SE2030254A1

SE2030254A1 - A high-frequency mode stirrer for reverberation chambers

Info

Publication number: SE2030254A1
Application number: SE2030254A
Authority: SE
Inventors: Kent Thomra; Robert Rehammar; Sara Catteau
Original assignee: Bluetest Ab
Priority date: 2020-08-14
Filing date: 2020-08-14
Publication date: 2021-09-14
Also published as: WO2022033770A1; SE543894C2

Abstract

A method for calibrating a reverberation chamber. The method comprises arranging a high-frequency mode stirrer (100) on a spatially configurable platform in the reverberation chamber. The high-frequency mode stirrer (100) comprises: an electrically conductive member (101) arranged to reflect electromagnetic radiation; one or more apertures (102) arranged extending through the member (101), wherein the apertures (102) are arranged to diffract and to diffuse the electromagnetic radiation; and one or more electrically conductive plates (103) arranged on the member (101), wherein the plates (103) are arranged to scatter the electromagnetic radiation. The method further comprises arranging a reference antenna in the reverberation chamber, arranging a measurement antenna in the reverberation chamber, and measuring losses between the reference antenna and the measurement antenna. The method also comprises altering a spatial configuration of the platform when measuring losses and calibrating the reverberation chamber based on the measured losses.

Description

A HIGH-FREQUENCY MODE STIRRER FOR REVERBERATIONCHAMBERS TECHNICAL FIELD The present disclosure relates to test equipment for antenna systems andwireless devices in general. There are also disclosed systems and methodsfor measuring the performance of antenna systems and for testing wireless devices.

BACKGROUND Reverberation chambers (RCs), also known as electromagnetic reverberationchambers (ERCs) or mode-stirred chambers (MSCs) have become effectivetools for measuring over-the-air (OTA) performance of various wirelessdevices. RCs are mainly used for evaluating antenna system performance inradio frequency reflective environments, i.e., when the device under test (DUT) is subjected to multipath propagation. ln an RC, the signal is injected or picked up by the DUT in a closed chamber,or cavity, comprising inwardly radio frequency reflective walls. An injectedsignal arrives at the DUT after multiple reflections through many differenttrajectories. This creates a radio frequency signal fading state at the receiver.By moving mode stirring plates and/or a turntable upon which the DUT isarranged, the geometry of the chamber changes, which in turn changes thefading state that the DUT experiences. Thus, a rich isotropic multipath (RIMP)environment is efficiently generated where a large number of fading states with different incident wave compositions can be tested in an efficient manner.

With the expansion of the available frequency range in fifth generation (5G)cellular networks to the mm-wave region (e.g. >20 GHz), there is a need tocharacterize devices at these frequencies as well. Accurate Characterizationof a DUT in an RC requires accurate calibration of the RC, which includes determining and compensating for the loss between the DUT and ameasurement antenna in the RC. However, measuring the loss between theDUT and the measurement antenna becomes increasingly challenging as thefrequency increases as, i.a., the loss in the cables used to connect to theantennas increases with frequency, which decreases the signal to noise ratio.

There is a need for improved RC calibration methods and mode stirrers for mm-wave Characterization.

SUMMARY lt is an object of the present disclosure to provide for improved RC calibration methods and mode stirrers for mm-wave characterization.

This object is obtained by a method for calibrating a reverberation chamber.The method comprises arranging a high-frequency mode stirrer on a spatiallyconfigurable platform in the reverberation chamber. The high-frequency modestirrer comprises: an electrically conductive member arranged to reflectelectromagnetic radiation; one or more apertures arranged extending throughthe member, wherein the apertures are arranged to diffract and to diffuse theelectromagnetic radiation; and one or more electrically conductive platesarranged on the member, wherein the plates are arranged to scatter theelectromagnetic radiation. The method further comprises arranging areference antenna in the reverberation chamber, arranging a measurementantenna in the reverberation chamber, and measuring losses between thereference antenna and the measurement antenna. The method also comprisesaltering a spatial configuration of the platform when measuring losses andcalibrating the reverberation chamber based on the measured losses.

The high-frequency mode stirrer facilitates the distribution of high-frequencypower, i.e. reducing inhomogeneity, within the RC when the reference antennais placed off the spatially configurable platform. The stirrer is particularlyeffective at the range 20 GHz and above, especially compared to a prior artmode stirrer - referred to as a low-frequency mode stirrer from here on - which in general is a construction with metallic or othenNise electromagnetic reflective elements that can be moved to different orientations and locations inthe RC to achieve different boundary conditions in the RC.

According to aspects, the reference antenna is arranged such that a main lobeof the reference antenna is aimed with a line of sight intersecting the high-frequency mode stirrer. This can also be expressed as having the main lobedirected towards the high-frequency mode stirrer. This way, the beam of thereference antenna is always illuminating the high-frequency mode stirrer,which guarantees good stirring at the first reflection of the beam.

According to aspects, the plates are adjustably and releasably attached to themember. This provides reconfigurability for different RC scenarios.

According to aspects, the method further comprises arranging a blockingscreen to block the line of sight between the measurement antenna and the reference antenna. This reduces inhomogeneity during the calibration.

According to aspects, the losses between the reference antenna and the measurement antenna are measured with a network analyzer.

According to aspects, the method further comprises arranging one or morelow-frequency mode stirrers in the reverberation chamber, and altering aspatial configuration of the one or more low-frequency mode stirrers whenmeasuring losses. The low-frequency mode stirrers provide additional stirringand the RC can easily be reconfigured to a conventional RC by lifting out thehigh-frequency mode stirrer.

According to aspects, at least one of the plates is arranged perpendicular to asurface of the member at a mounting position of the at least one plate. Thisway, the plate can easily be mounted to the member 101 with, e.g., a nut anda bolt. Other fastening means are also possible.

According to aspects, the electrically conductive member of the high-frequencymode stirrer is formed in an arcuate shape. This provides good stirring whenplaced on a rotating platform and also effectively uses the limited space on theplatform.

According to aspects, the electrically conductive member of the high-frequencymode stirrer comprises a plurality of surfaces connected to each other to forma Z-fold configuration, wherein a fold angle is formed between two adjacentsurfaces in the plurality of surfaces. The Z-fold configuration facilitates fitting alarger surface area of the electrically conductive member into a small volumein the RC. ln addition, the adjustable fold angles facilitate reconfiguring theshape of the high-frequency mode stirrers. This can be helpful for fitting thehigh-frequency mode stirrers onto differently sized spatially configurable platforms.

According to aspects, the method further comprises adjusting any of size,shape, placement, and orientation of the one or more electrically conductiveplates in dependence of the shape of the reverberation chamber and itscontents and of a frequency range of the electromagnetic radiation. Accordingto further aspects, the method comprises adjusting at least one fold angle independence of the shape of the reverberation chamber and its contents andof the frequency range of the electromagnetic radiation. According to otheraspects, the method comprises adjusting any of size and shape of the one ormore apertures in dependence of the shape of the reverberation chamber andits contents and of the frequency range of the electromagnetic radiation.Adjusting the plates, fold angles, and apertures, as well as the number ofplates, apertures, and the surfaces in the Z-fold, may be done to optimize stirring according to a specific scenario.

There is also disclosed herein a method for measuring performance of a deviceunder test (DUT) in a reverberation chamber over a frequency band. Themethod comprises calibrating the reverberation chamber over the frequencyband using the calibration method discussed above. The reverberationchamber comprises the high-frequency mode stirrer. The method furthercomprises measuring performance of the DUT in the reverberation chamber over the frequency band.

According to aspects, the high-frequency mode stirrer is arranged on thespatially configurable platform in the reverberation chamber during the calibration step and during the measurement step. According to other aspects,the high-frequency mode stirrer is arranged on the spatially configurableplatform in the reverberation chamber during the calibration step and isarranged outside the reverberation chamber during the measurement step.

There is also disclosed herein a calibration kit for calibrating a reverberationchamber. The kit comprises a high-frequency mode stirrer arranged on aspatially configurable platform in the reverberation chamber. The high-frequency mode stirrer comprises: an electrically conductive member arrangedto reflect electromagnetic radiation; one or more apertures arranged extendingthrough the member, wherein the apertures are arranged to diffract and todiffuse the electromagnetic radiation; and one or more electrically conductiveplates arranged on the member, wherein the plates are arranged to scatter theelectromagnetic radiation. The kit further comprises a control unit comprisingprocessing circuitry and an interface. The control unit is configured to: measurelosses between a reference antenna in the reverberation chamber and ameasurement antenna in the reverberation chamber; altering a spatialconfiguration of the platform when measuring losses; and calibrate thereverberation chamber based on the measured losses.

There is also disclosed herein a computer program product comprising acomputer program configured to execute a method according to thediscussions above, and a computer readable storage medium on which the computer program is stored.

There is also disclosed herein a high-frequency mode stirrer for modifyingelectromagnetic boundary conditions in a reverberation chamber. The high-frequency mode stirrer comprises: an electrically conductive member arrangedto reflect electromagnetic radiation; one or more apertures arranged extendingthrough the member, wherein the apertures are arranged to diffract and todiffuse the electromagnetic radiation; and one or more electrically conductiveplates arranged on the member, wherein the plates arranged to scatter theelectromagnetic radiation, and wherein the plates are adjustably andreleasably attached to the member.

According to aspects, the high-frequency mode stirrer comprises aplurality of legs arranged to raise the high-frequency mode stirrer relative to aspatially configurable platform when the high-frequency mode stirrer isarranged on the platform. This way, the high-frequency mode stirrer can beplaced on top of a platform without interfering with, e.g., cables and cableconnectors. According to other aspects, the high-frequency mode stirrercomprises at least one handle for manually lifting the high-frequency modestirrer. This way, the high-frequency mode stirrer can be lifted in and out of an RC with minimal effort.

The high-frequency mode stirrer may comprise fluted knobs for attaching it toa spatially configurable platform. This way, the high-frequency mode stirrer canbe securely attached and detached quickly. Furthermore, the high-frequencymode stirrer may comprise hinges or the like to be foldable to some extent tofacilitate moving the stirrer. The stirrer may also comprise a plurality of partsthat are disassemblable.

The methods disclosed herein are associated with the same advantages asdiscussed above in connection to the different measurement devices. Thereare furthermore disclosed herein control units adapted to control some of theoperations described herein.

Generally, all terms used in the claims are to be interpreted according to theirordinary meaning in the technical field, unless explicitly defined otherwiseherein. All references to "a/an/the element, apparatus, component, means,step, etc." are to be interpreted openly as referring to at least one instance ofthe element, apparatus, component, means, step, etc., unless explicitly statedothenivise. The steps of any method disclosed herein do not have to beperformed in the exact order disclosed, unless explicitly stated. Furtherfeatures of, and advantages with, the present invention will become apparentwhen studying the appended claims and the following description. The skilledperson realizes that different features of the present invention may becombined to create embodiments other than those described in the following,without departing from the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The present disclosure will now be described in more detail with reference tothe appended drawings, where Figure 1 illustrates an example high-frequency mode stirrer; Figure 2 illustrates a reverberation chamber comprising an example high- frequency mode stirrer; Figures 3-6 illustrate top views of example high-frequency mode stirrers;Figure 7 is a plot showing the Rician K-value versus frequency; Figure 8 is a plot showing chamber losses versus frequency; Figure 9 is a flow chart illustrating methods; Figure 10 shows an example control unit; Figure 11 illustrates a computer program product; and Figures 12 and 13 are flow charts illustrating methods.

DETAILED DESCRIPTION Aspects of the present disclosure will now be described more fully withreference to the accompanying drawings. The different devices and methodsdisclosed herein can, however, be realized in many different forms and shouldnot be construed as being limited to the aspects set forth herein. Like numbersin the drawings refer to like elements throughout.

The terminology used herein is for describing aspects of the disclosure onlyand is not intended to limit the invention. As used herein, the singular forms"a", "an" and "the" are intended to include the plural forms as well, unless thecontext clearly indicates otherwise.

With the expansion of the available frequency range in 5G to the mm-waveregion (>20 GHz), there is a need to characterize devices at these frequenciesas well. The increase in the upper limit of the usable frequencies has also pushed the limit for spurious emission measurements higher, as this limit isgenerally twice the carrier frequency. Such measurements can be done in a reverberation chamber (RC).

An RC is essentially a cavity resonator with a high Q-factor. The spatialdistribution of the electromagnetic field strengths is strongly inhomogeneous,i.e. standing waves are present. This can be reduced with one or more modestirrers (also known as mode tuners). A mode stirrer is a construction withmetallic or othen/vise electromagnetic reflective elements that can be movedto different orientations and locations in the RC to achieve different boundaryconditions in the RC. The lowest usable frequency (LUF) of an RC dependson the dimensions of the chamber and stirrer design. Larger chambers presenta lower LUF than smaller chambers. Consequently, the volume V to someextent determines the Q-factor of the RC and has an impact on the LUF. Thesize and shape of a mode stirrers further affects its capability of stirring at highfrequencies, i.e. to reduce inhomogeneity in the RC. To increase stirring at allfrequencies, the device under test (DUT) is often placed on a spatiallyconfigurable platform, e.g. a rotating platform, such as a turntable, which isrotating during measurements.

The RC is a useful tool in identifying spurious emissions as it detects poweremitted from DUTs over a wide frequency range and in any direction. Todetermine the spurious power level at the DUT, the loss between the DUT andthe measurement antenna must be determined and compensated for.Measurements of the loss between the DUT and the measurement antennabecomes increasingly challenging as the frequency increases as the loss inthe cables used to connect to the antennas increases with frequency, whichdecreases the signal to noise ratio. To deal with this, the shortest cablespossible should be used. To facilitate the use of short cables, a referenceantenna for calibration, that would often be placed where the DUT will belocated, i.e. on a spatially configurable platform, can be placed off the platformand be pointed towards a mode stirring device located on the platform.

Since many DUTs are large, shrinking the RC is not a viable option to increasethe frequency capabilities. Therefore, the present disclosure relates to thespecific design features of a high-frequency mode stirring device that facilitatethe distribution of high-frequency power within the RC when the referenceantenna is placed off the spatially configurable platform.

Figure 1 shows an example embodiment of the disclosed high-frequency modestirrer. The mode stirrer consists of a folded electrically conductive membercomprising a sheet mounted around the rim of a rotating platform.Perpendicular plates are added to the flat surfaces to increase the directionsof energy scatter. Furthermore, apertures in the folded conductive sheet areadded to increase diffraction and diffusion. ln other words, there is herein disclosed a high-frequency mode stirrer 100 formodifying electromagnetic boundary conditions in a reverberation chamber.The high-frequency mode stirrer 100 comprises an electrically conductivemember 101 arranged to reflect electromagnetic radiation. ln the example ofFigure 1, the member can comprise a sheet. Other shapes are, however,possible. The member comprises a good electrical conductor, e.g. copper.One or more apertures 102 are arranged extending through the member 101.The apertures 102 are arranged to diffract and to diffuse the electromagneticradiation. One or more electrically conductive plates 103 are arranged on themember 101. The plates 103 are arranged to scatter the electromagneticradiation and the plates 103 are adjustably and releasably attached to themember 101.

The disclosed high-frequency mode stirrer 100 is suitable for reducinginhomogeneity in the RC at high frequencies. Although it can stir at anyfrequency range, it is particularly effective at 20 GHz and above, especiallycompared to a prior art mode stirrer - referred to as a low-frequency modestirrer from here on - which in general is a construction with metallic orothen/vise electromagnetic reflective elements that can be moved to differentorientations and locations in the RC to achieve different boundary conditionsin the RC.

Figures 3 - 6 show top views of high-frequency mode stirrers 100a, 100b, 100c,and 100d, which are examples of a high-frequency mode stirrer 100. As isshown in the examples of Figures 1, 2, 5, and 6, the electrically conductivemember 101 of the high-frequency mode stirrer 100 may comprise a pluralityof surfaces connected to each other to form a Z-fold configuration. ln thisconfiguration, a fold angle A is formed between two adjacent surfaces in theplurality of surfaces. This fold angle may be adjustable. A Z-fold resembles theletter Z when comprising three surfaces. However, the high-frequency modestirrer 100 may comprise any number of surfaces. Furthermore, all surfaces inthe plurality do not necessarily have the same dimensions. A mode stirrer 100comprising more than two surfaces comprises a plurality of adjustable foldangles, which may be equal or different. The Z-fold mode stirrers may beplaced on a line, as is shown in Figure 5, or around the rim of a circle, as isshown in Figure 6. Other arrangements are also possible. The Z-foldconfiguration facilitates fitting a larger surface area of the electricallyconductive member 101 into a small volume in the RC. ln addition, theadjustable fold angles facilitate reconfiguring the shape of the high-frequencymode stirrers. This can be helpful for fitting the high-frequency mode stirrers onto differently sized spatially configurable platforms.

The electrically conductive member 101 of the high-frequency mode stirrer100may comprise an arcuate shape, as is shown in the examples of Figures 3 and4. The arcuate shape is part of a cylinder in Figure 3 and the arcuate shape isa full cylinder in Figure 4. The cylinder may comprise end plates 107 and 108placed at respective ends of the cylinder, thereby forming a drum-shapedmember 101. Figures 1 and 2 show other examples of end plates 107 and 108.

The one or more electrically conductive plates 103 arranged on the member101 in the examples of Figures 1 and 2 comprise trapezoidal sheets with amounting means for attaching them to the electrically conductive member 101.Other shapes are also possible. The size, shape, placement, and orientationof the plates 103, as well as the number of plates, affect the effectiveness ofthe stirring, which can be different at different frequencies. These parameters further affect polarization balance in the RC, i.e. a ratio of orthogonalpolarizations. The size, shape, placement, and orientation of the apertures102, as well as the number of apertures, also affect the stirring and the polarization balance. ln a preferred embodiment, at least one of the plates 103 is arrangedperpendicular to the surface of the member 101 at a mounting position of theat least one plate 103. This way, the plate can easily be mounted to themember 101 with, e.g., a nut and a bolt. Other fastening means are also possible.

The high-frequency mode stirrer 100 may comprise a plurality of legs 104arranged to raise the high-frequency mode stirrer 100 relative to a spatiallyconfigurable platform 210 when the high-frequency mode stirrer 100 isarranged on the platform 210. This way, the high-frequency mode stirrer 100can be placed on top of a platform without interfering with, e.g., cables and cable connectors.

The high-frequency mode stirrer 100 may comprise at least one handle 105for manually lifting the high-frequency mode stirrer 100. This way, the high-frequency mode stirrer100 can be lifted in and out of an RC with minimal effort.

The high-frequency mode stirrer 100 may comprise fluted knobs 106 forattaching it to a spatially configurable platform 210. This way, the high-frequency mode stirrer 100 can be securely attached and detached quickly.Furthermore, the high-frequency mode stirrer 100 may comprise hinges or thelike to be foldable to some extent to facilitate moving the stirrer. The stirrer may also comprise a plurality of parts that are disassemblable. lt is an advantage that the high-frequency mode stirrer 100 is easily moved -an advantage made even greater with any of the optional legs, handles, andfluted knobs. This provides a flexibility when using the RC. ln an examplescenario, a conventional RC is used for DUT Characterization (e.g. measuringspurious emission) without the disclosed high-frequency mode stirrer 100 fora lower frequency range (e.g. 100 MHz - 20 GHz). Thereafter, the high- frequency mode stirrer 100 is placed on the spatially configurable platform 210 and the DUT is characterized for an upper frequency range (e.g. 20 - 70 GHz).This way, the DUT can be characterized for a large range of frequencies withminimal reconfiguration of the RC, and therefore minimal effort and time. Thehigh-frequency mode stirrer 100 may be used for both measurements of theDUT and for calibration of the RC, or it can be used only for calibration. ln thelatter case, the mode stirrer 100 is lifted into the RC before calibration at the upper frequency range and is removed aftenlvards. lt is naturally possible to take advantage of the benefits of the disclosed high-frequency mode stirrer 100 when it is placed on other locations than on thespatially configurable platform 210 in the RC or when it is placed in other environments.

There is also disclosed herein a reverberation chamber 210 comprising thehigh-frequency mode stirrer 100, as shown in the example of Figure 2. Thereverberation chamber 210 may comprise any of: a spatially configurableplatform 210, a reference antenna 230, a measurement antenna 240, ablocking screen 250, and one or more low-frequency mode stirrers 260. Thereverberation chamber may also comprise a control unit 1060 for RCcalibration, which is discussed in more detail below.

As mentioned, calibration is crucial for DUT Characterization in an RC; lossbetween the DUT and the measurement antenna must be determined andcompensated for. Therefore, there is also herein disclosed a method forcalibrating a reverberation chamber 210.

The reference antenna is used for the calibration. instead of being placedwhere the DUT will be located, i.e. on the spatially configurable platform, it isplaced off the platform and is pointed towards the high-frequency mode stirringdevice located on the platform. This facilitates the use of short cables, whichimproves the signal to noise ratio. The moving platform and high-frequencymode stirrer distribute the energy transmitted by the reference antennathroughout the chamber, creating an isotropic environment even when thereference antenna is highly directive, which is an advantage. The chamber loss is measured between the directive reference antenna and a measurement antenna, which is optionally located behind the blocking screen, while theplatform moves. The high-frequency mode stirrer 100 could be used to allowmeasurement of highly directive antennas or systems in an RC. These typesof systems are becoming more common at higher frequencies, and the priorart RC designs may not stir the high frequency energy sufficiently without thisadditional type of stirrer. ln other words, there is disclosed herein a method for calibrating areverberation chamber 210, which is illustrated in Figure 9. The methodcomprises arranging S1 a high-frequency mode stirrer 100 on a spatiallyconfigurable platform 220 in the reverberation chamber 210. The high-frequency mode stirrer 100 comprises: an electrically conductive member 101arranged to reflect electromagnetic radiation; one or more apertures 102arranged extending through the member 101, wherein the apertures 102 arearranged to diffract and to diffuse the electromagnetic radiation; and one ormore electrically conductive plates 103 arranged on the member 101, whereinthe plates 103 are arranged to scatter the electromagnetic radiation. Themethod further comprises arranging S2 a reference antenna 230 in thereverberation chamber 210. The method also comprises arranging S3 ameasurement antenna 240 in the reverberation chamber 210 and measuringS4 losses between the reference antenna 230 and the measurement antenna240. The method further comprises altering S5 a spatial configuration of theplatform 220 when measuring S4 losses and calibrating S6 the reverberationchamber 210 based on the measured losses. Altering S5 a spatialconfiguration can mean to rotate the platform if the platform is a turntable. Thealtering occurs at the same time as when the measurements occur. ln anexample, the measurements comprise gathering 1000 samples over 10seconds, wherein the platform is a turntable that is rotating during those 10seconds.

After the calibration method has been performed. The calibrated RC can beused to characterize the DUT in various ways. For example, spuriousemissions of the DUT can be measured. ln that case, the DUT can be operated as “stand alone", i.e. it is not necessary to connect a measurement instrumentto it, and a spectrum analyzer is connected to the measurement antenna.

Another example is to measure in-band radiated emissions.

According to aspects, the reference antenna 230 is arranged such that a mainlobe of the reference antenna 230 is aimed with a line of sight intersecting thehigh-frequency mode stirrer 100. Since the main lobe has an angular crosssection (e.g. specified by the half power beam width), “line of sight” is notnecessarily a straight line from the peak power of the lobe to the center of thehigh-frequency mode stirrer. Furthermore, it is not necessary that the holemode-stirrer is illuminated. As such, roll, pitch, and jaw of the referenceantenna, as well as its position in the RC, may be adjusted in dependence ofthe shape of the reverberation chamber 210 and its contents and of thefrequency range of the electromagnetic radiation. The disclosed high-frequency mode stirrer 100 together with the reference antenna 230 ensureadequate stirring. The design of the disclosed mode stirrer provides sufficientscattering, diffusing, and diffracting of the electromagnetic radiation. Since thebeam of the reference antenna is always illuminating at least part of the high-frequency mode stirrer 100 (the main lobe of the reference antenna 230 isaimed with a line of sight intersecting the high-frequency mode stirrer 100),good stirring is guaranteed at the first reflection of the beam, especially sincethe high-frequency mode stirrer 100 is arranged on the spatially configurableplatform 220, which is moving during the measurements. This mechanic canbe compared to a beam that sometimes hits a wall of the chamber, which isstatic and provides poor stirring, which is a scenario that sometimes happenin a conventional RC with conventional low-frequency mode stirrers.Furthermore, stirring should preferably be achieved as early as possible (e.g.at the first reflection) since every reflection in the RC is lossy, which is aproblem that increases with frequency. Therefore, the disclosed high-frequency mode stirrer 100 and the disclosed calibration method performsmuch better compared to prior art solutions.

Measuring S4 losses between the reference antenna 230 and the measurement antenna 240 can be to measure scattering parameters between the reference antenna 230 and the measurement antenna 240. ln that case,the losses between the reference antenna 230 and the measurement antenna240 may be is measured with a network analyzer. ln practice, chamber lossesare determined by average measurements for many different positions of themode stirrers (for any frequency), and many positions of the spatiallyconfigurable platform. RC calibration methods are further described in Furht,Borko, and Syed A. Ahson, eds. Long Term Evolution: 3GPP LTE radio andcellular technology. Crc Press, 2016. Measuring losses can also be to take theratio of measured power delivered to the measurement antenna over poweravailable to the reference antenna when the reference antenna is transmittingand the measurement antenna is receiving. This may also be done vice versa since the equipment is reciprocal.

The method may further comprise arranging S7 a blocking screen 250 to blockthe line of sight between the measurement antenna 240 and the referenceantenna 230. This reduces inhomogeneity during the calibration. The blockingscreen 250 may also be arranged such that it blocks the line of sight betweenthe measurement antenna 240 and the DUT during Characterization of theDUT.

The method may further comprise arranging S8 one or more low-frequencymode stirrers 260 in the reverberation chamber 210 and altering S9 a spatialconfiguration of the one or more low-frequency mode stirrers 260 whenmeasuring S4 losses. Altering a spatial configuration can, e.g., be to move amode stirrer back and forth on a line. With this feature, the RC can easily bere-arranged to a conventional RC for lower frequencies by lifting out the high-frequency mode stirrer 100 from the RC.

According to the discussion above, the electrically conductive member 101 ofthe high-frequency mode stirrer 100 may be formed in an arcuate shape and/orthe electrically conductive member 101 of the high-frequency mode stirrer 100may comprise a plurality of surfaces connected to each other to form a Z-foldconfiguration, wherein a fold angle A is formed between two adjacent surfacesin the plurality of surfaces.

According to aspects, the plates 103 are adjustably and releasably attached tothe member 101. Therefore, the method may further comprise adjusting S01any of size, shape, placement, and orientation of the one or more electricallyconductive plates 103 in dependence of the shape of the reverberationchamber 210 and its contents and of a frequency range of the electromagneticradiation. The contents include items inside the RC and their shape andelectromagnet properties. The items can be the spatially configurable platform210, the reference antenna 230, the measurement antenna 240, the blockingscreen 250, one or more low-frequency mode stirrers 260, the DUT, and thecontrol unit 1060. As previously mentioned, at least one of the plates 103 maybe arranged perpendicular to a surface of the member 101 at a mountingposition of the at least one plate 103. The method may also comprise adjustingS02 at least one fold angle A in dependence of the shape of the reverberationchamber 210 andelectromagnetic radiation. The method may further comprise adjusting S03 its contents and of the frequency range of the any of size and shape of the one or more apertures 102 in dependence of theshape of the reverberation chamber 210 and its contents and of the frequencyrange of the electromagnetic radiation. The apertures can be adjusted by, e.g., covering parts of the apertures with a metal cover.

Adjusting the plates, fold angles, and apertures, as well as the number ofplates, apertures, and the surfaces in the Z-fold, may be done to optimizestirring according to a specific scenario. A scenario can e.g. be a frequencyrange of 20 - 70 GHz in a 2 x 2 x 2 m^3 RC comprising a turntable with a 0.5-m dimeter and 0.3-m height. Example dimensions of the apertures and platesare cross sections with dimeters in the range of 0.1 to 20 cm. An exampledimension of a flat high-frequency mode stirrer is 0.5 x 0.5 m^2. Thedimensions of the mode stirrer may naturally also be adjusted for the differentscenarios mentioned above. As mentioned, adjustments also affect polarization balance in the RC, i.e. a ratio of orthogonal polarizations.

There is also disclosed herein a method for measuring performance of a deviceunder test (DUT) in a reverberation chamber 210 over a frequency band, as isillustrated in Figure 13. The method comprises calibrating SA1 the reverberation chamber 210 over the frequency band according to thecalibration method discussed above, wherein the RC comprises the high-frequency mode stirrer 100 discussed above. The method further comprisesmeasuring SA2 performance of the DUT in the reverberation chamber 210over the frequency band. Measuring performance can be, e.g., spurious emission measurements or in-band radiated emissions measurements.

According to aspects, the high-frequency mode stirrer 100 is arranged on thespatially configurable platform 220 in the reverberation chamber 210 duringthe calibration SA1 step and during the measurement SA2 step. According toother aspects, the high-frequency mode stirrer 100 is arranged on the spatiallyconfigurable platform 220 in the reverberation chamber 210 during thecalibration SA1 step and is arranged outside the reverberation chamber 210during the measurement SA2 step.

One way of quantifying how well stirred the energy is in an RC is, is with theRician K-value, which is a measure of how much energy that reaches themeasurement antenna directly from the reference antenna. This energy is notstirred, so the smaller the Rician K-value is, the better. Figure 7 shows themeasured Rician K-value with and without an example of the disclosed high-frequency mode stirrer in an RC. lt should be noted that conventional low-frequency mode stirrers are present in both cases. The average K-value forthe frequency range 24 to 67 GHz is reported for both cases in the table below.The disclosed high-frequency mode stirrer improves the K-value by almost 10dB.

Case Average Rician K-value [dB]No high-frequency mode stirrer -9.5558With a high-frequency mode stirrer -19.191 lt has also been confirmed that the chamber loss measured with the modestirrer is the same as the chamber loss measured by a reference antenna located on the rotating platform from 6 to 30 GHz. Figure 8 shows the chamberloss measured with these two methods. The peak-to-peak difference is generally below 1 dB between the three measurements.

Figure 10 schematically illustrates, in terms of a number of functional units, thecomponents of the control unit 1060 according to an embodiment of thediscussions herein. Processing circuitry 1010 is provided using anycombination of one or more of a suitable central processing unit CPU,multiprocessor, microcontroller, digital signal processor DSP, etc., capable ofexecuting software instructions stored in a computer program product, e.g. inthe form of a storage medium 1030. The processing circuitry 1010 may furtherbe provided as at least one application specific integrated circuit ASIC, or field programmable gate array FPGA.

Particularly, the processing circuitry 1010 is configured to cause the controlunit 1060 to perform a set of operations, or steps, such as the methodsdiscussed in connection to Figures 9 and 12. For example, the storage medium1030 may store the set of operations, and the processing circuitry 1010 maybe configured to retrieve the set of operations from the storage medium 1030to cause the control unit 1060 to perform the set of operations. The set ofoperations may be provided as a set of executable instructions. Thus, theprocessing circuitry 1010 is thereby arranged to execute methods as hereindisclosed.

The storage medium 1030 may also comprise persistent storage, which, forexample, can be any single one or combination of magnetic memory, opticalmemory, solid state memory or even remotely mounted memory.

The control unit 1060 may further comprise an interface 1020 forcommunications with at least one external device, such as the referenceantenna 230, the measurement antenna 240, the spatially configurableplatform 220, the low-frequency mode stirrers 260, at least one DUT, and measurement equipment. As such the interface 1020 may comprise one or more transmitters and receivers, comprising analogue and digital components and a suitable number of ports for wireline or wireless communication.

The processing circuitry 1010 controls the general operation of the control unit1060 e.g. by sending data and control signals to the interface 1020 and thestorage medium 1030, by receiving data and reports from the interface 1020,and by retrieving data and instructions from the storage medium 1030. Othercomponents, as well as the related functionality, of the control node are omittedin order not to obscure the concepts presented herein.

A central function of the control unit 1060 is to transmit test signals via theinterface 1020 to, e.g., the reference antenna 230, the measurement antennaand/or the DUT. A test signal may, e.g., comprise control signaling and datasignals. The test signal may be a baseband signal, or a radio frequency signal.The control unit may also be configured to control operation of the spatiallyconfigurable platform 220 and the low-frequency mode stirrers 260, accordingto a pre-determined pattern of displacement, or adaptively in response to somefeedback signal.

The different control programs that the control unit executes can be stored inthe storage medium 1030. ln summary, there is disclosed herein a calibration kit for calibrating areverberation chamber 210. The kit comprises a high-frequency mode stirrer100 arranged on a spatially configurable platform 220 in the reverberationchamber 210. The high-frequency mode stirrer 100 comprises: an electricallyconductive member 101 arranged to reflect electromagnetic radiation; one ormore apertures 102 arranged extending through the member 101, wherein theapertures 102 are arranged to diffract and to diffuse the electromagneticradiation; and one or more electrically conductive plates 103 arranged on themember 101, wherein the plates 103 are arranged to scatter theelectromagnetic radiation. The calibration kit further comprises a control unit1060 comprising processing circuitry 1010 and an interface 1020. The controlunit 1060 is configured to: measure SX1 losses between a reference antenna 230 in the reverberation chamber 210 and a measurement antenna 240 in thereverberation chamber 210; altering SX2 a spatial configuration of the platform220 when measuring SX1 losses; and calibrate SX3 the reverberationchamber 210 based on the measured losses. The steps executed by thecontrol unit are demonstrated in Figure 12.

Figure 11 schematically illustrates a computer program product 1100,comprising a set of operations 1110 executable by the control unit 1060. Theset of operations 1110 may be loaded into the storage medium 1030 in thecontrol unit 1060. The set of operations may correspond to the methodsdiscussed above in connection to Figures 9 and 12. ln the example of Figure 11, the computer program product 1100 is illustratedas an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc)or a Blu-Ray disc. The computer program product could also be embodied asa memory, such as a random-access memory (RAM), a read-only memory(ROM), an erasable programmable read-only memory (EPROM), or anelectrically erasable programmable read-only memory (EEPROM) and moreparticularly as a non-volatile storage medium of a device in an externalmemory such as a USB (Universal Serial Bus) memory or a Flash memory,such as a compact Flash memory. Thus, while the computer program is hereschematically shown as a track on the depicted optical disk, the computerprogram can be stored in any way which is suitable for the computer programproduct.

Claims

1. A method for calibrating a reverberation Chamber (210), the method comprising: arranging (S1) a high-frequency mode stirrer (100) on a spatially configurableplatform (220) in the reverberation chamber (210), the high-frequency modestirrer (100) comprising an electrically conductive member (101) arranged to reflect electromagnetic radiation, one or more apertures (102) arranged extending through the member(101), wherein the apertures (102) are arranged to diffract and to diffusethe electromagnetic radiation, and one or more electrically conductive plates (103) arranged on the member(101), (103)electromagnetic radiation; wherein the plates are arranged to scatter the arranging (S2) a reference antenna (230) in the reverberation chamber (210); arranging (S3) a measurement antenna (240) in the reverberation chamber(210); measuring (S4) losses between the reference antenna (230) and the measurement antenna (240); altering (S5) a spatial configuration of the platform (220) when measuring (S4) losses;and calibrating (S6) the reverberation chamber (210) based on the measuredlosses.

2. The method according to claim 1, wherein the reference antenna (230) isarranged such that a main lobe of the reference antenna (230) is aimed with a line of sight intersecting the high-frequency mode stirrer (100).

3. The method according to any previous claim, wherein the plates (103)are adjustably and releasably attached to the member (101 ).

4. The method according to any previous claim, further comprising arranging (S7) a blocking screen (250) to block the line of sight between themeasurement antenna (240) and the reference antenna (230).

5. The method according to any previous claim, wherein the losses betweenthe reference antenna (230) and the measurement antenna (240) are measured with a network analyzer.

6. The method according to any previous claim, further comprising arranging (S8) one or more low-frequency mode stirrers (260) in thereverberation chamber (210), and altering (S9) a spatial configuration of the one or more low-frequency modestirrers (260) when measuring (S4) losses.

7. The method according to any previous claim, wherein at least one of theplates (103) is arranged perpendicular to a surface of the member (101) at a mounting position of the at least one plate (103).

8. The method according to any previous claim, wherein the electricallyconductive member (101) of the high-frequency mode stirrer (100) is formed in an arcuate shape.

9. The method according to any previous claim, wherein the electricallyconductive member (101) of the high-frequency mode stirrer (100) comprisesa plurality of surfaces connected to each other to form a Z-fold configuration,wherein a fold angle (A) is formed between two adjacent surfaces in the plurality of surfaces.

10. The method according to any previous claim, further comprising adjusting (S01) any of size, shape, placement, and orientation of the one ormore electrically conductive plates (103) in dependence of the shape of thereverberation chamber (210) and its contents and of a frequency range of the electromagnetic radiation.

11. The method according to claim 9, further comprising adjusting (S02) at least one fold angle (A) in dependence of the shape of thereverberation chamber (210) and its contents and of the frequency range ofthe electromagnetic radiation.

12. The method according to any previous claim, further comprising adjusting (S03) any of size and shape of the one or more apertures (102) independence of the shape of the reverberation chamber (210) and its contents and of the frequency range of the electromagnetic radiation.

13. A method for measuring performance of a device under test (DUT) in a reverberation chamber (210) over a frequency band, the method comprising calibrating (SA1) the reverberation chamber (210) comprising the high-frequency mode stirrer (100) over the frequency band using the methodaccording to any of claims 1-12, and measuring (SA2) performance of the DUT in the reverberation chamber (210)over the frequency band.

14. The method according to claim 13, wherein the high-frequency modestirrer (100) is arranged on the spatially configurable platform (220) in thereverberation chamber (210) during the calibration (SA1) step and during themeasurement (SA2) step.

15. The method according to claim 13, wherein the high-frequency modestirrer (100) is arranged on the spatially configurable platform (220) in thereverberation chamber (210) during the calibration (SA1) step and is arrangedoutside the reverberation chamber (210) during the measurement (SA2) step.

16. A calibration kit for calibrating a reverberation chamber (210) comprising: a high-frequency mode stirrer (100) arranged on a spatially configurableplatform (220) in the reverberation chamber (210), the high-frequency mode stirrer (100) comprising an electrically conductive member (101) arranged to reflect electromagnetic radiation, one or more apertures (102) arranged extending through the member(101), wherein the apertures (102) are arranged to diffract and to diffusethe electromagnetic radiation, and one or more electrically conductive plates (103) arranged on the member(101), (103)electromagnetic radiation, wherein the plates are arranged to scatter the a control unit (1060) comprising processing circuitry (1010) and an interface(1020), the control unit (1060) configured to measure (SX1) losses between a reference antenna (230) in thereverberation chamber (210) and a measurement antenna (240) in thereverberation chamber (210), altering (SX2) a spatial configuration of the platform (220) when measuring (SX1) losses, and calibrate (SX3) the reverberation chamber (210) based on the measuredlosses.

17. A computer program product (1100) comprising a computer program(1110) configured to execute a method according to at least one of claims 1-16, and a computer readable storage medium (1120) on which the computerprogram is stored.

18. A high-frequency mode stirrer (100) for modifying electromagneticboundary conditions in a reverberation chamber, the high-frequency modestirrer (100) comprising an electrically conductive member (101) arranged to reflect electromagneticradiation, one or more apertures (102) arranged extending through the member (101),wherein the apertures (102) are arranged to diffract and to diffuse theelectromagnetic radiation, and one or more electrically conductive plates (103) arranged on the member (101), wherein the plates (103) arranged to scatter the electromagnetic radiation, and wherein the plates (103) are adjustably and releasably attachedto the member (101).

19. The high-frequency mode stirrer (100) according to claim 18, wherein atleast one of the plates (103) is arranged perpendicular to the surface of the member (101) at a mounting position of the at least one plate (103).

20. The high-frequency mode stirrer (100) according to any of claims 18-19,wherein the electrically conductive member (101) comprises an arcuate shape.

21. The high-frequency mode stirrer (100) according to any of claims 18-20,wherein the electrically conductive member (101) comprises a plurality ofsurfaces connected to each other to form a Z-fold configuration, wherein a foldangle (A) is formed between two adjacent surfaces in the plurality of surfaces.

22. The high-frequency mode stirrer (100) according to any of claims 18-21,comprising a plurality of legs (104) arranged to raise the high-frequency modestirrer (100) relative to a spatially configurable platform (220) when the high-frequency mode stirrer (100) is arranged on the platform (220).

23. The high-frequency mode stirrer (100) according to any of claims 18-22,comprising at least one handle (105) for manually lifting the high-frequencymode stirrer (100).

24. A reverberation chamber (210) comprising the high-frequency modestirrer (100) according to any of claims 18-23.