SE544144C2 - A hybrid antenna measurement chamber - Google Patents

Abstract

A measurement chamber (100) for measuring performance of an antenna under test, AUT, (110) arranged inside the measurement chamber. The measurement chamber comprises a radio frequency reflective surface (122) arranged circumferentially about a main axis (A) of the measurement chamber (100). The reflective surface (122) is arranged to form a waveguide extending along the main axis (A). The waveguide has two waveguide openings (121) at respective ends of the waveguide. The measurement chamber (100) further comprises a mode generator antenna (130) arranged inside the measurement chamber. The mode generator antenna is arranged to transmit and/or to receive (131) a radio frequency signal to/from the AUT (110) via at least a part of the waveguide. The radio frequency signal comprises a plurality of differentorder propagating modes. The mode generator antenna (130) and radio frequency scattering properties inside the measurement chamber (100) are arranged to present a selected mode configuration at the AUT.

Description

TITLE A HYBRID ANTENNA IVIEASUREIVIENT CHAIVIBER 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 Over-the-air (OTA) characterization of antenna systems evaluates the impactof hardware, wave propagation, and signal processing on the overall antennasystem. Challenges in OTA characterization come from the global shifttowards multi-antenna systems (as in multiple-input multiple-output, l\/lll\/IO,antenna systems, or massive l\/lll\/IO systems), advanced signal processing(e.g. hybrid analog-digital beamforming), and much higher levels of integrationbetween individual components (e.g., antennas, power amplifiers, filters, etc.).Conductive testing (i.e. not wirelessly) of antenna systems is not sustainablefor a large number of antenna ports, and is even more difficult with massivel\/lll\/IO systems, especially when operated at higher frequency bands, e.g., atmmWave. High levels of integration also make conductive testing challenging.Furthermore, the global shift towards multi-antenna systems requires theantenna systems to be evaluated in terms of many different performancefigures-of-merits (FOl\/ls).

Today, there are no antenna measurement systems or techniques that supportall required performance FOl\/ls in order to test their conformance tointernational standards using a single measurement setup or even a singleantenna measurement chamber. l\/loreover, standardized measurementchambers and techniques are in many cases complex, and hence not so cost- efficient.

Therefore, there is a need for antenna measurement systems and techniquesthat are flexible, and cost and time effective.

SUMMARY lt is an object of the present disclosure to provide improved measurementchambers and measurement methods for measuring performance of an antenna under test.

This object is at least in part obtained by a measurement chamber formeasuring performance of an antenna under test, AUT, arranged inside themeasurement chamber. The measurement chamber comprises a radiofrequency reflective surface arranged circumferentially about a main axis A ofthe measurement chamber. The reflective surface is arranged to form awaveguide extending along the main axis A. The waveguide has twowaveguide openings at respective ends of the waveguide. The measurementchamber further comprises a mode generator antenna arranged inside themeasurement chamber. The mode generator antenna is arranged to transmitand/or to receive a radio frequency signal to/from the AUT via at least a partof the waveguide. The radio frequency signal comprises a plurality of different-order propagating modes. The mode generator antenna and radio frequencyscattering properties inside the measurement chamber are arranged to present a selected mode configuration at the AUT.

The disclosed measurement chamber enables an increased flexibility,compared to known techniques, of generating and reconfiguring any desiredantenna testing conditions in a single measurement environment, i.e.,chamber, while at the same time keeping the measurement time and costsdown. For example, the measurement chamber enables characterization ofantenna systems in anechoic environment, the environment of a reverberationchamber, or anything in between in a single measurement system. l\/lorespecifically, the measurement chamber allows for different testing conditionsranging from isotropic multipath environment to a single line of sightenvironment, and anything in between. This allows for testing the AUT in many different scenarios, e.g. different beamforming and multiple-input multiple-output antenna system scenarios. The measurement chamber is capable ofcharacterizing the AUT in at least total radiated power, total isotropicsensitivity, effective isotropic radiated power, effective isotropic sensitivity,error vector magnitude, adjacent channel leakage ratio, and spectrumemission mask. Furthermore, the measurement chamber has high powerhandling capabilities.

According to aspects, at least one delimiting surface of the measurementchamber forms a body with a through hole along the main axis (A), whereinthe at least one delimiting surface of the measurement chamber constitutes the waveguide This provides a cost effective and easy to assemble waveguide. For example,two walls, the ceiling, and the floor of a chamber may be covered or coatedwith electrically conductive material, such as metal (e.g. aluminum or copper).

According to aspects, at least one delimiting surface of a reverberationchamber forms a body with a through hole along the main axis A, where the atleast one delimiting surface of the reverberation chamber constitutes thewaveguide. ln that case, the two remaining walls of the reverberation chambermay comprise radio frequency absorbent material This way, a normal reverberation chamber may be converted into the measurement chamber.

According to aspects, a waveguide opening comprises a section with blinds.The blinds are arranged to reflect radio frequency signals when in a closedstate and to let radio frequency signals pass through when in an opened state.

Preferably, radio frequency absorbent material is arranged such that radiofrequency signals incident on the section with blinds is attenuated when theblinds are in the opened state. The blinds may be partially open. This way, theamount of absorption of the radio frequency absorbent material may becontrolled, i.e. the amount of attenuation of the electromagnetic signal incidenton the section with blinds is controlled. Such controllable attenuation could beused for having the measurement chamber operating mostly like a reverberation Chamber, but with some attenuation to give the measurementchamber much higher power capabilities (over a normal reverberationchamber), which is an advantage.

According to aspects, at least one delimiting surface of a reverberationchamber forms a body with a through hole along the main axis A, where the atleast one delimiting surface of the reverberation chamber constitutes thewaveguide. ln that case, the two remaining walls of the reverberation chambermay comprise one or more holes arranged to pass the radio frequency signal to/from the AUT and the mode generator antenna.

This way, particular scattering properties of the middle compartment can beseparated from wave propagation towards/from the AUT/mode generator antenna.

According to aspects, the one or more surfaces in the measurement chamberoutside of the waveguide comprise radio frequency absorbent material.

This way, the AUT and mode generator antenna can be placed in anechoiccompartments while a middle compartment presents an environment similar tothat in a reverberation chamber. The benefits of a reverberation chamber canthen be combined with the benefits of deterministic wave propagation directions given by an anechoic environment.

According to aspects, the measurement chamber comprises one or more mode stirrers.

The mode stirrer (also called tuner) can reduce the inhomogeneity of standingwaves in a cavity, which is advantageous when the measurement chamber isoperating at or close to a normal reverberation chamber. The mode stirrer mayalso constitute the optional reflective element used to present a selected modeconfiguration at the AUT. The mode stirrer may be curved or adapted forcertain propagations/directions and may be movable or reconfigurable. Themode stirrer may cover a whole wall, ceiling or floor. This way, the waveguide dimensions of the waveguide may be reconfigurable.

According to aspects, the waveguide openings may be closed off by respectivemodular wall sections. ln that case, the AUT and/or the mode generator antenna is arranged on the one or more modular wall sections.

The modular wall sections can be used to quickly swap between different modegenerator antennas arranged in different wall sections and/or betweendifferent AUTs arranged in different wall sections.

The above object is also at least in part obtained by a method for measuringperformance of an antenna under test, AUT, arranged inside a measurementchamber. The method comprises configuring a radio frequency reflectivesurface circumferentially about a main axis of the measurement chamber. Thereflective surface is arranged to form a waveguide extending along the mainaxis, where the waveguide has two waveguide openings at respective ends ofthe waveguide. The method further comprises configuring a mode generatorantenna inside the measurement chamber. The mode generator antenna isarranged to transmit and/or receive a radio frequency signal to the AUT via atleast a part of the waveguide. The radio frequency signal comprises a pluralityof propagating modes. The method also comprises arranging the modegenerator antenna and the radio frequency scattering properties inside themeasurement chamber to present a selected mode configuration at the AUT.This can be done by extracting the propagation properties of the measurementchamber, e.g. via computer simulations and/or via routine experimentation. Byknowledge of the propagation properties, that is, chamber modes, of themeasurement chamber, the mode generator antenna can be constructed tocouple to the modes in whatever way is advantageous for the testing to bedone. The method further comprises measuring performance of the AUT.

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 the operations described herein.

Generally, all terms used in the claims are to be interpreted according to theirordinary meaning in the technical field, unless explicitly defined otherwise herein. 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 statedotherwise. 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 Figures 1-4 schematically illustrate example measurement chambers.

Figure 5 is a flowchart 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.

Challenges of OTA characterization of antenna systems come from the global shift towards multi-antenna systems, more advanced (digital) signal processing, and much higher levels of integration between individualcomponents and sub-systems. l\/lulti-antenna systems and signal processingallows for various beamforming and l\/lll\/IO techniques, such as: beamforming,which serves single users by directing the energy of the electromagnetic signaltoward the user; generalized beamforming, which serve single users bysending the same data stream in different directions and possibly formingzeros (nulls) in the directions of other users; single-user l\/lll\/IO (SU-l\/lll\/IO),which increases data rates by transmitting several data streams to a user; multi-user l\/lll\/IO (l\/lU-l\/lll\/lO), which simultaneously serve multiple users.

Performance testing of such multi-antenna systems generally requirescomplicated test methods and there are many critical figures of merit (FOl\/l)for performance of the antenna system. Especially relevant FOl\/ls are: the totalradiated power (TRP) in transmit mode; the total isotropic sensitivity (TIS) inthe receive mode; the effective isotropic radiated power (EIRP) in transmitmode; the effective isotropic sensitivity (EIS) in receive mode; the error vectormagnitude (EVl\/l), the adjacent channel leakage ratio (ACLR); and thespectrum emission mask (SEl\/l). l\/lany of these FOl\/ls are dependent on, i.a,noise, interfering signals, nonlinear distortion and impedances, e.g., theantenna impedance presented to a nonlinear component connected to it. lt isnoted that many other FOl\/ls may also be relevant.

There are no known measurement systems that can support all requiredmeasurement FOl\/ls using a single measurement setup nor a single antennameasurement chamber, i.e., a do-it-all chamber. The subsequent use ofmultiple conventional chambers is too expensive to satisfy all the impendingneeds of antenna characterization. Furthermore, a multi-room measurementcampaign is time-consuming. FOl\/I measurements are typically done at manyoccasions, as in, e.g., production testing, conformance testing, performancetesting, device characterization during the design phase, etc.

The state-of-the-art antenna measurement methods typically utilize large-scale anechoic chambers (ACs). One example is indoor anechoic chamber(IAC), where a measurement probe antenna is placed in the radiating near field region of the antenna under test (AUT). The method can be used toperform the most comprehensive far- and near-field tests. A drawback is thatthe test range is relatively large compared to a second example: the compactantenna test range (CATR), which is similar to lAC but is more compact dueto quasi-optical transformations, typically performed through reflectorsurfaces. A third example is the plane wave synthesizer, PWS (or plane wavegenerator, PGS), which synthesize a plane wave via an array antenna directlyilluminating the DUT. This room can be compact as well but requires carefulcalibration and is not the most cost-effective solution. Reverberation chambers(RCs) represent a relatively new and more cost-effective measurementtechnology, especially for TRP and TRP-based figures-of-merit, as comparedto ACs, but can be utilized for a limited number of measurement metrics andpropagation scenarios. At least one limitation of the AC-based methods is thatonly a single angle-of-arrival (AoA)/angle-of-departure (AoD) can be emulated.This problem is resolved when measuring in RCs, which create a so-called Fïayleigh channel.

The herein disclosed measurement chamber 100 enables an increasedflexibility, over known techniques, of generating and reconfiguring any desiredantenna testing conditions in a single measurement environment, i.e.,chamber, while at the same time keeping the measurement time and costsdown. For example, the measurement chamber 100 enables characterizationof antenna systems in an anechoic environment, the environment of areverberation chamber, or anything in between in a single measurementsystem. l\/lore specifically, the measurement chamber 100 allows for differenttesting conditions ranging from isotropic multipath environment (as inconventional RC) to a single line of sight environment (as in conventional AC),and anything in between. This allows for testing the AUT in many differentscenarios, e.g. different beamforming and l\/lll\/IO scenarios. The measurementchamber 100 is capable of characterizing the AUT in at least TRP, TIS, EIRP,EIS, EVM, ACLR, and SEl\/I. The measurement chamber is enabled bygenerating a selected mode configuration at the AUT, where thecorresponding complex-valued fields in the AUT test zone are controlled (power, incident angles, time delay). The mode configuration at the AUT isrelated to how the measurement chamber is arranged. A basic example is thata simple rectangular waveguide can support ordinary rectangular modes ofelectromagnetic wave propagation. By changing the shape or adding elementsin the chamber, these modes can be shaped to arrange for a desired modeconfiguration at the AUT. Another example is a circular waveguide whichsupports other modes than the rectangular ones. ln whatever arrangement thechamber is configured, locally around the AUT, the mode configuration at handcan be decomposed in local plane waves presented to the AUT. By doing so,the AUT can be tested under the plane wave conditions desired for the specific measurement or test to be made.

Figure 1 shows an example measurement chamber 100 for measuringperformance of an antenna under test, AUT, 110 arranged inside themeasurement chamber. The measurement chamber comprises a radiofrequency reflective surface 122 arranged circumferentially about a main axisA of the measurement chamber 100. The reflective surface 122 is arranged toform a waveguide extending along the main axis A. The waveguide has twowaveguide openings 121 at respective ends of the waveguide. Themeasurement chamber 100 further comprises a mode generator antenna 130arranged inside the measurement chamber. The mode generator antenna isarranged to transmit and/or to receive 131 a radio frequency signal to/from theAUT 110 via at least a part of the waveguide. The radio frequency signalcomprises a plurality of different-order propagating modes. The modegenerator antenna 130 and radio frequency scattering properties inside themeasurement chamber 100 are arranged to present a selected mode configuration at the AUT.

The selected mode configuration at the AUT 110 is achieved by generatingpropagating modes that interact with radio frequency scattering propertiesinside the measurement chamber 100. The plurality of different-orderpropagating modes is propagating inside the waveguide. ln addition to theradio frequency reflective surfaces 122 of the waveguide, there may be anoptional reflective element inside the chamber, such as a movable reflective plate. ln other words, the plurality of different-order propagating modes isgenerated explicitly by utilizing the scattering properties of the reflectivewaveguide walls and elements inside the chamber to present a selected modeconfiguration at the AUT 110. Hence, to present a selected mode configurationat the AUT, particular signal(s) from the mode generator antenna 130 areselected in conjunction with the scattering properties inside the measurementchamber. This can be done by extracting the propagation properties of themeasurement chamber, e.g. via computer simulations and/or via routineexperimentation. By knowledge of the propagation properties, that is, chambermodes, of the measurement chamber, the mode generator antenna can beconstructed to couple to the modes in whatever way is advantageous for theparticular testing to be done. Whatever way is advantageous may, e.g., be found via computer simulations and/or via routine experimentation.

The radio frequency reflective surfaces 122 of the waveguide and optionalreflective element inside the chamber preferably comprise a good electricalconductor, such as aluminum, copper, or brass. l\/letalized polymers or electrically conductive polymers are also possible.

Preferably, the one or more signals from the mode generator antenna 130 andthe scattering properties inside the measurement chamber are reconfigurable.This way, many different mode configurations may be presented to the AUT110. The scattering properties inside the measurement chamber may bereconfigurable by, e.g., having a wall of the waveguide be movable or byhaving the reflective element inside the chamber be movable. The modegenerator antenna can be a single antenna, a co-located antenna array, aplurality of co-located antenna arrays, and/or a plurality of distributedantennas. The mode generator antenna may comprise an antenna arraywherein all the radiating elements are not spaced equally relative to eachother. Figure 1 shows a measurement chamber 100 with the mode generatorantenna 130 and the AUT 100 arranged at the opposite sides of themeasurement chamber. Figure 2 shows a measurement chamber with themode generator antenna 130 arranged at two opposite sides of the measurement chamber. 11 Fïeconfiguring the one or more signals from the mode generator antenna maybe done by adjusting relative phases and amplitudes transmitted by individualradiating elements (when there is a plurality of them). This is similar tobeamforming and/or any l\/lll\/IO functionality in a conventional array antenna.Reconfigurability may also be achieved by changing the position of the modegenerator antenna. This can mean to move all radiating elements in an array equally or to move all or some radiating elements differently.

Some example scenarios the measurement chamber 100 is capable ofcharacterizing the AUT under are: a plane wave emitted in the broadsidedirection of the mode generator antenna; a plane wave emitted in the off-broadside direction of the mode generator antenna; multiple plane wavesemitted in different off-broadside directions of the mode generator antenna atdifferent time intervals; characterization in the proximity of other active devices(antennas, transceivers, etc.) that may interfere with the AUT. All of these scenarios represent different selected mode configuration at the AUT.

The AUT may comprise multiple antennas, as in a co-located array or as in adistributed system. The AUT may comprise a transceiver, as in a radio basestation, a point-to-point radio, or a handheld device. lt is also noted that severalAUTs may be tested at the same time, e.g. a plurality of handheld devices.The chamber may further comprise a movable pedestal 230 (shown in Figure 2) which the AUT can be placed upon.

According to aspects, at least one delimiting surface of the measurementchamber forms a body with a through hole along the main axis (A), whereinthe at least one delimiting surface of the measurement chamber constitutesthe waveguide. A particular example is a rectangular chamber wherein twowalls arranged at opposite sides of the main axis A, the floor, and the ceilingconstitute the waveguide. Example dimensions of a rectangular measurementchamber 100 could be a 2 m x 2 m cross section and a length of 3 m. Suchmeasurement chamber may have other shapes too, such as curved walls, ora circular, elliptical, or polygon shape circumferentially arranged along themain axis A. Other shapes forming a waveguide are also possible. 12 According to aspects, at least one delimiting surface of a reverberationchamber forms a body with a through hole along the main axis A, where the atleast one delimiting surface of the reverberation chamber constitutes thewaveguide. ln that case, the two remaining walls of the reverberation chambermay comprise radio frequency absorbent material. This way, a reverberationchamber may be converted into the measurement chamber 100. Areverberation chamber is a cavity resonator with a high Q-factor and withminimum absorption of electromagnetic energy. A particular example is arectangular reverberation chamber wherein two walls arranged at oppositesides of the main axis A, the floor, and the ceiling constitute the waveguide.Other shapes forming a waveguide are also possible.

A radio frequency absorbent material generally comprises lossy materials thatattenuate transmission and reflection of electromagnetic radiation. As such, aradio frequency absorbent material should be neither a good electrical isolator(as in, e.g., rubber) nor a good electrical conductor (as in, e.g., copper). Anexample of a radio frequency absorbent material is a foam material loaded withiron and/or carbon. Radio frequency absorbent material can be resonant, i.e.a particular frequency is attenuated (e.g. 25 GHz), or broadband, i.e. a spanof frequencies is attenuated (e.g. 1 GHz to 50 GHz). The attenuation ofelectromagnetic radiation in a direction is dependent on the thickness of theradio frequency absorbent material in the same direction. One example ofattenuation per length is 10 dB/cm at 2 GHz. Another example is 150 dB/cmat 30 GHz. These two examples of attenuation per length could be applicableto the disclosed measurement chamber 100.

A waveguide opening may comprise a section with blinds. The blinds arearranged to reflect radio frequency signals when in a closed state and to letradio frequency signals pass through when in an opened state. The sectionmay be part of or the whole waveguide opening 121. Preferably, radiofrequency absorbent material is arranged such that radio frequency signalsincident on the section with blinds is attenuated when the blinds are in theopened state. The blinds preferably comprise a good electrical conductor, suchas aluminum, copper, or brass. The blinds may comprise rectangular sheets 13 similar to normal window blinds. However, any shape that may be arranged toreflect radio frequency signals when in a closed state and to let radio frequencysignals pass through when in an opened state is possible. The blinds may bepartially open. This way, the amount of absorption of the radio frequencyabsorbent material may be controlled, i.e. the amount of attenuation of theelectromagnetic signal incident on the section with blinds is controlled. Suchcontrollable attenuation could be used for having the measurement chamberoperating mostly like an RC, but with some attenuation to give themeasurement chamber much higher power capabilities (over a normal RC),which is an advantage.

According to aspects, at least one delimiting surface of a reverberationchamber forms a body with a through hole along the main axis A, where the atleast one delimiting surface of the reverberation chamber constitutes thewaveguide. ln that case, the two remaining walls of the reverberation chambermay comprise one or more holes 423 arranged to pass the radio frequencysignal to/from the AUT 110 and the mode generator antenna 130. This way,particular scattering properties of the middle compartment can be separatedfrom wave propagation towards/from the AUT/mode generator antenna. ln theexample of Figure 4, the measurement chamber 100 comprises a hole atrespective sides of the waveguide along the axis A. ln the figure, the two holes423 constitute the two waveguide openings 121. The holes 423 may optionallycomprise blinds. The mode generator antenna may comprise distributed unitswhere some are arranged inside the waveguide and some are arrangedoutside the waveguide, i.e. on the other side of the hole 423. The surfaceextending in the same plane as the hole has a radio frequency reflectivesurface facing into the waveguide. lt is noted that any number of holes on eachrespective wall is possible. Through blinds, reflective doors, reflective movableplates, or the like, the holes may be reconfigurable. Thus, the number of holes and their respective position may be reconfigurable.

The one or more surfaces in the measurement chamber 100 outside of thewaveguide may comprise radio frequency absorbent material. For example, ifthe measurement comprises holes 423, as in Figure 4, all surfaces outside of 14 the waveguide may be covered in radio frequency absorbent material. Thisway, the AUT and mode generator antenna can be placed in anechoiccompartments while a middle compartment presents an environment similar tothat in a reverberation chamber. The benefits of a reverberation chamber canthen be combined with the benefits of deterministic wave propagation directions given by an anechoic environment.

The measurement chamber 100 may comprise one or more mode stirrers 210,220. The mode stirrer (also called tuner) can reduce the inhomogeneity ofstanding waves in a cavity, which is advantageous when the measurementchamber is operating at or close to a normal RC. The mode stirrer may alsoconstitute the optional reflective element used to present a selected modeconfiguration at the AUT. The mode stirrer could comprise a flat rectangularmetal plate. Other shapes are also possible. The mode stirrer may be curvedor adapted for certain propagations/directions and may be movable orreconfigurable. The mode stirrer may cover a whole wall, ceiling or floor. This way, the waveguide dimensions of the waveguide may be reconfigurable.

The waveguide openings 121 may be closed off by respective modular wallsections. ln that case, the AUT 110 and/or the mode generator antenna 130may be arranged on the one or more modular wall sections. Example of suchwall sections are shown in Figures 3 and 4. The walls, ceilings, and floors ofthe wall sections may optionally be clad completely in a radio frequencyabsorbent material. The modular wall sections can be used to quickly swapbetween different mode generator antennas arranged in different wall sectionsand/or between different AUTs arranged in different wall sections.

As mentioned previously, the measurement chamber 100 is, according todifferent aspects, capable of characterizing the AUT in at least TRP, TIS, EIRP,EIS, EVM, ACLR, and SEl\/l. Below follow examples of how suchcharacterization could be achieved. As also mentioned previously, themeasurement chamber 100 enables characterization of antenna systems in ananechoic environment, the environment of a reverberation chamber, or anything in between in a single measurement system. Presenting the environment of a reverberation Chamber could be achieved by, e.g., theclosing of the aforementioned blinds, or by having a reverberation chambercomprising one or more holes 423 constituting the waveguide, wherein theholes 423 may be closed. Presenting an anechoic environment could beachieved by, e.g., arranging radio frequency absorbent material on the one or more surfaces in the measurement chamber 100 outside of the waveguide.

To measure TRP or TIS, one could configure the measurement chamber 100to act as a reverberation chamber and measure TRP or TIS according to well know procedures of measuring TRP or TIS in a reverberation chamber.

To measure EIRP, one could configure the measurement chamber 100 to ananechoic environment, and then configure the mode generator antenna so thatthe different modes of the chamber can be resolved. The AUT can then beconfigured to radiate (i.e. to couple) optimally for whichever mode is desiredand then measured using the mode generator antenna. lf the results aresought for in plane wave basis, the mode generator antenna is excited in a manner to resolve a particular mode.

To measure EIS, one could configure the measurement chamber 100 in thesame way as for EIRP, but wherein the AUT 110 is transmitting withdecreasing output power according to normal the EIS measurement procedure.

To measure EVI\/I, one could arrange the measurement chamber 100 in thesame way as for EIRP. The AUT 1 10 is then set to transmit know symbols andthese are decoded using the mode generator antenna. Any directionaldependence of EVI\/I can be resolved in the same manner as directions areresolved in EIRP measurements.

To measure ACLR or SEI\/I, one could arrange the measurement chamber 100in the same way as to measure TRP.

Figure 5 is a flowchart illustrating methods. There is illustrated a method for measuring performance of an antenna under test, AUT, 110 arranged inside a 16 measurement chamber 100. The method comprises configuring S1 a radiofrequency reflective surface 122 circumferentially about a main axis A of themeasurement chamber 100. The reflective surface 122 is arranged to form awaveguide extending along the main axis A, where the waveguide has twowaveguide openings 121 at respective ends of the waveguide. The methodfurther comprises configuring S2 a mode generator antenna 130 inside themeasurement chamber. The mode generator antenna is arranged to transmitand/or receive 131 a radio frequency signal to the AUT 110 via at least a partof the waveguide. The radio frequency signal comprises a plurality ofpropagating modes. The method also comprises arranging S3 the modegenerator antenna 130 and the radio frequency scattering properties inside themeasurement chamber 100 to present a selected mode configuration at theAUT. This can be done by extracting the propagation properties of themeasurement chamber, e.g. via computer simulations and/or via routineexperimentation. By knowledge of the propagation properties, that is, chambermodes, of the measurement chamber, the mode generator antenna can beconstructed to couple to the modes in whatever way is advantageous for thetesting to be done. The method further comprises measuring S4 performanceof the AUT.

Claims (9)

1. A measurement chamber (100) for measuring performance of anantenna under test, AUT, (110) arranged inside the measurement chamber, the measurement chamber comprising: a radio frequency reflective surface (122) arranged circumferentially about amain axis (A) of the measurement chamber (100), the reflective surface (122)arranged to form a waveguide extending along the main axis (A), thewaveguide having two waveguide openings (121) at respective ends of the waveguide; and a mode generator antenna (130) arranged inside the measurement chamber,the mode generator antenna arranged to transmit and/or to receive (131) aradio frequency signal to/from the AUT (110) via at least a part of thewaveguide, wherein the radio frequency signal comprises a plurality ofdifferent-order propagating modes, and wherein the mode generator antenna(130) and radio frequency scattering properties inside the measurementchamber (100) are arranged to present a selected mode configuration at theAUT.

2. The measurement chamber (100) according to claim 1, wherein at leastone delimiting surface of the measurement chamber forms a body with athrough hole along the main axis (A), wherein the at least one delimiting surface of the measurement chamber constitutes the waveguide.

3. The measurement chamber (100) according to claim 1, wherein at leastone delimiting surface of a reverberation chamber forms a body with a throughhole along the main axis (A), wherein the at least one delimiting surface of thereverberation chamber constitutes the waveguide, and wherein the tworemaining walls of the reverberation chamber comprise radio frequency absorbent material.

4. The measurement chamber (100) according to any previous claim,wherein a waveguide opening comprises a section with blinds, the blindsarranged to reflect radio frequency signals when in a closed state and to letradio frequency signals pass through when in an opened state.

5. The measurement chamber (100) according to claim 1, wherein at leastone delimiting surface of a reverberation chamber forms a body with a throughhole along the main axis (A), wherein the at least one delimiting surface of thereverberation chamber constitutes the waveguide, and wherein the tworemaining walls of the reverberation chamber comprise one or more holes(423) arranged to pass the radio frequency signal to/from the AUT (110) andthe mode generator antenna (130).

6. The measurement chamber (100) according to claim 5, wherein the oneor more surfaces in the measurement chamber (100) outside of the waveguide comprise radio frequency absorbent material.

7. The measurement chamber (100) according to any previous claimcomprising one or more mode stirrers (210,220).

8. The measurement chamber (100) according to any previous claim,wherein the waveguide openings (121) are closed off by respective modularwall sections, wherein the AUT (1 10) and/or the mode generator antenna (130) are/is arranged on the one or more modular wall sections.

9. A method for measuring performance of an antenna under test, AUT,(110) arranged inside a measurement chamber (100), the method comprising: configuring (S1) a radio frequency reflective surface (122) circumferentiallyabout a main axis (A) of the measurement chamber (100), wherein thereflective surface (122) is arranged to form a waveguide extending along themain axis (A), the waveguide having two waveguide openings (121) atrespective ends of the waveguide; configuring (S2) a mode generator antenna (130) inside the measurementchamber, wherein the mode generator antenna arranged to transmit and/orreceive (131) a radio frequency signal to the AUT (110) via at least a part ofthe waveguide, wherein the radio frequency signal comprises a plurality ofpropagating modes; arranging (S3) the mode generator antenna (130) and the radio frequencyscattering properties inside the measurement chamber (100) to present aselected mode configuration at the AUT; and measuring (S4) performance of the AUT.