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Accuracy
On Convergence of the Upper Bound on the Ratio of Gain to Quality Factor
Alex J. Yuffa, Marc Andrew Valdez, Benoıt Derat, October 2021
An antenna’s practical far-field distance can be estimated from the upper bound on the ratio of its gain to quality factor. This upper bound is an infinite series that can be truncated based on the desired accuracy. We investigate the convergence properties of this bounding series. We find that the number of terms required for convergence depends on the antenna’s electrical radius in a way similar to the Wiscombe criterion used in Mie scattering theory. For typical experimental accuracy requirements, such convergence can significantly reduce the effective far-field distance.
On the Uncertainty Sources of Drone-Based Outdoor Far-Field Antenna Measurements
Cosme Culotta-L´opez, Stuart Gregson, Andrian Buchi, Carlo Rizzo,Diana Trifon, Snorre Skeidsvoll, Ines Barbary, Joakim Espeland, October 2021
Unmanned Aerial Systems (UAS), colloquially known as drones, offer unparalleled flexibility and portability for outdoor and in situ antenna measurements, which is especially convenient to assess the performance of systems in their realworld conditions of application. As with any new or emerging measurement technology, it is crucial that the various sources of error must be identified and then estimated. This is especially true here where the sources of error differ from those that are generally encountered with classical antenna measurement systems. This is due to the larger number of mechanical degrees of freedom, and to the potentially less repeatable and controllable environmental conditions. In this paper, the impact of some of these various error terms is estimated as part of an ongoing measurement validation campaign. A mechanically and electrically time invariant reference antenna was characterized at ESAESTEC’s measurement facilities which served here as an independent reference laboratory. The reference results were compared and contrasted with measurements performed outdoors at Quad- SAT’s premises using QuadSAT’s UAS for Antenna Performance Evaluation (UAS-APE). While a direct comparison between the measurement results from ESA-ESTEC and QuadSAT delivers information about the various uncertainties within a UAS-APE system in comparison to classical measurement facilities’ and the validity of such a system for antenna testing, other tests aim at providing an estimation of the impact of each error source on the overall uncertainty budget, thus paving the way towards a standardized uncertainty budget for outdoor UAS-based sites.
Base Station Specific Absorption Rate Assessment Based on a Combination of Over-The-Air Measurements and Full-Wave Electromagnetic Simulations
Benoit Derat, Mert Celik, Davide Colombi, Bo Xu, Christer Tornevik, David Schaefer, Winfried Simon, October 2021
Radio Base Stations (RBS) must comply with applicable radio frequency electromagnetic field exposure regulations. Although compliance evaluation is typically carried out using field strength acquisitions or computations, Specific Absorption Rate (SAR) measurement is the reference method for low-power RBS, such as those used for indoor coverage. As classical robotbased probing is extremely time-consuming, especially when the whole-body SAR in a large phantom is to be assessed, faster alternative techniques are of high interest. Such solutions are becoming even more crucial, as the number of test modes is multiplying with modern communication technologies. This paper introduces an alternative, based on the convergence of Over- The-Air (OTA) measurements, equivalent current reconstruction and full-wave electromagnetic simulation. A first set of results demonstrates the relevance of this combination, by comparing actual dosimetric measurements to OTA-based reconstructed SAR values in a flat body mannequin, for a commercial lowpower RBS. A test system is realized which enables OTA electric field phase evaluations for a self-powered device under test, using digitally modulated signals. This proof of concept establishes the applicability of the technique to actual regulatory testing conditions.
Validation of Over-The-Air Testing Accuracy at Mid-Range Distance for Massive MIMO Base Stations
Benoit Derat, Mert Celik, Aidin Razavi, Aurelian Bria, Jonas Friden, October 2021
5G base stations are gradually evolving into Active Antenna Systems, improving the link budget with beamsteering capabilities. As such antenna arrays are typically eight wavelength large or more, the question of reducing the footprint of far-field testing facilities has experienced a growing interest. Recent research results have established that it is possible to conduct accurate Over-The-Air measurements around the peak radiation, at an effective far-field distance which can be as low as 20% of the Fraunhofer distance, depending on the electrical size of the antenna aperture. This paper complements the published validations of this finding, with an application to commercial massive MIMO base stations. The previously identified midrange far-field distance is even shown to be conservative for such devices. A mathematical analysis based on plane-wave expansion is proposed and allows for a general interpretation of this result.
Stochastic Filtering Technique for UAV-Based Communications On The Move Terminal Tracking Accuracy Evaluation
Saki Omi, Hyo-Sang Shin, Antonios Tsourdos, Joakim Espeland, Andrian Buchi, October 2021
Along with the growth of communication and satellite industry, the importance of satellite antenna evaluation is increasing. Particularly Communication On The Move (COTM) terminal antenna, including the communication between new types of constellations on LEO and MEO, requires tracking accuracy test for the communication on moving vehicles. The conventional test facilities are locally fixed and lack flexibility. To make the antenna measurement more accessible, we are developing a methodology for in-situ measurement by introducing multiple Unmanned-Aerial-Vehicles (UAVs) system with RF payload. Thanks to the dynamic flexibility of UAVs, this system can flexibly change the test configuration on site and make new test scenarios available, such as emulating the orbit of non-GEO satellites during the measurement. However, one of the challenges of the proposed system is the additional uncertainties during the measurement due to the mobility of UAVs. To overcome this challenge, we design recursive stochastic filtering and fusion approaches, and evaluate their estimation performance via numerical simulations. By introducing stochastic filter and fusion algorithms, the effect of error is mitigated, and better accuracy can be achieved compared to an existing method. This project is performed in collaboration with Cranfield University in the UK and QuadSAT in Denmark.
Precise Phase Center Localization of Automotive LTE Antennas in the Installed State Through Phaseless LTE Uplink Measurements
P. Berlt, C. Bornkessel, and M. A. Hein, October 2021
With the event of integrated and multi-standard wireless links, phaseless antenna measurements are attracting more and more interest in research. Especially in the context of connected and automated driving, antennas, frontends, and digital signal processing units merge into telematic units and require new methods for performance evaluation in the installed state. The measurement of the phase diagram and the exact absolute positioning of electrically large antennas, i.e., antennas interacting with the car body, present challenges for safety-relevant applications and reliable test methods. This paper describes a way to determine the position of automotive antennas in the installed state with sub-wavelength precision from phaseless measurements. Realistic LTE uplink signals were used as test signals as they would be transmitted by an active device in a real-world scenario. The localization algorithm is based on orthogonal power measurements of the transmitted signal on a cylinder surface and a non-linear optimization. By comparison with a conventional localization based on spherical far-field data, an accuracy of the approach of less than 1 cm was achieved, which is less than λ/16 at the considered frequency of 1870 MHz.
Advanced Diagnostics on a Large Array by the Equivalent Current Technique
L. Scialacqua, F. Scattone, A. Giacomini, L.J. Foged, F. Mioc, October 2021
Diagnostic techniques are crucial in antenna development and testing to enhance the Device Under Test (DUT) performances and identify the cause of possible failures in the qualification process. Among different approaches [1]-[8], it has been demonstrated that the equivalent currents method (EQC) [8]-[9], implemented in [10], is one of the most efficient for investigations in various application areas [11]-[13]. Indeed, the generality of the 3D reconstruction surface enclosing the DUT is a key feature, it ensures that this technique is unique and highly suitable for diagnostics, respect to traditional methods based on plane wave expansion. To handle electrically large problems, the EQC method has been initially based on a Fast Multipole Method (FMM) [14]. The recent advent of 5G technologies has led to an increasing need in terms of antenna electrical dimensions. Therefore, a novel technique based on a Nested Skeletonization Scheme (NSS) has been implemented to guarantee a further reduction of memory requirements and computational time. The new capability has been demonstrated in the past for a patch array antenna [15]. In this paper, the diagnostic capabilities of the EQC approach are applied to an early prototype of an electrically large array antenna for 5G antenna measurements applications [16].
Pointwise Probe Correction Applied to a Robot-Based mm-Wave Antenna Test Range
R. Moch, D. Heberling, October 2021
Robot-based measurement systems typically have a larger tolerance with respect to their positioning accuracy than conventional systems, e.g. roll-over-azimuth positioners. However, for spherical near-field measurements, the positioning accuracy of the probe is an important uncertainty in the required near-field-to-far-field transformation. One way to account for those non-idealities is to use the higher-order pointwise probe correction (PPC). It allows to consider the actual position and orientation of the probe by additional rotations and translations of the probe receive coefficients. To evaluate the PPC, the occurring position tolerances and the differences in the transformed farfield patterns of a standard gain horn are investigated at 60GHz. Using an onset measurement as reference, it is shown that the PPC provides improvements of 􀀀41dB and 􀀀65dB for the co- and cross-polarized measurements, respectively. In addition, an offset measurement is shown where the measurement sphere is shifted relatively to the AUT. The pointwise implementation of the correction method allows to reproduce the far-field pattern without additional measurement points, while the transformation without PPC fails. Thus, the implementation of the PPC not only enables the processing of irregular sampling grids, but also increases the measurement accuracy by including the actual position and orientation of the probp>
X/Ku/Ka-band high Gain Reflector Antenna Intercomparison Campaign Results
M.A.Saporetti, L.J. Foged, F. Tercero, C. Culotta-López, M. Böttcher, Y. Alvarez-Lopez, Oskar Zetterstrom, M. Sierra Castañer, October 2021
Antenna measurement Intercomparison Campaigns represent a successful activity within the working group on antenna measurement of the European Association on Antennas and Propagation [1] since the group foundation in 2005. These campaigns, constitute an important resource for participating facilities to demonstrate their measurement proficiency, useful internally but also towards obtaining or maintaining official accreditations. In this paper we present the completion of a campaign involving a high gain X/Ku/Ka-band reflector, MVG SR40 fed by an MVG SH4000 Dual Ridge Horn. Preliminary results were shown in [2]. Results from seven facilities are compared through plots of gain/directivity patterns. The data is used to generate reference patterns and establish accurate gain performance data based on the uncertainty estimates provided by each facility. Statistical analysis of the measured data such as Equivalent Noise Level and Birge ratio of each measurement with respect to the established reference will also be shown.
Errors and Prerequisites of the Short-Time Measurement and Transformation of Continuously Modulated Fields
Fabian T. Faul and Thomas F. Eibert, October 2021
Near-field far-field transformations (NFFFTs) are usually performed for time-harmonic fields. In cases where insitu antenna measurements are required and the antenna under test (AUT) is not accessible for specifically tailored test signals, the need for handling time-modulated fields arises. The shorttime measurement (STM) approach offers a way to deal with continuously modulated fields while a time-harmonic NFFFT can be employed. We present results of numerical simulations to demonstrate and characterize the STM approach for the case of a cylindrical measurement geometry as found in UAV-based antenna measurements. We further derive guidelines from the simulation results that describe the applicability of the STM for different measurement situations.
Additional Tools for Locating and Quantifying a Range’s Stray Signals
Scott T. McBride, October 2021
Earlier works have shown the benefits of imaging stray signals in a range with planar-scanner data. This paper discusses some additional tools that can be employed for stray-signal identification. Related range diagnostics are presented that employ Fourier spectral and holographic processing of 1D linear scans through the quiet zone. For the special case of a compact range, the interpretation of arrival angles from the paraboloidal reflector surface is explored. Measured data from multiple facilities are presented that were used to locate, quantify, and remedy the unwanted signals.
Experimental Validation of Full Probe Correction Technique using Wideband and Dual-Polarized Probes in Spherical NF Antenna Measurements
F. Saccardi, A. Giacomini, L. J. Foged, T. Blin, October 2021
Full Probe Compensation (PC) techniques for Spherical Near Field (SNF) antenna measurements have recently been proposed and validated with success [1]-[4]. Such techniques allow the use of antennas with more than a decade of bandwidth as near field probes in most systems. The clear advantage is that multi-service/frequency measurements campaigns can be performed dramatically reducing the number of probes hence decreasing the downtime between two measurements. This is a highly desirable feature for modern antenna measurement applications such as automotive. The use of a dual-polarized probes further improves the measurement efficiency as two orthogonal field components are measured at the same time. The possible differences between the pattern radiated by the two ports of the probe should sometimes be considered to keep the overall measurement accuracy. The full PC technique objective of this paper accounts for generic dual-polarized probes and is validated for the first time. For this purpose, measurements of three monocone antennas from 450 to 6000 MHz performed with only one wideband (15:1) dual-polarized probe will be considered.
NFC Reader Antenna Design and Considerations for Automotive Applications
Ali Attaran, Nevin Altunyurt, John Locke, Aaron DeLong, October 2021
This paper presents antenna design and packaging consideration for near field communication (NFC) system that is being used in automotive security systems, and, more specifically, to an NFC reader for obtaining access to, and controlling activation of, a transportation vehicle such as a motor vehicle. Various important studies for automotive applications were performed in this work such as a magnetic wall method. This magnetic wall method can prevent the reduction in NFC reading range caused by proximity to body sheet metal. It provides a unique and superior magnetic shielding effect as compared to ferrite sheets because it is not temperature dependent and can be implemented with minimal cost and complexity. The proposed design can be easily fabricated on the back face of the NFC reader antenna PCB using conventional PCB techniques.
Experimental validation of a phaseless, non-redundant plane-polar antenna characterization
F. Bevilacqua, A. Capozzoli, C. Curcio, F. D’Agostino, F. Ferrara, C. Gennarelli, R. Guerriero, A. Liseno, M. Migliozzi, Y. Vardaxoglou, October 2021
Owing to the increasing interest in high frequencies, as the millimeter wave range, wherein accurate phase measurements are increasingly difficult and expensive, phaseless near-field techniques are prime candidates for antenna characterization. In this paper, an experimental validation of a phaseless near-fieldfar- field (NF-FF) transformation with plane-polar scanning for antenna characterization is presented. A proper representation of problem unknowns and data, using the available information on the antenna under test (AUT) and on the scanning geometry, is adopted in order to improve the reliability and the accuracy of the proposed characterization algorithm. By exploiting the nonredundant sampling representations of electromagnetic fields and by using an oblate spheroid to model the AUT, a remarkable reduction (about 90%) of the required NF samples is achieved. Experimental results on data acquired at the University of Salerno Antenna Characterization Lab are reported to validate experimentally the effectiveness of the proposed characterization technique.
Cellular 4G LTE MIMO Antenna System Modeling Utilizing Measured Vehicle-Level Antenna Patterns
Daniel N. Aloi, Jia Li, Esosa Ekhoragbon, Leo Lanctot, John Locke, October 2021
Cellular LTE MIMO downlink performance, for 4x4, 4x2, and 2x2 LTE MIMO architectures, in terms of average data throughput and availability, were investigated in an urban canyon environment of Frankfurt, Germany at 2110 MHz on a Sport Utility Vehicle (SUV) with metal and glass roofs for a virtual route. This study utilized the following measured antenna radiation patterns for total polarization on the SUV at 2110 MHz for the mobile station: 1) roof-mounted antenna on metal roof; 2) roof-mounted antenna on glass roof; 3) interior-mounted planarinverted F antenna; and 4) interior-mounted planar-inverted F antenna rotated 90 degrees. This research was carried out using a three-dimensional simulation software suite that enabled users to simulate electromagnetic wave propagation and wireless network planning. The following observations were obtained from this research. First, the MIMO architectures for the SUV with metal roof exhibited approximately 5% higher average data throughput levels compared to the same MIMO architectures on the SUV with glass roof. Second, the throughput availability for the 4x4 and 4x2 MIMO systems were comparable. Lastly, the average throughput for the 4x4 MIMO system was higher than the 4x2 and 2x2 MIMO systems for the SUV regardless of roof material.
Unifying G/T and Noise Figure Metrics for Receiver Systems
Roy Monzello, November 2020
The conventional method for comparing the performance of antenna-receiver systems is the classical G/T metric. The G/T metric is the ratio of antenna-circuitgainrelative to the thermal noise temperature evaluated at the input of the low noise amplifier; the thermal noise at the input to the LNA consists of the received sky noise, the LNA's effective input noise temperature, and post LNA noise referenced to the LNA's input. While this has been a standard for many years, it will be shown that G/T does an incomplete job of describing the performance under all conditions. The noise figure metric was developed as a characteristic describing signal-to-noise degradation to be applied to circuit based input/output topologies, and cannot easily be applied to hybrid systems such as an antenna-receiver system in which the input power is described by spatial field density levels, and the output power is stated in terms of a circuit-based voltage-current environment. This paper presents a noise figure metric which has been expanded to include systems that are a hybrid of wave and circuit characteristics such as the marriage of an antenna and receiver. It will also be shown that whereas a system's noise figure is dependent upon a chosen noise reference temperature, the intrinsic Effective Input Noise Temperature of the system is an invariant that does not change when a different reference temperature is selected. It will also be shown that, in contrast to G/T, the effective input noise temperature of an antenna/receiver system will accurately predict the system's output SNR for all values of system input SNR. It will be shown in detail, how to measure the antenna/receiver system's Effective Input Noise Temperature (TE), resulting in the following equation: TE = (TD1 - Y£ TD2 )/(Y - 1) Where: TD1 , and TD2 are measured noise power densities at the face of the antenna, TE is the Effective Input Noise Temperature of the system, and "Y" is the classical "Y factor" metric.
Three Antenna Polarization Measurement Revisited
Michael Francis,Ronald Wittmann, November 2020
Three-antenna methods [1] are fundamental to modernantenna metrology. They enable the simultaneous determination of the on-axis polarizations and gains of three unknown antennas. For example, on-axis characterization of a probe antenna is necessary for the accurate far-field measurement of test antenna transmitting and receiving functions. Recently after renovation of antenna ranges, NIST has beeninvolved in an internal program to re-certify its polarizationcharacterization services. While reviewing the theory [2], werealized that a small modification to the standard algorithmcould improve the accuracy of the polarization determinationin many cases. Three-antenna techniques measure the antennas in pairswith one antenna of each pair rotating about its axis (Figure1). The ideal form of the measured signal is very simple (6). Previous methods [3][8], take an economical approach in which a minimal number of measurements are used to extractthe polarization parameters from the model. Some allow forthe averaging of multiple determinations to improve results. We propose, on the other hand, to use the discrete Fourier transform (DFT) to isolate the exp (¤i?) behavior in the data[9], [10]. The pair-polarization ratios (8) are easily computedfrom this transform. References [9] and [10] only came tolight after our analysis was completed. Rather the drop theproject, we have decided to offer this note as a tutorial andto call attention to what appears to be an under-appreciatedapproach to polarization measurement. All of the above methods work well when the error signalis small. Otherwise, the global nature of Fourier interpolationis expected to yield advantages over any local analysis. This hypothesis is supported by the simulations discussed below. Data were simulated for a number of combinations of axialratio, tilt angle, and sense of polarization. Noise was added atvarious levels. NOTE: The abstract refers to a figure, equations, and references not included in the abstract for brevity but which are available upon request
Three Antenna Polarization Measurement Revisited
Michael Francis,Ronald Wittmann, November 2020
Three-antenna methods [1] are fundamental to modernantenna metrology. They enable the simultaneous determination of the on-axis polarizations and gains of three unknown antennas. For example, on-axis characterization of a probe antenna is necessary for the accurate far-field measurement of test antenna transmitting and receiving functions. Recently after renovation of antenna ranges, NIST has beeninvolved in an internal program to re-certify its polarizationcharacterization services. While reviewing the theory [2], werealized that a small modification to the standard algorithmcould improve the accuracy of the polarization determinationin many cases. Three-antenna techniques measure the antennas in pairswith one antenna of each pair rotating about its axis (Figure1). The ideal form of the measured signal is very simple (6). Previous methods [3][8], take an economical approach in which a minimal number of measurements are used to extractthe polarization parameters from the model. Some allow forthe averaging of multiple determinations to improve results. We propose, on the other hand, to use the discrete Fourier transform (DFT) to isolate the exp (¤i?) behavior in the data[9], [10]. The pair-polarization ratios (8) are easily computedfrom this transform. References [9] and [10] only came tolight after our analysis was completed. Rather the drop theproject, we have decided to offer this note as a tutorial andto call attention to what appears to be an under-appreciatedapproach to polarization measurement. All of the above methods work well when the error signalis small. Otherwise, the global nature of Fourier interpolationis expected to yield advantages over any local analysis. This hypothesis is supported by the simulations discussed below. Data were simulated for a number of combinations of axialratio, tilt angle, and sense of polarization. Noise was added atvarious levels. NOTE: The abstract refers to a figure, equations, and references not included in the abstract for brevity but which are available upon request
Correction of the Measured Phase of the Radiation Pattern of Millimeter-Wave Antennas
Antonius van den Biggelaar,Ben Jamroz,Dylan Williams,Bart Smolders,Ulf Johannsen, November 2020
To characterize the radiation characteristics of an antenna, determining the power pattern of the antenna is often sufficient. In some cases, however, both the amplitude and phase response are important. For instance, for accurate channel modeling, the antenna has to be de-embedded, requiring knowledge of the complex radiation pattern of the antenna. A vector network analyzer typically measures complex S-parameters, hence, determining the complex radiation pattern seems like a straightforward task. When measuring at higher frequencies, as the wavelength becomes shorter, antenna phase measurements are very sensitive to positioning and alignment errors. Using sophisticated measurement tools, the position and orientation of the antennas can be determined, and this information can be used to correct the measurement data. The stringent requirements on positioning and alignment at millimeter-wave frequencies, however, makes correcting the data based on physical insight, in some cases, a more practical solution. The results of a radiation pattern measurement of a WR-28 rectangular open-ended waveguide will be shown in the full paper. The magnitude of the radiation pattern is symmetric in its two principal planes, which is to be expected, but the phase of the radiation pattern is not symmetric. To explain this lack of symmetry, a two-parameter misalignment model will be presented. It will be shown that the measured phase is much more sensitive to the misalignment than the measured magnitude, explaining why the symmetry is only lacking in the measured phase. Based on the 1,708 available planar cuts, the two parameters in the misalignment model are determined with great confidence. Subsequently, the parameters are used to correct the phase of the measured radiation pattern, restoring the expected symmetry in the phase measurement.
CATR Reflector Measurement System with Multiple Reflectors for Multiple Angles of Arrival in Millimeter Wave Frequency Bands
Benoit Derat,Adrian Cardalda-Garcia,Engelbert Tyroller,Corbett Rowell, November 2020
This paper presents a novel method using multiple compact antenna test range (CATR) reflectors to simulate the Radio Resource Management (RRM) measurements required for 5G devices capable of beam-forming in the millimeter wave frequency range (i.e. FR2). Four CATR reflectors are arranged on a semi-circle with the device under test (DUT) on a dual axis positioner in the center of the intersection of four planar waves in order to generate five sets of two Angles of Arrival (AoA), thereby capable of simulating multiple basestations from different directions for the 5G device to monitor and perform handovers. The reflectors create far-field conditions at the device under test (DUT) such that quiet zones of up to 20-30cm in size can be achieved. Absorber baffles are strategically placed as to reduce scattering from adjacent reflectors. In addition to RRM measurements, one reflector can be used to also perform in-band RF beam characterization[JMFL2] while additional reflectors can measure out of band emissions at the same time, thereby decreasing total measurement times by a factor of 2-3 times.


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