number of emitting/receiving points. This very specific way of transmitting/receiving EM waves will allow scanning directive multi-beam channels with sparsely [31] distributed ports, i.e. with much fewer active electronic channels than in current state-of-the-art phased- array solutions. Thus, a much sparser sampling of the "array" and hence much lower consumption: an improvement by a factor of 20 at least is achievable. This low-complexity approach will drive next generation of communication and sensing systems . [ 0030 ] The resulting conformal attributes brings electronics inside the antenna, rather than the other way around, this facilitates thermal management making use of the presence of the radiating surfaces to further dissipate heat (" forward dissipation" ) . To ensure proper 3D integration, new connectors housing AS IC circuits are combined with waveguiding technologies in 3D-printed templates . The required curved structures can be reali zed with flexible materials , i . e . flexible coated polymer substrates on one side and flexible electronics on the other side . Alternatively, the upper radiating structures can be combined with rigid curved structures obtained through 3D-printing . This comes with the advantage of an increased freedom in design and thus a potential improvement in terms of RF-perf ormances (bandwidth, losses , Signal-to-Noise-Ratio ( SNR) , Error- Vector-Magnitude (EVM) ) . Such freedom will benefit from material engineering [ 32-38 ] for new 3D distributed circuits and systems in f lexible/ stretchable substrates .

Brief description of drawings

[ 0031 ] The foregoing features and advantages , as well as others , will be described in detail in the following description of speci fic embodiments given by way of illustration and not limitation with reference to the accompanying drawings , in which :

[ 0032 ] Figure 1 schematically illustrates a test system according to an example embodiment of the present disclosure ;

[ 0033 ] Figure 2 schematically illustrates a test system according to another example embodiment of the present disclosure ;

[ 0034 ] Figure 3 schematically illustrates a test system according to another example embodiment of the present disclosure ; [ 0035 ] Figure 4 schematically illustrates a test system according to another example embodiment of the present disclosure ;

[ 0036 ] Figure 5 schematically illustrates a test system according to another example embodiment of the present disclosure , and illustrates a correlator of the test system in more detail according to an example embodiment of the present disclosure ;

[ 0037 ] Figure 6 schematically illustrates a test system according to yet another example embodiment of the present disclosure ;

[ 0038 ] Figure 7 schematically illustrates a test system according to yet another example embodiment of the present disclosure ;

[ 0039 ] Figure 8 schematically illustrates a test system according to yet another example embodiment of the present disclosure ;

[ 0040 ] Figure 9 schematically illustrates a test system comprising a circular array scanner formed as a hal f-circle according to an example embodiment of the present disclosure ;

[ 0041 ] Figure 10 schematically illustrates a test system comprising an antenna array comprising a metasurface according to an example embodiment of the present disclosure ;

[ 0042 ] Figure 11 schematically illustrates a test system comprising an antenna array comprising a metasurface according to another example embodiment of the present disclosure ;

[ 0043 ] Figure 12 illustrates schematically illustrates a test system and illustrates a signal processing circuit in detail according to an example embodiment of the present disclosure ; [ 0044 ] Figure 13 schematically illustrates a 180 ° hybrid circuit of Figure 12 ;

[ 0045 ] Figure 14 schematically illustrates the 180 ° hybrid circuit of Figure 13 in more detail according to an example embodiment of the present disclosure ;

[ 0046 ] Figure 15 is a cross-section view of a transmitter/receiver comprising a flexible substrate ;

[ 0047 ] Figure 16 illustrates an embedded connector of the transmitter/receiver of Figure 15 in more detail according to an example embodiment ; and

[ 0048 ] Figure 17 illustrates example applications of the transmitter/receiver of Figures 15 and 16 according to example embodiments of the present disclosure .

Description of embodiments

[ 0049 ] Like features have been designated by like references in the various figures . In particular, the structural and/or functional features that are common among the various embodiments may have the same references and may dispose identical structural , dimensional and material properties .

[ 0050 ] For the sake of clarity, only the operations and elements that are useful for an understanding of the embodiments described herein have been illustrated and described in detail .

[ 0051 ] Unless indicated otherwise , when reference is made to two elements connected together, this signi fies a direct connection without any intermediate elements other than conductors , and when reference is made to two elements coupled together, this signi fies that these two elements can be connected or they can be coupled via one or more other elements . [0052] In the following disclosure, unless indicated otherwise, when reference is made to absolute positional qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or to relative positional qualifiers, such as the terms "above", "below", "higher", "lower", etc., or to qualifiers of orientation, such as "horizontal", "vertical", etc., reference is made to the orientation shown in the figures.

[0053] Unless specified otherwise, the expressions "around", "approximately", "substantially", "nearly" and "in the order of" signify within 10 %, and preferably within 5 %.

[0054] Figure 1 schematically illustrates a test system 100 according to an example embodiment of the present disclosure. The test system 100 is for example configured for performing time and frequency domain measurement of stochastic fields.

[0055] The test system 100 for example comprises a transmitter/receiver 102 comprising an antenna array. The transmitter/receiver 102 comprises in particular an annular or cylindrical, or substantially annular or cylindrical, structure 104, which is shown in cross-section in Figure 1. As described in more detail below, rather than being cylindrical, the structure 104 could be tubular, or partannular or part-tubular .

[0056] Antennas 106 of the antenna array are mounted on the structure 104. In the example of Figure 1, the antennas 106 are inward-facing antennas mounted on an inner surface of the structure 104.

[0057] The antennas 106 are for example implemented by Vivaldi antennas, patch antennas, or other types of antenna. The antennas are for example configured to transmit and/or receive RF or mm-wave signals to/from a device under test (DUT) 107 positioned within the structure 104. In some embodiments, the antenna array is a dual-polarized antenna array in which at least some of the antennas 106 are capable of receiving and/or transmitting X polarized signals, and at least some of the antennas 106 are capable of receiving and/or transmitting Y polarized signals. In some embodiments, one or more of the antennas 106 is a dual-polarity antenna capable of receiving and/or transmitting both X and Y polarized signals .

[0058] In the example of Figure 1, there are eight antennas 106. More generally there are at least two antennas 106, and preferably at least 6 antennas. The antennas 106 are for example arranged such that there is a regular angular separation a between each antenna. Thus, in the case of eight antennas, the angular separation a is for example equal to 45°. More generally, the angular separation a is equal to 360°/n, where n is the number of antennas 106. The angular separation a for example defines a spatial scanning resolution of the transmitter/receiver 102.

[0059] The antennas 106 are for example sensitive to electromagnetic waves of a frequency that will depend on the emission frequencies of the DUT 107. In some embodiments, the antennas 106 are configured to receive and/or transmit electromagnetic waves within a range of frequencies within the frequency range 1 to 100 GHz, wherein the range of frequencies has a central frequency of wavelength .

[0060] An inner diameter D of the structure (104) is for example of between 2 and 50 , and for example between 4 and 10 .

[0061] While in the example of Figure 1 the structure 104 is circular in cross-section, in alternative embodiments it could have other forms, such the form of a polygon having a number of sides equal to the number n of antennas. Whatever the form of the structure 104 , the antennas are for example mounted such that a distance d between each antenna 106 and an axis a (AXIS a ) of the structure 104 is the same . For example , the DUT 107 is position at or close to a point along the axis a, or is moved along a conveyor or rail that is perpendicular to the axis a such that the DUT 107 pas ses through the transmitter/receiver 102 on or close to the axis a .

[ 0062 ] In some embodiments , the structure 104 is made o f metal , such as aluminum or copper . While this choice might be considered to lead to multiple reflections within the structure 104 , advantageously the antennas 106 are configured to absorb all , or substantially all , power emitted by the DUT 107 , which is enabled for example by impedance matching at each of the antenna ports . Additionally or alternatively, complete information concerning the radiated fields can be obtained from the set of antenna port , based on activeimpedance detection .

[ 0063 ] The antennas 106 of the antenna array are for example each coupled via corresponding cables to a correlator 108 . Additionally or alternatively, the antennas 106 are coupled to the correlator 108 via another type of link, such as by optical links between the antennas 106 and the correlator 108 . In such a case , the emission and/or reception signal at each antenna 106 is for example modulated on an optical carrier . This has the advantage of reducing interference with respect to the frequency band of the DUT 107 .

[ 0064 ] The test system 100 further comprises , for example , a time and frequency waveform generator 110 coupled to the correlator 108 , and/or a time and frequency domain instrument 112 coupled to the correlator 108 . [ 0065 ] The correlator 108 is for example capable of synchronously selecting at least two of the antennas of the antenna array, thereby allowing a cross-correlation measurement to be performed . For example , the implementation of such a correlator is described in more detail in WO2021 / 123447 , in the name of the present applicant , the contents of which is hereby incorporated by reference in its entirety .

[ 0066 ] The correlator 108 is for example configured to generate time and frequency domain correlations between : signals generated by the time and frequency waveform generator 110 for transmission via any selected pair of the antennas 106 ; and/or between signals received via any selected pair of the antennas 106 . Additionally or alternatively, the correlator 108 is configured to select one of the antennas 106 for transmission of a signal supplied by the generator 110 , and to measure at the same time signals at one or more of the other antennas 106 in order to perform a scan on the DUT 107 . Received signals from pairs of the antennas 106 are for example supplied by the correlator 108 to the time and frequency domain instrument 112 , which is for example configured to extract a radiation diagram of the DUT 107 based on the cross-correlations between the signals received from the antennas 106 . An advantage of using the cross-correlations is that the noise seen by the antennas 106 can be cancelled and a relatively high-resolution radiation diagram can be obtained .

[ 0067 ] Figure 1 illustrates , on the left , an enlarged view of one of the antennas 106 ' and part of the two neighboring antennas 106 , according to an example in which the antennas 106 are Vivaldi antennas . For example , the antenna 106 ' comprises first and second lobes 114a, 114b, separated by an air gap 116 across which a feeding line 118 is positioned, the feeding line 118 being isolated from the lobes 114a, 114b. It can be seen the first or second lobes 114a and 114b are each common with a lobe of a corresponding neighboring antennas 106.

[0068] Figure 2 schematically illustrates a test system 200 according to another example embodiment of the present disclosure. The test system 200 is similar to the test system 100, except that the transmitter/receiver 102 is replaced by a transmitter/receiver 202, which is similar to 102, but additionally comprises one or more thermal sensors (T) and/or one or more visual sensors (V) mounted on the structure 104. In the example of Figure 2, combined sensors 204 are provided having both a thermal sensor T and a visual sensor V. Furthermore, in the example of Figure 2, the number m of thermal and visual sensors is the same as the number n of antennas 106 of the antenna array, and one thermal and/or visual sensor is for example positioned between each pair of adjacent antennas 106. In alternative embodiments, it would be possible for m to be greater than or less than n.

[0069] The thermal sensors T are for example spin-cross-over sensors comprising a layer of spin-cross-over material comprising for example [ Fe (HB ( 1 , 2 , 4-triazol-l- yl ) 3 ) 2 ] bis [hydrotris (l,2,4-triazol-l-yl)borate]Fe(II) ] . Such a sensor is for example described in more detail in WO 2021/240014 in the name of the present applicant, the contents of which is hereby incorporated by reference in its entirety .

[0070] The correlator 108 is for example configured to receive temperature readings from the thermal sensors T and/or from the visual sensors V in addition to the signals received from the antennas 106. [ 0071 ] Figure 3 schematically illustrates a test system 300 according to another example embodiment of the present disclosure . The test system 300 of Figure 3 is for example similar to the test system 100 of Figure 1 , except that the structure 104 of the transmitter/receiver 102 is in the form of a cylinder . The ring of antennas 106 forming the antenna array is illustrated at one end of this cylinder . There may additionally be one or more further rings of antennas (not visible in Figure 3 ) on the inner surface of the structure 104 .

[ 0072 ] A left L of the structure 104 of Figure 3 is for example of at least 10 .

[ 0073 ] In some embodiments , the structure 104 of Figure 3 is capable of rotation around the axis a, for example thanks to a mechanism (not illustrated) configured to hold and rotate the structure 102 , while permitting the connection between the correlator 108 and the antennas 106 . Thus , as the DUT is positioned within the structure 104 or passed through the structure 102 on a rail or conveyor, the signals from the DUT 107 are for example sampled multiple times at di f ferent points of rotation of the structure 104 such that variations between the antennas can be varied .

[ 0074 ] Figure 4 schematically illustrates a test system 400 according to another example embodiment of the present disclosure . The test system 400 of Figure 4 is for example similar to the test system 300 of Figure 3 , except that , in addition to the transmitter/receiver 102 , there are multiple further transmitter/receivers 402 , which are similar to the transmitter/receiver, and aligned along the same axis a . For example , there are four transmitter/receiver modules 102 , 402 in the embodiment of Figure 4 , each comprising 8 antennas , and optionally thermal or visual sensors . In alternative embodiments, there could be a different number of transmitter/receiver modules, for example two or more modules A distance offset (DISTANCE OFFSET) between the transmitter/receiver modules 102, 402 defines a relative longitudinal sampling distance as the DUT 107 is passed along the axis a and through the cylindrical structure of each module .

[0075] Figure 5 schematically illustrates a test system 5 according to another example embodiment of the present disclosure, and illustrates a correlator 108 of the test system in more detail according to an example embodiment of the present disclosure. It is assumed in this example that there are eight transmitter/receiver modules 102, each having eight antennas.

[0076] The correlator 108 for example comprises a 2:8 correlator 502 associated with each module 102, each 2:8 correlator 502 having eight inputs/outputs , one being coupled to each of the eight antennas of the corresponding module 102. Furthermore, each 2:8 correlator 502 has two input/outputs , and is configured to permit any pair of antennas among the eight to be coupled respectively to the two input/outputs.

[0077] The correlator 108 also for example comprises a 2:16 correlator 504 having 16 inputs/outputs coupled respectively to the two inputs/outputs of each of the eight correlators 502. Furthermore, the 2:16 correlator 504 has two input/outputs, and is configured to permit any pair of input/outputs of the 16 inputs/outputs of the 2:8 correlators 502 to be coupled to the two inputs/outputs of the 2:16 correlator 504.

[0078] The two input/outputs of the 2:16 correlator 504 are for example coupled to a signal processing circuit 506, which is for example configured to perform dual-channel down- conversion on the signals , and further comprises instrumentations for processing the signals .

[ 0079 ] Of course , while Figure 5 provides an example of eight modules of eight antennas , the principles described could be applied to a di f ferent number of modules and/or to a di f ferent number of antennas in each module .

[ 0080 ] Figure 6 schematically illustrates a test system 600 according to yet another example embodiment of the present disclosure . The test system 600 of Figure 6 is for example similar to the test system 400 of Figure 4 , except that , whereas all of the transmitter/receiver modules 102 , 402 in Figure 4 have the same diameter, in the example of Figure 6 some of the transmitter/receiver modules 402 have a di f ferent diameters d' to the transmitter/receiver module 102 . In the example of Figure 6 , there are four transmitter/receiver modules aligned along the axis a, the first and last modules from left to right having a diameter d, and the second and third modules from left to right having a diameter d' , where d' <d . An advantage of providing transmitter/receiver modules of di f ferent diameters is that this permits a variation in the sensitivity and noise levels allowing a compensation for these ef fects .

[ 0081 ] Figure 7 schematically illustrates a test system 700 according to yet another example embodiment of the present disclosure . The test system 700 of Figure 7 is for example similar to the test system 400 of Figure 4 , except that it additionally comprises a conveyor or rail 702 configured to pass DUTs from left to right through each transmitter/receiver module 102 , 402 . For example , according to the embodiments described herein, the DUTs can be supplied at a relatively fast rate , such that the test time of each DUT is as low as a few milliseconds . [ 0082 ] In some embodiments , the conveyor or rail 702 comprises means for attaching the DUTs in a secure manner while they are transported along the axis a, and can be rotated around the axis a such that , rather than the modules 102 , 402 rotating, the DUT is rotated during sampling .

[ 0083 ] Figure 8 schematically illustrates a test system 800 according to yet another example embodiment of the present disclosure . The test system 800 is for similar to test system 700 of Figure 7 , but comprises modules of varying diameters , as described in relation with Figure 6 .

[ 0084 ] Figure 9 schematically illustrates a test system 900 comprising a circular array scanner formed as a hal f-circle according to an example embodiment of the present disclosure . Indeed, while the embodiments of Figures 1 to 8 concern transmitter/receiver modules having structures of an annular, cylindrical or tubular shape , it would also be possible to have one or more transmitter/receiver modules having a partannular, part-cylindrical or part-tubular structure 904 , as represented in Figure 9 . In other words , the ring, cylinder or tube is not closed, but at least partially open along its length . Figure 9 illustrates an example in which the opening is 180 ° , but more generally it is for example between 60 ° and 120 ° . The antenna array of antennas 106 is then for example also formed around a segment of circuit , rather than 360 ° . An advantage of this part-cylindrical or part-tubular shape is that it provides additional space for implementing the rail or conveyor 702 on which the DUTs are placed .

[ 0085 ] Figure 10 schematically illustrates a test system 100 comprising an antenna array comprising a metasurface according to an example embodiment of the present disclosure . In particular, the test system 1000 is similar to the test system 100 of Figure 1 , except that the transmitter/receiver 102 is replaced by a transmitter/receiver 1002 based on a metasurface 1004 having excitation/detection elements 1006 , which can be considered as antennas , even i f their ef fect is to propagate modulated surface waves based on radiating current flows over the textured surface . Indeed, as known by those skilled in the art , a metasurface is a surface formed of conductive islands on a surface , and at certain points excitation/detection elements are positioned . These excitation/detection elements 1006 are coupled to the correlator 108 in the same manner as described in relation with Figure 1 . The metasurface 1004 is for example formed on a substantially cylindrical substrate , although other shapes could be envisaged, j ust like the structure 104 . In some embodiments , an add-on lateral face 1008 is provided in order to alleviate border ef fects at the edge of the metasurface . Such a solution can support multi-beam testing of a DUT , as represented in Figure 10 by the DUT 107 emitting two beams Beam- 1 and Beam-2 .

[ 0086 ] Figure 11 schematically illustrates a test system 1100 comprising an antenna array comprising a metasurface according to another example embodiment of the present disclosure . The test system 1100 is similar to the test system 1000 of Figure 10 , except that either an add-on lateral face is provided, or other compensation elements 1102 are added around the end of the metasurface 1004 in order to compensate for edge ef fects . These compensation elements 1102 are for example dummy elements or the like .

[ 0087 ] Figure 12 illustrates schematically illustrates a test system 1200 and illustrates a signal processing circuit in detail according to an example embodiment of the present disclosure . The embodiment of Figure 12 is for example capable of providing precise temperature readings by using two different temperature measurement techniques, as will now be described in more detail.

[0088] The test system 1200 for example comprises the transmitter/receiver 202 of Figure 2 comprising the thermal sensors T. This for example permits the correlator 108 to supply thermal readings TR.

[0089] Additionally, the RF fields captured by the antennas 106 of the antenna array are for example used to estimate temperature. This for example providing by the correlator 108 an antenna input signal (Antenna Input) based on Multi-Channel Sensing, and after amplification by an amplifier A, supplying the signal to a first input port of a 180° hybrid circuit (180° Hybrid) 1202. A second output of the correlator 108 provides a reference signal (Reference) , for example chosen a coming from the antenna having a highest signal-to-noise ratio in the antenna array. After amplification by another amplifier A, the reference signal is supplied to a second input port of the 180° hybrid circuit 1202. A first output port of the 180° hybrid circuit 1202 is coupled to a further amplifier A, and then via a channel-A filter 1204 to the input of a splitter 1206. Similarly, a second output port of the 180° hybrid circuit 1202 is coupled to a further amplifier A, and then via a channel-B filter 1208 to the input of a splitter 1210.

[0090] The channels A and B from first outputs of the splitters 1206 and 1210 respectively are for example provided to a correlator 1212, which generates a cross-correlation in order to generate, after a diode 1213, a correlation of channels Al and Bl 1214.

[0091] The channels A and B from second outputs of the splitters 1206 and 1210 respectively are for example provided to a further 180° hybrid circuit (180° Hybrid) 1216, the outputs of which are coupled to a correlator 1212, which generates a cross-correlation in order to generate, after a diode 1219, a correlation of channels A2 and B2 1220.

[0092] Combination of interferometric radiometry (with embedded reference thermal sensors) combined with the nearfield scanning system provides hybrid Electromagnetic-Thermal imaging. The system is inspired from classical astrophysical receivers at microwave frequencies for instantaneous measurements in a relatively short period of time. The system is combined with calibration procedures based on reference signals as shown in Figure 12. Figure 12 for example uses the following components: Low-noise Amplifier (A) , Band-Pass filters 1204, 1208, Hybrid 180° circuit, Power-Splitters 1210, 1206, Detectors. The Hybrid 180° circuit uses custom broadband Low-Noise X-Topology Architecture for Miniature Hybrid 180°. The X-Topology design also provides robust solution against signal impairments. The following equations can be derived from Figure 12 [18-23] :

2^2 reference ‘ "-Channel- A ₂ (4)

[0093] T _Antenna is the antenna temperature, T _{Receiver-Noise} : is the receiver noise temperature, A : is the radiometer bandwidth, T: is the integration time, k _Receiver : is a constant relative to the type of receiver and imaging approach.

[0094] Accurate extraction of the temperature distribution can be obtained through correlation of the signals from the antenna array elements with the reference signal (dynamic) . The selection of the dynamic reference signal is done based on real-time SNR metrics. For example, a processing circuit (not illustrated in Figure 12) is configured to process the correlation channels Al, Bl, A2, B2 and the temperature readings TR in order to provide calibrated high precision temperature readings .

[0095] Figure 13 schematically illustrates a 180° hybrid circuit 1202, 1216 of Figure 12 having two input ports Port- 1, Port-3 and two output ports Port-2, Port-4.

[0096] Figure 14 schematically illustrates the 180° hybrid circuit of Figure 13 in more detail according to an example embodiment of the present disclosure. The input port Port-1 is for example coupled to the output port Port-2 via a circuit ODD related to ODD excitation (short-circuit conditions) , and to the output port Port-4 via a circuit EVEN related to EVEN excitation (open-circuit conditions) . Similarly, the input port Port-3 is for example coupled to the output port Port-4 via a circuit ODD related to ODD excitation (short-circuit conditions ) , and to the output port Port-2 via a circuit EVEN related to EVEN excitation ( open-circuit conditions ) .

[ 0097 ] Each of the circuits ODD for example comprises the connection of a resistor Ro in parallel with a capacitor Co , and in parallel with the series connection of a resistor ro and an inductance Lo , between the input port and an intermediate node INTI . Furthermore , it comprises the connection of a resistor Rol , in parallel with the series connection of a resistor Ro2 and an inductor Lol , between the intermediate node INTI and the output port .

[ 0098 ] Each of the circuits EVEN for example comprises a first and second branches coupled in parallel with each other between the input port and the output port . The first branch for example comprises a resistor Rel in series with a capacitor Cel . The second branch for example comprises an inductor Le in series with a resistor re between the input port and an intermediate node INT2 , and the connection of a resistor Re in parallel with a capacitor Ce between the intermediate node INT2 and the output port .

[ 0099 ] Figure 15 is a cross-section view of a transmitter/receiver 1500 comprising a flexible substrate . In particular, Figure 15 for example illustrates 3D integration of conformal chip-package-PCB-Radiator systems accounting for thermal management TM ( including harvesting) . A structure

1504 is for example tubular or part-tubular and comprises a thermal management layer TM on an outside , and conductors

1505 within the TM layer that are coupled by through via waveguiding 1507 through an intermediate flexible or rigid layer 1508 , to antenna elements 1506 , which are for example dual-polari zed elements of a dual-polari zed array . For example , the antenna elements 1506 are mounted on chip- package-PCB (printed circuit board) radiators 1509 . [ 0100 ] Figure 16 illustrates an embedded connector 1602 of the transmitter/receiver of Figure 15 in more detail according to an example embodiment , which for example comprises a redistribution layer (RDL ) , an up/down converter (U/D Converter ) 1604 , an N-Channel RFIC (AS IC - Application Speci fic Integrated Circuit ) 1606 and a DSP ( Digital Signal Processor ) AS IC 1608 . The embedded connector 1602 further comprises , for example , correlation and matching tuners .

[ 0101 ] While the embodiments of Figures 15 and 16 comprise antenna elements 1506 on the inside surface , it would equally be possible to provide antenna elements on the outer surface in place of the conductors 1505 .

[ 0102 ] Figure 17 illustrates example applications of the transmitter/receiver 1500 of Figures 15 and 16 according to example embodiments of the present disclosure . For example , the flexible substrate of the transmitter/receiver 1500 is used to provide a conformal skin that covers a part of a human or animal body, such as a hand-conformal skin 1702 , a foot- conformal skin 1704 or a lombar-conf ormal skin 1706 . Signals captured by the transmitter/receiver 1500 are for example provided to a correlator and used, for example via wireless information trans fer to a device 1708 , to visuali ze radiation information concerning the environment surrounding the skin, or internal parts of the body on which the skin is mounted .

[ 0103 ] Various embodiments and variants have been described . Those skilled in the art will understand that certain features of these embodiments can be combined and other variants will readily occur to those skilled in the art .

[ 0104 ] Finally, the practical implementation of the embodiments and variants described herein is within the capabilities of those skilled in the art based on the functional description provided hereinabove . [0105] Some further example embodiments of the present disclosure are described in the following paragraphs.

[0106] Example embodiment 1: A cylindrical structure covered with inward-pointed antennas.

[0107] Example embodiment 2: the example embodiment 1, wherein the antennas are collectively able to absorb, within some frequency bands, nearly all the power from any source located inside the cylinder.

[0108] Example embodiment 3: the example embodiment 2, where the absorbing ports correspond to (input impedances of) receivers .

[0109] Example embodiment 4: the example embodiment 1, 2 or 3, wherein the signals from/at any pair of receivers can be correlated with each other.

[0110] Example embodiment 5: Aggregation strategies (Fig.4) for combining multiple slices of N 3D elements of dualpolarized arrays into a full array state (FAS) , for example to form one single beam, or for using them to form separate beams in the sub-array state (SAS) .

[0111] Example embodiment 6: any of the example embodiments 1 to 5, wherein the 3D cylindrical slides can be of different diameters (Fig.6) to allow for additional functionalities related to calibration, de-embedding and amplitude/phase accuracy improvement .

[0112] Example embodiment 7: Any of example embodiments 1 to 6, with a rotary system (Fig.3, Fig.7, Fig.8) added for higher spatial resolution.

[0113] Example embodiment 8: A cylindrical structure covered with inward-pointed (Fig.9) and outward-pointed (Fig.10) 2D emitting/receiving network for synthesizing modulated surface [7-8] waves, for example in combination with Spintronic sensors for improved EM-Thermal resolutions. Implementation of integrated random generator arrays will bring close to the 3D antenna arrays wave-form-shaping capabilities.

[0114] Example embodiment 9: Combination of interferometric radiometry (with embedded reference thermal sensors) combined with the near-field scanning system provides hybrid Electromagnetic-Thermal imaging (Fig.11) . The thermal sensors can be combined with Spin-Cross-Over (SCO) [15-16] sensing layers .

[0115] Example embodiment 10: Combination of interferometric radiometry (with embedded reference thermal sensors) combined with the near-field scanning system provides hybrid Electromagnetic-Thermal imaging. The system is inspired from classical astrophysical receivers at microwave frequencies for instantaneous measurements in a relatively short period of time. The system is combined with calibration procedures based on reference signals as shown in Figure 12. Figure 12 for example uses the following components: Low-noise Amplifier (A) , Band-Pass filters 1204, 1208, Hybrid 180° circuit, Power-Splitters 1210, 1206, Detectors. The Hybrid 180° circuit uses custom broadband Low-Noise X-Topology Architecture for Miniature Hybrid 180°. The X-Topology design also provides robust solution against signal impairments. The following equations can be derived from Figure 12 [18-23] :

[0116] T _Antenna is the antenna temperature, T _{Receiver-Noise} : is the receiver noise temperature, A : is the radiometer bandwidth, T: is the integration time, k _Receiver : is a constant relative to the type of receiver and imaging approach.

[0117] Accurate extraction of the temperature distribution can be obtained through correlation of the signals from the antenna array elements with the reference signal (dynamic) . The selection of the dynamic reference signal is done based on real-time SNR metrics.

[0118] In prior realizations [18-23] the reference signals are considered fixed (static) and the correlations/pseudo- correlations are based on signal-channel signal analysis. We propose a multi-channel architecture solution using two-point correlation functions with dynamic reference signal. Furthermore EM-Thermal relations are exploited for improved real-time calibration procedures.

[0119] Example embodiment 11: 3D integration (for both inward-pointed and outward-pointed radiators) of Conformal

Chip-Package-PCB-Radiator systems (Fig.12 (a) ) accounting for thermal management (including harvesting) . All electronic circuitry will be brought inside the cylindric enclosure resulting in improved EMC/EMI performances.

[0120] Example embodiment 12: any of the example embodiments 1 to 11, in combination with Spintronic sensors for improved EM-Thermal resolutions.

[0121] Example embodiment 13: any of the example embodiments 1 to 12, with adds-on of lateral faces for closed enclosures based EM-Thermal sensing chambers.

[0122] Example embodiment 14: ASIC-based implementation solutions co-integrating antenna arrays with Active- Impedance-Tuners (AIT (Fig.l2 (b) ) for minimally invasive antenna array to DUT interf erences/couplings . ASIC-embedded connectors are used for building scalable and conformal antenna array systems for MIMO/Massive MIMO applications.

[0123] Example embodiment 15: Use of FPGA/ASIC dedicated processing including accelerators for building Digital-Twin platform unifying Modeling & Measurement in one single framework .

[0124] Example embodiment 16: Any of the example embodiments 1 to 15, with OTA Testing in production-Line with monitoring of faulty devices and extracting device to device Monte-Carlo based variations. (Fig.13) .

[0125] Example embodiment 17: Use of curved structures (Fig.14) realized with flexible materials, i.e. flexible coated polymer substrates on one side and flexible electronics on the other side. Alternatively, the upper radiating structures can be combined with rigid curved structures obtained through 3D-printing. This comes with the advantage of an increased freedom in design and thus a potential improvement in terms of RF-perf ormances . [ 0126 ] Example embodiment 18 : Combination of 3D radiating structures with thermal [ 39-40 ] sensing and management solutions including harvesting [ 41 ] cells co-integrated with Front-End-Modules for improved energy ef ficiency .

[ 0127 ] Example embodiment 20 : A transmitter and/or receiver comprising :

- a first cylindrical or part-cylindrical structure covered with a first antenna array formed of a plurality of inward-pointing antennas and/or a plurality of outward-pointing antennas , each of the antennas of the first antenna array being configured to transmit and/or receive electromagnetic waves , for example in the GHz range , and for example in the wavelength range 1 to 100 GHz .

[ 0128 ] Example embodiment 21 : Example embodiment 20 , further comprising :

- a correlator coupled to each of the antennas of the first antenna array and configured to generate time and frequency domain correlations between : signals generated by a time and frequency waveform generator for transmission via any selected pair of the antennas ; and/or between signals received via any selected pair of the antennas .

[ 0129 ] Example embodiment 22 : Example embodiment 20 , further comprising :

- one or more second cylindrical or part-cylindrical structures covered with a second antenna array formed of a plurality of inward-pointing antennas and/or a plurality of outward-pointing antennas , each of the antennas of the second antenna array being conf igured to transmit and/or receive electromagnetic waves . [ 0130 ] Example embodiment 23 : Example embodiment 22 , further comprising :

- a correlator coupled to each of the antennas of the first and second antenna arrays and configured to generate time and frequency domain correlations between : signals generated by a time and frequency waveform generator for transmission via any selected antenna of the first antenna array and any selected antenna of the second antenna array; and/or between signals received at any selected antenna of the first antenna array and at any selected antenna of the second antenna array .

[ 0131 ] Example embodiment 24 : Example embodiment 22 or 23 , wherein the first and one or more second cylindrical or part cylindrical structures are arranged such that their axes are aligned, in other words they are consecutive along a common axis .

[ 0132 ] Example embodiment 25 : Any of example embodiments 22 to 24 , wherein a diameter of the first cylindrical or part cylindrical structure is di f ferent from a diameter of the one or more second cylindrical or part cylindrical structures .

[ 0133 ] Example embodiment 26 : Any of example embodiments 20 to 25 , wherein each antenna of the antenna array comprises a correlation tuner configured to dynamically absorb incident waves based on speci fic criteria .

[ 0134 ] Example embodiment 27 : Any of example embodiments 20 to 26 , further comprising :

- a DUT ( device under test ) support passing through the first cylindrical or part cylindrical structure ; and

- a mechanism for rotating, around the axis of the first cylindrical or part cylindrical structure , the DUT support with respect to the first cylindrical or part cylindrical structure.

[0135] Example embodiment 28: Any of example embodiments 20 to 27, wherein the first cylindrical or part cylindrical structure further comprises one or more visual sensors and/or one or more thermal sensors, the transmitter and/or receiver for example being configured to make temperature readings, for example based on interferometer radiometry techniques, using a selected pair of antennas of the first antenna array, the selection involving selection, as a reference antenna, an antenna having a maximum signal to noise ratio (SNR) , the one or more thermal sensors for example being used for calibration

[0136] Example embodiment 29: Example embodiment 28, wherein the thermal sensors for example comprise a Spin-Cross-Over sensing layer, for example as described in the publication W02021/240014 .

[0137] Example embodiment 30: Any of example embodiments 20 to 29, further comprising multi-channel full-crossover correlators .

[0138] Example embodiment 31: Any of example embodiments 20 to 30, further comprising Active-Impedance-Tuners cointegrated with the first antenna array.

[0139] Example embodiment 32: Any of example embodiments 20 to 31, further comprising a 180° hybrid substantially as illustrated in Figure 14.

[0140] Example embodiment 33: Any of example embodiments 20 to 32, wherein the first cylindrical or part cylindrical structure is formed of flexible materials, such as a flexible coated polymer substrate on a first side of the structure, and/or flexible electronics on a second side of the structure opposite to the first side. [0141] Example embodiment 34: Any of example embodiments 20 to 32, wherein the first cylindrical or part cylindrical structure is formed of the first antenna array combined with rigid curved structures obtained through 3D-printing.

[0142] Example embodiment 35: A circuit comprising first, second, third and fourth ports coupled via a 180° hybrid substantially as illustrated in Figure 14.

[0143] Example embodiment 36: A device for medical imaging of part of the human body comprising the transmitter and/or receiver of any of the example embodiments 20 to 32.

[0144] Example embodiment 37: A method of OTA (over-the-air ) testing of a DUT comprising receiving, by the antennas of the first antenna array of the receiver of any of claims 1 to 15, signals emitted by the DUT, and determining a crosscorrelation in the frequency and time domains between signals received via pairs of the antennas of the first antenna array, and for example extracting device to device Monte-Carlo-based variations .

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