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Accuracy
Generalized Test-Zone Field Compensation
T M Gemmer, D Heberling, October 2019
Antenna measurement errors occur due to reflections and diffractions within the measuring chamber. In order to extract and correct the undesired signals, a technique based on test-zone field compensation and spherical wave expansion is applied to Compact Antenna Test Range (CATR) and Spherical Near-Field (SNF) measurements of a base transceiver station antenna. The required spherical test-zone field is acquired by simulating the corresponding measurement environment with the multi-level fast multipole method. Due to the numerical complexity of the problem, only the parts of the chamber with a significant influence on the measurement results are modeled. Comparing the determined directivities after applying the correction method, an exact overlap is achieved between the SNF and CATR solution.
Impact of Phase Curvature on Measuring 5G Millimeter Wave Devices
A Scannavini, F Saccardi, L J Foged, Kun Zhao, , ,, October 2019
Wireless industry through 3GPP has standardized 5G in both FR1 (sub 6 GHz) and FR2 (24.25-52.6 GHz) frequency ranges. While FR1 will be using frequencies already in place for LTE-4G technology, FR2 is dealing with mmWave frequencies. Due to the high free space path loss (FSPL), 5G at mmWave would impose the use of directive antennas on both ends of the communication link, the User Equipment (UE) and the Base Station (BS). A black box approach (i.e. the location of the antenna within the device is unknown) has been agreed to be used for Over The Air (OTA) measurements. The physical center of the device must be aligned with the center of the measurement setup. Hence, the test antennas will likely be offset with respect to the center of the coordinate system. The measurement distance will be for most systems sufficient to minimize the amplitude error while will introduce a phase deviation between the actual spherical wave and the desired plane wave which may cause an effective phase shaping of the radiated beam of the small phased array under test. In this paper we will analyze the impact of the phase curvature on the beam antenna pattern and spherical coverage for the different testing environments. Specifically, simulation of a 5G terminal device with multiple beams will be considered and realistic spherical near field measurement at different finite distances will be emulated also taking into account different measurement antennas (probes).
Comparative Testing of Devices in a Spherical Near Field System and Plane Wave Generator
F Scattone, D Sekuljica, A Giacomini, F Saccardi, A Scannavini, L J Foged, E Kaverine, N Gross, P O Iversen, October 2019
The Plane Wave Generator (PWG) is an array of elements generating an approximately plane wave over a finite volume in the test area called Quiet Zone (QZ). The plane wave condition can be achieved in close proximity to the array with suitably optimized complex coefficients. The PWG thus achieve far-field testing conditions in a manner similar to the Compact Antenna Test Range (CATR) but with a reduced distance to the QZ [1-2]. As a complete system the PWG has the advantage of reduced physical size compared to the a CATR with equivalent testing capabilities, in particular at lower frequencies. In [3-4], the concept of a high performance, dual polarized PWG supporting up to 1:10 bandwidth was presented. A prototype of a dual polarized PWG has been designed, manufactured and tested in the 600MHz to 6GHz frequency range. This paper presents the initial verification of the prototype PWG. The testing is performed using a representative analog beam forming network with narrow bandwidth. The QZ uniformity of the PWG is verified by spherical near-field measurements and back-propagation. The peak gain of a low directivity antenna is measured at different distances in the QZ and compared to reference measurements in a spherical near-field system. The aim of the comparison is to access the measurement accuracy of the PWG.
Experimental validation of Reference Chip Antennas for 5G Measurement Facilities at mm-Wave
A Giacomini, L Scialacqua, F Saccardi, L J Foged, E Szpindor, W Zhang, M Oliveira, P O Iversen, J M Baracco, October 2019
In this paper, the experimental validation of a micro-probe fed reference antenna targeting the upcoming 5G applications (24.25-29.5GHz band) is presented. The main purpose of these reference antennas is to serve as "gold standards" and to perform gain calibration of 5G test facilities through the substitution method. The outline of these antennas is based on a square array of four printed patches enclosed in a circular cavity. The RF input interface is a stripline-to-coplanar waveguide transition and allows for feeding the device with a micro-probe. Performance obtained by high-fidelity modeling is reported in the paper and correlated to experimental data. Interaction and unwanted coupling with the test equipment are discussed. The use of echo-reduction techniques and spatial filtering is investigated to mitigate these effects.
Virtual Drive Testing based on Automotive Antenna Measurements for Evaluation of Vehicle-to-X Communication Performances
F Saccardi, A Scannavini, L Scialacqua, L J Foged, N Gross, A Gandois, S Dooghe, P O Iversen, October 2019
In vehicle communications, so as Vehicle-to-X (V2X), field trials are challenging due to high mobility scenarios and dynamic network conditions. It is complex to interpret measurements, to isolate performance from different components in an integrated system. Consequently, it is desirable to test under repeatable laboratory conditions in the early stages of the development cycle, where designers can quickly validate performance and make rapid modifications to prototype hardware and software cost-effectively. Virtual Drive Test (VDT) has attracted great interest from industry and academia. The objective of VDT is to recreate an approximation of the real-world communication conditions in a controlled laboratory environment. VDT is appealing, since testing can be performed in an automated, controllable and repeatable manner, which can considerably reduce testing time and costs, and meanwhile accelerate actual infrastructure deployment. In this paper we present a new VDT technique which allows to evaluate the V2X communications performances taking into account the measured characteristics of transmit and receive antennas installed on vehicles. The proposed VDT technique is a multistage process where radiation characteristics of the vehicle mounted antennas are first measured in free-space conditions in a controlled and repeatable laboratory environment. The Spherical Wave Expansion (SWE) is then applied to the acquired data in order obtain the Spherical Wave Coefficients (SWC) of the measured devices. From the SWC, the transmission formula (or coupling equation) normally involved for probe correction purposes in spherical near field measurements, is then applied in order to evaluate the coupling between two vehicles. The transmission formula has been properly adapted in order to consider variable distances between the vehicles and arbitrary vehicle orientation so that a generic road path can be easily emulated. In the proposed formulation also variable ground conditions can be considered allowing for a more realistic emulation of the final environment. The proposed technique is presented taking into account measurements of a representative scaled automotive scenario.
A Simple High-Perfomance P-Band First-Order Dual-Port Probe for Spherical Near-Field Antenna Measurements based on the Shorted Annular Patch Antenna
M Brandt-Møller, M Fröhner, O Breinbjerg, October 2019
This paper presents a new type of P-band first-order dual-port probe for spherical near-field antenna measurements. The probe is based on the well-known shorted annular patch antenna but some extensions are introduced for the probe application. This probe is mechanically simple which facilitates its manufacturing and operation. In addition, it has high performance for impedance bandwidth, pattern, directivity, and gain.
Practical Considerations in Compressed Spherical Near-Field Measurements
Cosme Culotta-López, Brett Walkenhorst, Quang Ton, Dirk Heberling, October 2019
The major drawback of Spherical Near-Field (SNF) measurements is the comparatively long measurement time, since the scanning of a whole sphere enclosing an Antenna Under Test (AUT) is required to calculate the Spherical Mode Coefficients (SMCs) required for the computation of the far field. Since the SMCs prove to be sparse under certain conditions, efforts have been made to apply compressed-sensing techniques to reduce the measurement time by acquiring a smaller number of sampling points. These approaches have been successfully tested in simulation using classically acquired measured data. This decouples the measurements from practical problems, such as basis mismatch due to the finite precision of the mechanical positioner and environment effects. In this paper, results from a sparse data acquisition performed with a physical system are reported. To decouple the error introduced by the approach itself from the error introduced by non-idealities in the measurement system, an AUT is measured using both traditional near-field sampling and compressed near-field sampling. The classically acquired data is used both as reference and as source to simulate a synthetic compressed measurement. The effects introduced by real considerations are calculated by comparison between the synthetic compressed measurement and the acquired one, while the error of both is evaluated by comparison to the reference measurement. The results further demonstrate the viability of this method to accelerate SNF measurements and pave the way for further research.
Improvements in the Measurement of Very Low Cross Polarization Using the Three Antenna Polarization Technique
A C Newell, P Vizcaino, D Gentle, Z Tian, , ,, October 2019
The Three-antenna polarization measurement technique is used to determine the axial ratio, tilt angle and sense of polarization of three antennas from measurements on each of three antenna pairs. The three antennas are generally nominally linearly polarized and the measurement data consists of the change in amplitude from the initial antenna orientation where they are co-polarized to the orientation where one of the antennas is rotated about its axis to the null amplitude position. The sign of the phase change is also noted and the phase change at the null position is known from theoretical calculations to be either plus or minus 90 degrees. The correct sign is determined from the sign of the phase change. For antennas with axial ratios in the range of 50 to 80 dB that will be used as near-field probes or as feeds for reflector antennas, it is imperative to measure the polarization parameters as accurately as possible. The primary source of uncertainty in the measurement is due to scattered signals in the measurement range that arise from multiple reflections between the two antennas and from the absorber on the chamber walls. For antennas with very large axial ratios, the scattered signals can be larger than the true measurement signal. These scattered signals can change the sign of the phase and produce large errors in the amplitude at the null. If the separation distance between the antennas is adjusted after rotating to the null to produce a maximum amplitude, the scattered signal is in phase with the true measurement signal. If the distance is adjusted for the minimum at the null, the scattered and true signals are out of phase. Measurements at these two positions will produce the best measurement of the phase sign and the true amplitude. But if measurements are being performed at a number of frequencies, the maximum and minimum amplitude positions will be different for each frequency, and this will complicate automated multifrequency measurements. New improvements have been developed in the details of the measurements that greatly improve the determination of the phase sign and the amplitude at the null for multiple frequency measurements and these will be described and illustrated in the following paper. With these improvements, the estimated uncertainty of a 60 dB axial ratio is on the order of 1.8 dB. A new technique has also been developed to improve the source correction of the pattern data for probes with large axial ratios that guarantees that the on-axis polarization of the pattern data will be identical to the results of the Three-antenna measurement. The probe correction processing will then produce the highest accuracy results for the polarization of the AUT.
Portable Laser Guided Robotic Metrology System
Peter A Slater, James M Downey, Marie T Piasecki, Bryan L Schoenholz, October 2019
This paper introduces the new Portable Laser Guided Robotic Metrology (PLGRM) system at the National Aeronautics and Space Administration's (NASA) Glenn Research Center. Previous work used industrial robots in fixed facilities to characterize antennas and required fixtures that do not lend themselves to portable applications. NASA's PLGRM system is designed for in-situ antenna measurements at a remote site. The system consists of a collaborative robot arm mounted on a vertical lift and a laser tracker, each on a mobile base. Together, they enable scanning a surface larger than the robot's reach. To accomplish this, the robot first collects all points within its reach, then the system is moved and the laser tracker is used to relocate the robot before additional points are captured. The PLGRM implementation will be discussed including how safety and planning are combined to effectively characterize antennas. Software defined triggering is a feature, for flexible integration of vector network analyzers and antenna controllers. Lastly, data will be shown to demonstrate system functionality and accuracy.
3D Printed Magneto-Electric Phased Array Antenna for Various 5G New Radio Bands
Connor Laffey, Philip Nguyen, Ghanshyam Mishra, Satish K. Sharma, October 2019
A dual linear polarized 3D printed magneto-electric phased array antenna for various 5G New Radio (NR) frequency bands is proposed and its beam steering performance is investigated. The magneto-electric radiating element exhibits a well-defined stable pattern quality, low variation in the impedance over a wider bandwidth and high port to port isolation in a dual polarization configuration. The analog beamforming network (BFN) of the array is also designed. The fabricated board will be combined with the 3D printed array aperture for experimental verification of the scan performance.
Comparison of Antenna Measurements Obtained Using an Electro-Optical Probe System to Conventional RF Methods
William Dykeman, Benjamin Marshall, Dale Canterbury, Corey Garner, Richard Darragh, Ali Sabet, October 2019
There are certain applications where the use of electro-optical (EO) probes to acquire near-field measurements can provide major advantages as compared to conventional RF measurement techniques. One such application is in the area of high power RF measurements that are required for calibration and test of active electronically scanned arrays (AESA). The family of EO probes presented herein utilizes the Pockels effect to measure the time-varying electric fields of the antenna under test (AUT). The use of a non-invasive, broadband EO probe facilitates measurement of the tangential electric field components very close to the AUT aperture in the reactive near-field region. This close proximity between the AUT and the measurement probe is not possible with conventional metallic probes. In this paper, the far field gain patterns acquired using the EO probe will be compared to the corresponding gain patterns obtained from conventional far-field and near-field methods. The measurement results, along with the advantages and disadvantages of the EO system configuration, will be presented.
Recent Changes to the IEEE std 1502 Recommended Practice for Radar Cross-Section Test Procedures
Eric Mokole, Vince Rodriguez, Jeff Fordham, L J Foged, ,, October 2019
Radar scattering is typically represented as the RCS of the test object. The term RCS evolved from the basic metric for radar scattering: the ratio of the power scattered from an object in units of power per solid angle (steradians) normalized to the plane-wave illumination in units of power per unit area. The RCS is thus given in units of area (or effective cross-sectional area of the target, hence the name). Note that the RCS of the test object is a property of the test object alone; it is neither a function of the radar system nor the distance between the radar and the test object, if the object is in the far field. Because the RCS of a target can have large amplitude variation in frequency and angle, it is expressed in units of decibels with respect to a square meter and is abbreviated as dBsm (sometimes DBSM or dBm2). In terms of this definition, the RCS of a radar target is a scalar ratio of powers. If the effects of polarization and phase are included, the scattering can be expressed as a complex polarimetric scattering (CPS) matrix. The measurement of the RCS of a test object requires the test object to be illuminated by an electromagnetic plane wave and the resultant scattered signal to be observed in the far field. After calibration, this process yields the RCS of the test object in units of area, or the full scattering matrix as a set of complex scattering coefficients. This paper describes the planned upgrades to the old IEEE Std 1502™-2007 IEEE Recommended Practice for Radar Cross-Section Test Procedures [1]. The new standard will reflect the recent improvements in numerical tools, measurement technology and uncertainty estimates in the past decade.
Dipole-Field Simulations: Evaluation of NIST Spherical Near-Field Software
Ronald C Wittmann, Michael H Francis, November 2018
We use a simple program to compute fields radiated by a collection of elementary electromagnetic dipoles located at arbitrary points within the measurement sphere. The simulated measurement data have been used to provide a direct and convincing demonstration of the accuracy and robustness of both the standard and position compensated NIST SNF code.
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.
Reducing the Scanning Time in Near-Field Measurements with an Optimized Sampling and an Optimized Controller on Arduino Due
Vincenzo Avolio, Amedeo Capozzoli, Laura Celentano, Claudio Curcio, Angelo Liseno, Salvatore Savarese, November 2018
The aim of the paper is to address a relevant issue in the Near-Field (NF) measurements: the reduction of the measurement time. Generally speaking, for a given hardware, two main directions can be pursued. The first requires the adoption of an optimal field sampling strategy that reduces the number of sampling points, and the length of the scanning path, without impairing accuracy. The second strategy adopts an optimized control system able to exploit at the best the available hardware (scanning system and measurement instrument). Indeed, the latency of the instrument defines the maximum probe velocity during the field acquisition. Accordingly, unlike the conventional continuous scanning, an optimized controller can speed up the scanning by moving the probe along the measurement trajectory with a variable velocity, accelerating and decelerating between two consecutive sampling points, to increase the average speed. However, the use of an optimized controller is fruitful only when the optimized sampling scheme allows large distances between two consecutive sampling locations, to increase as much as possible the maximum probe speed. In this paper, by suitably using both the above strategies, it is proposed a fast NF system, implemented on a microcontroller Arduino Due, an extremely cheap and off the shelf hardware, that is able to handle the scanner and realize the synergy between the optimized sampling and the optimized control strategy. The simulation and experimental results show a dramatic reduction of the measurement time (up to one order of magnitude) with a high tracking precision (also in accordance with the proposed methodology), and of the costs with respect to standard solutions.
Using Standard Wideband Antennas as Probe in Spherical Near Field Measurements with Full Probe Correction: Experimental Validation
F Saccardi, A Giacomini, L J Foged, L M Tancioni, S Khlif, Martin Kuhn, ,, November 2018
Full probe compensation techniques for Spherical Near Field (SNF) measurements have recently been proposed [1-5]. With such techniques, even antennas with more than decade bandwidth are suitable probes in most systems. The abolition of otherwise frequent probe changes during multi-service campaigns is a highly desirable feature for modern measurement applications such as automotive. In this paper, a standard dual-ridge horn with 15:1 bandwidth is investigated experimentally as probe in a SNF automotive range. The accuracy of the probe compensation technique is validated by comparison to standard single probe measurement.
Asymptotic Simulation Methods in Anechoic Chamber Design
M H Vogel Altair, Engineering Hampton, U S A D D Campbell, November 2018
When designing an anechoic chamber, determination of the extent and quality of the quiet zone is crucial. While rigorous simulation methods can be used for this in principle, in practice such methods quickly become too computationally expensive with increasing frequency. In this paper, the authors evaluate a couple of asymptotic approaches based on ray tracing, and quantify their value for anechoic-chamber design.
A Compressed Sampling for Spherical Near-Field Measurements
Cosme Culotta-López, Dirk Heberling, Arya Bangun, Arash Behboodi, Rudolf Mathar, November 2018
Spherical near-field measurements are regarded as the most accurate technique for the characterization of an Antenna Under Tests (AUT) radiation. The AUT's far-field radiation characteristics can be calculated from the Spherical Mode Coefficients (SMC), or spherical wave coefficients, determined from near-field data. The disadvantage of this technique is that, for the calculation of the SMC, a whole sphere containing the AUT must be Nyquist-sampled, thus directly implying a longer measurement time when only a few cuts are of interest. Due to antennas being spatially band-limited, they can be described with a finite number of SMC. Besides, the vector containing the SMC can be proved sparse under certain circumstances, e.g., if the AUT's radiation pattern presents information redundancy, such as an electrical symmetry with respect to coordinate system of the measurement. In this paper, a novel sampling strategy is proposed and is combined with compressed-sensing techniques, such as basis pursuit solvers, to retrieve the sparse SMC. The retrieved sparse SMC are then used to obtain the AUT's far-field radiation. The resulting far-field pattern is compared for both simulated and measured data. The reduced number of points needed for the presented sampling scheme is compared with classical equiangular sampling, together with the estimated acquisition time. The proposed sampling scheme improves the acquisition time with a reasonable error.
Near-Field Spherical Scanning Measurement of a 3D Printed Horn at WR-8 Frequencies
Ronald C Wittmann, Michael H Francis, David R Novotny, Joshua A Gordon, Michael S Allman, November 2018
The National Institute of Standards and Technology (NIST) has measured a WR-8, 3D printed horn at 112.25, 118.75, and 125.25 GHz using the near-field spherical scanning method. The data were processed with both the NIST standard software and the probe-position compensation software. We conclude that the positioning capability of the NIST Configurable Robotic Millimeter-wave Antenna System is so accurate that probe-position compensation is negligible at these frequencies.
Low-Cost Pressure/Temperature Measurements of Wideband Antennas
L Boskovic, M Ignatenko, D S Filipovic, November 2018
This paper discusses design and fabrication of a low cost, combined pressure / thermal test-bench engineered for environmental tests of UAV mounted antennas. Both test-beds are mainly made of commercial of-the-shelf (COTS) parts and in-house made frames. They occupy small space and do not require specific professional skills for operation or high maintenance cost. Measurement setup is designed to reliably reproduce temperature and pressure corresponding to altitudes from sea level to 6000 m (20000 ft) with dynamic load equivalent for 200 m/s (400 knots) of air speed. Experimental results of radome enclosed wideband antenna are presented.


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