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

Alignment

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.

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.

Assessment of a 3D-Printed Aluminum Corrugated Feed Horn at 118.7503 GHz
Joshua Gordon, Lavanya Periasami, Albin Gasiewski, David Novotny, Michael Francis, Ronald Wittmann, Jeffrey Guerrieri, October 2017

We investigate all-metal 3D printing as a viable option for millimeter wave applications. 3D printing is finding applications across many areas and may be a useful technology for antenna fabrication. The ability to rapidly fabricate custom antenna geometries may also help improve cub satellite prototyping and development time. However, the quality of an antenna produced using 3D printing must be considered if this technology can be relied upon. Here we investigate a corrugated feed horn that is fabricated using the powder bead fusion process for use in the PolarCube cube satellite radiometer. AlSi10Mg alloy is laser fused to build up the feed horn, including the corrugated structure on the inner surface of the horn. The intricate corrugations, and tilted waveguide feed transition of this horn made 3D printing a compelling and interesting process to explore. We will discuss the fabrication process and present measurement data at 118.7503 GHz. Gain extrapolation and far-field pattern results obtained with the NIST robotic antenna range CROMMA are presented. Far-field pattern data were obtained from a spherical near-field scan over the front hemisphere of the feed horn. The quasi-Gaussian HE11 hybrid mode supported by this antenna results in very low side lobe levels which poses challenges for obtaining good SNR at large zenith angle during spherical near field measurements. This was addressed through using a single alignment and electrical calibration while autonomously changing between extrapolation and near-field measurements using the robotic arm in CROMMA. The consistency in parameters between extrapolation and near-field measurements allowed the extrapolation data to be used in-situ as a diagnostic. Optimal near-field scan radius was determined by observing the reflection coefficient S11 during the extrapolation measurement. The feed horn-to-probe antenna separation for which |S11| was reduced to 0.1 dB peak-to-peak was taken as the optimal near-field scan radius for the highest measurement SNR. A comparison of these measurements to theoretical predictions is presented which provides an assessment of the performance of the feed horn.

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

Filtering Antenna-to-Antenna Reflections in Antenna Extrapolation Measurements
Robert Horansky, Mohit Mujumdar, Dylan Williams, Kate Remley, Joshua Gordon, David Novotny, Michael Francis, October 2017

At NIST, we have developed a precision, wide-band, mmWave modulated-signal source with traceability to primary standards. We are now extending the traceability path for this modulated-signal source into free space to be used for verifying over-the-air measurements in 5G, wireless receivers. However, to obtain a traceable modulated signal in free space, the full scattering matrix of the radiating antenna must be measured. We have extended the extrapolation methods used at NIST, based on the work of Newell, et al. [1]. The extrapolation measurement provides a very accurate, far-field, on-axis, scattering matrix between two antennas. When combined with scattering-matrix measurements made with permutations of pairs of three antennas, far-field scattering, and, thus, gain, is obtained for each antenna. This allows an accurate extrapolation of the antenna’s near-field pattern. We have incorporated the extrapolation fitting algorithms into a Monte Carlo uncertainty engine called the NIST Microwave Uncertainty Framework (MUF) [2]. The MUF provides a framework to cascade scattering matrices from various elements, while propagating uncertainties and maintaining any associated correlations. By incorporating the extrapolation measurements, and the three-antenna method into the MUF, we may provide traceability of all measurement associated with the gain, including the scattering parameters. In this process, we studied several aspects of the gain determination. In this work, we show simulations determining the efficacy of filtering to reduce the effect of multiple reflection on the extrapolation fits. We also show comparisons of using only amplitude (as is traditionally done) to using the full complex data to determine gain. Finally, we compare uncertainties associated with choices in the number of expansion terms, systematic alignment errors, uncertainties in vector network analyzer calibrations and measurements, and phase error introduced by cable movement. With these error mechanisms and their respective correlations, we illustrate the NIST MUF analysis of the antenna scattering-matrix with data at 118 GHz. [1] A. C. Newell, R. C. Baird, and P. Wacker “Accurate Measurement of Antenna Gain and Polarization at reduced distances by an extrapolation technique” IEEE Transactions on Antennas and Propagation. Vol. 21, No 4, July 1973 pp. 418-431. [2] D. F. Williams, NIST Microwave Uncertainty Framework, Beta Version. NIST, Boulder, CO, USA, Jun. 2014. [Online]. Available: http://www.nist.gov/pml/electromagnetics/related-software.cfm

A Broadband Patch Antenna with an Anisotropic Superstrate - Design and Measurement Challenges
David Tonn, Susan Safford, October 2017

Microstrip patch antennas are well known in the field of communications and other areas where antennas are used. They consist of a metallic conducting surface deposited onto a grounded dielectric substrate and are widely used in situations where a conformal antenna is desired. They are also popular antennas for array applications. But most patch antennas are typically resonant structures owing to the standing wave of current that forms on them. This resonant behavior limits the impedance bandwidth of the antenna to a few percent. In this paper we shall present an approach for improving the bandwidth of a resonant patch antenna which employs an engineered anisotropic superstrate. By proper design of this superstrate and its tensor, and proper alignment of it with the axis of the patch, an antenna with improved impedance bandwidth results. Some of the challenges associated with the measurement of the anisotropic superstrate will be discussed, ranging from 3D simulations to physical models tested in the laboratory. A final working model of the antenna will be discussed; this model consists of a stacked patch arrangement and was designed to operate at the GPS L1 and L2 frequencies. Data collected from 3D simulations using CST Microwave Studio along with laboratory and anechoic chamber measurements will be presented, showing how the bandwidth at both of these frequencies can be increased while maintaining circular polarization in both passbands. Tolerance to errors in alignment and fabrication will also be presented. Additionally, some lessons learned on anechoic chamber measurements of the antenna’s gain and axial ratio will be discussed.

Channel De-embedding and Measurement System Characterization for MIMO at 75 GHz
Alexandra Curtin, David Novotny, Alex Yuffa, Selena Leitner, October 2017

As modern antenna array systems for MIMO and 5G applications are deployed, there is increased demand for measurement techniques for timely calibration, at both research and commercial sites.[1] The desired measurement method must allow for the de-embedding of information about the closed digital signal chain and element alignment, and must be performed in the near-field. Current means of measuring large arrays cover a variety of methods. Single-element gain and pattern calibration must cover the parameter space of element weightings and is extremely time-consuming, to the point where the measurement may take longer than the duration over which the array response is stable.[4] Two other popular methods are the transmission of orthogonal codes and the use of holography to reconstruct a full-array pattern. The first of these methods again requires extremely long measurement time. For an array of N elements and weightings per element W_n, the matrix of orthogonal codes must be of an order greater than NW_n.[4][3]. This number varies with the form of W_n depending on whether the array is analog or digital, but in both cases for every desired beam configuration, an order-N encoding matrix must be used. The second method relies on illuminating subsets of elements within an array and reconstructing the full pattern.[2] Each illuminated subset, however, neglects some amount of coupling information inherent to the complete system, making this an imperfect method. In this work we explore the development of a sparse set of measurements for array calibration, relying on coherent multi-channel data acquisition of wideband signals at 75 GHz, and the hardware characterization and post-processing necessary to perform channel de-embedding at an elemental level for a 4x1 system. By characterizing the complete RF chain of our array and the differential skew and phase response of our measurement hardware, we identify crucial quantities for measuring closed commercial systems. Additionally, by combining these responses with precise elemental location information, we consider means of de-embedding elemental response and coupling effects that may be compared to conventional single-element calibration information and full-pattern array measurements. [1] C. Fulton, M. Yeary, D. Thompson, L. Lake, and A. Mitchell. Digital phased arrays Challenges and opportunities. Proceedings of the IEEE, 104(3):487–503, 2016. [2] E. N. Grossman, A. Luukanen, and A. J. Miller. Holographic microantenna array metrology. Proceedings of SPIE, Passive Millimeter-Wave Imaging Technology VIII, 5789(44), 2005. [3] E. Lier and M. Zemlyansky. Phased array calibration and characterization based on orthogonal coding Theory and experimental validation. 2010 IEEE International Symposium on Phased Array Systems and Technology (ARRAY), pages 271–278, 2010. [4] S. D. Silverstein. Application of orthogonal codes to the calibration of active phased array antennas for communication satellites. IEEE Transactions on Signal Processing, 45(1):206–218, 1997.

A Multi-Robot Large Antenna Positioning System for Over-The-Air Testing at the National Institute of Standards and Technology
David Novotny, Joshua Gordon, Alexendra Curtin, Michael Allman, Jeffrey Guerrieri, Kim Hassett, Quang Tom, George McAdams, October 2017

NIST has been using coordinated robotics in the Configurable Robotic Milli-Meter wave Antenna (CROMMA) system to assess antenna performance and radiative emissions since 2010. The focus to date has been using coordinated motion to arbitrarily position and correct antenna alignment for high frequency (>60 GHz) applications. Coordinated robotic motion was originally chosen to overcome the systematic alignment and range configurability limitations inherent in legacy stacked-stage ranges. A limitation with CROMMA is the relatively small spatial reach of the robotic arm (2.5 m), which limits antenna size and the number of wavelengths in separation achievable for lower frequencies. To overcome these limitations and address other dynamic testing requirements, NIST proposed the Large Antenna Positioning System (LAPS). The LAPS consists of two kinematically linked robotic systems, one of which is integrated with an 8 m linear rail system. The stationary robot is a 6 axes, 2.5m horizontal/4.4m vertical reach robotic arm, while the robot integrated with the linear rail system is a 6 axes, 3m horizontal/5.5m vertical reach robot arm. This configuration allows antennas to be positioned within a 5m x 6m x 10m volume. The motion system can operate in either a coordinated or independent motion control state, allowing independent or dynamic dual-robot motion. The coordinated capabilities of the system are designed to support not only traditional antenna measurement geometries (i.e. spherical, cylindrical, planar, gain-extrapolation), but also intended to be used to dynamically interact with changing RF conditions. The robots can independently scan or interrogate multiple bearings of a device under test, or trace out complex 6D paths during system testing. Initial data on performance of the system, including comparison of robot kinematics, RF acquired data, and physical locations verified by a laser tracker, will be presented.

Efficient Diagnosis of Radiotelescopes Misalignments
Amedeo Capozzoli, Angelo Liseno, Claudio Curcio, Salvatore Savarese, Pietro Schipani, November 2016

An innovative method for the diagnosis of large reflector antennas from far field data in radio astronomical application is presented, which is based on the optimization of the number and the location of the far field sampling points required to retrieve the antenna status in terms of feed misalignments. In these applications a continuous monitoring of the Antenna Under Test (AUT), and its subsequent reassessment, is necessary to guarantee the optimal performances of the radiotelescope. The goal of the method is to reduce the measurement time length to minimize the effects of the time variations of both the measurement setup and of the environmental conditions, as well as the issues raised by the complex tracking of the source determined by a prolonged acquisition process. Furthermore, a short measurement process helps to shorten the idle time forced by the maintenance activity. The field radiated by the AUT is described by the aperture field method. The effects of the feed misalignments are modeled in terms of an aberration function, and the relationship between this function and the Far Field Pattern is recast in the linear map by expanding on a proper set of basis functions the perturbation function of the Aperture Field. These basis functions are determined using the Principal Component Analysis. Accordingly, from the Far Field Pattern, assumed measured in amplitude and phase, the unknown parameters defining the antenna status can be retrieved. The number and the position of the samples is then found by a Singular Values Optimization (SVO).

Quiet-Zone Qualification of a Very Large, Wideband Rolled-Edge Reflector
Anil Tellakula, William Griffin, Scott McBride, November 2016

Installing a large compact range reflector and electromagnetically qualifying the quiet zone is a major undertaking, especially for very large panelized reflectors. The approach taken to design the required rolled-edge reflector geometry for achieving a 5 meter quiet zone across a frequency range of 350 MHz to 40 GHz was previously presented [1]. The segmentation scheme, fabrication methodology, and intermediate qualification of panels using an NSI-MI developed microwave holography tool were also presented. This reflector has since been installed and the compact range qualified by direct measurement of the electromagnetic fields in the quiet zone using a large field probe. This paper presents the comparison and correlation between the holography predictions and the field probe measurements of the quiet zone. Installation and alignment techniques used for the multiple panel reflector are presented.  Available metrology tools have inherent accuracy limitations leading to residual misalignment between the panels.  NSI-MI has overcome this limitation by using its holography tool along with existing metrology techniques to predict the field quality in the quiet zone based on surface measurements of the panels.   The tool was used to establish go/no-go criteria for panel alignment accuracy achieved on site. Correlation of the holography predictions with actual field probe measurements of the installed reflector validates the application of the holography tool for performance prediction of large, multiple-panel, rolled-edge reflectors. Keywords: Rolled-Edge Reflector, Compact Range, Field-Probing, Quiet Zone, Microwave Holography

Spherical Near-Field Alignment Sensitivity for Polar and Equatorial Antenna Measurements
Patrick Pelland, Greg Hindman, Daniël van Rensburg, November 2016

Spherical near-field (SNF) antenna test systems offer unique advantages over other types of measurement configurations and have become increasingly popular over the years as a result. To yield high accuracy far-field radiation patterns, it is critical that the rotators of the SNF scanner are properly aligned. Many techniques using optical instruments, laser trackers, low cost devices or even electrical measurements [1 - 3] have been developed to align these systems. While these alignment procedures have been used in practice with great success, some residual alignment errors always remain. These errors can sometimes be quantified with high accuracy and low uncertainty (known error) or with large uncertainties (unknown error). In both cases, it is important to understand the impact that these SNF alignment errors will have on the far-field pattern calculated using near-field data acquired on an SNF scanner. The sensitivity to various alignment errors has been studied in the past [4 - 6]. These investigations concluded that altering the spherical acquisition sampling grid can drastically change the sensitivity to certain alignment errors. However, these investigations were limited in scope to a single type of measurement system. This paper will expand upon this work by analyzing the effects of spherical alignment errors for a variety of different measurement grids and for different SNF implementations (phi-over-theta, theta-over-phi) [7]. Results will be presented using a combination of physical alignment perturbations and errors induced via simulation in an attempt to better understand the sensitivity to SNF alignment errors for a variety of antenna types and orientations within the measurement sphere. Keywords: Spherical Near-Field, Alignment, Uncertainty, Errors. References [1]     J. Demas, “Low cost and high accuracy alignment methods for cylindrical and spherical near-field measurement systems”,  in the proceedings of the 27th annual Meeting and Symposium, Newport, RI, USA, 2005. [2]     S. W. Zieg, “A precision optical range alignment tecnique”, in the proceedings of the 4th annual AMTA meeting and symposium, 1982. [3]     A.C. Newell and G. Hindman, “The alignment of a spherical near-field rotator using electrical measurements”,  in the proceedings of the 19th annual AMTA meeting and symposium, Boston, MA, USA, 1997. [4]     A.C. Newell and G. Hindman, “Quantifying the effect of position errors in spherical near-field measurements”,  in the proceedings of the 20th annual AMTA meeting and symposium, Montreal, Canada, 1998. [5]     A.C. Newell, G. Hindman and C. Stubenrauch, “The effect of measurement geometry on alignment errors in spherical near-field measurements”,  in the proceedings of the 21st annual AMTA meeting and symposium, Monterey, CA, USA, 1999. [6]     G. Hindman, P. Pelland and G. Masters, “Spherical geometry selection used for error evaluation”,  in the proceedings of the 37th annual AMTA meeting and symposium, Long Beach, CA, USA, 2015. [7]     C. Parini, S. Gregson, J. McCormick and D. Janse van Rensburg, Theory and Practice of Modern Antenna Range Measurements. London, UK: The Institute of Engineering and Technology, 2015

Predicting the Performance of a Very Large, Wideband Rolled-Edge Reflector
Anil Tellakula,William R. Griffin, Scott T. McBride, November 2015

Achieving a very large quiet zone across a wide frequency band, in a compact range system, requires a physically large reflector with a suitable surface accuracy. The size of the required reflector dictates attention to several important processes, such as how to manufacture the desired surface across a large area and the practicality of transportation and installation. This inevitably leads to the segmentation of the reflector into multiple panels; which must be fabricated, installed, and aligned to each other to conform to the required geometry. Performance predictions must take into account not only the surface accuracy of the individual panels but also their alignment errors. This paper presents the design approach taken on a recent project for a compact range system utilizing a blended rolled-edge reflector that produces a 5 meter quiet zone across a frequency range of 350 MHz to 40 GHz. It discusses the physical segmentation strategy, the fabrication methodology, the intermediate qualification of panels, the panel alignment technique, and the laser-based metrology methodology employed. Performance analysis approach and results will be presented for the geometry as conceived and then for the realized panelized reflector as machined and aligned.

Spherical Geometry Selection Used for Error Evaluation
Greg Hindman,Patrick Pelland, Greg Masters, November 2015

ABSTRACT Spherical near-field error analysis is extremely useful in allowing engineers to attain high confidence in antenna measurement results. NSI has authored numerous papers on automated error analysis and spherical geometry choice related to near field measurement results. Prior work primarily relied on comparison of processed results from two different spherical geometries: Theta-Phi (0 =?= 180, -180 = f = 180) and Azimuth-Phi (-180 =?= 180, 0 = f = 180). Both datasets place the probe at appropriate points about the antenna to measure two different full spheres of data; however probe-to-antenna orientation differs in the two cases. In particular, geometry relative to chamber walls is different and can be used to provide insight into scattering and its reduction.  When a single measurement is made which allows both axes to rotate by 360 degrees both spheres are acquired in the same measurement (redundant). They can then be extracted separately in post-processing. In actual fact, once a redundant measurement is made, there are not just two different full spheres that can be extracted, but a continuum of different (though overlapping) spherical datasets that can be derived from the single measurement. For example, if the spherical sample density in Phi is 5 degrees, one can select 72 different full sphere datasets by shifting the start of the dataset in increments of 5 degrees and extracting the corresponding single-sphere subset. These spherical subsets can then be processed and compared to help evaluate system errors by observing the variation in gain, sidelobe, cross pol, etc. with the different subset selections. This paper will show the usefulness of this technique along with a number of real world examples in spherical near field chambers. Inspection of the results can be instructive in some cases to allow selection of the appropriate spherical subset that gives the best antenna pattern accuracy while avoiding the corrupting influence of certain chamber artifacts like lights, doors, positioner supports, etc. Keywords: Spherical Near-Field, Reflection Suppression, Scattering, MARS. REFERENCES Newell, A.C., "The effect of measurement geometry on alignment errors in spherical near-field measurements", AMTA 21st Annual Meeting & Symposium, Monterey, California, Oct. 1999. G. Hindman, A. Newell, “Spherical Near-Field Self-Comparison Measurements”, Proc. Antenna Measurement Techniques Association  (AMTA) Annual Symp., 2004. G. Hindman, A. Newell, “Simplified Spherical Near-Field Accuracy Assessment”, Proc. Antenna Measurement Techniques Association (AMTA) Annual Symp., 2006. G. Hindman & A. Newell, “Mathematical Absorber Reflection Suppression (MARS) for Anechoic Chamber Evaluation and Improvement”, Proc. Antenna Measurement Techniques Association (AMTA) Annual Symp., 2008. Pelland, Ethier, Janse van Rensburg, McNamara, Shafai, Mishra, “Towards Routine Automated Error Assessment in Antenna Spherical Near-Field Measurements”, The Fourth European Conference on Antennas and Propagation (EuCAP 2010) Pelland, Hindman, “Advances in Automated Error Assessment of Spherical Near-Field Antenna Measurements”, The 7th European Conference on Antennas and Propagation (EuCAP 2013)

Achieving Impressive Global Positioning and Stability in a High Fidelity Antenna Measurement System
Jacob Kunz,Eric Kim, November 2015

Highly accurate antenna measurements can require precise alignment and positioning of the probe antenna to the antenna under test. The positioning of the antenna during acquisition can involve the movement of several simultaneous axes of motion. This places a global positioning accuracy requirement on the positioning system. To achieve precision in global positioning and alignment, an understanding of dominant error factors such as load induced deflection/resonance, thermal deflection, positioning error sources and mechanical alignment tolerances is essential. This paper focuses on how global accuracy and stability were achieved, addressing these factors, on a recently delivered large far field antenna measurement system.  The system involved eight axes of positioning with the ability to position 950 lbs antenna under test 19.5 ft above the chamber floor achieving 0.007 inch and 0.005 degrees positioning accuracy relative to the global range coordinate system. Stability of the probe antenna after motion was within 0.001 inch. Key Words: Global Position Accuracy, Far Field, Position Stability, Simultaneous Motion, Position Error Correction, High Accuracy, Precise Motion

Use of a Closed-Loop Tracking Algorithm for Orientation Bias Determination of an S-Band Ground Station
Bryan Welch,Dean Schrage, Marie Piasecki, November 2015

The Space Communications and Navigation (SCaN) Testbed project completed installation and checkout testing of a new S-Band ground station at the NASA Glenn Research Center in Cleveland, Ohio in 2015.  As with all ground stations, a key alignment process must be conducted to obtain offset angles in azimuth (AZ) and elevation (EL).  In telescopes with AZ-EL gimbals, this is normally done with a two-star alignment process, where telescope-based pointing vectors are derived from catalogued locations with the AZ-EL bias angles derived from the pointing vector difference.  For an antenna, the process is complicated without an optical asset.  For the present study, the solution was to utilize the gimbal control algorithm’s closed-loop tracking capability to acquire the peak received power signal automatically from two distinct NASA Tracking and Data Relay Satellite (TDRS) spacecraft, without a human making the pointing adjustments.  Briefly, the TDRS satellite acts as a simulated optical source and the alignment process proceeds exactly the same way as a one-star alignment.  The data reduction process, which will be discussed in the paper, results in two bias angles which are retained for future pointing determination.  Finally, the paper compares the test results and provides lessons learned from this activity.

The Boresight Roll for Antenna Range Characterization and Diagnostics
Jason Jerauld,Justin Dobbins, November 2015

The boresight roll scan is a simple yet powerful tool for antenna range characterization and diagnostics. In this type of measurement a linearly-polarized antenna with high axial ratio (such as a standard gain horn) is rotated about its mechanical boresight axis while magnitude and phase data are collected. Post-processing of these data provides a wealth of information about the source polarization characteristics, and can also be used to diagnose common problems such as receiver compression, mechanical misalignment, drift, and flexing cables. This paper describes the theory and implementation of the boresight roll scan, and provides examples of how different types of range errors manifest in the processed data.

Computational Electromagnetic Modeling of Near-Field Antenna Test Systems Using Plane Wave Spectrum Scattering Matrix Approach
Allen Newell,Stuart Gregson, November 2014

In recent years a number of analyses and simulations have been published that estimate the effect of using a probe with higher order azimuthal modes with standard probe corrected spherical transformation software.  In the event the probe has higher order modes, errors will be present within the calculated antenna under test (AUT) spherical mode coefficients and the resulting asymptotic far-field parameters [1, 2, 3, 4] where the simulations were harnessed to examine these errors in detail.  Within those studies, a computational electromagnetic simulation (CEM) was developed to calculate the output response for an arbitrary AUT/probe combination where the probe is placed at arbitrary locations on the measurement sphere ultimately allowing complete near-field acquisitions to be simulated.  The planar transmission equation was used to calculate the probe response using the plane wave spectra for actual AUTs and probes derived from either planar or spherical measurements.  The planar transmission formula was utilized as, unlike the spherical analogue, there is no limitation on the characteristics of the AUT or probe thereby enabling a powerful, entirely general, model to be constructed.  This paper further extends this model to enable other measurement configurations and errors to be considered including probe positioning errors which can result in ideal first order probes exhibiting higher order azimuthal mode structures.  The model will also be used to determine the accuracy of the Chu and Semplak near-zone gain correction [5] that is used in the calibration of pyramidal horns.  The results of these additional simulations are presented and discussed. Keywords: near-field, antenna measurements, near-field probe, spherical alignment, spherical mode analysis. REFERENCES A.C. Newell, S.F. Gregson, “Estimating the Effect of Higher Order Modes in Spherical Near-Field Probe Correction”, Antenna Measurement Techniques Association (AMTA) 34th Annual Meeting & Symposium, Bellevue, Washington October 21-26, 2012. A.C. Newell, S.F. Gregson, “Higher Order Mode Probes in Spherical Near-Field Measurements”, 7th European Conference on Antennas and Propagation (EuCAP 2013) 8-12 April 2013. A.C. Newell, S.F. Gregson, “Estimating the Effect of Higher Order Modes in Spherical Near-Field Probe Correction”, Antenna Measurement Techniques Association (AMTA) 35th Annual Meeting & Symposium, Columbus, Ohio, October 6-11, 2013. A.C. Newell, S.F. Gregson, “Estimating the Effect of Higher Order Azimuthal Modes in Spherical Near-Field Probe Correction”, The 8th European Conference on Antennas and Propagation (EuCAP 2014) 6-11 April 2014. T.S. Chu, R.A. Semplak, “Gain of Electromagnetic Horns,’’ Bell Syst. Tech. Journal, pp. 527-537, March 1965

Antenna Alignment and Positional Validation of a mmWave Antenna System Using 6D Coordinate Metrology
David Novotny,Joshua Gordon, Jeff Guerrieri, November 2014

Antenna alignment for near-field scanning was typically done at NIST with multiple instruments (theodolites, electronic levels, motor encoders) to align multiple stacked motion stages (linear, rotation).  Many labs and systems are now using laser trackers to measure ranges and perform periodic compensation across the scan geometry.  We are now seeing the use of laser trackers with 3D coordinate metrology to align ranges and take positional data.  We present the alignment techniques and positional accuracy and uncertainty results of a mmWave antenna scanning system at 183 GHz. We are using six degree-of-freedom (6DOF) AUT and Probe measurements (x, y, z, yaw, pitch, roll) to align the AUT and then to align the scan geometry to the AUT.  We are using a combination of 3DOF laser tracker measurements with a combined 6DOF laser tracker/photogrammetry sensor. We combine these measurements using coordinated spatial metrology to assess the quality of each motion stage in the system, tie the measurements of each individual alignment together, and to assess scan geometry errors for position and pointing.  Finally we take in-situ 6DOF position measurements to assess the positional accuracy to allow for positional error correction in the final pattern analysis. The knowledge of the position and errors allow for the correction of position and alignment of the probe at every point in the scan geometry to within the repeatability of the motion components (~30 µm). The in-situ position knowledge will eventually allow us to correct to the uncertainty of the measurement (~15 µm). Our final results show positioning errors on the spherical scan surface have an average error of ~30 µm with peak excursions of ~100 µm. This robust positioning allows for accurate analysis of the RF system stability. Our results show that at 183 GHz, our RF repeatability with movement over 180° orientation change with a 600 mm offset to be less than ±0.05 dB and ±5°.

Achieving High Accuracy from a Near-field Scanner without Perfect Positioning
George Cheng,Yong Zhu, Jan Grzesik, November 2014

We propose a technique which achieves highly accurate near-field data as well as far-field patterns despite the positioning inaccuracy of the scanner in the antenna near-field measurements. The method involves position sensing hardware in conjunction with data processing software. The underlying theory is provided by the Field Mapping Algorithm (FMA), which transforms exactly the measured field data on a conventional planar, spherical, or cylindrical surface, indeed on any enclosing surface, to any other surface of interest.  In our modified near-field scanning system, a position recording laser device is attached to the probe. The positions of data grid points are thus found and recorded along with the raw RF data.  The raw data acquired over an irregular, imperfect surface is subsequently converted exactly to a designated, regular surface of canonical type based on the FMA and its associated position information.  Once the near-field data is determined at all required grid points, the far-field pattern per se is obtained via a conventional near-field-to-far-field transformation.  Moreover, and perhaps just as importantly, the interplay between our FMA and the free-form position/RF recording methodology just described allows us to bypass entirely the arduous task of strict antenna alignment.  The free-form position/RF data are simply propagated by the FMA software to some perfectly aligned reference surface ideally adapted as a springboard for any intended far-field buildup. Our proposed marriage of a standard scanning system and a position recorder, with otherwise imperfect RF/location data restored to ideal status under the guidance of the FMA, clearly offers the advantage of high precision at minimal equipment cost.  It is, simply stated, a win-win budget/accuracy RF measurement solution. Two analytic examples and one measurement case are given for demonstration.  The first example is a circular aperture within an infinite conducting plane, the second is a 10 lambda x 10 lambda dipole array antenna.  The measurement case involves a waveguide slot array antenna.  In all three cases, the near-field data were deliberately acquired over imperfectly located grid points. The FMA was then applied to obtain near-field data at the preferred, regularly arranged grid points from these position compromised values.  Excellent grid-to-grid near-field comparison and calculated far-field results were obtained.

Dual Compact Range Electrical Versus Mechanical Bore Sight Alignment
Hulean Tyler,Frank Soliman, David Kim, November 2014

There are many methods of aligning feeds on a dual cylindrical parabolic sub-reflector compact range.  Presented in this paper is a laser tracker and Field probe method that was used to align the RF feed to the sub-reflectors.   The laser tracker provides real time positional error measurements that are mapped and these results are used to fine tune the alignment of RF feed to the phase centers of the dual cylindrical parabolic sub-reflectors.  Field probe test scans are performed to verify QZ performance of various alignment positions measured comparing scans of amplitude, phase and taper.  The laser tracker alignment method provides an efficient and a highly accurate method to achieving precision alignment of the RF feed to the sub-reflector system installed into the dual reflector compact range.  High accuracy antenna measurements in a compact range require precision alignment of the RF feed to the sub-reflectors phase center.  The quality and size of the RF plane wave field of the quiet zone (QZ) performance is affected by the alignment of the RF feed and sub-reflector system combination.   This alignment is accomplished through mechanical adjustments of the x-y-z axis RF feed positioning system.   Measurements of both mechanical and electrical bore site is performed and compared across the full measurement spectrum to verify the compact antenna test range (CATR) system positioning accuracy.







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