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Measurement of Antenna System Noise Temperature Using Planar Near-Field Data
Allen Newell, Patrick Pelland, Stuart Gregson, Daniël Janse van Rensburg, October 2017
This paper presents the results of a new measurement technique to determine antenna system noise temperature using data acquired from a planar near-field measurement. The ratio of antenna gain to system noise temperature (G/T) is usually determined in a single measurement when the antenna is alternately pointed towards the “cold sky” and a hot radio source such as the sun or a star with a known flux density. The antenna gain is routinely determined from near-field measurements and with the development of this new technique, the system noise temperature can also be determined. The ratio of G/T can therefore be determined from planar near-field data without moving the antenna to an outdoor range. The noise temperature is obtained by using the plane-wave spectrum of the planar near-field data and focusing on the portion of the spectrum in the evanescent or “imaginary space” portion of the spectrum. Near-field data is obtained using a data point spacing of l/4 or smaller and the plane-wave spectrum is calculated without applying any probe correction or Cos(q) factor. The spectrum is calculated over real space corresponding to propagating modes of the far-field pattern and also the evanescent or imaginary space region where . Actual evanescent modes are highly attenuated in the latter region and therefore the spectrum in this region must be produced by “errors” in the measured data. Some error sources such as multiple reflections will produce distinct localized lobes in the evanescent region and these are recognized and correctly identified by using a data point spacing of less than l/2 to avoid aliasing errors in the far-field pattern. It has been observed that the plane wave spectrum beyond these localized lobes becomes random with a uniform average power. This region of the spectrum must be produced by random noise in the near-field data that is produced by all sources of thermal noise in the electronics and radiated noise sources received by the antenna. By analysing and calibrating this portion of the spectrum in the evanescent region the near-field noise power can be deduced and the corresponding noise temperature determined. Simulated and measured data will be presented to illustrate and validate the measurement and analysis techniques. Keywords — Planar Near-Field, G/T, Figure-of-Merit Measurements, Simulation, Plane Wave Spectrum.
Acquisition, Reconstruction, and Transformation of a Spiral Near-Field Scan
Brett Walkenhorst, Scott McBride, October 2017
The topic of non-redundant near-field sampling has received much attention in recent literature. However, a practical implementation has so far been elusive. This paper describes a first step toward such a practical implementation, where the practicality and generality are maximized at the expense of more acquired data points. Building on the theoretical work of faculty at the University of Salerno and University of Naples, the authors have acquired a set of near-field data using a spiral locus of sample points and, from those data, obtained the far-field patterns. In this paper, we discuss the acquisition system, the calculation and practical implementation of the spiral, the phase transformations, interpolations, and far-field transforms. We also present the resultant far-field patterns and compare them to patterns of the same antenna using conventional near-field scanning. Qualitative results involving aperture back-projection are also given. We summarize our findings with a discussion of error, uncertainty, acquisition time, and processing time in this simplified approach to non-redundant sampling in a practical system.
Channel De-embedding and Measurement System Characterization for MIMO at 75 GHz
Alexandra Curtin, David Novotny, Alex Yuffa, Selena Leitner, October 2017
As modern antenna array systems for MIMO and 5G applications are deployed, there is increased demand for measurement techniques for timely calibration, at both research and commercial sites.[1] The desired measurement method must allow for the de-embedding of information about the closed digital signal chain and element alignment, and must be performed in the near-field. Current means of measuring large arrays cover a variety of methods. Single-element gain and pattern calibration must cover the parameter space of element weightings and is extremely time-consuming, to the point where the measurement may take longer than the duration over which the array response is stable.[4] Two other popular methods are the transmission of orthogonal codes and the use of holography to reconstruct a full-array pattern. The first of these methods again requires extremely long measurement time. For an array of N elements and weightings per element W_n, the matrix of orthogonal codes must be of an order greater than NW_n.[4][3]. This number varies with the form of W_n depending on whether the array is analog or digital, but in both cases for every desired beam configuration, an order-N encoding matrix must be used. The second method relies on illuminating subsets of elements within an array and reconstructing the full pattern.[2] Each illuminated subset, however, neglects some amount of coupling information inherent to the complete system, making this an imperfect method. In this work we explore the development of a sparse set of measurements for array calibration, relying on coherent multi-channel data acquisition of wideband signals at 75 GHz, and the hardware characterization and post-processing necessary to perform channel de-embedding at an elemental level for a 4x1 system. By characterizing the complete RF chain of our array and the differential skew and phase response of our measurement hardware, we identify crucial quantities for measuring closed commercial systems. Additionally, by combining these responses with precise elemental location information, we consider means of de-embedding elemental response and coupling effects that may be compared to conventional single-element calibration information and full-pattern array measurements. [1] C. Fulton, M. Yeary, D. Thompson, L. Lake, and A. Mitchell. Digital phased arrays Challenges and opportunities. Proceedings of the IEEE, 104(3):487–503, 2016. [2] E. N. Grossman, A. Luukanen, and A. J. Miller. Holographic microantenna array metrology. Proceedings of SPIE, Passive Millimeter-Wave Imaging Technology VIII, 5789(44), 2005. [3] E. Lier and M. Zemlyansky. Phased array calibration and characterization based on orthogonal coding Theory and experimental validation. 2010 IEEE International Symposium on Phased Array Systems and Technology (ARRAY), pages 271–278, 2010. [4] S. D. Silverstein. Application of orthogonal codes to the calibration of active phased array antennas for communication satellites. IEEE Transactions on Signal Processing, 45(1):206–218, 1997.
Parametric Modeling of Antenna Radiation Patterns in Both Spatial and Frequency Domains
Zubiao Xiong, October 2017
A complete characterization of the radiation and scattering phenomena is essential to the ray tracing simulators. In the ray tracing modeling, the electromagnetic field quantities are traced along the ray paths and determined by the antenna radiation pattern and the scattering patterns of the obstacles. The polarimetric patterns may be prepared in advance from the measurements or numerical simulations, and reused by the ray tracing simulators for various situations. However, the prefabricated pattern data set usually contain only a limited quantity of samples at discrete angular directions and frequencies. The lack of full representations of the desired patterns hinders the accurate calculation of ray field quantities. Although interpolation can be done using multidimensional splines or polynomials, the accuracy is not assured by the problems’ physics. Especially, it is difficult to tackle the phase wrapping problem in the multidimensional case, which might lead to wrong phase interpolation. In this paper, model based parameter estimation (MBPE) is used to circumvent the requirement of obtaining all samples of the desired radiation and scattering patterns in both spatial (angular) and frequency domains. Since any function defined on the surface of a sphere can be represented by a sum of spherical harmonic functions, we utilize the spherical harmonic expansion in the spatial domain firstly. Specifically, in order to avoid the singularities of conventional vector spherical harmonics at the north and south poles, scalar spherical harmonics is used instead. The expansion coefficients are vector-valued frequency domain responses, independent to the angular variables. Then each coefficient is expanded by using the singularity expansion method, which leads to a rational function characterized by its poles and residues in the frequency domain. Since the poles are the characteristic of the considered object (antenna or scatter), it is reasonable to assume that all spherical harmonic components have the same poles. Therefore, the parameters to be estimated are the frequency domain poles and the corresponding residues for each spherical harmonic component. By following this method, a physically-based, closed-form, reduced-order parametric model can be established from the sampled pattern data. The proposed method will be validated by simulations and measurements.
A Novel and Innovative Near Field System for Testing Radomes of Commercial Aircrafts
Marc Le Goff, Nicolas Adnet, Nicolas Gross, Luc Duchesne, Arnaud Gandois, Ludovic Durand, October 2017
The maintenance of aircraft radomes is of particular importance for the commercial aviation industry due to the necessity to ensure the correct functioning of the radar antenna, housed within such protective enclosures. Given that the radar component provides weather assessment, as well as guidance and navigation functions (turbulence avoidance, efficiency of route planning in case of storms, etc.), it is imperative that every repaired radome be tested with accuracy and reliability to ensure that the enclosed weather radar continues to operate in accordance with the after-repair test requirements of the RTCA/DO-213. Recently, this quality standard was updated and published under the name RTCA/DO-213A, establishing more stringent measurement requirements and incorporating the possibility of measuring radomes using Near-Field systems. Consequently, a compliant multi-probe Near- Field system concept – AeroLab – has been specifically designed to measure commercial aircraft nose-radomes, in order to meet the new standard requirements. AeroLab performs Near-Field measurements. Near-Field to Far-Field transformations are then applied to the results. Such a Near-Field system allows the test range to be more compact than traditional Far-field test ranges, and thus be independent from the updated Far-Field distance which has progressed from D²/2l to 2D²/l in the new standard RTCA/DO-213A. AeroLab enables the evaluation of the transmission efficiency and beamwidth. It also allows for accurate evaluations of the side-lobe levels by providing improved visualization of principal cut views selected from 3D patterns. Moreover, depending upon the weather radar system inside the radome under test, 2 distinct scan sequences must now be taken into account: “elevation over azimuth” and “azimuth over elevation”. AeroLab emulates both of these motion sequences through a monolithic gimbal. Furthermore, thanks to its multi-probe array, such measurements are performed in a fraction of the time spent in current mono-probe test facilities (less than 4 hours, i.e. 1/3 less time than single probe scanners). Keywords: RTCA/DO-213A, radome measurement system, after-repair tests, multi-probe measurement system, Near-Field system.
Characterization of a Photonics E-Field Sensor as a Near-Field Probe
Brett Walkenhorst, Vince Rodriguez, James Toney, October 2017
In this paper, we explore the possibility of using a photonics-based E-field sensor as a near-field probe. Relative to open-ended waveguide (OEWG) probes, a photonics probe could offer substantially larger bandwidths. In addition, since it outputs an optical signal, a photonics probe can offer signal transport through optical fiber with much lower loss than what can be achieved using RF cables. We begin with a discussion of the theory of the device followed by a summary of results of a photonics sensor that was tested in a spherical near-field (SNF) range. In these tests, data were collected with the photonics probe in the test antenna position to characterize various probe parameters including polarization discrimination, probe gain, effective dynamic range, and probe patterns. In the same set of tests, the photonics device was placed in the probe position in the range and used to measure patterns of two different antennas: a standard gain horn and a slotted waveguide array antenna. The resultant patterns are shown and compared to patterns collected with traditional RF probes. We conclude the paper with a discussion of some of the advantages and disadvantages of using a photonics probe in a practical system based on the lessons learned in the SNF testing.
International Facility Comparison Campaign at L/C Band Frequencies
Maria Saporetti, Lars Foged, Yasar Kurdi, Antonis Alexandridis, Cosme López, Fernando Las-Heras, Manuel Castañer, October 2017
Comparison activities in which a number of measurement facilities compare their measurements of the same antenna in a standard configuration have become important for documentation and validation of laboratory expertise and competence. It is also mandatory to have regular participation in such activities to obtain and maintain accreditations like ISO 17025. The main goal of the facility comparison activities is to provide a formal opportunity for the participants to validate and document their achieved measurement accuracy and procedures by comparison with other facilities. Since 2004, comparison campaigns with different scopes have been conducted on antenna measurements within various European activities: EurAAP (European Association on Antennas and Propagation) supported by the European Cooperation in Science and Technology (COST) in the programs ASSIST IC0603 and VISTA IC1102 and the 6th EU framework network “Antenna Centre of Excellence” (ACE). Results of these activities have led to improvement in antenna measurement procedures and protocols in facilities and contributions to standards. Due to the direct benefits to the participants, the activities have been very successful and partial results have been published in IEEE referenced papers during the years. The large amount of measured data available have fostered fruitful discussion and research on the improvement of standard procedures, protocols and tools for performance verification like the facility comparison campaigns. As a further benefit, the campaigns have initiated a dialogue among different laboratories throughout Europe and USA and is spreading into Asia. In this paper we report on a recent EurAAP facility comparison campaign involving a medium gain ridge horn, MVI-SH800. The campaign covers measurement in the L and C band frequencies in different facilities in Europe and USA. The horn is equipped with an absorber plate to enhance the correlation in different facilities by reducing the sensibility to the measurement set-up. The results of 8 facilities will be shown in terms of gain and directivity patterns, equivalent noise level and the declared uncertainty will be checked against the whole set of measurements.
Multi-Band Compact MIMO Antenna System for LTE and WLAN Communications
Jiukun Che, Chi-Chih Chen, October 2017
In this paper, a novel compact 2-channel MIMO antenna design for all cellular and Wi-Fi communication needs from vehicular is discussed. The entire antenna system fits within the 13cm (diameter) by 9cm (height) volume. It consists of 2 vertical multi-band cellular antenna elements and two vertical multi-band Wi-Fi antenna elements. All four antennas share a 13cm diameter circular ground plane. Each antenna element design is a PCB based slot-loaded multi-band monopole. This particular element design as well as their mounting positions were chosen to minimize mutual coupling and blockage in order to maximize MIMO performance, i.e. diversity gain. In addition, the center region of the antenna volume also accommodates a raised L1-band GPS antenna. A prototype antenna was subsequently fabricated. The measured antenna performance compared well with simulated results before and after being mounted on a 4 feet diameter ground plane. The effect of the radome was also assessed and was found to be insignificant. The cellular antenna produced realized gain of over 2 dBi in lower cellular band (0.7 GHz to 1 GHz), and over 5dBi in the higher cellular band (1.7-2.1GHz and 2.3GHz-2.5GHz). The Wi-Fi antenna produced realized gain of over 5dBi in both 2.4 GHz and 5.8 GHz bands. The far-field pattern correlation coefficient was also calculated to evaluate the diversity gain performance of antenna system. For the cellular band, the correlation number is lower than 0.55 for 0.7 to 1 GHz, and lower than 0.35 for all the other band. For the entire Wi-Fi band, the correlation number is lower than 0.4.
An Experimental and Computational Investigation of High-Accuracy Calibration Techniques for Gain Reference Antennas
Olav Breinbjerg, Kyriakos Kaslis, Jeppe Nielsen, October 2017
Gain is a principal property of antennas; it is essential in establishing the link budget for communication and sensing systems through its presence in Friis’ transmission formula and the radar range equation. The experimental determination of antenna gain is most often based on a gain-transfer technique involving a reference antenna for which the gain has been calibrated to high accuracy; this is typically a pyramidal horn antenna [1]. The required accuracy of antenna gain obviously depend on the application; in some cases it can very high, ±0.1 dB or less, and this implies an even higher accuracy, of the order of ±0.01dB, for the gain reference antenna. This work investigates the accuracy to which a gain reference antenna can be calibrated; the investigation is based on experimental spherical near-field antenna measurements [2] and computational integral equation / method of moments simulations [3]. While calibration of gain reference antennas has been studied in many previous works, even works from early 1950s [4]-[6], this work is novel in systematically supporting measurements with full-wave simulations. Such simulations facilitate the study of e.g. the effect of multiple reflections between antennas at short distances. We study two absolute calibration techniques for the gain of pyramidal horn antennas. The first technique determines gain as the product of directivity and radiation efficiency; this technique has been referred to as the pattern integration technique [7] (which is not an entirely adequate designation since gain cannot be determined from the radiation pattern). The second technique determines the gain from Friis’ transmission formula [8] for two identical antennas; this technique is generally referred to as the two-antenna technique [1]. These two calibration techniques involve very different steps and contain very different sources of error; for both techniques our investigation involves measurements as well as simulations. For the pattern integration technique we compare experimental and computational results for the directivity and demonstrate agreement within one-hundredth of a dB. The radiation efficiency is calculated by different techniques based on the surface impedance boundary condition for the metallic walls of the pyramidal horn. This technique is not influenced by proximity effects or by impedance mismatch between the measurement system and the gain reference antenna. For the two-antenna techniques we compare experimental and computational results for the gain and we compare the calculated distance-dependence with that of the extrapolation technique [9]. It is demonstrated how the use of the phase center distance in Friis’ transmission formula notably decreases the necessary separation between the antennas for a required accuracy, but that multiple reflections may then become a limiting factor. This technique is highly influenced by the impedance mismatch that must be accurately accounted for. We compare the gain values resulting from the pattern integration technique and the two-antenna technique, including their very different uncertainty estimates, for a C-band standard gain horn. The work is related to an on-going ESA project at the DTU-ESA Spherical Near-Field Antenna Test Facility for the on-ground calibration of the scatterometer antennas of the EUMETSAT MetOp Second Generation B-series satellites. IEEE Standard – Test Procedures for Antennas, Std 149-1979, IEEE & John Wiley & Sons, 1979. J.E. Hansen, “Spherical Near-Field Antenna Measurements”, Peter Perigrinus Ltd., London 1987. W.C. Jakes, “Gain of Electromagnetic Horns”, Proceedings of the IRE, pp. 160-162, February 1951. E.H. Braun, “Gain of Electromagnetic Horns”, Proceedings of the IRE, pp. 109-115, January 1953. W.T. Slayton, “Design and Calibration of Microwave Antenna Gain Standards”, Naval Research Laboratory, Washington D.C., November 1954. A. Ludwig, J. Hardy, and R. Norman, “Gain Calibration of a Horn Antenna Using Pattern Integration”, Technical Report 32-1572, Jet Propulsion Laboratory, California Institute of Technology, October 1972. H.T. Friis, “A Note on a Simple Transmission Formula”, Proceedings of the I.R.E. and Waves and Electrons, pp. 254-256, May 1946. A.C. Newell, R.C. Baird, P.F. Wacker, “Accurate Measurement of Antenna Gain and Polarization at Reduced Distances by an Extrapolation Technique”, IEEE Transactions on Antenna and Propagation, vol. 21, no. 4, pp. 418-431, July 1973.
High Performance Dual Polarized Near-Field Probe at V-Band Provides Increased Performances for Millimeter Wave Spherical Near-Field Measurements
Andrea Giacomini, Lars Foged, Edward Szpindor, Wenji Zhang, Per Iversen, October 2017
The expanding market for millimeter wave antennas is drivinga need for high performance near-field antenna measurement systems at these frequencies. Traditionally at millimeter waves, acquisition of two orthogonal polarizations have been achieved through mechanical rotation of a single polarized probe and an associated frequency conversion module. This generally results in the collection of two complete spherical data sets, one for each polarization,with both acquisitions significantly separated in time. To enable improvements in both measurement speed and accuracy, MVG have developed a new high performance dual polarized feed in V-band (50GHz-75GHz). This probe has been integrated in a millimeter wave Spherical Near-Field (SNF) system via two parallel receiver channels that are simultaneously sampled. This architecture more than doubles the acquisition speed and additionally ensures that the two polarization components are sampled at precisely the same point in space and time. This is particularly important when performing accurate polarization analysis (e.g. conversion of dual linear polarization to spherical/elliptical polarizations). The two measurement channels are calibrated via radiated boresight measurements over a range of polarization angles, generating a four term “ortho-mode” correction matrix vs. frequency. The SNF probe is based on an axially corrugated aperture providing a medium gain pattern (14dBi). The probe provides symmetric cuts and low cross-polarization levels in the diagonal planes. The directivity/beam-width of the aperture has been tailored to the measurement system, ensuring proper AUT illumination and sufficient gain to compensate for free space path loss. Dual polarization capability is achieved with an integrated turnstile OMT feeding directly into the probe circular waveguide and a conical matching stub at the bottom. Thanks to the balanced feed used for each polarization, the port-to-port coupling is sufficiently low to allow for simultaneous acquisition of the two linear field components. Input ports are based on standard WR-15 waveguide to simplify the integration with the front-end (dual channel receiver). The paper will present the detailed description and measured performances of the new dual polarized SNF probe. Additionally, measurement time and achieved accuracy will be compared between the single polarization probe architecture and the dual polarized probe installed in the same spherical near-field antenna measurement system.
Effects due to Antenna Mount in Base Station Antenna Measurements
John McKenna, Vivek Sanandiya, Larry Cohen, October 2017
Cellular Base Stations require efficient performance validation methods. One performance criterion is the Station radiation pattern. In directive pattern measurements, it is well documented that the Compact Antenna Test Range (CATR) and the Spherical Near Field (SNF) methods produce equivalent patterns. However, Base Station radiation patterns are not necessarily directive to the extent necessary for equivalent patterns among CATR and SNF methods. In deploying a number of Spherical Near Field and point source Compact Antenna Test Range (CATR) test facilities, we have observed the radiation pattern of base station antennas are more sensitive to the mount in a CATR than in a Spherical Near Field Antenna Test Range. This fact conflicts with intuition and theory. A barbeque spit positioner has been deployed in both spherical near field and point source compact ranges. Recently the point source compact range has been observed to yield patterns noticeable different depending on the antenna mount to the spit. On the other hand, the Spherical Near field implementation, in at least two deployments to Germany, has NOT manifested such a dependence on the mount, or, perhaps, such a dependency exists and yet has not been recognized. Measured Data will be presented showing radiation dependencies upon the mount in a CATR and SNF implementation. Explanations as to the Root Cause will be stated.
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.
On the Fly Multifrequency Measurements in Spherical Near Field Systems
Belén Galocha Iragüen, Pablo Caballero Almena, Cristian Martínez Portas, Fernando Rodríguez Varela, José Luis, Besada Sanmartín, Manuel Sierra Castañer, November 2018
This paper presents a technique for reduction the acquisition time in the measurement of antennas in spherical near field systems using multifrequency on-the-fly acquisitions. When these acquisitions are performed, a shift in the pattern is performed. This shift appears in polarization when the scan is in roll axis, or in pointing direction when the scan is azimuth or elevation axis. In any case, this shift has to be corrected in order to compensate the different trigger time for each frequency point. This paper presents a technique for compensating this rotation in spherical near field system, by rotation of the radiation pattern in the scan axis through an easy calculation of the that shift.
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.
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.
Spherical Phaseless Probe-Corrected Near-Field Measurements of the DTU-ESA VAST12 Reflector Antenna
Javier Fernández Álvarez, Jeppe M Bjørstorp, Olav Breinbjerg, November 2018
An experimental case of spherical probe-corrected phaseless near-field measurements with the two-scans technique is presented, based on magnitude measurements at two surfaces of the VAST12 reflector antenna performed at the DTU-ESA Facility. Phase retrieval using strictly the directly measured near-field magnitude was unfeasible in this setup, due to the small sphere separation allowed by the probe positioner, which led to incorrect and excessively slow convergence. Phase retrieval with larger separation between spheres has shown remarkable results. For these tests a measured magnitude was used in combination with calculated near-field magnitudes at different (larger and smaller) spheres with larger separations than allowed by the experimental setup. It has been seen that larger separation between measurement spheres improves accuracy of phase retrieval. A measurement with a backprojected measurement with 3 m sphere separation is of particular interest because it can be potentially replicated in the DTU-ESA Facility assuming such range of movement was allowed, while being accurate down to an error of less than-35dB. Measurements with larger spheres show even better accuracy. These good results were obtained with the normal spatial sampling rate for complex measurements and with a very simple Hertzian dipole initial guess, and show the superior performance of spherical phaseless measurements with the two-scans technique, compared to a planar setup.
Aircraft Radome Characterization via Multiphysics Simulation
Eamon Whalen, Gopinath Gampala, Katelyn Hunter, Sarthak Mishra, C J Reddy, November 2018
Altair Engineering Inc. Troy, MI USA- Figure 1. The electromagnetic, aerodynamic, and structural performance of a nose cone radome can be characterized by computational simulation, allowing for early design concept validation and reducing the dependence on physical testing. Abstract-Radomes protect antennas from structural damage due to wind, precipitation, and bird strikes. In aerospace applications, radomes often double as a nose cone and thus have a significant impact on the aerodynamics of the aircraft. While radomes should be designed not to affect the performance of the underlying antennas, they also must satisfy structural and aerodynamic requirements. In this paper, we demonstrate a multiphysics approach to analysis of airborne radomes not only for electromagnetic (EM) performance, but also for structural, aerodynamic, and bird strike performances, as depicted in figure 1. We consider a radome constructed using composite fiberglass plies and a foam core, and coated with an anti-static coating, paint, and primer. A slotted waveguide array is designed at X-band to represent a weather radar antenna. The transmission loss of the radome walls is analyzed using a planar Green's function approach. An asymptotic technique, Ray-Launching Geometric Optics (RL-GO), is used to accurately simulate the nose cone radome and compute transmission loss, boresight error, and sidelobe performance. In addition to EM analysis, Computational Fluid Dynamics (CFD) analysis is used to predict pressures resulting from high air speeds, which are then mapped to an implicit structural solution to assess structural integrity using the Finite Element Method (FEM). We also demonstrate damage prediction due to a "bird strike" impact using an explicit structural FEM solver. The multiphysics simulation techniques demonstrated in this paper will allow for early design validation and reduce the number of measurement iterations required before a radome is certified for installation.
Compact Antenna Measurement Range for OTA testing of Active Antenna System Base Stations
L M Tancioni, A Jernberg, P Noren, P Iversen, A Giacomini, A Scannavini, R Braun, M Boumans, H Karlsson, , ,, November 2018
Measurement scenarios for 5G mobile communications are nowadays challenging the industry to define suitable turn-key solutions that allow Over the Air (OTA) testing of non-connectorized devices. In order to respond to the needs of an effective measurement solution, that allow measuring all the required OTA parameters at both sub6GHz and mm-Wave frequencies and that could be deployed in a very short time, the Compact Antenna Test Range (CATR) was chosen. In this paper, we will summarize the performance and the testing capabilities of a short focal-length, corner-fed CATR design, providing a 1.5 m x 1.5 m cylindrical Quiet Zone, operating from 1.7 GHz to 40 GHz and upgradeable to 110 GHz, allowing OTA measurements of Active Antenna System (AAS) Base Stations (BS), installed at Ericsson premises in Gothenburg, Sweden in 2017.

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