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Validation of Additive Manufacturing for Broadband Choked Horns at X/Ku Band by Extensive Antenna Measurements
A Giacomini, R Morbidini, V Schirosi, F Saccardi, L J Foged, B Jun Gerg, D Melachrinos, M Boumans, November 2018

Additive manufacturing has become a popular alternative to traditional CAM techniques, as it has reached a suitable maturity and accuracy for microwave applications. The main advantage of the additive technologies is that the manufacturing can be performed directly from the 3D CAD model, available from the numerical simulation of the antenna, without significant modifications. This is a highly desirable feature, in particular for time and cost critical applications such as prototyping and manufacturing of small quantities of antennas. Different 3D-printing/additive manufacturing technologies are available in industry today. The purpose of the paper is an investigation on the accuracy and repeatability of the Selective Laser Melting (SLM) manufacturing technique applied to the construction of a batch of 15 broad band fully metallic chocked horns, operating at X/Ku band, manufactured in parallel. Manufacturing accuracy and repeatability has been evaluated using RF parameters as performance indicators comparing measured data and high accuracy simulations. The radiation patterns have been correlated to the numerical reference using the Equivalent Noise Level, while manufacturing repeatability is quantified on input matching by defining an interference level. These indicators have also been compared to state-of-the-art values commonly found for traditional manufacturing.

Modeling of Tapered Anechoic Chambers
Zubiao Xiong, Zhong Chen, November 2018

A hybrid method that combines the finite element method (FEM), the Floquet mode analysis and the shooting and bouncing ray method (SBR) is presented to solve the quiet-zone field in large tapered anechoic chambers. In the method, the field equivalence principle is employed to replace the throat of the tapered chamber by a set of equivalent electric and magnetic currents. The Floquet mode analysis is employed to approximate the rest of the absorber lined walls by virtual surfaces with equivalent reflection coefficients. The total quiet-zone field then becomes the superposition of the field radiated by the equivalent currents, and the field scattered by the virtual reflective surfaces. The scattered field is calculated from the SBR method. The required equivalent currents of the throat and the reflection coefficients of absorber array walls are computed with the use of the FEM, which allows the considerations of the complex structure and near-field interaction. Numerical examples are presented to demonstrate the feasibility of the proposed method.

Over-the-Air Performance Evaluation of NB-IoT in Reverberation Chamber and Anechoic Chamber
Jun Luo, Edwin Mendivil, Michael Christopher, November 2018

NB-IoT (Narrowband Internet of Things) is a narrowband radio technology showing very different characteristics compared with traditional wireless protocols. For the first time based on authors' best knowledge, this paper compares the Over-the-Air (OTA) performance of NB-IoT in the Reverberation Chamber (RC) and Anechoic Chamber (AC), which involves two major RF test environment variations in the OTA test arena. In this paper, the Total Radiated Power (TRP) and Total Isotropic Sensitivity (TIS), related to the transmitter and receiver performance of NB-IoT, respectively, are investigated. For TIS test, an early exit algorithm with 95% confidence level based on Chi-Square distribution has been developed to improve the test speed. The test results show a good match (Within CTIA allowed measurement uncertainty) between AC and RC. Our analysis also includes several key parameters, such as test repeatability, measurement uncertainty, and test time, which gives a comprehensive comparison of different aspects between RC and AC for NB-IoT OTA test. It could be noticed as well that the early exit algorithm based on Chi-Square distribution improves the test time performance significantly without compromising the test accuracy.

Coupling Suppression and Measurements on a Millimeter Wave Cylindrical Repeater
M Ignatenko, B Allen, S Sanghai, L Boskovic, D Filipovic, November 2018

This paper discusses some aspects of isolation improvement and associated measurements on a cylindrical millimeter-wave repeater operating over K, Ka and V bands. The isolation between the transmitting and receiving antennas is improved by means of reactive impedance surface implemented as tapered depth corrugations. The designed tapered depth profile broadens bandwidth of the surface compared to the traditional quarter wavelength corrugations. Required isolation of 80 dB and large electrical size of the platform make numerical analysis and actual measurements challenging. Details of the analysis and measurements are summarized. Along with external coupling, the coupling due to leakages from waveguide components and antennas is also discussed. Measurements confirm that the design goal isolation is accomplished.

Implementation of a Technique for Computing Antenna System Noise Temperature Using Planar Near-Field Data
A C Newell, C Javid, B Williams, P Pelland, D J Janse Van Rensburg, November 2018

This paper presents the second phase of the development of a new measurement technique to determine antenna system noise temperature using data acquired from a planar near-field measurement. In the first phase, it was shown that the noise temperature can be obtained using the plane-wave spectrum of the planar near-field data and focusing on the portion of the spectrum in the evanescent region or "imaginary space". 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 /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. In the current phase of tests, planar near-field data has been acquired on a measurement system and the analysis applied to determine the system noise parameters. Measurements have been performed with terminations inserted at three different locations in the RF receiving path: the IF input to the receiver, the input to the mixer and the input to the probe that is transmitting to a centre-fed reflector antenna. The terminations consist of either a load that serves as the "cold" noise source or a noise source with a known noise output for the "hot" noise source.

Optimized Compact Antenna Test Range with Short Focal Length for Measuring Large L/Ku-Band Active Antennas
A Jernberg, M Pinkasy, G Pinchuk, T Haze, R Konevky, L Shmidov, R Braun, G Baran, Pit-Radwar S A Baran@pitradwar Grzegorz, P Com, Iversen, A Giacomini, Marcel Boumans, November 2018

A new Compact Antenna Test Range (CATR) has been built, as a turnkey facility, with a cubic quiet zone (QZ) of 4.8m x 4.8m x 4.8m in the frequency range 0.9-18 GHz. The CATR has been installed in a new building with an isolated and stable foundation. The dimensions of a traditional CATR for such QZ size becomes impractical and requires a very large chamber. A new, diagonally fed, short focal length reflector has been developed to minimize the chamber size to fit the dimensions of 22 m x 14.5 m x 14.5 m.

Reference Chip Antenna for 5G Measurement Facilities at mm-Wave
A Giacomini, F Scattone, L J Foged, E Szpindor, W Zhang, P O Iversen, Jean-Marc Baracco, November 2018

In this paper, we present a chip antenna in the 27GHz band, targeting 5G measurements. This antenna can be used as reference in mm-wave measurement systems, such as the MVG µ-Lab, feeding the antenna under test through a micro-probe station. The reference antenna is employed to calibrate in gain through the substitution method. The antenna shown in this paper is an array of four patches, fed through a strip-line beam forming network. A transition strip-line to coplanar waveguide allows the antenna be fed by the micro-probe.

Near Field Reconstruction for Electromagnetic Exposure of 5G Communication Devices
Johan Lundgren, Jakob Helander, Mats Gustafsson, Daniel Sjöberg, Bo Xu, Davide Colombi, November 2018

Compliance with regulatory exposure requirements of power density for 5G systems will need accurate measurements. In this work a near field measurement technique for electromagnetic exposure of 5G communication devices is presented. The technique requires two measurements, one of a device under test and one of a small aperture as a calibration measurement. The method uses method of moments and involves reconstructing equivalent currents on a predefined surface. These currents are then used to generate and propagate the electromagnetic fields to an arbitrary plane and further compute the power density. The measurement data are obtained through a planar scan of a device under test using a probe and probe calibration using a small aperture to obtain an accurate field with absolute positioning. Measurement data is presented and compared with simulations for several distances and two antennas, operating at 28 GHz and 60 GHz. The computed power density agrees well with simulations.

Imaging a Range's Stray Signals with a Planar Scanner
Scott T Mcbride, John Hatzis, November 2018

The fundamental purpose of absorber treatment in an anechoic chamber is to ensure that only the direct-path signal is coupled between the range antenna(s) and the device under test. For many simple and standard geometries, this is readily accomplished with conventional processes and procedures. When the geometry and/or stray-signal requirements deviate from the norm, however, it can be very beneficial to have an easy and reliable way to locate and quantify sources of stray signals. This paper discusses a straightforward algorithm for creating images of those stray signals in a range when a planar scanner and broad-beamed probe are available in the test zone. Measured data from multiple facilities are evaluated, along with absorber-treatment improvements made based on some of the images produced.

Indoor Antenna Measurement Facility: Determination of the phase center position
Pierre Massaloux, Guillaume Cartesi, Philippe Berisset, November 2018

Indoor antenna measurement facilities are usually dedicated to characterize all the parameters of an antenna. In order to perform phase center position measurements, the CEA has designed a specific experimental layout to characterize this parameter with a very high accuracy. This paper describes this measurement facility and deals with technical decisions made during its design phase. Finally, we will talk about possibilities offered by this specific layout and the advantages of this layout compared to a classical antenna test-bench.

Antenna Modeling on Complex Platforms Through Constrained Equivalent Aperture Distributions
Leo Tchorowski, Inder " Jiti, " Gupta, November 2018

Accurate in situ antenna manifolds are desired for performance evaluation of radio frequency systems, including communication, navigation, and radar among others. In situ antenna measurements are the most accurate way to obtain antenna manifolds on the platform of interest, but are often impractical or impossible to obtain. Instead, combinations of simulations and measurements are used to estimate antenna manifolds on platforms. First, the gain and phase of the target antenna are measured on a simple ground plane, over the frequencies and field of view of interest. The measurements are then imported into computational electromagnetics codes to simulate platform scattering from the platform of interest. However, the representation of the measured data is not unique, which leads to inaccuracies and/or a large run time in computational electromagnetics codes. This paper presents a new method to represent measured antenna data in electromagnetics codes through aperture current distributions of simulated cross-slots and monopoles. A weighted sum of far-fields from the simulated equivalent elements approximates the measured antenna far-fields, with weights determined by the minimization of the L2-norm difference between measured far-fields and equivalent element far-fields. However, the least square solution may place large, unrealizable currents on the aperture. A constraint is introduced to limit the amount of current on the aperture, by minimizing the length of the solution vector. In this paper, the details of the suggested method will be presented. We will also illustrate the accuracy of the method through example simulations, where good agreement is achieved between truth data and equivalent antennas on complex platforms.

Effective Polarization Filtering Techniques for Ground Penetrating Radar Applications
Sebastian G Wirth, Ivor L Morrow, November 2018

The effect of different decomposition techniques on the imaging and detection accuracy for polarimet-ric surface penetrating data is studied. We derive the general expressions for coherent polarimetric decomposition using the Stokes parameters and model based polarimetric decomposition using the Yamaguchi technique. These techniques are applied to multi-frequency (0.4-4.8GHz) full polarimetric near-field radar measurements of scattering from surface laid calibration objects and shallow buried landmine types and show in detail how the decomposition results provide effective surface and sub-surface clutter reduction and guide the interpretation of scattering from subsurface objects. Data processing methods assume cross-polar symmetry and a novel bistatic calibration procedure was developed to enforce this condition. The Yamaguchi polarimetric decomposition provides significant clutter reduction and image contrast with some loss in signal power; while Stokes parameters also provide imagery localising targets, complementary information on the scattering mechanism is also obtained. Finally a third novel polarimetric filter was formulated based on differential interferometric polarimetric decomposition. The three combined techniques contribute to a significant improvement of subsurface radar performance and detection image contrast.

A study of the Low-frequency Coaxial Reflectometer measurement procedure for evaluation of RF absorbers' reflectivity -II
Anoop Adhyapak, Zhong Chen, November 2018

The Low frequency Coaxial Reflectometer is the recommended procedure to measure the absorbers' reflectivity as per the IEEE 1128-1998 standard. The standard recommends the operable frequency range up to 500 MHz with a permissible error of 2 dB and higher error beyond 600 MHz. This paper studies and discusses the error on different types of absorber. Each of the absorber type is simulated in the square section of the reflectometer setup to compute the absorber's reflectivity using Ansys HFSS. An effective time gating technique is applied to reduce the effect of edge effects. These results are compared to the unit cell simulation results with a plane wave excitation and periodic boundary conditions. The absorbers are then simulated in the complete reflectometer setup to include the mismatch associated with the transition and compared to the unit cell model results. The errors associated with the comparison of the absorbers' simulation results for these different models are analyzed. The combination of these different absorbers is simulated in unit cell model. The absorbers are placed in different regions and orientations inside the reflectometer. The comparison between the unit cell results of the combination of the absorbers and the results of the absorbers inside the reflectometer in different orientations give the effect of the non-uniform field distribution inside the reflectometer.

Enhanced PNF Probe Positioning in a Thermally-Uncontrolled Environment using Stable AUT Monuments
John H Wynne, Farzin Motamed, George E Mcadams, November 2018

The need for thermal stability in a test chamber is a well-established requirement to maintain the accuracy and repeatability sought for high frequency planar near-field (PNF) scanner measurements. When whole chamber thermal control is impractical or unreliable, there are few established methods for maintaining necessary precision over a wide temperature range. Often the antenna under test (AUT) itself will require a closed-loop thermal control system for maintaining stable performance due to combined effects from transmission heat dissipation and the environment. In this paper, we propose a new approach for near-field system design that leverages this AUT stability, while relaxing the requirement of strict whole chamber thermal control. Fixed reference monuments strategically placed around the AUT aperture perimeter, when measured periodically with a sensing probe on the scanner, allow for the modeling and correction of the scanner positioning errors. This process takes advantage of the assumed stability of the reference monuments and attributes all apparent monument position changes to distortions in the scanner structure. When this monument measurement process is coupled with a scanner structure that can tolerate wide thermal variations, using expansion joints and kinematic connections, a robust structural error correction model can be generated using a bilinear mapping function. Application of such a structure correction technique can achieve probe positioning performance similar to scanners that require tightly controlled environments. Preliminary results as well as a discussion on potential design variations are presented.

Laboratory Proofs on a Nonredundant Spherical NF-FF Transformation for a Quasi-Planar AUT Mounted in Offset Configuration
Francesco D ' Agostino, Flaminio Ferrara, Claudio Gennarelli, Rocco Guerriero, Massimo Migliozzi, November 2018

This communication provides an experimental assessment of an accurate near-field-far-field (NF-FF) transformation with spherical scan, properly developed to take into account a mounting in offset configuration of a quasi-planar antenna under test (AUT). Such a technique relies on the nonredundant sampling representation of electromagnetic fields and, unlike the classical NF-FF transformation, it allows the reconstruction of the far field radiated by an AUT from a minimum number of NF data, which remains practically the same both when the AUT is mounted in onset and offset configuration, since this number is related only to the surface modeling the AUT. Such a surface has been here chosen coincident with that formed by two circular bowls with the same aperture and eventually different bending radii. Experimental results assessing the validity of such a technique are reported.

Resurfacing the NASA Langley Experimental Test Range Reflector
Ron Schulze, Matthew Bray, Nathanael Flores-Palomera, Chris Vandelinder, Richard Boucher, George Szatkowski, Larry Ticatach, Angelo Cavone, Matthew Ayers, Michael Draszt, John Rooks, , , ,, November 2018

An ambitious resurfacing campaign was launched in late 2017 to correct for large reflector surface distortions present at the NASA LaRC Experiment Test Range (ETR) in support of performing Europa Clipper flight High Gain Antenna (HGA) measurements at X-and Ka-band frequencies. The effort was successful as the worst case peak-to-peak amplitude ripple was reduced from 4.0-dB to 1.5-dB across the 4.1-meter quiet zone.

Eliminate Celestial Noise Sources in Your SatCom G/T Measurements
Roy C Monzello, November 2018

The current method of measuring system G/T performance is with the use of celestial noise sources (sun and cold sky). This paper details a method using man-made noise sources to measure system performance within an anechoic chamber, followed by an outdoor measurement to obtain G/T performance in a real world operational environment. A simple method is presented and equations derived that relate system performance in unknown environments to performance with known noise sources.

Measurement Methodology For Fast Antenna Testing Using Existing PNF ranges
F D'agostino, F Ferrara, C Gennarelli, R Guerriero, M A F Saporetti, L J Saccardi, Foged, D Trenta, Damiano Trenta@esa, Int, ,, November 2018

In this paper, we investigate the achievable time savings in planar near-field (PNF) measurement of high gain antennas using a planar wide-mesh scanning (PWMS) approach [1-2]. The PWMS employs at least four times less measurements points than standard scanning without degrading the measurement accuracy leading to an under-sampling factor of four. Such mesh scanning can be implemented on standard planar near-field systems similar to the ESTEC, Hertz PNF scanner [3, 4]. The measurement accuracy vs time-saving for the wide-mesh approach is investigated using the numerical model of a highly-shaped Ku-band reflector antenna. This antenna is a realistic representation of what is currently flying on typical satellites with European coverage such as Eutelsat W [5]. The Near Field to Far Field transformation accuracy is investigated by comparing traditional and PWMS results using the same base data from the antenna model. A discussion on implementation on existing scanners and the relation with measurement time-savings is included. The experimental verification of the technique will be included in the conference presentation.

Uncertainty Analysis Technique for Planar Field-Probing Measurements and Quiet-Zone Simulations of a Compact Antenna Test Range
T M Gemmer, D Heberling, November 2018

The performance of a compact antenna test range is evaluated by field-probing measurements of the quiet zone. The comparison between the simulated and measured data, however, is misleading due to the finite measurement accuracy and the limited nature of the numerical model. In order to allow a comparison, the uncertainty terms of the field-probing measurements and the numerical model are identified based on the National Institute of Standards and Technology 18-term uncertainty analysis technique. The individual terms are evaluated with simulations or measurements using the equivalent-stray-signal model. Bearing the differences between the model and the actual measurements in mind, the electrical field can be estimated precisely within the overlapping region of both uncertainty budgets.

Measurements of the dynamic pattern of an electronically steerable phased antenna array with circular polarization in Ka-band
Matthias Tebbe, Georg Strauss, November 2018

This paper presents two methods for measuring dynamic antenna patterns of phased arrays in a compensated compact range. The first method uses the turntable of the compact range to counter steer the antenna beam. The dynamic pattern is created by measuring single points of the pattern over time. This method is successfully tested, and the measurement results show the effect of phase jumps during the steering process. The second method extends the range of application to fast steering phased arrays by decoupling the antenna scan angle and the azimuth angle of the turntable.

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