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This paper introduces the new Portable Laser Guided Robotic Metrology (PLGRM) system at the National Aeronautics and Space Administration's (NASA) Glenn Research Center. Previous work used industrial robots in fixed facilities to characterize antennas and required fixtures that do not lend themselves to portable applications. NASA's PLGRM system is designed for in-situ antenna measurements at a remote site. The system consists of a collaborative robot arm mounted on a vertical lift and a laser tracker, each on a mobile base. Together, they enable scanning a surface larger than the robot's reach. To accomplish this, the robot first collects all points within its reach, then the system is moved and the laser tracker is used to relocate the robot before additional points are captured. The PLGRM implementation will be discussed including how safety and planning are combined to effectively characterize antennas. Software defined triggering is a feature, for flexible integration of vector network analyzers and antenna controllers. Lastly, data will be shown to demonstrate system functionality and accuracy.
In this paper, we will discuss the impact of mounting structures on the installed performance of phased arrays. In particular, performance data for the Conformal, Lightweight Antennas for Aeronautical Communications Tech-nology (CLAS-ACT) antenna will be presented. Performance data from a series of mounting configurations will show that null depth and location is particularly susceptible to change while the main beam steering angle remains relatively stable. In addition, the Portable Laser Guided Robotic Metrology (PLGRM) system will be discussed as a suitable instrument for measuring antenna patterns in complex or difficult locations that are challenging for traditional ranges. The PLGRM system was recently developed at the National Aeronautics and Space Administration's (NASA) Glenn Research Center (GRC) and deployed to measure in situ antenna patterns.
A dual linear polarized 3D printed magneto-electric phased array antenna for various 5G New Radio (NR) frequency bands is proposed and its beam steering performance is investigated. The magneto-electric radiating element exhibits a well-defined stable pattern quality, low variation in the impedance over a wider bandwidth and high port to port isolation in a dual polarization configuration. The analog beamforming network (BFN) of the array is also designed. The fabricated board will be combined with the 3D printed array aperture for experimental verification of the scan performance.
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.
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.
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.
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.
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.
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.
Altair Engineering Inc. Troy, MI USA-https://www.altairhyperworks.com 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.
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.
In this contribution the signal received by an antenna is understood as an inner product built by the polarization vectors of the involved antennas. By using a suitable unitary transformation the polarization efficiency can be straightforwardly calculated without additional assumptions. By solving an eigenvalue problem given by a unitary operator which represents a rotation, a simple and illustrative interpretation is possible. The formulation is applied to derive the well-known relations of the improved three antenna polarization measurement technique given by Allen C. Newell, which is mainly based on the measurement of relative power levels. Some measurement results and the calculation of the achievable measurement accuracy are presented.
Radar data on the complete polarimetric responses from a 4" dihedral corner reflector from 4 to 18 GHz have been collected and studied. As a function of the azimuth, the vertically suspended object may present itself to the radar as a dihedral, a flat plate, an edge, a wedge, or combinations of these. A two-dimensional method-of-moment (2-D MOM) code is used to model the perfectly electrical conducting (PEC) body, which allows us to closely simulate the radar responses and to provide insight for the data interpretation. Of particular interest are the frequency and angular dependences of the responses which yield information about the downrange separation of the dominant scattering centers, as well as their respective odd-or even-bounce nature. Use of the corner reflector as a calibration target is discussed.
Specular reflectance data of indoor interior materials is a prerequisite to analysis of the channel characteristics for new millimeter and submillimeter indoor wireless communications. Antenna property such as gain and radiation pattern is one of the key measurement quantities in electromagnetic wave metrology. This paper describes a specular reflectance and antenna property measurement system and shows measurement results of the specular reflectance of an Acetal plate and the antenna property of a 24 dB horn antenna in 325-500 GHz frequency range.
In order to support near-field measurements of automobile antennas in as realistic as possible environments, an equivalent sources based near-field far-field transformation approach for near-field measurements above a possibly lossy dielectric half-space is presented and evaluated. Different possibilities for considering the half-space influence are discussed, where an approach with an appropriate half-space Green's function is found to be most accurate, as expected. The formulation of the equivalent sources transformation approach with the half-space Green's function and a formulation with free-space Green's function together with equivalent sources representation of the half-space influence are discussed and a variety of results are presented in order to corroborate the feasibility of the various approaches.
This paper presents a way to determine mutual coupling effects through analysis of the active voltage standing wave ratio (VSWR) to predict the presence of large reverse power levels in co-located multiple input multiple output (MIMO) radars in transmit mode. The methodology consists of measuring the forward and reverse waves on a dual directional coupler (DDC) to directly obtain the active reflection coefficient on a co-located MIMO radar system. The active VSWR of each individual antenna is computed from measurements of the active reflection coefficient. These results are compared against analytical methodologies.
The use of mode filtering to improve the quality of antenna measurements taken in non-anechoic environments is well known, [1, 2, 3, 4, 5]. In the far-field case [6, 7, 8], it has been shown that it is possible to use standard cylindrical near-field theory [8] to implement the necessary mode filtering using a singularly polarized, great circle, far-field pattern cut consisting of amplitude and phase data. The careful verification of this technique using a compact antenna test range (CATR) was reported in [7, 8] however that implementation had, as a prerequisite, the need to acquire the far-field data on a monotonic and equally spaced pattern abscissa. In many instances this is not convenient or perhaps impossible. This paper presents a recent development which allows data to be processed rigorously when having been acquired using an unequally spaced angular abscissa. This paper sets out the novel, far more sophisticated, algorithm together with results of actual range measurements that were processed using this new technique.
The Translated Spherical Wave Expansion (TSWE) has recently been proposed as a very effective Near-Field-to-Far-Field (NF/FF) transformation tool for down-sampled Spherical Near Field (SNF) measurements with offset Antenna Under Test (AUT). In case of electrically small probes and/or small AUT-probe view angles the TSWE can be accurately applied without compensating for the probe effect. Instead, when electrically larger probes and/or larger view angles are considered, the measured signal is affected by an averaging field effect that should be properly compensated to ensure a good accuracy. In this paper the TSWE technique is applied for the first time tacking into account the full effect of the measuring probe. To validate the proposed technique, a standard gain horn intentionally displaced in offset configuration have been measured in SNF geometry with a first order probe and two different wideband higher-order antennas as probe.
The Plane Wave Generator (PWG) is an array of elements with suitably optimized complex coefficients, generating a plane wave in the close proximity of the array. Thus, the PWG achieve far-field testing conditions in a Quiet Zone (QZ) at a reduced distance in a manner similar to what is achieved in a Compact Antenna Test Range (CATR) [1]. In this paper, the concept of a high performance, dual polarized PWG supporting up to 10:1 bandwidth is presented for the first time. A prototype of a dual polarized PWG has been designed, manufactured and tested in the 600MHz to 6GHz frequency range. The initial testing results on QZ uniformity and evaluation of possible measurement accuracy are presented.
The unknown-thru calibration technique is being used to achieve a system level calibration at millimeter wave frequencies (>50 GHz) on the robotic ranges at NIST. This two-port calibration requires the use of a full bi-directional measurement, instead of a traditional single-direction antenna measurement. We explored the value of the additional data acquired. We find that we can use this information to verify antenna/scan alignment, image the scattering from the positioner/facility, and perform a first order correction to the transmission data for uncertainties due to LO cable flexure.