AMTA Paper Archive


Welcome to the AMTA paper archive. Select a category, publication date or search by author.

(Note: Papers will always be listed by categories.  To see ALL of the papers meeting your search criteria select the "AMTA Paper Archive" category after performing your search.)


Search AMTA Paper Archive
    
    




Sort By:  Date Added   Publication Date   Title   Author

Accuracy

Effective Polarization Filtering Techniques for Ground Penetrating Radar Applications
Sebastian G Wirth, Ivor L Morrow, November 2018

The effect of different decomposition techniques on the imaging and detection accuracy for polarimet-ric surface penetrating data is studied. We derive the general expressions for coherent polarimetric decomposition using the Stokes parameters and model based polarimetric decomposition using the Yamaguchi technique. These techniques are applied to multi-frequency (0.4-4.8GHz) full polarimetric near-field radar measurements of scattering from surface laid calibration objects and shallow buried landmine types and show in detail how the decomposition results provide effective surface and sub-surface clutter reduction and guide the interpretation of scattering from subsurface objects. Data processing methods assume cross-polar symmetry and a novel bistatic calibration procedure was developed to enforce this condition. The Yamaguchi polarimetric decomposition provides significant clutter reduction and image contrast with some loss in signal power; while Stokes parameters also provide imagery localising targets, complementary information on the scattering mechanism is also obtained. Finally a third novel polarimetric filter was formulated based on differential interferometric polarimetric decomposition. The three combined techniques contribute to a significant improvement of subsurface radar performance and detection image contrast.

A study of the Low-frequency Coaxial Reflectometer measurement procedure for evaluation of RF absorbers' reflectivity -II
Anoop Adhyapak, Zhong Chen, November 2018

The Low frequency Coaxial Reflectometer is the recommended procedure to measure the absorbers' reflectivity as per the IEEE 1128-1998 standard. The standard recommends the operable frequency range up to 500 MHz with a permissible error of 2 dB and higher error beyond 600 MHz. This paper studies and discusses the error on different types of absorber. Each of the absorber type is simulated in the square section of the reflectometer setup to compute the absorber's reflectivity using Ansys HFSS. An effective time gating technique is applied to reduce the effect of edge effects. These results are compared to the unit cell simulation results with a plane wave excitation and periodic boundary conditions. The absorbers are then simulated in the complete reflectometer setup to include the mismatch associated with the transition and compared to the unit cell model results. The errors associated with the comparison of the absorbers' simulation results for these different models are analyzed. The combination of these different absorbers is simulated in unit cell model. The absorbers are placed in different regions and orientations inside the reflectometer. The comparison between the unit cell results of the combination of the absorbers and the results of the absorbers inside the reflectometer in different orientations give the effect of the non-uniform field distribution inside the reflectometer.

Enhanced PNF Probe Positioning in a Thermally-Uncontrolled Environment using Stable AUT Monuments
John H Wynne, Farzin Motamed, George E Mcadams, November 2018

The need for thermal stability in a test chamber is a well-established requirement to maintain the accuracy and repeatability sought for high frequency planar near-field (PNF) scanner measurements. When whole chamber thermal control is impractical or unreliable, there are few established methods for maintaining necessary precision over a wide temperature range. Often the antenna under test (AUT) itself will require a closed-loop thermal control system for maintaining stable performance due to combined effects from transmission heat dissipation and the environment. In this paper, we propose a new approach for near-field system design that leverages this AUT stability, while relaxing the requirement of strict whole chamber thermal control. Fixed reference monuments strategically placed around the AUT aperture perimeter, when measured periodically with a sensing probe on the scanner, allow for the modeling and correction of the scanner positioning errors. This process takes advantage of the assumed stability of the reference monuments and attributes all apparent monument position changes to distortions in the scanner structure. When this monument measurement process is coupled with a scanner structure that can tolerate wide thermal variations, using expansion joints and kinematic connections, a robust structural error correction model can be generated using a bilinear mapping function. Application of such a structure correction technique can achieve probe positioning performance similar to scanners that require tightly controlled environments. Preliminary results as well as a discussion on potential design variations are presented.

Laboratory Proofs on a Nonredundant Spherical NF-FF Transformation for a Quasi-Planar AUT Mounted in Offset Configuration
Francesco D ' Agostino, Flaminio Ferrara, Claudio Gennarelli, Rocco Guerriero, Massimo Migliozzi, November 2018

This communication provides an experimental assessment of an accurate near-field-far-field (NF-FF) transformation with spherical scan, properly developed to take into account a mounting in offset configuration of a quasi-planar antenna under test (AUT). Such a technique relies on the nonredundant sampling representation of electromagnetic fields and, unlike the classical NF-FF transformation, it allows the reconstruction of the far field radiated by an AUT from a minimum number of NF data, which remains practically the same both when the AUT is mounted in onset and offset configuration, since this number is related only to the surface modeling the AUT. Such a surface has been here chosen coincident with that formed by two circular bowls with the same aperture and eventually different bending radii. Experimental results assessing the validity of such a technique are reported.

Resurfacing the NASA Langley Experimental Test Range Reflector
Ron Schulze, Matthew Bray, Nathanael Flores-Palomera, Chris Vandelinder, Richard Boucher, George Szatkowski, Larry Ticatach, Angelo Cavone, Matthew Ayers, Michael Draszt, John Rooks, , , ,, November 2018

An ambitious resurfacing campaign was launched in late 2017 to correct for large reflector surface distortions present at the NASA LaRC Experiment Test Range (ETR) in support of performing Europa Clipper flight High Gain Antenna (HGA) measurements at X-and Ka-band frequencies. The effort was successful as the worst case peak-to-peak amplitude ripple was reduced from 4.0-dB to 1.5-dB across the 4.1-meter quiet zone.

Eliminate Celestial Noise Sources in Your SatCom G/T Measurements
Roy C Monzello, November 2018

The current method of measuring system G/T performance is with the use of celestial noise sources (sun and cold sky). This paper details a method using man-made noise sources to measure system performance within an anechoic chamber, followed by an outdoor measurement to obtain G/T performance in a real world operational environment. A simple method is presented and equations derived that relate system performance in unknown environments to performance with known noise sources.

Measurement Methodology For Fast Antenna Testing Using Existing PNF ranges
F D'agostino, F Ferrara, C Gennarelli, R Guerriero, M A F Saporetti, L J Saccardi, Foged, D Trenta, Damiano Trenta@esa, Int, ,, November 2018

In this paper, we investigate the achievable time savings in planar near-field (PNF) measurement of high gain antennas using a planar wide-mesh scanning (PWMS) approach [1-2]. The PWMS employs at least four times less measurements points than standard scanning without degrading the measurement accuracy leading to an under-sampling factor of four. Such mesh scanning can be implemented on standard planar near-field systems similar to the ESTEC, Hertz PNF scanner [3, 4]. The measurement accuracy vs time-saving for the wide-mesh approach is investigated using the numerical model of a highly-shaped Ku-band reflector antenna. This antenna is a realistic representation of what is currently flying on typical satellites with European coverage such as Eutelsat W [5]. The Near Field to Far Field transformation accuracy is investigated by comparing traditional and PWMS results using the same base data from the antenna model. A discussion on implementation on existing scanners and the relation with measurement time-savings is included. The experimental verification of the technique will be included in the conference presentation.

Uncertainty Analysis Technique for Planar Field-Probing Measurements and Quiet-Zone Simulations of a Compact Antenna Test Range
T M Gemmer, D Heberling, November 2018

The performance of a compact antenna test range is evaluated by field-probing measurements of the quiet zone. The comparison between the simulated and measured data, however, is misleading due to the finite measurement accuracy and the limited nature of the numerical model. In order to allow a comparison, the uncertainty terms of the field-probing measurements and the numerical model are identified based on the National Institute of Standards and Technology 18-term uncertainty analysis technique. The individual terms are evaluated with simulations or measurements using the equivalent-stray-signal model. Bearing the differences between the model and the actual measurements in mind, the electrical field can be estimated precisely within the overlapping region of both uncertainty budgets.

Measurements of the dynamic pattern of an electronically steerable phased antenna array with circular polarization in Ka-band
Matthias Tebbe, Georg Strauss, November 2018

This paper presents two methods for measuring dynamic antenna patterns of phased arrays in a compensated compact range. The first method uses the turntable of the compact range to counter steer the antenna beam. The dynamic pattern is created by measuring single points of the pattern over time. This method is successfully tested, and the measurement results show the effect of phase jumps during the steering process. The second method extends the range of application to fast steering phased arrays by decoupling the antenna scan angle and the azimuth angle of the turntable.

A New Dielectric Analyzer for Rapid Measurement of Microwave Substrates up to 6 GHz
John W Schultz, November 2018

This paper presents a new measurement method based on the parallel plate capacitor concept, which determines complex permittivity of dielectric sheets and films with thicknesses up to about 3.5 mm. Unlike the conventional devices, this new method uses a greatly simplified calibration procedure and is capable of measuring at frequencies from 10 MHz to 2 GHz, and in some cases up to 6 GHz. It solves the parasitic impedance limitations in conventional capacitor methods by explicitly modeling the fixture with a full-wave computational electromagnetic code. Specifically, a finite difference time domain (FDTD) code was used to not only design the fixture, but to create a database-based inversion algorithm. The inversion algorithm converts measured fixture reflection (S11) into dielectric properties of the specimen under test. This paper provides details of the fixture design and inversion method. Finally, example measurements are shown to demonstrate the utility of the method on typical microwave substrates.

Multi-Level Spherical Wave Expansion for Fast Near- Field to Far-Field Transformation
Fernando Rodríguez Varela, Manuel Sierra Castañer, Belén Galocha Iragüen, November 2018

Traditional near-field to far-field transformation algorithms based on modal expansion are unable to deal with arbitrary measurement surfaces. To approach these problems, a matrix inversion method can be used to retrieve the spherical wave expansion (SWE) of the antenna under test (AUT) fields. Modeling the antenna with a set of multiple SWEs centered at arbitrary points over its surface offers a flexible approach for the solution of field transformation problems over arbitrary surfaces. The coefficients of each SWE are obtained using an iterative inversion approach where the matrix-vector products can be replaced by multilevel operators based on recursive aggregations and interpolations of the partial SWE fields, reducing the computational complexity from í µí± ¶(í µí²‡ í µí¿’) to í µí± ¶í µí²‡ í µí¿ í µí°¥í µí°¨í µí° í µí²‡. The proposed algorithm is tested using synthetic data and measurements showing good scalability and reduced transformation error.

Correction of Non-ideal Probe Orientations for Spherical Near-Field Antenna Measurements
Rasmus Cornelius, Dirk Heberling, October 2017

Positioning in near-field antenna measurements is crucial and often an absolute position accuracy of ?\50 is required. This can be difficult to achieve in practice, e.g. for robotic arm measurement systems and/or high frequencies. Therefore, optical measurement devices are used to precisely measure the position and orientation. The information can be used to correct the position and orientation during the measurement or in the near-field to far-field transformation. The latter has the benefit that the measurement acquisition is typically faster because no additional correction movements are needed. Different methods for correction of non-ideal measurement positions in r, ? and f have been presented in the past. However, often not only the relative position but also the orientation between the antenna under test (AUT) and the probe coordinate system is not perfect. So far, correction and investigation of the related non-ideal probe orientations has been neglected due to the assumption that the probe receiving pattern is broad. In this paper, non-ideal probe orientations will be investigated and a spherical wave expansion procedure which corrects non-ideal probe orientations and positions will be presented. This is achieved by including an arbitrary probe pointing in the probe response calculation by additional Euler rotations of the probe receiving coefficients. The introduced pointwise higher-order probe correction scheme allows an exact spherical wave expansion of the radiated AUT field. The transformation is based on solving a system of linear equations and, thus, has a higher complexity compared to Fourier-based methods. However, it will be shown that most of the calculations can be precomputed during the acquisition and that solving the linear equation system can be accelerated by using iterative techniques such as the conjugate gradient method. The applicability of the proposed method is demonstrated by measurements where an intentional misalignment is introduced. Furthermore, the method can be used to include full probe correction in the translated spherical wave expansion algorithm. In conclusion, the proposed procedure is a beneficial extension of spherical wave expansion methods and can be applied in different measurement scenarios.

Highly accurate fully-polarimetric radar cross section facility for mono- and bistatic measurements at W-band frequencies
Andreas Olk, Kais-Ben Khadhra, Thiemo Spielmann, October 2017

New requirements in the field of autonomous driving and large bandwidth telecommunication are currently driving the research in millimeter-wave technologies, which resulted in many novel applications such as automotive radar sensing, vital signs monitoring and security scanners. Experimental data on scattering phenomena is however only scarcely available in this frequency domain. In this work, a new mono- and bistatic radar cross section (RCS) measurement facility is detailed, addressing in particular angular dependent reflection and transmission characterization of special RF material, e.g. radome or absorbing material and complex functional material (frequency selective surfaces, metamaterials), RCS measurements for the system design of novel radar devices and functions or for the benchmark of novel computational electromagnetics methods. This versatile measurement system is fully polarimetric and operates at W-band frequencies (75 to 110 GHz) in an anechoic chamber. Moreover, the mechanical assembly is capable of 360° target rotation and a large variation of the bistatic angle (25° to 335°). The system uses two identical horn lens antennas with an opening angle of 3° placed at a distance of 1 m from the target. The static transceiver is fed through an orthomode transducer (OMT) combining horizontal and vertical polarized waves from standard VNA frequency extenders. A compact and lightweight receiving unit rotating around the target was built from an equal OMT and a pair of frequency down-converters connected to low noise amplifiers increasing the dynamic range. The cross-polarization isolation of the OMTs is better than 23 dB and the signal to noise ratio in the anechoic chamber is 60 dB. In this paper, the facility including the mm-wave system is deeply studied along with exemplary measurements such as the permittivity determination of a thin polyester film through Brewster angle determination. A polarimetric calibration is adapted, relying on canonical targets complemented by a novel highly cross-polarizing wire mesh fabricated in screen printing with highly conductive inks. Using a double slit experiment, the accuracy of the mechanical positioning system was determined to be better than 0.1°. The presented RCS measurements are in good agreement with analytical and numerical simulation.

A High Precision Group Delay Measurement Method for Circular Polarized High Gain Antennas
Georg Strauss, October 2017

In this contribution we demonstrate a method to measure the absolute Group Delay (GD) of a high gain dual feed offset reflector antenna for circular polarized signals in Ku- and S-band by which we reach a measurement accuracy better than 10 picoseconds. At first we discuss the definition and different possible measurement methods of GD. We specifically show that the utilization of the antennas phase centre does not lead to the demanded measurement accuracy. Instead we propose a measurement method that uses an electrically small Reference Antenna (RA). We use the measurement of the GD of the RA as a reference for the GD of the Antenna Under Test (AUT). Therefore the exact positions of the reference planes of the corresponding wave guide ports have to be ensured. For this we made use of a theodolite. These measurements must be performed in a Compensated Compact Range to meet the strict requirements of plane waves. Here the CCR of the Lab for Satellite Communication, Munich University of Applied Sciences was used. The GD of the (electrically small) RA is determined by measuring the GD of two identical RAs separated by an exact known free space distance and by referencing these measurements to the measured GD of the same arrangement, where the free space is bypassed by a long high precision rectangular wave guide with well-known dimensions. We demonstrate that by using a soft gating method the accuracy of the measurement results can be tremendously improved. Measurement results parametrized by the width of the gate window in the time domain are discussed. We further discuss the accuracy of the measurement results quantitatively and we especially show, that the influence of an antenna misalignment is negligible, as long the alignment error is smaller than the one dB power beam width. The measurement campaign was commissioned by the European Space Agency (ESA) to meet the requirements of the project Atomic Clock Ensemble in Space (ACES). By ACES a microwave link is used to compare the times given by different atomic clocks in space and on earth, so three ACES ground terminals were tested.

Accuracy Enhancement of Ground Reflection Range Measurements Using a Two-Element Array Source Antenna
Artem Saakian, Frederick Werrell, October 2017

One of the sources of the measurement errors in outdoor antenna test ranges, when testing from VHF through C-Band, is the ground reflected signal between probe antenna and the antenna under test (AUT). Those errors are due to antenna(s) relatively large beam width(s) at these frequencies, especially when AUT is placed on the large platform such as an aircraft. If reflected wave is not eliminated by the use of absorbers at the reflection point or redirection by the use of diffraction fences, then the range operates as a ground reflection range (GRR), where the reflected signal creates a lobbing pattern when the direct and reflected signals are overlaying in- and out-of-phase as a function of position and frequency, causing undesirable amplitude variations at the test point. Ground reflections may be a major cause of error for GRR measurements when testing large antennas or antennas mounted on large structures which require a large displacement of the AUT during the antenna pattern collection process. A concept of using vertically positioned two-element array probe antenna (source antenna) to suppress ground-reflected signals in GRR-s is presented in this article. Suppression is achieved by pointing first null of the probes gain pattern towards the reflection point on the ground. All analytical evaluations are based on geometrical optics approach. Comparison of the proposed approach to a traditional single-element probe (source) antenna approach, demonstrates a significant improvement in measurement accuracy. Estimates and verifications of analytical evaluations are based on Computational Electromagnetics (CEM) modeling tool such as WIPL-D code. Simulations are performed in the VHF frequency band (200 MHz).

The Performance of Modal Filtering in Passive and Active Integrated Antenna Measurements at 160 GHz
Linus Boehm, Martin Hitzler, Alexander Foerstner, Christian Waldschmidt, October 2017

The results of integrated antenna measurements are often severely distorted by reflections from the measurement environment. In order to feed passiveintegrated antennas wafer probes have to be used. Wafer probes are not only electrically large, but are also located in the immediate environment of the antenna undertest (AUT) and reflect part of the radiated signals. This causes significant distortions and erroneous results in radiation pattern, directivity, and gain measurements.Custom wafer probes have been used to reduce reflections for meaningful measurement results, but these special probes are difficult to fabricate and expensive. If the antenna is measured within an active system that generates the transmit signal, wafer probes are not required to feed the AUT, but bond wires, circuit elementsclose to the antenna, and parasitic radiation of surface waves also add distortions, which still limit the achievable accuracy of the measurements. In this paper modal filtering is used to mitigate the influence of these unwanted distortions in post-processing for both standard wafer probe and active antennameasurements. In the first part of the paper the performance of the post-processing technique is assessed for standard probe measurements at 160 GHz by comparing the post-processed results to a measurement of the same antenna using a custom made wafer probe that was designed for minimum reflections. In the second part modal filtering is used to reduce unwanted reflections for an active antenna measurement at 160 GHz. When the active circuitry that generates thetransmit frequency is integrated on the same chip as the AUT, the phase of the transmit signal is unknown. As the phase information is required for the post processing,a static external probe antenna is used as a reference to eliminate the phase drift of the measured signal. It is shown that modal filtering can be applied to integrated antenna measurements above 100 GHz and that reflections from wafer probes, bond wires, and the PCB canbe reduced significantly for passive and active antenna measurements, respectively.

Dual Surface Source Reconstruction on Arbitrary Shape for Interference Elimination
Yoshiki Sugimoto, Hiroyuki Arai, October 2017

A technique of visualizing a surface current or a near-field equivalent source distribution is required for an antenna evaluation and its failure diagnostic. An inverse problem reconstructs the equivalent wave source distribution inside the measurement region by solving the propagation coefficient of the electromagnetic wave inversely from the near-field measured electromagnetic field the antenna under test (AUT) Since this method can set an arbitrary shape surface enclosing the AUT as a estimation surface, it is effective to visualize the internal equivalent source distribution. However under interference wave environments, the inverse source technique reconstructs the equivalent currents, including interference wave component as a part of internal source distribution. The estimation accuracy is particularly deteriorated under interference wave conditions. We propose a method of 2-step source reconstruction on arbitrary 3-D surface using dual measured electromagnetic surface, for reconstruct internal equivalent source accurately. First step, we set a shape of estimation surface similar to the shapes of measurement surface, to estimate the internal distribution accurately under well-posed conditions. Not only the shape of the estimation surface but also the sampling density is made same to the density of the measurement surfaces. In second step, to reconstruct an arbitrary shape surface from reconstructed internal field distribution in previous step. Since the inverse problem in this step is generally under ill-posed conditions, the regularization is applied to improve the accuracy of the solution. By this 2-step reconstruction, the interference wave is eliminated and the internal equivalent source on arbitrary surface is reconstructed. For example, we apply the proposed method to a 4-element linear patch array antenna, and the effectiveness of the proposed method is clarified. We also showed that the internal source distribution accurately reconstructed on an arbitrary surface even in the interference wave environments and identify the defective operation part of the AUT.

Validation of Measured Source Antenna Representation in the Numerical Simulation of a GNSS Antenna on Sentinel Satellite
Maria Saporetti, Lucia Scialacqua, Francesco Saccardi, Lars Foged, Jan Zackrisson, Luca Salghetti Drioli, Damiano Trenta, October 2017

The measured source or Huygens box antenna representation has become an increasing popular solution to create accurate computational models of measured source antennas for the numerical analysis of antenna placement on complex platforms such as satellites. The equivalent representation of the measured antenna is obtained through the equivalent current (EQC) or inverse source technique, which is a measurement post-processing method that represents the measured antenna in equivalent electric and magnetic currents on a surface conformal to the antenna. The highly accurate representation of the measured antenna can be used for both suspended and flush mounted antenna and the format is compatible with most commonly used commercial CEM solvers. This technique enables computation of complex antenna scenarios in which the source antenna is physically available but the computational details are unknown. This is often the case for space antenna testing in which antennas from different suppliers are integrated on a platform representing the complex scenario. In this paper, the validation of this technique in space antenna testing application is presented. The test object is a GNSS antenna mounted on a Sentinel satellite mock-up working at 1227 and 1575 GHz. The GNSS antenna and Sentinel satellite structure have been designed, manufactured and measured by RUAG SPACE. Simulations of the sentinel satellite using the measured source technique are compared to measurement of the satellite mock-up model at the working frequencies of 1227 MHz and 1575 MHz. Preliminary results of this validation activity have been previously presented. This paper reports on the full validation activity including the possibility to use different CEM solvers. The activity has been partly supported by ESA ESTEC contract 4000116755 “Time Efficient satellite antenna testing technique based on NF measurement and simulation with controlled accuracy”.

Ka-Band Measurement Results of the Irregular Near-Field Scanning System PAMS
Alexander Geise, Torsten Fritzel, Maurice Paquay, October 2017

The portable antenna measurement system PAMS was developed for arbitrary and irregular near-field scanning. The system utilizes a crane for positioning of the near-field probe. Inherent positioning inaccuracies of the crane mechanics are handled with precise knowledge of the probe location and a new transformation algorithm. The probe position and orientation is tracked by a laser while the near-field is being sampled. Far-field patterns are obtained by applying modern multi-level fast multipole techniques. The measurement process includes full probe pattern correction of both polarizations and takes into account channel imbalances. Because the system is designed for measuring large antennas the RF setup utilizes fiber optic links for all signals from the ground instrumentation up to the gondola, at which the probe is mounted. This paper presents results of the Ka-band test campaign in the scope of an ESA/ESTEC project. First, the new versatile approach of characterizing antennas in the near-field without precise positioning mechanics is briefly summarized. The setup inside the anechoic chamber at Airbus Ottobrunn, Germany is shown. Test object was a linearly polarized parabolic antenna with 33dBi gain at 33GHz. The near-fields were scanned on a plane with irregular variations of over a wavelength in wave propagation. Allowing these phase variations in combination with a non-equidistant grid gives more degree of freedom in scanning with less demanding mechanics at the cost of more complex data processing. The setup and the way of on-the-fly scanning are explained with respect to the crane speed and the receiver measurement time. Far-fields contours are compared to compact range measurements for both polarizations to verify the test results. The methodology of gain determination is also described under the uncommon near-field constraint of coarse positioning accuracy. Finally, the error level assessment is outlined on the basis of the classic 18-term near-field budgets. The assessment differs in the way the impact of the field transformation on the far-field pattern is evaluated. Evaluation is done by testing the sensitivity of the transformation with a combination of measured and synthetic data.

Serial-Robotic-Arm-Joint Characterization Measurements for Antenna Metrology
Michael Allman, David Novotny, Scott Sandwith, Alexandra Curtin, Josh Gordon, October 2017

The accurate alignment of antennas and field probes is a critical aspect of modern antenna metrology systems, particularly in the millimeter-wave region of the spectrum.Commercial off-the-shelf robotic arms provide a sufficient level of positional accuracy for many industrial applications.The Antenna Metrology Project in the Communications Technology Laboratory at the National Institute of Standards and Technology has shown that path-corrected commercial robotic arms, both in hardware and software analysis, can be used to achieve sufficient positioning and alignment accuracies (positioning error ~ /50) for antenna characterization measurements such as gain extrapolation and near-field pattern out to 183 GHz [1]. Position correction is achieved using a laser tracker with a 6 degree of freedom sensor attached to the robot end effector.The end effector’s actual position, measured using the laser tracker, is compared to its commanded position and a path correction is iteratively applied to the robot until the desired level of accuracy is achieved in the frequency range of interest.At lower frequency ranges (< 40 GHz), sufficient positional accuracy can be achieved, without path correction, using a using a calibrated kinematic model of the robot alone [2].This kinematic model is based on knowledge of the link frame transformations between adjacent links and captures deviations due to gravitational loading on the joints and small mechanical offsets between the joints.Additionally, the calibration procedure locates the robot’s base frame in the coordinate system of the robot’s end effector.Each link frame is described by four physical quantities, known as Denavit-Hartenberg (DH) parameters [3]. We performed calibration measurements of our CROMMA system’s DH parameters over a working volume of ~1 m3.We then use the laser tracker to compare the robot’s positional accuracy over this working volume with and without the calibrated kinematic model applied.The path errors for the calibrated case set an upper frequency limit for uncorrected antenna characterization measurements. [1]D. R. Novotny, J.A. Gordon, J.R. Guerrieri, “Antenna Alignment and Positional Validation of a mm Wave Antenna System Using 6D Coordinate Metrology, ” Proceedings of the Antenna Measurements Techniques Association, pp 247-252, 2014 [2]R.Swanson, G. Balandran, S. Sandwith, “50-micron Hole Position Drilling Using Laser Tracker Controlled Robots, ” Journal of the CMSC, Vol 9, No 1, Spring 2014 [3].J.J. Craig, “Introduction to Robotics: Mechanics and Control, 3rd ed.,” New Jersey, Prentice Hall, 2004, pp. 62-69







help@amta.org
2024 Antenna Measurement Techniques Association. All Rights Reserved.
AMTA_logo_115x115.png
 
 

CONNECT WITH US


Calendar

S M T W T F S
1 2
3 4 5 6 7 8 9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30
31