Test apparatus, test setup and method for measuring a radiation pattern of an antenna under test

Abstract

A test apparatus (14) for testing an antenna under test (16) has a measurement device (26), a turntable (24) and at least one stationary probe antenna (28). The measurement device (26) is a multi-channel measurement device, wherein the turntable (24) comprises a first portion (36), a second portion (38), a first rotatable RF joint (44) and a holding section (34), wherein the second portion (38) is attached rotatably to the first portion (36), and the first rotatable RF joint (44) provides a rotatable RF path between the first portion (36) and the second portion (38). The measurement device (26) and the holding section (34) are arranged spatially fixed with respect to each other at the second portion (38) of the turntable (24), and wherein the at least one stationary probe antenna (28) is electrically connected to the measurement device (26) for transmission of RF signals via the first rotatable RF joint (44). Further, a test setup (10) and a method are provided.

Description

[0001] Test apparatus, test setup and method for measuring a radiation pattern of an antenna under test

[0002] Technical Field

[0003] The invention relates to a test apparatus for testing an antenna under test, a test setup as well as a method for measuring a radiation pattern of an antenna under test.

[0004] Background

[0005] Test apparatuses and methods for measuring the radiation patterns of an antenna are very well known. For this purpose, the antenna is mounted on a turntable. By rotation around two axes, a sphere around the antenna under test is measured with a fixed probe antenna. To avoid disruptive reflections, the measurement is done in an anechoic chamber. The antenna ports to be measured are connected to a stationary measurement device, for example a vector network analyzer, with an RF cable by rotary RF joints. The probe antenna is also connected to the measuring device.

[0006] Measurements of a radiation pattern take a very long time as current antennas are multichannel antennas containing multiple subarrays in the same or at different frequency bands so that the measurement has to be repeated for each channel, i.e. port, of the antenna under test. It is commonly known to use switches for measuring passive multiport antennas, which enables a sequential measurement of the different channels. Even though such switches reduce rewiring time between measurements of two frequency bands, the measurement time is still very long for such a multichannel antenna.

[0007] For active antennas with integrated transmitters and receivers the problem occurs that the measurement of the exact pattern characteristics requires additional synchronization to capture the phase for the required near-farfield transformation. The article “Spherical Near Filed Antenna Measurements”; white paper , Keysight Technologies, USA , August 2nd, 2014, 5991-0480EN, discloses a measurement equipment for the measurement of mmW antennas, suggesting a transceiver module with a mixer to reduce the measurement frequency to a lower IF-frequency to capture the high frequency band of the antenna under test in the mmW range.

[0008] Summary

[0009] It is therefore the object of the invention to provide a test apparatus, a test setup and a method for measuring the radiation pattern that reduces the time needed for measuring a radiation pattern.

[0010] For this purpose, a test apparatus for testing an antenna under test is provided. The test apparatus comprises a measurement device, a turntable for holding and moving the antenna under test, and at least one stationary probe antenna. The measurement device is a multi-channel measurement device having more than or equal to four measurement channels and at least one probing port. The turntable comprises a first portion, a second portion, a first rotatable RF joint and a holding section for attaching the antenna under test, wherein the second portion is attached rotatably to the first portion, and the first rotatable RF joint provides a rotatable RF path between the first portion and the second portion. The measurement device and the holding section are arranged spatially fixed with respect to each other at the second portion of the turntable, and wherein the at least one stationary probe antenna is electrically connected to the measurement device for transmission of RF signals via the rotatable RF path of the first rotatable RF joint.

[0011] By arranging the measurement device on the turntable in a spatially fixed relation to the holding section and with that the antenna under test, each channel of the antenna can directly be connected to the measurement device, as no rotary joint has to be passed. In this way, all channels of the antenna may be measured at the same time with respect to magnitude and phase, thus drastically reducing the time needed for measuring a radiation pattern.

[0012] The second portion is rotatable around a first axis of rotation with respect to the first portion. The second portion is attached rotatably to the first portion via the first rotatable RF joint.

[0013] In particular, the first rotatable RF joint provides a rotatable RF path coaxial to the first axis of rotation.

[0014] For example, the measurement device has more than or equal to ten channels, in particular more than or equal to 16 channels.

[0015] In particular, the measurement device is electrically connectable directly, e.g. without an intervening rotatable RF joint to the antenna under test located in the holding section.

[0016] In an aspect, the first portion of the turntable is stationary and / or the second portion of the turntable is rotatable, in particular wherein the second portion is fully and endlessly rotatable with respect to the first portion, allowing quick and uncomplicated measurements of the radiation pattern of the antenna under test. In an embodiment, the second portion of the turntable has a first subportion and a second subportion, wherein the second subportion is attached rotatably to the first subportion, wherein the holding section and the measurement device are arranged at the second subportion, allowing for rotation of the holding section and thus the antenna under test around two axes of rotation.

[0017] The second subportion may be fully and endlessly rotatable with respect to the first subportion around a second axis of rotation.

[0018] In an aspect, the turntable comprises a second rotatable RF joint providing a RF path between the first subportion and the second subportion, wherein the at least one stationary probe antenna is electrically connected to the measurement device for transmission of RF signals via the rotatable RF path of the second rotatable RF joint. The rotatable RF joint providing high signal transmission quality between the stationary probe antenna and the measurement device.

[0019] The second rotatable RF joint may provide a rotatable RF path coaxial to the second axis of rotation and / or the second subportion may be attached rotatably to the first subportion via the second rotatable RF joint.

[0020] In particular, the second axis of rotation between the first subportion and the second subportion is orthogonal to the first axis of rotation between the first portion and the second portion.

[0021] In an aspect, the second subportion is rotatable with respect to the first subportion within the limits of a defined range of motion, in particular the defined range of motion is defined to more than or equal to 180°.

[0022] For avoiding disturbances of the measurement, the turntable may comprise a RF radiation absorber located between the measurement device and the holding section and / or the measurement device may comprise a RF radiation absorber located at the side of the measurement device facing the holding section.

[0023] In an embodiment, more than one, in particular three stationary probe antennas are provided, and the test apparatus comprises a stationary splitter or combiner electrically connected to the more than one probe antennas, wherein the measurement device comprises more than one, in particular three probing ports and a combiner or splitter, respectively, electrically connected to the probing ports, wherein the combiner and the splitter are electrically connected for transmission of RF signals via the first rotatable RF joint, in particular by only one RF transmission line. This way, simultaneous measurements in different frequency bands may be carried out with high quality even though the rotatable RF joint does only provide one RF path with high quality. If applicable, the combiner and the splitter are electrically connected also via the second rotatable RF joint.

[0024] For example, one probing port for each of the stationary probe antennas is provided.

[0025] An amplifier may be located in the RF transmission line between the combiner and the splitter or between the stationary probe anteima(s) and the respective splitter or combiner.

[0026] In order to improve the measurement quality further, more than one, in particular three stationary probe antennas may be provided, wherein the probe antennas may be arranged on an arc centered around the center of rotation of the holding section, in particular wherein the distance between the stationary probe antennas along the arc is adjustable and / or the probe antennas are mounted on an arched rail of the test apparatus.

[0027] In an aspect, at least one polarization switch is located in the electrical connection between the at least one stationary probe antenna and the measurement device, in particular between the splitter and the combiner or between the stationary probe antennas and the respective splitter or combiner, allowing for measurements of more than one polarization.

[0028] For example, one polarization switch for each probe antenna is provided.

[0029] In an embodiment, the measurement device is a network analyzer, in particular a vector network analyzer, and / or that the measurement device comprises at least one signal generator electrically connected to the at least one stationary probe antenna or electrically connectable to the antenna under test and / or the measurement device comprises at least one receiver for each of the measurement channels electrically connectable to the antenna under test or electrically connected to the at least one stationary probe antenna. Thus, a quick and high-quality measurement is ensured.

[0030] In an embodiment, the test apparatus comprises a stationary measurement computer and / or a stationary turntable controller, wherein the measurement computer and / or the turntable controller are electrically connected via a signal transfer connection and / or a data transfer connection to the measurement device via a rotatable signal path and / or data path provided by the first rotatable RF joint, allowing communication of the measurement device with stationary devices.

[0031] The signal path and / or data path is in particular different from RF path of the rotatable RF joints, for example non-coaxial to the respective axis of rotation.

[0032] The signal transfer connection and / or the data transfer connection may also be via the second rotatable RF joint.

[0033] The polarization switch may be connected to the measurement computer and / or the measurement device for control of the polarization switch by the measurement computer and / or the measurement device. In an aspect, the turntable is configured to provide a quiet zone with respect to the antenna under test, wherein the measurement device is located in the quiet zone, enabling a multichannel measurement for the antenna under test with a high quality.

[0034] Within this disclosure, a quiet zone is to be regarded as a volume in which the nearfield measurement has a low gradient in the phase and a substantially constant magnitude.

[0035] For above mentioned purpose, further a test setup comprising the test apparatus as described above and an antenna under test is provided, wherein the antenna under test is attached to the holding section of the test apparatus. The antenna under test is a multi-channel antenna, wherein the channels of the antenna are electrically connected to the measurement channels or the probing ports of the measurement device for transmission of RF signals.

[0036] The features and advantages described with respect to the test apparatus also apply to the test setup and vice versa.

[0037] Each channel of the antenna under test is electrically connected to one measurement channel of the measuring device.

[0038] The RF connection between antenna under test and the measurement device is in particular not established via a rotatable RF joint.

[0039] In an aspect, the antenna under test is a passive antenna, a MIMO antenna, an antenna for a mobile communication base station, and / or a directional antenna and / or the antenna under test has a blind spot, wherein the measurement device is located in the blind spot. Within this disclosure, a blind spot is considered a volume which is almost free of an electromagnetic field, when the antenna under test is transmitting. A blind spot may be determined by simulation. Thus, the test setup provides a versatile measurement environment. In order to further reduce the time needed for assessing an antenna under test, the test setup may be configured to measure the S-parameters, the voltage standing wave ratio (VSWR), the reflection coefficient, the isolation, and / or the input impedance of the antenna, in particular wherein cables connecting the antenna under test and the measurement device are low-loss cables and / or calibrated cables.

[0040] Further, for above mentioned purpose, a method for measuring the radiation pattern of an antenna under test using a test apparatus as described above or a test setup as described above are provided. The method comprises: a. rotating the antenna under test by rotating the second portion of the turntable with respect to the first portion of the turntable, b. generating an RF probing signal by the measurement device, c. transmitting the RF probing signal to and emitting the RF probing signal from the antenna under test, or transmitting the RF probing signal to and emitting the RF probing signal from the at least one probe antenna, d. receiving the RF probing signal by the probe antenna or the antenna under test and transmitting the received RF signal to the measurement device, and e. recording measurement data by the measurement device based on the received RF signal, and the rotational position of the second portion with respect to the first portion.

[0041] The features and advantages described with respect to the test apparatus and / or the test setup also apply to the method and vice versa. In case of a second rotatable RF joint, the measurement data is also based on the rotational position of the second subsection with respect to the first subsection.

[0042] In an aspect, the measurement is carried out for multiple channels, in particular all channels of the antenna under test at the same time, further reducing the measurement time needed. This may be realized by transmitting the measurement signals from the probe antenna, wherein the antenna under test receives the measurement signal.

[0043] For example, the measurement data is stored locally on the measurement device and / or the measurement data is transmitted from the measurement device to a measurement computer or a processing device after the radiation pattern has been acquired completely, further saving time during the actual measurement.

[0044] In an aspect, the measurement device measures the S-parameters, the VSWR, the reflection coefficient, the isolation, and / or the input impedance of the antenna under test at a single or more than one rotational position, extending the assessment of the antenna under test with little effort.

[0045] In particular, the cables connecting the antenna under test and the measurement device are low-loss cables and / or calibrated cables.

[0046] Brief Description of the Drawings

[0047] Further features and advantages will be apparent from the following description as well as the accompanying drawings, to which reference is made. In the drawings:

[0048] Fig. 1 shows a test setup according to an embodiment of the invention with a test apparatus according to an embodiment of the invention in a very schematic view, Fig. 2 illustrates a time sequence of a method according to an embodiment of the invention, and

[0049] Fig. 3 shows a schematic flow chart of the method of Figure 2.

[0050] Detailed Description

[0051] Figure 1 shows a test setup 10 according to an embodiment of the invention very schematically.

[0052] The test setup 10 comprises an anechoic chamber 12, a test apparatus 14 and an antenna under test 16.

[0053] The antenna under test 16 is a passive multi-channel antenna for a mobile communication base station.

[0054] The antenna under test 16 may be a Multiple-Input and Multiple-Output (MIMO) antenna and / or a directional antenna.

[0055] A channel of the antenna under test 16 is, for example, regarded as a signal path through which cable-bound radiofrequency signals (RF-signals) are received and emitted as electromagnetic radiation or vice versa. For example, one channel includes an antenna port 18 and an array of radiators.

[0056] The antenna under test 16 comprises at least four channels (indicated in Fig. 1), thus at least four antenna ports 18 and four arrays of radiators or two arrays of dual polarized radiators.

[0057] The antenna under test 16 may also comprise more than or equal to 10 channels, in particular more than or equal to 16 channels.

[0058] The radiators of the array of radiators as well as the probe antennas 28 are in particular dual polarized radiators.

[0059] In an embodiment, the antenna under test 16 is a multiband antenna with at least one array of radiators for receiving and transmitting radiofrequency radiation in a first frequency band, at least one array of radiators for receiving and transmitting radiofrequency radiation in a second frequency band, and at least one array of radiators for receiving and transmitting radiofrequency radiation in a third frequency band.

[0060] Further, the antenna under test 16 may comprise a remote electric tilt device (RET device 22) for adjusting the electrical tilt of the antenna under test 16. One RET device 22 may be provided for some or all of the arrays of radiators or one RET device 22 is provided for each frequency band, i.e. the arrays of radiators of the respective frequency band.

[0061] Further, the antenna under test 16 may have a blind spot in its radiation pattern.

[0062] The test apparatus 14 comprises a turntable 24, a measurement device 26, at least one probe antenna 28, a turntable controller 30 and a measurement computer 32.

[0063] Of the test setup 10, the antenna under test 16, the turntable 24, the measurement device 26 and the probe antenna 28 are located within the anechoic chamber 12.

[0064] The turntable controller 30 and the measurement computer 32 are preferably located outside the anechoic chamber 12.

[0065] The turntable 24 comprises a holding section 34 which is, in the shown embodiment, rotatable around two axes, namely a first axis Al and a second axis A2.

[0066] The antenna under test 16 is mounted to the holding section 34 of the turntable 24. As such, the antenna under test 16 has a center of rotation C being the center of rotation of the holding section 34 around the first axis Al and the second axis A2 (Fig. 1 not to scale). To this end, the turntable 24 further comprises a first portion 36 and a second portion 38, which has a first subportion 40 and a second subportion 42. The turntable 24 further comprises a first rotatable RF joint 44 and a second rotatable RF joint 46.

[0067] The portions 36, 38 and the subportions 40, 42 of the turntable 24 may be made of pipes or hollow profiles. The pipes or hollow profiles may be covered by additional absorbers or absorbing material to reduce reflections.

[0068] As such, within the pipes or hollow profiles, the turntable 24 provides a quiet zone with respect to an antenna under test 16 mounted to the holding section 34.

[0069] The first portion 36 of the turntable 24 is stationary, for example mounted fixedly to the floor of the anechoic chamber 12.

[0070] The second portion 38 is connected to the first portion 36 by the first rotatable RF joint 44 so that the second portion 38 is rotatable around a first axis Al with respect to the first portion 36. More precisely, the first subportion 40 is connected to the first RF joint 44.

[0071] The second subportion 42 is attached to the first subportion 40 via the second RF joint 46 to the effect that the second subportion 42 is rotatable with respect to the first subportion 40 around a second axis A2.

[0072] The first axis Al and the second axis A2 are orthogonal to one another.

[0073] The first rotatable RF joint 44 may provide a full and endless rotation for the second portion 38 with respect to the first portion 36.

[0074] The second RF joint 46 provides a full and endless rotation for the second subportion 42 with respect to the first subportion 40. It is also conceivable, that the first or the second RF joint 44, 46 have a limited defined range of motion, in particular of more than or equal to 180°.

[0075] The holding section 34 of the turntable 24 is provided on the second subportion 42 and has a center of rotation C with respect to the first and second axis Al, A2.

[0076] The measurement device 26 is also located on the second portion 38, more precisely the second subportion 42, so that the measurement device 26 and the holding section 34 are spatially fixed with respect to each other.

[0077] The measurement device 26 is, for example, mounted in the quiet zone provided by the turntable 24.

[0078] Between the measurement device 26 and the holding section 34, i.e. the antenna under test 16, a RF radiation absorber 48 of the turntable 24 may be located (indicated in dashed lines in Figure 1).

[0079] The absorber 48 may be a section of the pipe or hollow profile of one of the portions 36, 38 or subportions 40, 42 of the turntable 24.

[0080] Alternatively or in addition, the measurement device 26 may also comprise an RF absorber 48, at least at its side which is facing the holding section 34.

[0081] The measurement device 26 is, for example, located in the blind spot of the antenna under test 16.

[0082] The measurement device 26 is a network analyzer, in particular a vector network analyzer.

[0083] The measurement device 26 is a multichannel measurement device 26 having at least four measurement channels and at least one probing port. The measurement device 26 has the same amount of probing ports as probe antennas 28 are provided. The measurement device 26 may also comprise more probing ports than probe antennas 28.

[0084] For example, the measurement device 26 comprises one dedicated signal generator 47 for each of its probing ports. It is also conceivable that several probing ports share one signal generator 47.

[0085] The measurement device 26 may have more than or equal to 10 channels, in particular more than or equal to 16 channels.

[0086] A channel of the measurement device 26 may be understood as a measurement port connected to a receiver 49 for measurements of impinging RF frequency signals.

[0087] For example, the measurement device 26 comprises one dedicated receiver 49 for each of its channels.

[0088] Each of the channels of the antenna under test 16 is electrically connected to one of the channels of the measurement device 26 in the shown embodiment. Preferably, the measurement device 26 comprises the same amount of or more than the amount of channels of the antenna under test 16.

[0089] The electric connection is such that cable-bound radiofrequency (RF) signals can be transmitted between the measurement device 26 and the antenna under test 16.

[0090] For this connection, low-loss cables 50 that have been calibrated (i.e. calibrated cables) are used.

[0091] The measurement device 26 is thus directly connected to the antenna under test 16, i.e. without any intervening rotary joints. The probing ports of the measurement device 26 are connected to the probe antennas 28 via a single RF transmission line 52, wherein, in this embodiment, each probe antenna 28 is connected to a different probing port of the measurement device 26.

[0092] The RF transmission line 52 between the measurement device 26 and the probe antennas 28 is such that cable-bound RF signals can be transmitted between the probe antennas 28 and the measurement device 26.

[0093] The RF transmission line 52 between the measurement device 26 and the probe antennas 28 is provided through the first and second rotatable RF joint 44, 46.

[0094] To this end, the first RF joint 44 provides a RF path between the first portion 36 and the first subportion 40 of the second portion 38. Similarly, the second RF joint 46 provides a RF path between the first subportion 40 and the second subportion 42

[0095] In particular, the RF joints 44, 46 provide only one RF path each, which is coaxial to the respective axis of rotation Al, A2.

[0096] Thus, the RF transmission line 52 comprises only one RF path with sufficient quality for measurements of the radiation pattern.

[0097] Each of the probe antennas 28 is configured to transmit and receive RF radiation in a different frequency band, namely the first, the second or the third frequency band of the antenna under test 16.

[0098] The probe antennas 28 are mounted to a stationary arched rail 54 mounted to a wall or ceiling of the anechoic chamber 12.

[0099] The arched rail 54 may extend vertically so that the probe antennas 28 are arranged vertically one above another, or it may extend horizontally so that the probe antennas 28 are arranged horizontally one beside the other. The position of the rail 54 and the arc of the rail 54 are such that the center of the arc coincides with the center of rotation C of the holding section 34, i.e. of the antenna under test 16. As such, the probe antennas 28 mounted to the arched rail 54 all have the same distance to the center of rotation C.

[0100] Further, the probe antennas 28 are arranged with the same distance between one another, wherein the distance is adjustable. This way, it can be assured that the measurement points of the probe antennas 28 are always on the sphere defined by the antenna under test 16.

[0101] In order to transmit radiofrequency signals via the RF transmission line 52 from the measurement device 26 to the probe antennas 28, the test apparatus 14 comprises a combiner 56 and a splitter 58.

[0102] The combiner 56 is located on the second subportion 42 of the turntable 24 close to the measurement device 26. Its inputs are electrically connected to each of the probing ports and its output is electrically connected to the RF transmission line 52.

[0103] The splitter 58 is stationary. The splitter 58 may be located at the first portion 36 of the turntable or between the first portion 36 and the probe antennas 28.

[0104] The input of the splitter 58 is electrically connected to the RF transmission line 52, thus with the combiner 56. The outputs of the splitter 58 are electrically connected to the probe antennas 28. Thus, only one RF transmission line 52 is needed that has to pass the RF joint 44, 46.

[0105] Further, an amplifier 60 may be located in the RF transmission line 52 between the combiner 56 and the splitter 58. The amplifier 60 may also be located between the splitter 58 and the respective probe antennas 28.

[0106] Further, the test apparatus 14 may comprise a polarization switch 62 located between the splitter 58 and the probe antennas 28. The polarization switch 62 comprises three switches being connected at one side with the outputs of the splitter 58 and on the other side each with the two ports for the different polarities of each of the probe antennas 28, wherein one switch is provided for each probe antenna 28.

[0107] The measurement computer 32 and the turntable controller 30 are stationary and in particular located outside the anechoic chamber 12.

[0108] They are connected to the measurement device 26 via a signal transfer connection and / or a data transfer connection that pass through the first and second RF joints 44, 46.

[0109] To this end, the first and second RF joints 44, 46 provide also a rotatable path for signal and / or data transfer, respectively, via which the signal / data transfer connection from the measurement computer 32 and / or turntable controller 30 to the measurement device 26 is realized.

[0110] The rotatable path for signal and / or data transfer is in particular different from the RF path through the rotatable RF joints 44, 46. In particular, the rotatable path for signal and / or data transfer are non-coaxial with respect to the respective axis of rotation.

[0111] The polarization switch 62 may also be connected to the measurement computer 32 or directly to the measurement device 26 through the signal path or data path provided by the joints 44, 46.

[0112] Even though a setup has been described in which the measurement channels of the measurement device 26 is directly connected to the channels of the antenna under test 16 and the probing ports are connected to the probe antennas 28, it is also conceivable that the probing ports are directly connected to the antenna under test 16 and that the measurement channels are connected to the probe antennas 28. In this case, the functions of the combiner 56 and the splitter 58 are swapped. Only one of these options has been explained in detail for the sake of clarity without excluding the other option

[0113] Figure 2 illustrates a time sequence of a measurement of the radiation pattern of the antenna under test 16 and Figure 3 shows a flowchart of the method.

[0114] The control of the following sequence may be exercised by the measurement computer 32 or by the measurement device 26 itself.

[0115] At SI, the antenna under test 16 is rotated into a starting position. To this end, the holding section 34 and with that the antenna under test 16 is rotated around the first axis Al and the second axis A2.

[0116] At S2, the rotation of the antenna under test 16 around the second axis A2 is initiated. The rotation around the second axis corresponds to changing the azimuth denoted cp.

[0117] The rotation around the second axis A2 is "endless", i.e. the range of motion is not limited. During the measurement of the radiation pattern, the motion describes several full rotations, i.e. (p will be within N x 360°, wherein N is an integer.

[0118] The rotation around the second axis A2 may be carried out continuously, as shown in the first row R1 in Figure 2 indicating the angular velocity co of (p. It is also conceivable, that cp is changed stepwise, i.e. that the rotation around the first axis Al is a stepwise rotation.

[0119] At S3, the rotation of the antenna under test 16 around the first axis Al is started. The first axis Al corresponds to the elevation and is denoted with the angle T This is indicated in Figure 2 in the second row R2 denoting a constant angular velocity co for T

[0120] The rotation around the first Al axis may be between -90° to +90°, i.e. limited defined range of 180°. The rotation around the first axis Al and the second axis A2 is controlled by the turntable controller 30, which is in turn controlled by the measurement computer 32 or the measurement device 26.

[0121] The rotation of the first axis and the second axis Al, A2 may be synchronized with respect to each other.

[0122] At S4, the polarization switch 62 is set to a first polarization value, for example +45°. This may be omitted, if the polarization is already set to the correct and desired polarization or if polarization is not of importance.

[0123] The polarization switch 62 may be controlled by the measurement computer 32 or the measurement device 26.

[0124] Measurement sweeps are trigged at S5. The sweeps may be initiated by trigger events in regular intervals. The intervals may be timewise intervals or angular intervals.

[0125] For example after, each predetermined rotation of $ and / or cp a measurement sweep is initiated. For example, the angular interval for h is 0.5° to 3° and the angular interval for cp may be between 1° and 5°.

[0126] This trigger of the measurement sweep is shown in the third row R3 of Figure 2.

[0127] During the measurement sweep at S6, whose duration is depicted in the fourth row R4 of Figure 2, the measurement device 26 generates at least one probing signal and transmits the probing signal to the probe antennas 28 (or the antenna under test 16 if the antenna is connected to the probing ports), where it is radiated as RF radiation into the anechoic chamber 12.

[0128] The probing signal is then received by the antenna under test 16 and transmitted to the measurement channel of the measurement device 26 (or it is received by the probe antenna 28). During the frequency sweep, the probing signal is swept through various frequencies as indicated in the fifth row R5 of Figure 2 showing multiple frequency points for which measurement data is acquired during one measurement sweep.

[0129] In case of multiple probe antennas 28 or the multichannel antenna under test 16 being connected to the probing ports, multiple RF probing signals are generated by the measurement device 26 for different frequency bands, wherein within each of the frequency bands a frequency sweep is carried out.

[0130] During the measurement sweep, the RF signal input at the measurement channels of the measurement device 26 is recorded and associated with the current rotational position (e.g. value for cp and h) of the antenna under test 16. Further, the recorded measurement data may also include information about the corresponding RF probing signal and values derived from the received signal at the measurement channel.

[0131] At the end of the measurement sweep, the measurement is completed at S7, as indicated in the sixth row R6 of Figure 2.

[0132] As a plurality of probing signals is used and all of the channels of the antenna under test 16 are connected to the measurement device 26, the measurement is carried out for multiple channels of the antenna under test 16 at the same time. Thus, the measurement time for measuring a complete radiation pattern of the antenna under test 16 is drastically reduced.

[0133] Then, the data measured during the measurement sweep is stored locally on the measurement device 26 during the time interval indicated in the last row R7 of Figure 2 (S8).

[0134] It is conceivable that the measurement data is transmitted to the measurement computer 32 at S 8 and stored at the measurement computer 32. Then, at S9, the polarization switch 62 is actuated so that the polarization is switched to a second polarization value, for example -45°.

[0135] After the polarization has been switched, the next measurement (indicated with "Pol2" in Figure 2) is triggered (S5), the measurement sweep is carried out and completed (S6, S7) and the corresponding measured data is stored (S8).

[0136] Figure 2 shows also this second measurement sweep and further measurement sweeps, which resembles the first measurement sequence but further down the time axis.

[0137] Between the end of the data storage at S8 and the subsequent measurement sweep trigger at S5, a time interval without any measurements is provided to allow for tolerances during the measurement, indicated with "tol" in Figure 2.

[0138] As can be seen in Figure 2, many more measurement sweeps are carried out during the measurement of the radiation pattern in the same way as described above, i.e. the actions at S5 to S9 are repeated multiple times.

[0139] Once the radiation pattern has been acquired completely (at S10), i.e. when the second axis A2 has completed the predefined rotations, for example N x 360° rotation, the rotation around the first and second axes Al, A2 is stopped.

[0140] The measured data is then (at Si l) transmitted from the measurement device 26 to the measurement computer 32. It is also conceivable, that the stored measurement data is transmitted to a processing device. The processing device may be a remote computer, e.g. a cloud.

[0141] In another embodiment of the method, after the end of the measurement at S10, the RET device 22 is activated to tilt the corresponding beam for a predefined step, e.g. 1° (S12). Then, a second radiation pattern is acquired, i.e. the holding section 34 and thus the antenna under test 16 is rotated into the starting position (SI) and the acquisition is repeated (S2-S10).

[0142] Once this measurement is completed, the tilt may further be adjusted in the next step and the next acquisition is started until radiation patterns for the full tilt range of the RET device 22 have been acquired.

[0143] The data transfer at Si l may be done after each acquisition of a radiation pattern, i.e. before S12, or after the acquisitions for all tilt values have been completed.

[0144] This way, the radiation patterns even for the full operational range of the RET device 22 can be acquired fully automatically.

[0145] Further, in an embodiment of the method, the S-parameters of the antenna under test 16 may be measured.

[0146] To this end, the voltage standing wave ratio (VSWR), the reflection coefficient, the isolation and / or the input impedance of the antenna under test 16 is measured. This may be done at a single, specific measurement position of the antenna under test 16, i.e. at specific values for cp and h and / or before the antenna under test 16 is moved into the starting position.

[0147] For example, at Al (indicated in dashed lines in Figure 3), the antenna under test 16 is moved into the measurement position and at A2 the measurements necessary to determine the S-parameters are carried out.

[0148] The measurement of the S-parameters is possible because the antenna under test 16 and the measurement device 26 are spatially fixed with respect to one another and connected by low loss calibrated cables 50.

[0149] Due to this fact, the S-parameters may also be determined after the acquisition of the radiation pattern or various times at different rotational positions of the antenna under test 16.

Claims

Claims1. Test apparatus for testing an antenna under test (16), comprising a measurement device (26), a turntable (24) for holding and moving the antenna under test (16), and at least one stationary probe antenna (28), wherein the measurement device (26) is a multi-channel measurement device having more than or equal to four measurement channels and at least one probing port, wherein the turntable (24) comprises a first portion (36), a second portion (38), a first rotatable RF joint (44) and a holding section (34) for attaching the antenna under test (16), wherein the second portion (38) is attached rotatably to the first portion (36), and the first rotatable RF joint (44) provides a rotatable RF path between the first portion (36) and the second portion (38), and wherein the measurement device (26) and the holding section (34) are arranged spatially fixed with respect to each other at the second portion (38) of the turntable (24), and wherein the at least one stationary probe antenna (28) is electrically connected to the measurement device (26) for transmission of RF signals via the rotatable RF path of the first rotatable RF joint (44).

2. Test apparatus according to claim 1, characterized in that the first portion (36) of the turntable (24) is stationary and / or the second portion (38) of the turntable (24) is rotatable.

3. Test apparatus according to claim 1 or 2, characterized in that the second portion (38) of the turntable (24) has a first subportion (40) and a second subportion (42), wherein the second subportion (42) is attached rotatably to the first subportion (40), wherein the holding section (34) and the measurement device (26) are arranged at the second subportion (42).

4. Test apparatus according to claim 3, characterized in that the turntable (24) comprises a second rotatable RF joint (46) providing a RF path between the first subportion (40) and the second subportion (42),wherein the at least one stationary probe antenna (28) is electrically connected to the measurement device (26) for transmission of RF signals via the rotatable RF path of the second rotatable RF joint (46).

5. Test apparatus according to any of the preceding claims, characterized in that the turntable (24) comprises a RF radiation absorber (48) located between the measurement device (26) and the holding section (34) and / or that the measurement device (26) comprises a RF radiation absorber (48) located at the side of the measurement device (26) facing the holding section (34).

6. Test apparatus according to any of the preceding claims, characterized in that more than one, in particular three stationary probe antennas (28) are provided, and the test apparatus (14) comprises a stationary splitter (58) or combiner (56) electrically connected to the more than one probe antennas (28), wherein the measurement device (26) comprises more than one, in particular three probing ports and a combiner (56) or splitter (58), respectively, electrically connected to the probing ports, wherein the combiner (56) and the splitter (58) are electrically connected for transmission of RF signals via the first rotatable RF joint (44), in particular by only one RF transmission line (52).

7. Test apparatus according to any of the preceding claims, characterized in that more than one, in particular three stationary probe antennas (28) are provided, wherein the probe antennas (28) are arranged on an arc centered around the center of rotation (C) of the holding section (34), in particular wherein the distance between the stationary probe antennas (28) along the arc is adjustable and / or the probe antennas (28) are mounted on an arched rail (54) of the test apparatus (14).

8. Test apparatus according to any of the preceding claims, characterized in that at least one polarization switch (62) is located in the electrical connection between the at least one stationary probe antenna (28) and themeasurement device (26), in particular between the splitter (58) and the combiner (56) or between the stationary probe antennas (28) and the respective splitter (58) or combiner (56).

9. Test apparatus according to any of the preceding claims, characterized in that the measurement device (26) is a network analyzer, in particular a vector network analyzer, and / or that the measurement device (26) comprises at least one signal generator (47) electrically connected to the at least one stationary probe antenna (28) or electrically connectable to the antenna under test (16) and / or the measurement device (26) comprises at least one receiver (49) for each of the measurement channels electrically connectable to the antenna under test (16) or electrically connected to the at least one stationary probe antenna (28).

10. Test apparatus according to any of the preceding claims, characterized in that the test apparatus (14) comprises a stationary measurement computer (32) and / or a stationary turntable controller (30), wherein the measurement computer (32) and / or the turntable controller (30) are electrically connected via a signal transfer connection and / or a data transfer connection to the measurement device (26) via a rotatable signal path and / or data path provided by the first rotatable RF joint (44).

11. Test apparatus according to any of the preceding claims, characterized in that the turntable (24) is configured to provide a quiet zone with respect to the antenna under test (16), wherein the measurement device (26) is located in the quiet zone.

12. Test setup comprising the test apparatus (14) according to any of the preceding claims and an antenna under test (16), wherein the antenna under test (16) is attached to the holding section (34) of the test apparatus (14), wherein the antenna under test (16) is a multi-channel antenna, wherein the channels of the antenna under test (16) are electrically connected to themeasurement channels or the probing ports of the measurement device (26) for transmission of RF signals.

13. Test setup according to claim 12, characterized in that the antenna under test (16) is a passive antenna, a MIMO antenna, an antenna for a mobile communication base station, and / or a directional antenna and / or that the antenna under test (16) has a blind spot, wherein the measurement device (26) is located in the blind spot.

14. Test setup according to claim 12 or 13, characterized in that the test setup (10) is configured to measure the S-parameters, the VSWR, the reflection coefficient, the isolation, and / or the input impedance of the antenna under test (16), in particular wherein cables connecting the antenna under test (16) and the measurement device (26) are low-loss cables (50) and / or calibrated cables.

15. Method for measuring the radiation pattern of an antenna under test (16) using a test apparatus (14) according to any of the claims 1 to 11 or a test setup (10) according to any of the claims 12 to 14, the method comprising: a. rotating the antenna under test (16) by rotating the second portion (38) of the turntable (24) with respect to the first portion (36) of the turntable (24), b. generating an RF probing signal by the measurement device (26), c. transmitting the RF probing signal to and emitting the RF probing signal from the antenna under test (16), or transmitting the RF probing signal to and emitting the RF probing signal from the at least one probe antenna (28), d. receiving the RF probing signal by the probe antenna (28) or the antenna under test (16), and transmitting the received RF signal to the measurement device (26), ande. recording measurement data by the measurement device (26) based on the received RF signal and the rotational position of the second portion (38) with respect to the first portion (36).

16. Method according to claim 15, characterized in that the measurement is carried out for multiple channels, in particular all channels of the antenna under test (16) at the same time.

17. Method according to claim 15 or 16, characterized in that the measurement device (26) measures the S-parameters, the VSWR, the reflection coefficient, the isolation, and / or the input impedance of the antenna under test (16) at a single or more than one rotational position.

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