System and method for volumetric scanning of radio frequency signals

Abstract

To provide a system and method for scanning radio frequency signals from a device under test (DUT) over a wide range at low cost.SOLUTION: A system 400 includes: a gantry 401 with a carrier 402b robotically movable along a beam 402a in a first direction; a robotic arm 403 mounted on the carrier 402b and extending from the beam 402a; and a control system. The gantry 401 moves the robotic arm 403 along the beam 402a in a second direction orthogonal to the first direction. An RF probe 404 is mounted on a free end of the robotic arm 403 and is configured to communicate with an antenna under test (AUT) of the DUT. A control system coordinates movements of the gantry 401 and robotic arm 403 to move the RF probe 404 in a scanning pattern about the DUT.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure generally relates to a system and method for scanning radio frequency signals to and / or from a device (i.e., to, from, or both to and from the device) fixed within a volume of space surrounding a device under test, and more particularly to such a system and method in the case of antenna testing.

[0002] [Cross - Reference to Related Applications] This application claims priority to U.S. Provisional Application No. 63 / 609,033, filed on Dec. 12, 2023, the disclosure of which is incorporated herein by reference in its entirety.

Background Art

[0003] Wireless communication technologies have advanced rapidly in recent years. One such advancement is the use of phased arrays. Phased arrays are mainly used in the aerospace defense industry but have migrated and are being incorporated into commercial products. Phased arrays are now used in 5G millimeter wave (mmWave) communication, which enables the generation of extremely narrow beams. These arrays typically use variable - gain amplifiers and phase shifters to synthesize a plane wave in a desired direction from a common RF signal.

[0004] Another development in the wireless communication industry is the emergence of low earth orbit (LEO) satellite Internet services. This technology has led to the replacement of conventional reflector-based residential satellite antennas with flat panel phased array antennas. These antennas are expected to play a central role in the development of non-terrestrial networks for 6G applications aimed at providing mobile phone coverage in remote areas. These networks are expected to facilitate communication between ground stations, satellites, and mobile users using satellites, balloons, and / or high-altitude gliders (i.e., satellites, balloons, or high-altitude gliders, or one or more of them) equipped with multiple phased array antennas.

[0005] However, several challenges have been raised in testing these evolved antenna systems. Conventional antenna pattern measurement techniques such as far-field range, compact range, or near-field scanners are not suitable for testing these systems due to the tight integration of the antenna and the wireless architecture. This integration has made it impossible to introduce RF (Radio Frequency) connectors that require over-the-air (OTA) testing between the wireless circuitry and the antenna. Furthermore, the size of the phased array, especially for large devices such as satellites or vehicles, requires the use of a large compact antenna test range (CATR) with a parabolic reflector to generate a uniform plane wave to irradiate the antenna under test (AUT).

[0006] Industrial robots and collaborative robots (cobots) that replace one or both axes of a two-axis scanner for performing near-field scanning of AUTs have been introduced into the industrial world. However, these robot systems have limitations such as being unable to maintain a spherical shape when the AUT is scanned, and it is difficult to accurately position the robot due to inherent sag and other related effects inherent in each joint of the robot. Furthermore, to use a robot arm for near-field scanning, it is necessary to calibrate or record the actual position using an expensive laser interferometer tracker at each step in the measurement process. SUMMARY OF THE INVENTION MEANS FOR SOLVING THE PROBLEM

[0007] Generally, in a first aspect, the system of the inventive concept comprises a gantry having a carrier movable along a beam in a first direction. A robot arm having a fixed end attached to the carrier and extending from the beam is moved by the gantry in a second direction perpendicular to the first direction along the beam. An RF probe is attached to the free end of the robot arm and is configured to communicate with a test target antenna (AUT) of a device under test (DUT) fixed within a volume of space surrounding the DUT. A control system is configured to coordinate the movement of the gantry and the robot arm to move the RF probe in a scanning pattern around the DUT.

[0008] Embodiments of the present system can include one or more of the following features. The first and second directions can extend horizontally parallel to the support surface of the chamber that houses the system, and the robotic arm can extend downward from the beam. Alternatively, the first direction can extend horizontally, the second direction can extend vertically, and the robotic arm can extend horizontally from the beam. The robotic arm can have at least four degrees of freedom, or at least six degrees of freedom. The RF probe can be a compact antenna test range (CATR) assembly. The DUT can be a satellite, a ground vehicle, an aircraft, a ship, or an aerospace vehicle, and the volume of the space traversed by the RF probe is at least as large as the volume of the space surrounding the DUT.

[0009] In another aspect, a method is provided for scanning radio frequency (RF) signals to and / or from a device under test (DUT) that is fixed within the volume of space surrounding the DUT. The method includes providing a gantry having a robotically movable carrier along a beam in a first direction, providing a robotic arm having a fixed end attached to the carrier and extending from the beam, wherein the gantry is configured to move the robotic arm in a second direction orthogonal to the first direction along the beam, providing an RF probe attached to the free end of the robotic arm and configured to communicate with the AUT, and coordinating the movement of the gantry and the robotic arm to move the RF probe in a scan pattern around the DUT.

[0010] The above aspects and features of the inventive concept, as well as other aspects and features, will become readily apparent from the following detailed description with reference to the accompanying drawings.

Brief Description of the Drawings

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DETAILED DESCRIPTION OF THE INVENTION

[0012] Referring to FIGS. 1 and 2, large compact antenna test chambers 100 and 101 for satellite testing are shown. These chambers are designed to maintain an RMS accuracy of less than 30 μm across the entire surface of both reflectors. In particular, FIG. 1 shows a prior art example of a compact antenna test range with a composite reflector for satellite testing at Airbus. A range feed can be seen on the left side, and a sub-reflector can be seen on the right side.

[0013] Moving on to FIG. 2, another example of a prior art compact antenna test range with a composite reflector for satellite testing at Airbus is shown. In this configuration, the main reflector is placed on the right side and the sub-reflector is placed on the left side. The feed is located between two round columns on the right side. These chambers are typically isolated from external radio wave interference using an inner wall filled with foam pyramids that minimize the reflection of radio frequency signals, mimicking outer space. The physical size of the device, as well as the necessary distances from the device to the reflector and feed antenna, means that the main practical way to evaluate antenna performance from multiple directions is to operate the DUT in two dimensions. This can be a significant challenge, especially in the case of large vehicles, and may also mean that the acceleration and movement speed are slow due to the mass of the positioning system.

[0014] Referring to FIGS. 3A - 3D, a prior art "robot tool workspace" is shown. This workspace is generated by an off-the-shelf robot simulation and programming tool such as RoboDK for robots mounted on the ceiling above the desired test volume. These figures show all the possible locations where a selected robot can place a designated tool tip point "C". In this case, point "C" represents the desired center of the relative test volume with respect to the reflector, and its placement is based solely on the movable ranges of each axis of the robot.

[0015] Figures 3A and 3B show two extreme ends of the reach of a robotic arm in its workspace that is smaller than the workspace of the robot with a tool added. In these figures, the wrist of the robot is oriented to position the tool tip at the same point. This represents the maximum range of a single-axis scan around the DUT, i.e., theta. However, it has already been revealed that this range is limited to an angle less than 90 degrees.

[0016] Figures 3C and 3D show two possible paths that the robot can take to achieve this. Both of these paths are valid in this given workspace, but neither is actually possible. In the first case as shown in Figure 3C, the elbow of the robot collides with the ceiling. In the second case as shown in Figure 3D, the elbow is constrained to point downward, but then it collides with the reflector. These limitations highlight the difficulty of using a robotic arm for a near-field scan of the AUT.

[0017] These figures show the essential limitations of the prior art robotic tool workspace. The range of motion of the robotic arm, the possibility of collisions, and the physical location of the robot base with respect to the AUT all contribute to limiting the workspace. These limitations may constrain the ability of the robot to scan the AUT accurately and efficiently, highlighting the difficulty of using a robotic system for testing an evolutionary antenna system.

[0018] In its simplest form, the inventive concept consists of a multi-axis positioning system capable of manipulating an elongated object with up to six degrees of freedom (three rotations and three translations) over a large area. This multi-axis positioning system has an RF measurement system attached to perform radiometric or over-the-air measurements of the underlying radio architecture in addition to antennas, arrays, or other antenna systems in large devices under test (DUTs). In one embodiment, the system consists of an X-Y gantry system capable of accurately moving an attachment structure to which a robotic arm is attached for manipulating an RF field probe to any location within a single plane. In other embodiments, the probe can be attached directly to an X-Y scanner. In some embodiments, the probe can be attached to a rotary positioner having one or two orthogonal axes capable of tilting and / or rotating (i.e., tilting or rotating or both) the orientation of the probe relative to the system's reference coordinate frame and / or in response to the X-Y position of the gantry (i.e., relative to the system's reference coordinate frame, or in response to the X-Y position of the gantry, or by both). In such an arrangement, the available angular range covered by the system is defined by the arctangent of the ratio of the gantry's travel range to the height of the probe above the AUT. In some embodiments, the elevation angle can be changed using a linear positioner or other translation positioner that can translate in at least one additional orthogonal direction relative to the X-Y positioner. In some embodiments, the positioner can be attached to the rotary tilt arrangement described above. In other embodiments, the rotary tilt device can be attached to the linear positioner or split into two separate axes on either side of the positioner. In one embodiment, the probe can be attached to a secondary carrier that travels along a curved arc defining the radius of the probe system and moves along a predefined curved path to produce changes in both tilt and elevation angles.In some embodiments, the arc can be attached to a rotating stage attached to a gantry carrier to generate a rotational axis orthogonal to the movement generated by the arc. In some embodiments, the arc can terminate at the axis of rotation, while in other embodiments, the arc can support a balancing operation along both sides of the orthogonal axis of rotation. The lower end of the arc can also terminate at a height suitable for removing the DUT, or can extend below the raised DUT to enable capturing more coverage than a hemispherical coverage. In some embodiments, the moving carrier on the arc can be replaced with a plurality of probes that simultaneously measure different positions. In some embodiments, rather than the probe carrier moving along the arc, the entire arc can rotate about an axis. In some embodiments, the arc can be replaced with a linear armature or other structure capable of holding one or more probes directed towards the center of the desired test volume. In some embodiments, the probes can be tilted or moved along the armature. In some embodiments, the armature can be multi-dimensional, thereby enabling the probes to be positioned to cover a portion of the surface surrounding the AUT. It will be apparent to those skilled in the art that the choice of coordinate orientation and the "UP" direction in all of these descriptions is completely arbitrary. While some orientations may be preferred, embodiments of the present invention can provide support from any direction around the DUT and can scan above, below, to the side of, or all around the DUT. In this description, the AUT is assumed to be a planar array and the scan space is generally "above" the DUT. However, this is for illustrative convenience only and should not be considered as limiting the embodiments described in the claims.

[0019] In some embodiments, the RF probe consists of a lightweight compact range reflector and a feed assembly that supports one or more polarization states (e.g., FIG. 4 described below). In other embodiments, the probe can be a single or multiple individual antennas, a plane wave generator, an antenna having a lens that generates plane wave illumination, or other suitable sensors or transmitters. In some embodiments, the polarization state can be controlled by rotating the feed to change the polarization. In other embodiments, the polarization state can be controlled by rotating the reflector or the entire probe assembly around the central axis of the projected quiet zone test volume.

[0020] In some embodiments, the reflector substrate is made of a lightweight machinable foam. In other embodiments, the reflector is made of a thin carbon fiber shell or a fiberglass shell. In still other embodiments, the reflector is made by molding various suitable plastics or other lightweight materials such as expanded foam. In other embodiments, the reflector is 3D printed. In each of the various dielectric embodiments, the reflector substrate (after suitable surface preparation) can be metallized by a plurality of techniques including conductive paint, electroless plating, and vacuum metal evaporation. Alternatively, a thin metal shell can be made by a process such as electroforming and then attached to a lightweight (e.g., foam) structural substrate. In each embodiment, the structure that supports the feed antenna can be directly integrated with the reflector and made of a similar material, or separated and integrated from a rigid material that holds the feed at a suitable location. In some embodiments, the feed support structure is gravity-free when the system is moved around the AUT It can include a passive compensation mechanism or an active compensation mechanism that corrects for the inherent sag between the feed and the reflector caused by direction.

[0021] In some embodiments, the feed assembly includes a mechanism for manipulating the position and orientation of the feed relative to the reflector. In some embodiments, the feed is dual polarized, while in other embodiments, the feed can have only a single polarization. The feed can receive linearly polarized or circularly polarized waves in one or both of the orthogonal polarizations. In some embodiments, a feed roll axis can be provided to change the polarization of the feed. In some embodiments, the feed can be broadband to cover the entire desired operating range. In other embodiments, the feed and any associated components can be made swappable using an alignment method to ensure that the replacement feed is in focus. In other embodiments, the entire CATR assembly or probe assembly can be swapped on a positioning system to change the frequency range or test volume size. In some embodiments, a rack for holding multiple CATR assemblies, probe assemblies, or feed assemblies can be integrated within a gantry system. In some embodiments, automatic or semi-automatic swapping of the CATR assembly, probe assembly, or feed assembly can be incorporated. In some embodiments, a standard robotic tool change assembly can be used to swap the feed, with only manual reconnection of the cable assembly being required. In other embodiments, blind-mate connectors can be used to avoid the need for manual cable connections.

[0022] In some embodiments, one or more of the amplifier circuit section, up / down conversion circuit section, and digital radio circuit section can be disposed near the feed antenna, behind the reflector, or within the moving structure of the gantry system. In some embodiments, a test instrument including a receiver, transmitter, network analyzer, or communication tester can be disposed behind the reflector or within the moving structure of the gantry system. In other embodiments, RF cables routed across the gantry system return signals to a centralized location. In some embodiments, a cable chain or other means is used to carry the cables for RF signals, control signals, and power to the various components of the system. In some embodiments, the target RF / microwave signal is carried throughout the path, while in other embodiments, up-conversion / down-conversion is used at various locations along the path to reduce the loss of the IF signals and LO signals carried over longer distances of the system. In some embodiments, RF over fiber is used and RF signal cables, IF signal cables, and / or LO signal cables (i.e., RF signal cables, IF signal cables, or LO signal cables, or one or more of them) are replaced with lightweight, low-loss, and low-cost optical fiber cables that can easily handle the various bends associated with all of the axes of motion. In some cases, digital signals for control and / or data (i.e., for control or data or both) are carried via the optical fiber cable.

[0023] In some embodiments, an RF absorber (anechoic material) is used to cover any exposed components of the positioning system and probe assembly that could cause unwanted signals to reflect back into the test volume. In some embodiments, the feed assembly includes an absorber “fence” to prevent signals from the feed from reaching the test volume directly. In some embodiments, the support structure between the feed and the reflector, as well as all cables and equipment, are covered by an absorber to ensure that the feed signal to the reflector is not contaminated by reflections. In some embodiments, the robot arm or other armature mechanism, and gantry components that may be exposed to leakage from the feed around the reflector or near direct or reflected paths from the reflector or the probe assembly itself, are also covered by sufficient absorbers to prevent large multipath ripples in the test volume. In some embodiments, high-power absorbers can be used to ensure handling of the high power density generated by the focused plane wave signal. In some embodiments, forced air cooling can be used to remove excess heat. In other embodiments, pulse-width modulation measurements can be used to limit the average power applied to the absorber.

[0024] In some embodiments, the system can use one laser or a combination of lasers for visual alignment of the test volume with respect to the DUT. These lasers can have dot patterns, line patterns, crosshair patterns, or other graticule patterns that indicate different degrees of freedom of the positioning system. The lasers can be attached to each of those components of the X - Y gantry within the test volume to highlight their locations. Alternatively, or additionally, those lasers can also be attached to a robot, an armature, or a probe / CATR assembly. In the case of a system with a fixed target height into the quiet zone test volume, one or more laser assemblies of fixed heights can be attached around the gantry or on a moving armature to indicate the height of the test volume. In a sufficiently flexible (e.g., robot - based) embodiment, the lasers can be attached to a moving arm or a probe / CATR assembly. In some embodiments, the moving laser assembly can be attached to coincide with the orientation of the probe or the reflector and can be embedded in an absorber to minimize its impact. In other embodiments, the lasers can be attached with a known offset in an orientation between the laser pointing direction and the centerline of the probe, behind the probe or the reflector. During alignment, the probe is rotated away from the desired test volume and the lasers are used while the system is being aligned. After alignment, the known offset is used and the probe is rotated back to the currently aligned coordinate system.

[0025] In some embodiments, one or more cameras can be used to perform DUT coordinate alignment instead of or in addition to a laser. A digital reticle overlaid on the display can be used instead of or in addition to a laser. Similar to the laser, the location of the camera can be in a location that can be used while the system is operating, can be moved to a predetermined location for calibration, and then hidden to avoid RF reflections and interference. In some embodiments, a 3D camera, sensor, photogrammetry, or other mechanism can be used to generate a model of the DUT for alignment purposes and obstacle avoidance. In some embodiments, a CAD model of the DUT can be imported into the control software to provide this map. Some embodiments can use any combination of the above.

[0026] Next, a system for scanning radio frequency (RF) signals to and / or from a device under test (DUT) (i.e., to the device under test (DUT), from the DUT, or both) according to an embodiment of the inventive concept will be described with reference to FIG. 4.

[0027] Referring to FIG. 4, a system 400 for scanning radio frequency (RF) signals to and / or from a device under test (DUT) (i.e., to the DUT, from the DUT, or both) within a volume of space surrounding the DUT is shown. The DUT includes an antenna under test (AUT). The system 400 includes a gantry 401 having a carrier 402b that is robotically movable in a first direction along beam 402a. As shown in this figure, the first direction can extend horizontally parallel to the support surface of the chamber that houses the system 400. Alternatively, the first direction can extend vertically parallel to the wall of the chamber.

[0028] A robotic arm 403 having a fixed end attached to a carrier 402b is provided to extend from a beam 402a. The gantry 401 is configured to move the beam in a second direction orthogonal to the first direction, and as a result, move the robotic arm 403 in this second direction. In some embodiments, the robotic arm 403 can have at least four degrees of freedom, providing flexibility in the positioning of the RF probe. In other embodiments, the robotic arm 403 can have at least six degrees of freedom, providing further flexibility in the positioning of the RF probe.

[0029] An RF probe 404 is provided and attached to the free end of the robotic arm 403. The RF probe 404 is configured to communicate with the AUT. The RF probe 404 can be a compact antenna test range (CATR) assembly. This CATR assembly is designed to generate a uniform plane wave that irradiates the AUT with a much lower total path loss and physical size than assemblies typically associated with direct far-field irradiation.

[0030] A control system (not shown in FIG. 4) is configured to coordinate the movement of the gantry 401 and the robotic arm 403 to move the RF probe 404 in a scan pattern around the DUT. This scan pattern enables the RF probe 404 to capture RF signals from various angles and positions around the DUT, providing a comprehensive evaluation of the performance of the AUT.

[0031] By way of example, the DUT can be a satellite, a ground vehicle, an aircraft, a ship, or an aerospace vehicle. The volume of the space traversed by the RF probe 404 is at least as large as the volume of the space surrounding the DUT. This enables the system 400 to accommodate DUTs of various sizes and shapes, making the system 400 versatile for testing a wide range of devices.

[0032] To perform the desired scan of the AUT, the probe must follow a given trajectory in space while maintaining its orientation towards the center of the test volume. In some embodiments, the path of the required trajectory and the movement of the axes of the positioner are pre - calculated on a control computer. In some embodiments, the movement is calculated on the fly in an embedded controller. In some embodiments, sag or other error corrections are applied based on the position of each trajectory or each configuration to keep the probe on the path and orientation of the desired trajectory. In some embodiments, the trajectory is selected to generate a path on a sphere and to measure data of the spherical angular coordinates of theta and phi (φ). In one such embodiment, the coordinate system is oriented such that, as shown in FIG. 5A described below, in a polar configuration, theta = 0 along the orthogonal bore - site direction of the AUT (i.e., the φ - axis is along the bore - site of the AUT). In the case of a normal planar array, only the upper hemisphere needs to be measured, and due to clearance issues, it may not be possible to achieve coverage beyond 60 degrees to 75 degrees. For this coordinate system, for each step of theta from 0 to the maximum allowable clearance, a conical cut of φ (blue line) can be taken for 360 degrees around the bore - site φ - axis. Alternatively, a partial great - circle cut of theta (red line) can be taken across the AUT between the negative and positive maximum ranges of the theta angle. FIG. 5B described below shows an alternative embodiment of a spherical scan algorithm where equatorial coordinates or azimuth and elevation coordinates are used around the bore - site direction. In this case, the bore - site of the AUT is in the equatorial plane, and the plane of the AUT is in the plane of a great - circle cut (e.g., φ = ±90 degrees) such that the poles of the spherical coordinate system are in the plane of the AUT. In this scenario, the upper hemisphere of the AUT is covered for theta ranging from 0 degrees to 180 degrees, which corresponds to elevation angles of ±90 degrees from the bore - site direction and azimuth angles of ±90 degrees of φ.It will be apparent to those skilled in the art that the selection of (0,0) in this given coordinate system is to some extent arbitrary, and any other desired combination can be used. Similarly, the orientation of the polar / phi axis can be easily chosen anywhere around the bore site axis to align the measurement coordinates with the desired conventional coordinates of the DUT. Considering the case where the gap problem may prevent the measurement of the entire upper hemisphere, it should be noted that, as shown in Figure 5C described below, the range of allowable angles for each cross-section varies around the hemisphere based on the total angle from the bore site axis.

[0033] Referring next to Figure 5A, in one such system 400, the coordinate system is oriented in a polar configuration. In this configuration, theta along the orthogonal bore site direction of the antenna under test (AUT) is equal to 0. This means that the phi axis is along the bore site of the AUT. This orientation enables a wide range of scans of the AUT from various angles and provides a detailed evaluation of the AUT's performance. Due to the polar configuration of the coordinate system, the RF probe 404 can capture RF signals from various angles and positions around the DUT, providing a wide range of evaluation of the AUT's performance.

[0034] In some cases, the system 400 can be configured to adjust the orientation of the coordinate system based on specific requirements of the test process. For example, the system 400 can adjust the orientation of the coordinate system to accommodate DUTs of various sizes and shapes, thereby making the system 400 versatile for testing a wide range of devices. In other cases, the system 400 can maintain a fixed orientation of the coordinate system throughout the test process. This can simplify the test process and reduce the complexity of the system 400.

[0035] It should also be noted that the orientation of the coordinate system in the pole configuration as shown in Fig. 5A is just one possible configuration. System 400 can be configured to use the orientation of other coordinate systems, such as the Cartesian coordinate system or the cylindrical coordinate system, according to the specific requirements of the test process. The selection of the orientation of the coordinate system can have a significant impact on the accuracy and efficiency of the test process, and thus is an essential part of System 400.

[0036] Referring to Fig. 5B, an alternative spherical scan algorithm is shown in which equatorial coordinates or azimuth and elevation coordinates are used centered on the bore site direction. In this case, the bore site of the AUT is in the equatorial plane, and the plane of the AUT is in the plane of the great circle cross-section (e.g., phi = ±90 degrees) such that the poles of the spherical coordinate system are in the plane of the AUT. This configuration enables a wide range of scans of the AUT from various angles and provides a detailed evaluation of the AUT's performance.

[0037] In this configuration, System 400 can adjust the orientation of the coordinate system to accommodate DUTs of various sizes and shapes, thereby making System 400 versatile for testing a wide range of devices. The equatorial configuration or the azimuth and elevation configuration of the coordinate system enables the RF probe 404 to capture RF signals from various angles and positions around the DUT, providing a wide range of evaluations of the AUT's performance.

[0038] Here too, it should be noted that the orientation of the coordinate system in the equatorial configuration or the azimuth and elevation configuration as shown in Fig. 5B is just one possible configuration. System 400 can be configured to use the orientation of other coordinate systems according to the specific requirements of the test process. The selection of the orientation of the coordinate system can have a significant impact on the accuracy and efficiency of the test process, and thus is an essential part of System 400.

[0039] Referring to FIG. 5C, it should be noted that the range of acceptable angles for each cross-section varies around the hemisphere based on the total angle from the bore site axis. This variation is due to the fact that the gap problem may prevent measurements of all upper hemispheres. As a result, the range of acceptable angles for each cross-section is adjusted to accommodate these gap problems, thereby ensuring that the RF probe 404 can continue to capture RF signals from various angles and positions around the DUT.

[0040] In some cases, the system 400 can adjust the range of acceptable angles for each cross-section based on specific requirements of the test process. For example, the system 400 can increase or decrease the range of acceptable angles for each cross-section to accommodate DUTs of various sizes and shapes. This flexibility enables the system 400 to test a wide range of devices, thereby making the system 400 versatile for various test scenarios.

[0041] The range of acceptable angles for each cross-section as shown in FIG. 5C is only one possible configuration. The system 400 can be configured to use other ranges of acceptable angles for each cross-section depending on specific requirements of the test process. The selection of the range of acceptable angles for each cross-section can have a significant impact on the accuracy and efficiency of the test process and is therefore an essential part of the system 400.

[0042] When the collimated beam is enabled by the CATR, it is not absolutely necessary to keep the range length constant. For other applications, it may be possible to correct the path loss and phase change according to the distance from the AUT. Therefore, in some embodiments, it is possible to make a choice to scan while maintaining the probe system in a fixed plane and tilt the angle of the probe to stay on the bore site to the AUT.

[0043] Figures 6A and 14 show grids every 15 degrees from a projection onto a plane for theta angles from the polar spherical configuration of Fig. 12(a) up to 75 degrees. Obviously, an infinite distance is required to approach theta = 90 degrees. Fig. 6B shows the same grid every 15 degrees of the azimuth and elevation configuration of Fig. 5B projected onto a plane for the azimuth and elevation ranges with the bore site as the center up to plus or minus 75 degrees. In this case, as both angles approach 75 degrees, the above problem becomes apparent, and the green circle indicates the cut-off of the same polar angle from the bore site direction at 75 degrees. Here, it should be noted that the planar scan technique requires a more stringent tolerance with respect to the angle indication direction of the CATR probe. The reason is that a small angular error due to sag or other indication errors can cause a larger deviation in the position of the uniform illumination area from the reflector as the probe moves further away from the desired test area. This emphasizes the need for positioning calibration and validation checks and a method for applying corrections depending on the selected movement trajectory.

[0044] It will be obvious that many other scan surfaces and measurement grids can be used. For example, in some embodiments, cylindrical coordinates or Cartesian plane coordinates can be used. In some embodiments, a conformal surface can be scanned around the DUT to maintain a minimum safe distance for measurement. In some embodiments, an algorithm of uniformly spaced points (a grid of constant density) can be used either on a spherical surface or on any other desired surface. However, for example, placing points at intervals on a spherical surface does not impose a requirement that measurements must be made over that spherical surface.

[0045] Next, referring to FIG. 7, in some cases, in order to scan other items located at different locations on different antennas under test (AUT) or devices under test (DUT), the center coordinates of any of the above-described test volume configurations can be changed using a volume positioning system. This flexibility enables the system 400 to accommodate DUTs of various sizes and shapes, thereby making the system 400 versatile for testing a wide range of devices. Alternatively, multiple DUTs can be configured to be tested in the same overall test volume, and the system can automate the sequential scanning of different DUTs.

[0046] As an aside, it is also extremely important for the system to have sufficient safety measures to protect the system components themselves in addition to the life and body and the expensive devices being tested. In some embodiments, by using a collaborative robot (cobot) for the baseline device, a torque-based fail-safe mechanism is provided when something comes into contact with the robot and tools (e.g., CATR probes), resulting in a force exceeding a given threshold. In other embodiments, a light curtain and a door safety interlock can be used to prevent movement when the user is within the operating area. In addition to the collision protection features available in normal robots, some embodiments can use other sensors including sonar and lidar to provide real-time mapping and detection of objects around the reflector / probe assembly while avoiding interference with the RF tests being performed. Radar-based solutions can potentially cause interference with the desired tests but can be an option in some cases.

[0047] Alternatively, or additionally, some embodiments can provide real-time optical tracking of a measurement system using a stationary camera and / or a carrier-mounted camera and / or a probe-mounted camera. Techniques including stereo vision, photogrammetry, etc. can be used to rapidly generate a 3D model of the test environment and ensure that the measurement system is operating as expected and not entering a predefined or automatically recognized restricted access area where a collision could occur. In some systems, laser interferometry and / or one or more laser trackers (i.e., laser interferometry or one or more laser trackers or both) can be used for both real-time feedback of the exact position of the probe system and compensation for sag and other errors. Alternatively, the laser tracker can also be used only during installation for calibration of the system.

[0048] Another test application supported by the volumetric scanning system of the present inventive concept enables tracking of a movement trajectory, in which a phased array or a mechanical tracking antenna is evaluated as to whether it can maintain a communication link to a moving endpoint (e.g., a satellite or a moving vehicle). In this scenario, the desired path is unlikely to be represented by a simple movement of theta or phi about any single spherical axis, and it is rare to reach the zenith directly above the antenna element. Even in the simplest "static" case, the positioning system needs to be able to follow a complex angular path over the upper hemisphere. In some embodiments of the present inventive concept, the system is equipped with a second RF probe and is configured to coordinate the movement of the two RF probes to emulate a respective first ground base station and a second ground base station that communicate with a satellite while the satellite is in orbit. This aspect of the present inventive concept is described next with respect to FIGS. 8A - 12.

[0049] Referring to FIGS. 8A and 8B, the relationship between the angles from the zeniths of both the satellite and the terrestrial station and the corresponding orbital angles is shown. In these figures, the range of azimuth angles for which communication is maintained is projected onto the Earth's surface.

[0050] FIG. 8A shows the relationship between the angles from the zeniths of both the satellite and the terrestrial station and the corresponding orbital angles, and FIG. 8B shows the range of azimuth angles projected onto the Earth's surface for which communication must be maintained. The corresponding orbital angles are shown in relation to the angles from the zeniths of both the satellite and the terrestrial station. The azimuth angle corresponds to the direction of the satellite from the terrestrial station in the horizontal plane. The orbital angle corresponds to the position of the satellite in its orbital path, and the angle from the zenith corresponds to the angle between the line of sight from the terrestrial station to the satellite and the vertical direction. The relationship between these two angles determines the movement trajectory that the RF probe follows during the scan process.

[0051] FIGS. 9A and 9B plot the range of zenith angles of a satellite passing directly overhead (FIG. 9A) and the corresponding angular velocity as seen by the terrestrial station when the satellite passes (FIG. 9B). Any movement trajectory must emulate the azimuth and zenith angles and the associated angular velocity related to the terrestrial station of the desired orbital path.

[0052] FIG. 9A plots the range of zenith angles of a satellite passing directly overhead. The zenith angle corresponds to the angle between the line of sight from the terrestrial station to the satellite and the vertical direction. The range of zenith angles determines the range of positions that the RF probe 404 can occupy during the scan process. This range of positions enables the RF probe 404 to capture RF signals from various angles and positions around the DUT, providing a comprehensive evaluation of the performance of the AUT.

[0053] Figure 9B plots the corresponding angular velocity as seen by a ground station when the satellite passes by. The angular velocity corresponds to the rate of change of the angle between the line of sight from the ground station to the satellite and the perpendicular direction. The range of the angular velocity determines the speed at which the RF probe 404 moves during the scan process. This speed affects the speed at which the RF probe 404 captures RF signals, and as a result, impacts the efficiency of the test process.

[0054] Figure 10 shows a set of variables used to solve the case of the simple zenith movement trajectory of FIGS. 9A and 9B. That is, this figure shows the variables used to calculate the movement trajectory of the RF probe during the scan process. Other movement trajectories are much more complex but can be solved relatively easily using vector algebra.

[0055] Accordingly, in one embodiment, the positioning system and control software use orbital mechanics to calculate the desired movement trajectory and reproduce it in real time when the communication link is evaluated. In some embodiments, a channel emulation method or other communication test method can be used to simulate expected time / position-dependent channel impairments such as path loss and Doppler changes according to the distance and speed of the actual satellite, as well as expected atmospheric losses, dispersion, multipath, etc. In another embodiment, the positioning system can be configured to follow real-time movement trajectory information supplied from another emulator or simulation source. In yet another embodiment, to simulate a bank or turn at a corner, the movement of a second endpoint (e.g., a plane or RV) can be added to the scenario with additional changes to the movement trajectory. It will also be apparent to those skilled in the art that other movement trajectory scenarios are possible, including vehicle to terrestrial network scenarios and vehicle to vehicle scenarios in ground-based, airborne, or space-based configurations, or any combination thereof.

[0056] Similarly, the calculation of the movement trajectory can be performed to execute the behavior of any of the endpoints. In one embodiment, these positions and velocities are reproduced on the surface of a sphere centered on the AUT, while in an alternative scenario, they can be generated along other desired geometric shapes similar to the shape of a planar surface or a spherical measurement grid.

[0057] To explain in detail the concept of tracking the movement trajectory, as another important test case, there is an evaluation of a handover scenario where, for example, one satellite is moving out of range (setting) while another satellite is coming into range (rising). The same scenario also exists for satellites when a satellite migrates from one ground station to another and all active end-user backhaul links must be maintained during the migration. FIG. 11 to be described next shows one embodiment of a system for testing such a scenario. In this scenario, a second gantry beam and a carrier having a second robotic arm and a CATR probe are used to generate a second plane wave beam into a desired test volume. In the case of the illustrated embodiment of the test method, each probe irradiates different AUTs on the DUT to test the handover between simultaneous beams in different directions from different phased arrays on the DUT.

[0058] Referring to FIG. 11, a system 400a according to an embodiment of the inventive concept is shown. The system 400a includes a second gantry beam 405a and a second carrier 405b having a second robotic arm 406 and a second CATR probe 407 used to generate a second plane wave beam into a desired test volume. In this configuration, each probe may irradiate different AUTs on the DUT. This setting enables the testing of handovers between beams occurring simultaneously in different directions from different phased arrays on the DUT.

[0059] In this system 400a, the second gantry beam 405a and the carrier 405b are configured to move in a manner similar to the first gantry beam and carrier, thereby providing a second degree of freedom of movement for the second robotic arm 406. The second robotic arm 406 is attached to the second carrier 405b and extends from the second gantry beam 405a. The second robotic arm 406 can have at least four degrees of freedom or at least six degrees of freedom, thereby providing flexibility in positioning the second RF probe 407.

[0060] The second RF probe 407 is attached to the free end of the second robotic arm 406 and is configured to communicate with different AUTs on the DUT. The second RF probe 407 can be a CATR assembly, similar to the first RF probe. This CATR assembly is designed to generate a uniform plane wave that irradiates the AUT with much lower total path loss and physical size than assemblies typically associated with direct far-field irradiation.

[0061] A control system (not shown in FIG. 11) is configured to coordinate the movement of the second gantry beam 405a, the second carrier 405b, and the second robotic arm 406 to move the second RF probe 407 in a scan pattern around the DUT. This scan pattern enables the second RF probe 407 to capture RF signals from various angles and positions around the DUT, providing a comprehensive evaluation of the performance of different AUTs on the DUT.

[0062] The same system 400a can also be used in other methodologies to test other scenarios such as MIMO / massive MIMO, multiple simultaneous beams from the same AUT, or signal-to-interference (SIR) tests on a single AUT, as shown in FIG. 12. This flexibility allows the system 400a to accommodate a wide range of test scenarios, thereby making the system 400 versatile for various test applications.

[0063] The robotic arm generally has more degrees of freedom than would be required to emulate two spherical axes of motion for the movement. However, as described above, due to physical size constraints, potential collision points, and the physical location of the robot base with respect to the AUT, the available workspace is greatly reduced. However, as shown in FIG. 13, if a collision-free path for the center point C in the green plane is provided such that all desired angles of incidence (e.g., from theta = 0 degrees to 75 degrees) can be sequentially reached without encountering obstacles, one embodiment of the system and associated algorithms moves only the base of the robot in the direction opposite to the movement path of C in the robot tool workspace to maintain C at the desired center of the test volume as the probe is moved over the desired angle range. The net effect in the DUT coordinate system is that point C remains fixed while the base of the robot moves along the path in the robot workspace in the reverse direction.

[0064] When using eight degrees of freedom by adding a two-axis gantry system to a six-axis robot, there may still be multiple possible paths, but not all of them are optimal from the perspectives of total momentum, the movement speed of each axis, etc. A path that minimizes the overhung load, maximizes the available angular velocity in the spherical coordinate system, and minimizes vibration or other disturbances is preferable to a path that changes the directions of the movements of various axes or has a sharp change in the movements of various axes. One way to restrict the system is to prioritize a certain specific axis of movement over other axes of movement. Another solution is to lock a certain specific axis in a specific configuration in order to reduce the overall degrees of freedom.

[0065] For example, in one embodiment as represented in FIG. 14, the elbow can be locked and the arm can be made substantially straight (avoiding the positioning singularity of the elbow joint at the straight position), and when the adjacent wrist joint of the robot is constrained such that the arm is substantially vertical and the joint remains parallel to the desired theta cutting plane, it can be maintained in an approximately right angle orientation that gives the maximum angular spread of the reflector / probe. In this scenario, the full range of motion of theta from 0 to maximum is achieved by the second "tilt" axis of the shoulder joint and the gantry moving radially to a position approximately proportional to the cosine of the theta angle (and corresponding tilt angle) along a line perpendicular to this tilt axis. Due to the constraints of height versus range length versus robot arm length, the wrist joint also still has to make minor adjustments along an arc as well. For a constant angular velocity, the linear velocity of the gantry must similarly vary according to the cosine of the theta angle. In this embodiment, referring to FIG. 15, the phi axis rotation is achieved by moving the X-Y gantry circularly at the current radius related to the theta angle and rotating the vertical shoulder joint at the top of the robot in the opposite direction to compensate for the circular motion of the gantry carrier and the robot base. Thus, by simply adding a few constraints, the motion calculations are reduced from eight independent axes to three or four tightly coupled motions of the theta and phi movements. By using a slightly larger gantry or by using the elbow for the remaining motion, it should be noted that the entire theta cross-section from the maximum of -theta (negative theta) to the maximum of +theta (positive theta) can be reached in one cross-section if necessary. However, for that, it may be necessary to reverse the motion on the gantry for a part of the motion, which is somewhat undesirable.

[0066] An alternative embodiment of the scan algorithm using a similar method removes the constraint that the gantry carrier and the robotic arm move parallel to the plane of the theta rotation of the reflector, and instead constrains the carrier on the gantry to (generally) remain within a plane that is perpendicular to the plane of movement and coincides with the wrist of the robot. In this scenario, the arm remains extended at all positions again, but as the reflector moves upward as shown in FIG. 16 and is moved across the test volume, the carrier follows a circular arc rather than moving along a radial line. The phi rotation is achieved in the same way as in the above embodiment.

[0067] It will be apparent to those skilled in the art that these are only two possible embodiments of the motion algorithm possible by following a simple set of rules.

[0068] One problem with any mechanical positioning system used for RF measurements is that as the angular resolution of the measurement increases, the amount of time required to accelerate and decelerate between measurement points becomes excessive. A smaller step size means that the positioner does not have time to accelerate to a high speed before it has to decelerate and stop. Thus, what is standardly implemented in the industry is to generate a trigger signal and synchronize the on-the-fly measurement to be recorded at a specific step size. This can be achieved relatively easily using a single-axis positioner with a digital encoder, by using a simple count-to-N counter to count the encoder pulses as the positioner moves and automatically generate a trigger pulse when the counter rolls over. The value of N specifies the periodicity of the trigger in position units and allows accurate measurements to be made at the desired position regardless of whether the positioner is accelerating, decelerating, or moving at a constant speed. Similarly, a stepper motor controller can generate the desired trigger pulse when signaling to count steps and take the next step corresponding to the desired trigger count.

[0069] However, when the movement exceeds a single axis, the desired trigger position is no longer a characteristic of a single movement axis, so the above method no longer functions. Querying each axis to identify the current position in order to generate the trigger pulse or command required for measurement is also not an effective method. The reason is that the accompanying communication latency always delays the trigger well beyond the desired trigger point. In some cases, it may be possible to compensate using skew correction, but skew varies with speed and is in the opposite direction when the positions are measured in reverse order.

[0070] To avoid this problem, it is necessary to pre-calculate or calculate on-the-fly the position of each of the eight axes of movement (steps and / or encoder counts (i.e., steps or encoder counts or both)) as a function of time. One possible implementation of the positioning algorithm described above calculates the corresponding trigger times in parallel based on the desired trigger angle / position. Subsequently, through a similar mechanism that streams the position information to each of the motor drives, the trigger pulses are generated at the appropriate times based on the parallel streams. Figure 17, described below, shows the use of multiple axes with varying speeds of movement to create a single movement of a probe tool centered on a virtual axis, and the resulting trigger generated in proportion to the angular speed of movement. This method can, of course, scale to any number of axes from two synchronized axes to much more complex positioning systems.

[0071] Referring to Figure 17, the method by which multiple axes with varying speeds of movement are used to create a single movement of a probe tool centered on a virtual axis is shown. In this configuration, the trigger is generated in proportion to the resulting angular speed of movement. By this method, the system is able to accurately capture RF signals from various angles and positions around the DUT, providing a broad evaluation of the AUT's performance.

[0072] In this scenario, due to the diverse movement speeds of multiple axes, the probe tool can trace a complex movement trajectory around the DUT. This movement trajectory is determined by a virtual axis, which is a conceptual axis that guides the movement of the probe tool. The virtual axis is not a physical component of the system 400; rather, it is a mathematical construct used to calculate the movement trajectory of the probe tool.

[0073] The trigger of the RF probe is generated in proportion to the resulting angular velocity. This means that the speed at which the RF probe 404 captures the RF signal is adjusted based on the speed at which the probe tool moves along the movement trajectory. Thereby, the system 400 can maintain a constant angular velocity during the scan process, ensuring an accurate and efficient test of the AUT.

[0074] An alternative embodiment of position-based trigger acquisition is to perform free running (sample-based) trigger acquisition or time-based trigger acquisition, where trigger pulses associated with each measurement, generated by a measurement device or an external timer to simultaneously log the current positions of all drive axes, are also supplied to the positioning system. The actual angular position of the probe can then be determined in real-time or in post-processing to align the measurement data with the associated positions. This may create a non-uniform angular interval of data in the case of a movement trajectory-based scenario where the angular velocity changes programmatically, but this approach of continuously capturing data in response to time rather than angle is much more reasonable.

[0075] Next, referring to FIG. 18, a general-purpose control system 1800 is shown. The control system 1800 includes a computer system 1801 that communicates with a gantry servo 1802, a robot servo 1803, an RF probe control circuit 1804, and a DUT control circuit 1805. The computer system 1801 functions as a central processing unit of the control system 1800 that coordinates the movement of the gantry 401 and the robot arm 403 and controls the operation of the RF probe 404 and the DUT.

[0076] In the case of the system of FIG. 4, the gantry servo 1802 controls the movement of the beam 402a in the second direction and the movement of the carrier 402b in the first direction. The gantry servo 1802 receives commands from the computer system 1801 and converts these commands into mechanical movements of the carrier 402b along the beam 402a. Thereby, the gantry 401 can position the fixed end of the robot arm 403 at any location within a two-dimensional plane above the DUT.

[0077] The robot servo 1803 controls the movement of the robot arm 403. The robot servo 1803 receives commands from the computer system 1801 and converts these commands into mechanical movements of the robot arm 403. Thereby, the robot arm 403 can position the RF probe 404 at various angles and positions around the DUT.

[0078] The RF probe control circuit 1804 controls the operation of the RF probe 404. The RF probe control circuit 1804 receives commands from the computer system 1801 and converts these commands into operation parameters of the RF probe 404. Thereby, the RF probe 404 can communicate with the AUT and capture RF signals from various angles and positions around the DUT.

[0079] The DUT control circuit 1805 controls the operation of the DUT. The DUT control circuit 1805 receives commands from the computer system 1801 and converts these commands into operation parameters of the DUT. As a result, the DUT can operate in a way that facilitates the test process.

[0080] It should be noted that the configuration of the control system 1800 as shown in FIG. 18 only represents one possible configuration. The system 400 can be configured to use other control systems according to specific requirements of the test process. As will be understood by those skilled in the art, the choice of the control system can have a significant impact on the accuracy and efficiency of the test process.

Claims

1. A system (400) for scanning radio frequency (RF) signals to and / or from a device under test (DUT) fixed within a volume of a space surrounding the DUT, wherein the DUT includes an antenna under test (AUT), the system (400) comprising: A gantry (401) having a carrier (402b) robotically movable in a first direction along a beam (402a); A robotic arm (403) having a fixed end attached to the carrier (402b) and extending from the beam (402a), the gantry (401) being configured to move the robotic arm (403) along the beam (402a) in a second direction orthogonal to the first direction; An RF probe (404) attached to the free end of the robotic arm (403) and configured to communicate with the AUT; A control system (1800) configured to coordinate movement of the gantry (401) and the robotic arm (403) to move the RF probe (404) in a scan pattern around the DUT. A system comprising the above.

2. The system (400) according to claim 1, wherein the first direction and the second direction extend horizontally parallel to a support surface of a chamber housing the system (400), and the robotic arm (403) extends downwardly from the beam (402a).

3. The system (400) according to claim 1, wherein the first direction extends horizontally and the second direction extends vertically, and the robotic arm (403) extends horizontally from the beam (402a).

4. The system (400) according to claim 1, wherein the robotic arm (403) has at least four degrees of freedom.

5. The system (400) according to claim 1, wherein the robotic arm (403) has at least six degrees of freedom.

6. The system (400) according to claim 1, wherein the RF probe (404) is a compact antenna test range (CATR) assembly.

7. The system (400) according to claim 1, wherein the DUT is a satellite, a ground vehicle, an aircraft, a ship, or an aerospace vehicle, and the volume of the space traversed by the RF probe (404) is at least as large as the volume of the space surrounding the DUT.

8. A system (400) for scanning radio frequency (RF) signals to and / or from a device under test (DUT) fixed within a volume of space surrounding the DUT, wherein the DUT includes an antenna under test (AUT), and the system (400) A gantry (401) having a first carrier (402b) robotically movable in a first direction along a first beam (402a) and a second carrier (405b) robotically movable in the first direction along a second beam (402a), wherein each of the first beam and the second beam is movable along a second direction orthogonal to the first direction. A first robotic arm (403) having a fixed end attached to the first carrier (402b) and extending from the first beam (402a), wherein the gantry (401) is configured to move the first robotic arm (403) along the second direction together with the first beam (402a). A second robotic arm (403) having a fixed end attached to the second carrier (405b) and extending from the second beam (402a), wherein the gantry (401) is configured to move the second robotic arm (403) along the second direction together with the second beam (402a). A first RF probe (404) attached to the free end of the first robotic arm (403) and configured to communicate with the AUT. A second RF probe (407) attached to the free end of the second robotic arm (403) and configured to communicate with the AUT. A control system (1800) configured to coordinate the movement of the gantry (401) and the first and second robotic arms to move the first and second RF probes in a scan pattern around the DUT. A system comprising... **Claim 9** The system (400) according to claim 19, wherein the DUT is a satellite, and the control system (1800) is configured to emulate a respective first ground base station and a second ground base station that communicate with the satellite while the satellite is in an orbit by coordinating the movement of the first RF probe and the second RF probe.

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