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Accuracy

The Cost of Accuracy - Mechanical Systems
Marion Baggett, November 2020

Accuracy in a measurement campaign is dependent on many factors. Some of these factors are in the physical components used, the requirements of the electromagnetics involved and the procedural requirements of the campaign. This paper will focus on how the mechanical accuracy of the equipment can impact total cost. The current stage in the life cycle of the AUT (design, production, repair) also impacts total cost. The affordability of the accuracy in terms of more costly equipment, calibration processes and operator and test range time may be the determining factor. Throughput needs may limit the accuracy that can be obtained. The accuracies required for each metric must then be evaluated against the accuracy of an available test range(s) or the renovation of an existing range or construction of a new range to meet the accuracy requirements. Two case studies included in this paper are: 1) the improvement of the positioning accuracy of a rotator via custom hardware and calibration for a severe global positioning accuracy specification and 2) the improvement of the planarity of an X-Y scanner system for use at increasing frequencies.

A Low-cost and In-field Antenna Characterizing Method Based on Statistics Measurement
Zhenyu Xu,Thomas Mauldin,Zheyi Yao,Tao Wei, November 2020

With the development of the Internet of Things (IoT) technology, the antenna becomes increasingly integrated and miniaturized. Vector Network Analyzer (VNA) is a standard instrument for characterizing antennas. However, IoT devices are small and scattered installed, which makes it costly to carry out in-field characterizing on IoT devices. Integrating an antenna characterizing system into IoT devices can release the difficulty significantly, but characterizing antennas usually requires a high-performance Analog to Digital Conversion system, which is expensive and power-consuming. However, the antennas are not required to be tested frequently, which means this is not a real-time application. Therefore, this paper proposes a method that can realize time-domain reflectometry based VNA with just a comparator or differential receiver. In this system, impulses are sent into the antenna, and the frequency response is captured by analyzing the time-domain reflection. Analog to Probability Conversion (APC), Probability Density Modulation (PDM), and Equivalent time sampling (ETS) concepts are used to reduce the real-time performance requirements of the ADC system, so that the cost and power consumption can be tolerable on a tiny IoT device. With this technology, the antennas could be characterized in-field and remotely, making the maintenance easier. This technology is implemented with Xilinx ZYNQ Ultrascale+ series FPGA. Two antennas are tested, and the experimental results show that the system can successfully measure the radiofrequency. The sampling rate is set to 89.6Ghz, and a micro-volt level voltage resolution is achieved. Since the essence of technology is a trade-off between time and performance, the sampling rate and resolution can be further increased theoretically according to specific applications.

Increasing 4-D Imaging Radar Calibration Accuracy Using Compact Antenna Test Range
Benoit Derat,Daniel Markert,Josef Schm?ller,Rong Chen Leng,Yaohui Liu,Ralf Reuter, November 2020

Advanced driver assistance systems (ADAS), such as blind spot warning and braking assistants, have been in use for years to improve road security. ADAS are currently further promoted through the autonomous driving trend. Due to their cost / performance trade-off, the automotive industry perceives 4-D high-resolution radar sensors, as one of the backbones of autonomous driving. With human safety being at stake, the topic of calibration of these sensors is obviously of the utmost importance. Performing an accurate calibration requires a test condition where the target is in the far-field of the radar under test (RUT). Due to the requirements for angular resolutions, 77 / 79 GHz radars with 15 cm radiation aperture or more are quite common. Applying Fraunhofer formula then results into a necessary measurement range length of 11.5m. Because of the high cost of ownership of an adequate anechoic range, radar manufacturers usually limit their measurements to the strict minimum and try to simplify the calibration process. A typical approach is to go for a diagonal calibration where the target is always at boresight for each beam-formed pattern of the RUT. This technique however delivers a sub-optimal compensation of the RUT biases. In particular, it creates high peak-to-side-lobe ratios (PSLR), where energetic echoes are observable in directions of side lobes of each beam. This paper introduces a new system for radar measurements, made of a short-size focal length offset-fed compact antenna test range (CATR), interfaced with an analog echo generator. With a chamber size of only 0.9 m x 2 m x 1.6 m, the setup has been designed to test apertures up to 30 cm size. The quality of the quiet zone achieved is discussed in the paper, as well as various uncertainty contributions relating to radar measurements. Tests are presented which involve a latest generation 4-D imaging radar on chip (RoC). Results obtained in the CATR are compared to a reference 7 m far-field range. Diagonal and full angular calibrations of the RoC are carried out and analyzed, demonstrating an improvement of 10 dB PSLR when the target is swept over the complete azimuth region.

Near-field testing with a 8.9x1.6 m2 planar scanner at Christiaan Huygens Laboratory (CHL)
Cornelis van't Klooster,Niels de Jong, November 2020

A near-field scanner has been upgraded, maintaining mechanical hardware more than 65 years old and extending it with suitable computer control to enable an 8.9x1.6m^2 scanplane. Already in 1957 X-band phase accuracies within 3 degrees were reported (ref.1). The facility is computer controlled, with servo's to enable position and polarisation control and a Rohde and Schwartz network analyser in the loop. It is positioned in an area near the main workshop and runs proprietary software for control, acquisition and transformation. An old satellite antenna has been aligned as Antenna Under Test (AUT) and measured near 12 GHz. It was measured before as reported in (ref.2). The antenna is an engineering model of an antenna used on the OTS satellite in mid 80's. It has a few properties which are worthwhile to use for inspection, to enable to get insight into scanner properties and transformation results. Deviation between electrical and mechanical axis, low cross polarisation, orthogonal channels and specific input impedance can be mentioned as points to verify and to control with verification measurements exploiting symmetries and flip-tests, rather than ticking off in an 18-term error budget usually adopted. Direct gain measurements have been established. The probe can be selected, either an open-ended waveguide or a circular waveguide with annular corrugation as probe for instance. It involves related discussion of probe correction. The first results show acceptable information for the facility, with initial comparison to previous results for pattern and absolute gain. It has allowed to survey alignment, assess scanner control properties and assess microwave component properties - with interest into direct gain measurements. A short historical description for the facility (ref.1) and antenna precedes a main discussion of the followed procedures and obtained results for the AUT with related discussion.

RFID in Packaging Surveillance: Impact of Simulation tools in design, coverage planning and placement of Smart readers along the supply chain.
Saranraj Karuppuswami,CJ Reddy, November 2020

Internet of things (IoT) has impacted global supply chains in terms of improving performance and increasing productivity. Modern IoT devices such as Radio Frequency Identification (RFID) tags play a pivotal role in packaging surveillance and monitoring of products as it moves along the supply chain. Additionally, recently these tags are equipped with sensing elements that convert the traceability-centric supply chain to value-centric by enhancing visibility of the nature of product as it moves along the supply chain. To utilize the full potential of such IoT technologies, an intelligent network planning is a pre-requisite that ensures good and reliable communication between the RFID tags, the reader, and the cloud. Traditionally, optimal positioning of these RFID devices to obtain a complete coverage is a difficult task that requires careful planning and physical experimentation which involves investing significant time and financial resources. To avoid such limitations, computer aided simulation of positioning the devices allows engineers to explore different scenarios to ensure complete coverage within a given area within a short time frame. The design and coverage planning of various entities of the RFID infrastructure is pivotal in realizing value-centric approach towards supply chain management. In this paper, two different case studies are presented that utilizes a grid-based optimization approach for coverage planning of passive and active RFID tags. For this purpose, first, a high-frequency solver FEKO is used for designing the RFID reader and tag antenna. Second, for the coverage analysis, a wave propagation tool WinProp is used for optimizing the position of the RFID readers and tags. The antennas are designed to operate at a UHF RFID frequency (915 MHz) and a semi-industrial warehouse setting is used for network planning. The details of the design and simulation of the individual entities of the RFID infrastructure along with two different scenarios for coverage analysis of active (battery-powered) RFID tags and passive (battery-less) RFID tags are presented in the paper. These simulations are the first step towards realizing the value-centric supply chain management approach.

Examination of EMC Chamber Qualification Methodology for Applications above 1 GHz Using Frequency Domain Mode Filtering
Zhong Chen,Stuart Gregson, November 2020

Anechoic chambers used for Electromagnetic Compatibility (EMC) measurements above 1 GHz are qualified based on the Site Voltage Standing Wave Ratio (SVSWR) method as per the international standard CISPR 16-1-4. The SVSWR measurements consist of a series of scalar measurements using a dipole-like antenna placed along several linear transmission paths that are located at the edge of the quiet zone (QZ). The measurement process is conceptually similar to measuring VSWR using a slotted line and a moving probe. A full set of tests is time consuming because of the number of positions, antenna heights, polarizations and frequencies that are generally required. To reduce the test burden, the SVSWR method intentionally under-samples the measurement by requiring only 6 measurement points along each 40 cm long linear path to characterize the standing wave. As a result, the test results are generally overly optimistic. At microwave frequencies (note the upper frequency limit is 18 GHz), this under-sampling becomes far more pronounced. In this paper, we explore the effectiveness of using Cylindrical Mode Coefficients (CMC) based frequency domain mode filtering techniques to obtain the VSWR. Here, we place the test antenna on the outer edge of the turntable to obtain a full rotational pattern cut of amplitude and phase data. The antenna is then mathematically translated to the rotation center, whereupon a band-pass filter that tightly encloses the test antenna mode spectrum is applied. The difference between the mode filtered antenna pattern and the original perturbed pattern is attributed to chamber reflections. The measurement is comparatively easy to implement with no special positioning equipment needed. In this paper we present measured results taken from two horizontal polarization measurements (where the antennas were oriented 90 degrees from each other), and one vertical polarization measurement. For an EMC chamber test at a fixed height, an entire measurement campaign reduces to taking three vector pattern cuts. In contrast to the conventional technique, the proposed novel method does not suffer from positional under-sampling, so it is well-placed to be applied at microwave frequencies and above.

Combining Measurements and Simulations for Antenna Coupling Analysis
Lars Foged,Lucia Scialacqua,Andrea Giacomini,Francesco Saccardi,Francesca Mioc, November 2020

In numerical simulation of antenna problems, accuracy of antenna representations is essential to ensure the reliability of results. Integration of measured Near Field (NF) representation of antenna in Computational Electromagnetic (CEM) solvers opens new perspectives to solve this problem. Moreover, it is possible to replace the simulated model of the antenna by a measured model, which represents the real antenna. No additional information about mechanical and/or electrical design of the antenna is required by the numerical solvers. Indeed, the measured NF model in terms of equivalent currents already provides a complete and detailed representation of the antenna itself. The applicability of this approach has been already studied for complex and/or large scenarios, antenna placement, scattering problems and EMC applications. Another interesting use of the combination between measurement and simulation is to enhance the evaluation of the antenna coupling. Previous investigations have been carried out on an H/V polarized array of three identical cavity-backed cross-dipole antennas. In this study only the radiation pattern of the central element of the array was measured (in a stand-alone configuration). Its representation in terms of equivalent currents was integrated in the simulation, for the calculation of the coupling with other elements. For each element two feeding ports, H/V polarization, have been investigated. In particular, measured patterns at five frequency points were used to determine the antenna coupling over the whole frequency band by simulation. A good agreement was found between the measured mutual S parameters on the real array and results obtained by the combination between measurement and simulations. This investigation demonstrated the validity of this approach. In this paper a continuation of the previous study will be performed, exploring the following topics: Enhancement of the representation of the NF source by inclusion of placement boundary condition. Use of measured NF source models to represent another element of the array, not only the central one. The calculation of the antenna coupling will be determined for these new configurations.

Definition, Implementation, and Evaluation of a Novel Spiral-Sampling Technique
Vivek Sanandiya,Scott McBride, November 2020

Building on the theory of spiral near-field acquisitions, the authors present a novel spiral acquisition implemented in a spherical near-field (SNF) chamber for a large automotive application. This new spiral permits the relaxation of certain restrictions associated with the standard spiral. Specifically, it allows us to eliminate extra or redundant rings beyond the poles, allows for greater control of the angular velocity ratio (i.e. gear ratio) between the theta and phi physical positioning axes, and does not require that the theta axis retrace between acquisitions. In this paper, we describe the new spiral?s motivations, implementation, advantages, and measurement results. We first discuss the new spiral sampling, its mathematical definition, and its comparison to a standard spiral. Next, we describe the practical considerations and implementation of the coordinated motion between theta and phi for spiral sampling over a spherical surface. Next, we present the results showing good pattern agreement between conventional SNF and the new spiral method. We also discuss the reductions in near-field acquisition time and total test time that were achieved using the new spiral.

Application of Kernel Density Estimation to Achieve Automated Near Real-Time Antenna Pattern Data Processing and Analysis in an Anechoic Chamber
Emily Mendoza,Shea Watson, November 2020

The Benefield Anechoic Facility (BAF) at Edwards Air Force Base is the world's largest known anechoic chamber. Due to its unmatched size and complement of test equipment, the BAF hosts far-field pattern measurements at all azimuth angles and multiple simultaneous elevations of installed antennas on large aircraft across a frequency range of 0.1 - 18 GHz. Antenna tests at the BAF rapidly produce large quantities of data, which often require immediate analysis to allow system owners to make relevant improvements. Historically, the BAF had accomplished quality assurance manually. Analysis was accomplished post-test by customers and the BAF team. Today, the BAF team has developed scripts that use kernel density estimation and basic machine learning to automatically check incoming data for errors and highlight unusual results for review. During a 2019 test of over sixty installed antennas on a B-1B bomber, the BAF team used these scripts to produce calibrated, quality-assured antenna patterns in near real-time. Rapid processing brings deficiencies to the customer's attention fast enough to allow corrections to be applied and re-tested during the same test event ? highly significant and valuable as aircraft and BAF schedule times are limited and may be a one-time opportunity to gather required data. This paper will explore the algorithm used to evaluate antenna patterns, as well as the expected characteristics of patterns that enable the selection of relevant data. Development and application of this algorithm found that using kernel density estimation to calculate the number of maxima in a pattern's distribution of gain values, then performing this recursively over only the main lobe, can identify problems such as incorrect switching, mismatched transmission lines, and multipath. Algorithm optimization was achieved using generated data, then verified by applying the algorithm to previous test data. For the B-1B, the script searched for data that deviated from an expected pattern with clean main and side lobes, minimal frequency dependency, and a low-power noise distribution at all azimuth angles outside the lobes. Finally, this paper will discuss the results of using this algorithm during a live test, and future improvements and applications for this data processing technique.

Microwave Material Characterization using Epsilon Near Zero (ENZ) Tunnel Structures
D.V.B. Murthy, C.J.Reddy, November 2020

Over the years many methods have been developed and used for measuring permittivity and permeability of materials. The most widely used methods are: 1) free-space techniques; 2) cavity perturbation techniques; and 3) transmission line of waveguide methods. Each technique has its own advantages and limitations. The free-space methods are employed when the material is available in a big sheet form. These measurements are less accurate because of unwanted reflections from surrounding objects, difficulty in launching a plane wave in a limited space, and unwanted diffraction from the edges of the sample. The resonant cavity measurement or cavity perturbation techniques are more accurate. Recently "epsilon-near-zero (ENZ) metamaterials have received much attention for several interesting phenomena like super-coupling, transparency and cloaking devices and pattern reshaping at microwave and optical frequencies. The rapid growth and excitement of ENZ materials was due to their ability to achieve very long wavelength in zero permittivity material, allowing propagation in a static-like manner. This paper presents the evaluation of complex dielectric permittivity and magnetic permeability of materials using planar ENZ tunnel structure with substrate integrated waveguide technology. The changes in resonance frequency and quality factor are related to the dielectric permittivity and magnetic permeability properties of the sample through Cavity Perturbation Technique. ENZ tunnel structure has very high sensitivity, which yields more accurate results when compared to other techniques, such as perturbation of conventional cavities. Design, optimization, and simulation of the ENZ tunnel structure at microwave frequencies is presented. Simulations are performed on various dielectric and magnetic samples using the cavity perturbation technique of the ENZ tunnel structure and validated with measured data.

Amplitude and Phase Uncertainty Analysis due to Cable Flexing in Robot-Based Measurement Systems
Roland Moch,Thomas Gemmer,Dirk Heberling, November 2020

The 18-term NIST error model is a common tool for analyzing potential sources of error in antenna measurements. One of the error terms to be considered describes the phase errors occurring in a measurement system. However, this quantity plays a rather negligible role for conventional ranges, such as roll-over-azimuth positioning systems. In particular, the contribution caused by flexing cables is normally insignificant. This results from the fixed installation of the cables or the decoupling of the movement at important points using rotary joints. Current developments in the field of antenna measurement technology focus, among other things, on performing measurements using industrial robot arms. These are characterized by their high flexibility regarding the various measurement sequences, such as planar, cylindrical or spherical measurements. However, it is to be expected that the high freedom of positioning possibilities will introduce additional phase uncertainties, since the RF cables in the cable carrier chain of the robot arm itself are often not decoupled. Instead, a single cable is used for each signal path, which follows the movements of the robot. The robot-based measurement system at the Institute of High Frequency Technology at RWTH Aachen University has been designed for frequencies above 60 GHz, where phase stability is a challenging task. Depending on the setup, it may even be required to pass Intermediate Frequency (IF) signals on the same cable as the Local Oscillator (LO) signals. This results in different test cases for the phase deviations depending on the frequency range of the IF (279 MHz) and LO (typically 10 GHz to 18 GHz) signals. Additional factors such as the measurement path of the robot or the position of the linear axis must also be taken into account. Therefore, a thorough analysis of the phase uncertainties caused due to flexing cables is of outstanding importance for robot-based measurement systems.

Adaptive Sampling for Compressed Spherical Near-Field Measurements
Cosme Culotta-L›pez,Dirk Heberling, November 2020

One of the main disadvantages of Spherical Near-Field (SNF) measurements is their acquisition time. This is due to the need of sampling a whole sphere around the Antenna Under Test (AUT) to perform the Near-Field-to-Far-Field Transformation (NFFFT). A step of the NFFFT is to decompose the measured signal in each one of the spherical waves it consists of, thus retrieving the Spherical Mode Coefficients (SMCs) associated to the AUT. Under typical measurement conditions, the SMCs of most physical AUTs prove sparse, i.e., most of their terms are zero or neglectable. Using this assumption, the system of linear equations with the SMCs as variables can be solved with fewer equations, that is, fewer measurement samples. This is done by applying an l1-minimization solver, following classical methodology from the field of compressed sensing. However, the location of the measurement points that generate non-redundant equations is not trivial. In typical compressed-sensing applications, a random sampling matrix is taken. Since a random matrix is inefficient for the acquisition with mechanical roll-over-azimuth positioner systems, a recent approach is to take an equidistant distribution of points on elevation and to calculate their corresponding pair on azimuth that delivers the minimum coherence of the sampling matrix. However, the number of sampling points M required for a successful reconstruction depends on the sparsity level of the SMCs of the unknown AUT, making its choice critical and based on a pessimistic approach. A method for the adaptive choice of M is suggested. After the acquisition of a starting set of M_0 measurement points, chosen using phase transition diagrams, the SMCs are estimated online with few iterations of an l1-minimization algorithm. Afterwards, further points are acquired, and the SMCs are estimated again using them. Following the evolution and the decrease of the variation between estimates, it is possible to truncate the measurement at a point where a successful reconstruction is guaranteed. The method for the construction of a minimum-coherent sampling matrix for adaptive acquisition and the truncation criteria for a specific accuracy are discussed with a focus onimplementation, and supported with numerical experiments, performed with measurementdata.

Sensitivity analysis of Fast Non-Redundant NF Sampling Methodologies with Probe Positioning errors
Maria Saporetti,Lars Foged,Francesco Saccardi,Francesco D'Agostino,Claudio Gennarelli,Rocco Guerriero,Flaminio Ferrara,Ruben Tena Sanchez,Damiano Trenta, November 2020

The planar wide-mesh scanning (PWMS) methodology is based on Non-redundant scanning schemes allowing faster measurements than classical Nyquist-compliant acquisitions based on denser, regular, equally spaced Near Field (NF) sampling. The methodology has no accuracy loss and has been validated at different bands and with different antennas [1]. The effectiveness of the PWMS technique has always been proven in error-free (or quasi-error-free) scenarios, assuming that possible errors introduced by the technique itself are independent of the typical source of measurement uncertainty. In this paper, we investigate for the first time the sensibility of the method wrt one of this error source included in the 18-terms lists [2], considered by the measurement community as an exhaustive list of the NF errors: X and Y probe positioning errors. Such errors are unknown and random and are associated to the mechanical vibrations and/or backlash of the system. The investigation has been done considering actual measurements of a multi-beam reflector antenna with approximately 35 dBi gain (MVG SR40 fed by two MVG SH5000 dual ridge horn). The AUT has been measured in planar geometry emulated by a 6-axis Staubli robot. The test was performed at 22-33 GHz. A set of measurements has been performed introducing a uniformly distributed random error in the range [0-1] mm, corresponding to ?/10 at 30 GHz. Errors are considered unknown. In the paper it will be shown that both in the classical and PWMS approaches the main beam is basically not affected by the introduced errors. The sidelobes are instead affected by such errors especially in the pattern cut where the beam is tilted. Such error levels obtained with the classical approach are comparable to those obtained with the PWMS approach, meaning that the latter is stable and against such type of perturbations.

NF-FF TRANSFORMATION WITH UNIFORM PLANAR SPIRAL SCANNING FOR VOLUMETRIC ANTENNAS
Francesco D'Agostino,Flaminio Ferrara,Claudio Gennarelli,Rocco Guerriero,Massimo Migliozzi,Giovanni Riccio, November 2020

NF-FF transformations have proven to be a convenient tool to accurately reconstruct the antenna pattern from NF measurements. In this framework, a very hot issue is the reduction of the time required to perform the measurements. To obtain a remarkable reduction of this time, nonredundant (NR) NF-FF transformations with planar spiral scannings have been developed in [1], by applying the NR representations of electromagnetic fields [2]. Optimal sampling interpolation (OSI) formulas have been used to efficiently reconstruct the massive NF data for the classical plane-rectangular (PR) NF-FF transformation from the NR spiral samples. The drastic measurement time-saving is due to the reduced number of needed NF samples acquired on fly, by adopting continuous and synchronized motions of the linear positioner of the probe and of the turntable of the AUT. However, such a time-saving is obtained at the expense of a nonuniform step of the spiral. Therefore, the linear positioner velocity is not constant, but must vary according to a not trivial law to trace the spiral, and this implies a complex control of the linear positioner. This work aims to develop an effective NF-FF transformation with planar spiral scanning for volumetric AUTs, wherein the spiral step is uniform and, hence, the linear positioner velocity becomes constant. To this end, the AUT is considered as enclosed in a sphere, the spiral is chosen in such a way that its step coincides with the sampling spacing needed to interpolate along a radial line according to the spatial band-limitation properties, and the NR representation along such a spiral is determined. Then, an OSI algorithm is developed to recover the NF data needed by the PR NF-FF transformation from the spiral samples. Numerical simulations assessing the accuracy of the developed NF-FF transformation will be shown.

Experimental Investigation of Different Floor Materials in Automotive Near Field Antenna Testing
Francesco Saccardi,Lars Foged,Francesca Mioc,John Estrada,Per Iversen,Michael Edgerton,Janalee Graham,Alessandro Scannavini, November 2020

Spherical near-field systems installed in shielded anechoic chambers are typically involved in modern automotive antenna measurements [1-3]. Such systems are often truncated at or close to the horizon to host the vehicle under test while limiting the size/cost of the chamber. The vehicle is usually placed on a metallic floor [4] or on a floor covered by absorbers [5]. The latter solution is intended to emulate a free space environment and is a key factor to perform accurate measurements down to 70 MHz. The availability of the free-space response also enables easy emulation of the car's behaviour over realistic grounds [6-7] while such emulations are more complex when a conductive ground is considered [8]. Conductive ground measurements also suffer from a strong interaction between the conductive floor and the measurement system and only in a limited number of situations such types of floor are a good approximation of realistic grounds (such as asphalts). However, the main advantage of conductive floor systems is the ease of accommodation of the vehicle under test which is simply parked in the center of the system. In absorber-based systems, instead, more time is generally needed to remove/place the absorber around the vehicle. Moreover, at low frequencies (70-400 MHz), large and bulky absorbers are normally used to ensure good reflectivity levels and the vehicle needs to be raised to avoid shadowing effect of absorbers. In this paper we investigate whether the measurement setup phase in absorber-based systems can be simplified by using smaller absorbers at low frequencies and/or not using them at all but considering conductive floors. The loss of accuracy in such scenarios will be studied considering a scaled vehicle and an implemented scaled automotive system where it is possible to access the full-spherical, real free-space scenario which is used as reference. The analysis is carried out considering (scaled) frequencies relevant to automotive applications in the 84-1500 MHz range. Two types of scaled absorbers, of different size and reflectivity, are considered to emulate the behaviour of the realistic full-scale 48-inch and 18-inch height absorbers. Measurements over metallic floor are included also in the analysis.

Near Field Measurements with Radically reduced Sampling requirement through Numerically defined expansion Functions
Maria Saporetti,Lars Foged,Francesco Saccardi,Giuseppe Vecchi,Marco Righero,Giorgio Giordanengo,Damiano Trenta, November 2020

We present an antenna measurement methodology requiring a radically lower number of field samples than the standard Nyquist-based theory maintaining a comparable accuracy. simulations and partial knowledge of the geometry of the Antenna Under Test are combined to build a set of numerically defined expansion functions: the method uses basic knowledge of the antenna and the assumption that scattering from large surfaces can be predicted accurately by numerical tools; areas of the antenna such as feeding structures are treated as unknown and represented by equivalent electric and magnetic currents on a conformal surface. In this way, the complexity, and thus the number of unknowns, is dramatically reduced wrt the full problem for most antennas. The basis functions representing the full antenna are used to interpolate a radically reduced set of measured samples to a fine regular grid of Near Field (NF) samples in standard geometries. Regular NF to Far Field (FF) transformation techniques are then employed to determine the FF. The sampling reduction is evaluated compared to a regular sampling on standard Nyquist-complaint grids. The method can be employed in standard sampling ranges. In [1] asymptotic simulation tools were used to build the numerical basis. In this paper, methods based on Surface Integral Equations (SIEs) are used to compute currents and fields. The currents induced on the antenna structure by each elementary source are computed and used to evaluate the radiated field. Both electric and magnetic elementary sources are placed around the antenna and the SIE problems use a fast algorithm to evaluate matrix-vector products. The methodology is validated with planar and spherical acquisitions on a reflector antenna (MVG SR40) fed by a dual ridge horn SH4000 and in a multi-feed configurations (using several SH5000) at 18 and 30 GHz. Patterns obtained with down-sampled fast approach are compared to standard measurements. Down-sampling factors up to 8 are achieved maintaining very high correlation levels with standard techniques.

Automotive OTA Measurement Techniques and Challenges
Patrick Pelland,Daniel Janse van Rensburg,Mihai Berbeci, November 2020

Characterizing the performance of automobile-mounted antennas has been an ongoing and evolving challenge for the antenna measurement community. Today, the automotive test environment poses unique challenges with its diversity and complexity of wireless on-board systems and the large electrical size of the test article. The evolution of cellular technologies over the past decade means that the basic mobile handset has now become a smartphone with significantly increased capability; this exact same trend has been mirrored by the automotive industry where we have witnessed the basic car radio and cassette player evolve into a multi-function infotainment unit. Modern vehicles include a multitude of wireless technologies, including cellular (2G, 3G, LTE), Bluetooth, WiFi, Global Navigation Satellite System (GNSS), collision avoidance radar, and more. Testing the complete vehicle is currently the only method available that certifies the correct mode of operation for each technology (including co-existence and interference) and also assures the manufacturer that the various sub-systems are performing as expected in the presence of all other sub-systems and the vehicle itself. While modern vehicles now function like large mobile devices, the conventional Over-the-Air (OTA) measurement systems and techniques available for small form factor devices (e.g. mobile phones) are ill-suited to testing such large devices. In this paper, we will highlight some of the unique challenges encountered in the automotive test environment. We will start by looking into existing methods of measuring radiation patterns of automobile-mounted antennas and providing a qualitative assessment of the various techniques with a focus on near-field solutions. A brief description of OTA testing will follow, coupled with an in-depth look into how techniques that are proven for handset type OTA measurements are being translated to automotive measurements. This section will provide a breakdown of key OTA test metrics, the measurement hardware typically required and key assumptions about the device under test. Finally, some performance tradeoffs and challenges associated with designing a multi-purpose antenna/OTA measurement system will be described.

Using High-Accuracy Swing Arm Gantry Positioners in Spherical Near-Field Automotive Measurement Systems
Tim Schwartz,Vivek Sanandiya,Eric Kim, November 2020

Spherical Near-Field (SNF) systems using a swing arm gantry configuration have been the go to solution for automotive measurement systems. Recent advances in the automotive industry have warranted a need for SNF systems with high mechanical positioning accuracy supporting measurements up to 40 GHz and beyond. This paper presents the design and implementation of a new swing arm gantry positioner having an 8-meter radius and a radial axis to support high frequency SNF measurements. We first define the relation of the gantry axis to the global coordinate system and discuss primary sources of errors. Next, a robust mechanical design is presented including design considerations and implementation. We then present errors measured using a tracking laser interferometer for probe position through the range of gantry axis travel. Static corrections for probe positioning errors are implemented in the control system using the radial axis. The resultant residual error for the swing arm gantry is then shown to have the accuracy required for high frequency SNF measurements.

Element Failure Detection of Antenna Array using Far-field Measurement with Shallow Neural Network
Michitaka Ameya, November 2020

In the 5G communication, antenna array has been widely used for high-speed wireless communication. For reliable antenna array system, the failure diagnosis of antenna array is one of the most important problems that has been studied for a long time. The back-projection method using near-field measurements is a one of the failure diagnosis technique based on the plane-wave expansion. However, when antenna elements are densely placed, it is difficult to estimate the excitation coefficients of the antenna elements with the back-projection method, because the obtained images from the conventional back-projection method has only a resolution of one wavelength. In addition, since there is usually a trade-off between measurement accuracy and measurement time. Therefore, it is difficult to satisfy the both requirements of accuracy and short measurement time. We have reported the element failure detection algorithm using a 2-layer shallow neural network with planar near-field measurement last year. In this report, the element failure detection of antenna array is performed with a minimum number of measurement points while maintaining enough accuracy by learning the relationship between excitation coefficients of antenna array and the electric far-field distribution by a shallow neural network. In the case of 64-elements short dipole antenna arrays, the estimation error of excitation coefficients of antenna array less than 1% are achieved by our trained neural network with a minimum number of far-field measurements with 50 dB SNR. The detailed algorithm and simulation results will be reported in the full-paper and the presentation.

2D RCS Prediction from Multistatic Near-Field Measurements on a Plane by Single-Cut Near-Field Far-Field Transformation and Plane-Wave Synthesis
Shuntaro Omi, Michitaka Ameya, Masanobu Hirose, Satoru Kurokawa, October 2019

A near-field far-field transformation (NFFFT) technique with a plane-wave synthesis is presented for predicting two-dimensional (2D) radar cross sections (RCS) from multistatic near-field (NF) measurements. The NFFFT predicts the FF of the OUT illuminated by each single source, then the plane-wave synthesis predicts the FF of the OUT each illuminated by each plane-wave by synthesizing the FFs given in the NFFFT step. The both steps are performed in the similar computational procedure based on a single-cut NFFFT technique that has been proposed previously. The method is performed at low cost computation because the NF and source positions are required only on a single cut plane. The formulation and validation of the method is presented.







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