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Compact Range

Stepped-Frequency CW RCS measurement in Semi-Anechoic Chamber
Papa Ousmane Leye, David Martinez, Shaikha Aldhaheri, Chaouki Kasmi, Nicolas Mora, October 2022

The RCS of a target can be estimated using electromagnetic modeling if accurate geometries and material descriptions are available. An exact numerical calculation often requires prohibitive processing times. Moreover, numerical predictions with approximate techniques are difficult as it is challenging to consider all the physical phenomena. Therefore, a suitable RCS measurement facility adapted to the target size and specifications is required to estimate the RCS of a given target and to validate the numerical predictions. In general, the measurement of RCS takes place in anechoic chambers that simulate free-space and far-field conditions and where the unwanted reflections (walls, target mount, objects in the range, and the target interactions) are reduced. This paper presents a broadband measurement and validation of the RCS of a metallic trihedral corner reflector of 30 cm sides when fully anechoic conditions are not available, and consequently, some undesirable echoes are present in the measurements. Firstly, the measurement facility calibration and the target calibration are outlined. A single target reference approach is performed using a sphere as a reference, and its scattering response is shortly described. Then, the measurement of the target is performed. After these steps, a processing procedure is applied to isolate the target response from the background and the close responses due to unwanted reflections. The post-processing technique and the acquisition system are presented and discussed. The measurements are performed at X band as a function of the viewing angle for vertical transmit and receive polarization. To validate the technique, the RCS of the trihedral corner reflector is numerically simulated using the Integral Solver (I-Solver) of CST, with a Gaussian excitation, for vertical transmit and receive polarization. Measurements are compared with results obtained from CST software and show a good agreement with the numerical simulations. This setup will be used for RCS measurement of different complex targets and compared with measurements from other facilities to analyze and evaluate the RCS measurement uncertainty.

Acceleration of Over-The-Air Measurements Under Extreme Temperature Conditions Through Optimization of Air Flow and Thermal Efficiency
Benoit Derat, Ralf Meissner, Anes Belkacem, Guenter Pfeifer, Constantin Sinn, Markus Herbrig, Jose Fortes, October 2022

5G communications have supported the deployment of millimeter-wave beam-steering technologies at an unprecedented commercial scale. Mobile phones operating in frequency ranges above 20 GHz integrate antenna arrays and radiofrequency front-ends which control magnitudes and phases of signals to enable adaptive beam-steering. As per the 3GPP Test Specifications, a large number of tests covering the various operational modes of such devices are required in order to establish that the performance is adequate for guaranteeing the integrity of the mobile network. The defined measurement methodology relies on Over-The-Air (OTA) evaluations in Compact Antenna Test Ranges (CATR). As mobile wireless user equipment are practically utilized in diverse environmental conditions, a part of the test plan imposes spherical OTA measurements at extreme temperature conditions ranging from -10 to +55° C. Such temperatures indeed influence the active electronics in the device under test (DUT) and hence the beam-forming performance. This paper presents an innovative realization of a CATR with embedded thermal chamber supporting the above-described test capabilities. Inventive steps are introduced to solve the complex engineering problem of allowing fast temperature ramps to go through the complete range in a few minutes, while allowing two-axis rotations of the DUT, and all of this with preventing damages from the anechoic chamber and positioner and limiting the radiofrequency impact of the thermal testing chain. Thermal and air flow simulation and measurement results are presented, establishing how the design allows sustaining high pressure with low air leakage. Measurements of the quality of quiet zone with and without thermal enclosure demonstrate the limited RF impact of the introduced materials encapsulating the DUT. The derived solution is applied to measurements of a commercial 5G mobile phone, illustrating the influence of the environment on the DUT operation and corroborating the need for such test scenarii.

Electromagnetic Field Transformations of Near-Field Data Without Global Reference for Magnitude and Phase
Alexander Paulus, Jonas Kornprobst, Thomas Eibert, October 2022

Over the past decades, near-field (NF) measurements have been established as a reliable alternative to direct far-field (FF) or compact-range measurements for the verification of radiation properties of antennas. Quantities of interest typically include the FF characteristic obtained by means of an NF FF transformation (NFFFT), which is a computational post-processing step applied to the NF data. Common NFFFTs work with time-harmonic data and require the acquisition of magnitudes and phases of the NF samples with respect to a common reference signal. In other words, classical NFFFTs require the observed magnitude and the observed phase data to be drift-free during the time span of the complete measurement. With increasing measurement frequency and exposed or complex measurement setups in uncontrollable environments, e.g., as encountered in outdoor NF antenna measurements with unmanned aerial vehicles (UAVs), phase stability quickly becomes a limiting factor. Therefore, nonlinear phaseless NFFFTs have been developed that do not require any phase information, which, however, heavily rely on accurate and globally consistent magnitude information and are notorious for their unreliable behavior. Recently, a linearized and reliable NFFFT operating on locally consistent, i.e., relative, phase information has been reported. By using local phase differences within the NF data, the method becomes immune to phase drifts of the reference signal. However, in real-world measurements in uncontrolled environments, drifts in the measured power or magnitude may occur as well, e.g., caused by temperature variations during UAV flights, which render common phaseless NFFFTs useless. In particular, this prevents the use of the otherwise reliable linearized transformation. We investigate NFFFTs requiring a variable degree of global synchronization. In particular, a linearized transformation utilizing only relative, i.e., locally synchronized, information, both in magnitude and phase, is presented. It is shown that the transformation yields similarly accurate results as transformations employing global data, while being immune to magnitude and phase drifts. Furthermore, we compare the overall benignancy of a complete set of retrieval problems: completely phaseless, magnitudeless and mixed relative/global magnitudes and phases. Transformation results for simulation data illustrate the accuracy and suitability of the transformations with relative data, even for electrically large problems.

Analytical and Experimental Studies of Ground Reflections on Bi-static Radar Signal Propagation
Andreas Schwind, Isabella Varga, Willi Hofmann, Matthias Hein, October 2022

Progressing towards highly automated vehicles, radar systems have been developed into reliable assistance systems of environmental perception for a wide spectrum of mobile applications in air, on sea and rails, and especially on roads. This success as well as further improvements necessitate the precise characterization of radar objects with radar cross-section (RCS) measurements throughout the manifold parameter space, including frequency, aspect angles or even illumination and observation angles in bi-static radar constellations. According to the IEEE RCS standard 1502-2020, parasitic effects from ground reflections have to be taken into account in the test setup in almost all RCS measurement systems. In ground-plane ranges, multipath signal propagation is even considered intentionally. In this paper, the influence of ground reflections on bi-static radar measurements has been investigated both analytically and experimentally. A geometry-based analytical model was applied to calculate interference and the resulting small-scale fading of the electric field strength at the receiver. The geometry consists of independently arranged transmitter, receiver, and scatterer. The model includes antenna crosstalk, ground reflections for different relative heights of transmitter and receiver, and the scattered signal contributions. As a result, six paths are considered in terms of their time delays and phases, resulting from the classical two-way propagation model in a point-to-point link plus the four-way radar propagation model including ground reflections. The model yields interference gains between 0 and 4, where the maximum value is uniquely obtained at equal distances between transmitter and scatterer, and between scatterer and receiver, respectively. The variations of the bi-static angle lead to further fluctuations, which confirm to expectation and will be described in the full paper. The analytical model was validated with bi-static radar measurements in a semi-anechoic chamber with a metallic ground floor. As a canonical radar target, a metal sphere was measured in the frequency range between 1GHz and 10GHz at different heights and distances. The measurement results confirm the analytical model and provide the basis for further extensions of practical relevance, e.g., the reflectivity parameters of the ground (e.g., dry and wet road surfaces). Funded by: Federal Ministry of Education and Research (BMBF), grant number 16ME0164K

A Near to Far-Field Transformation with Planar Wide-Mesh Scan from Near-Field Measurements Affected by 3-D Probe Positioning Errors
Florindo Bevilacqua, Francesco D'Agostino, Flaminio Ferrara, Claudio Gennarelli, Rocco Guerriero, Massimo Migliozzi, October 2022

The near-to-far-field transformation (NTFFT) technique adopting the plane-rectangular (PR) scanning is the most simple one from the analytical and computational points of view and can be suitably employed when characterizing antennas which exhibit pencil beam radiation patterns. In recent years, NTFFTs using the nonconventional planar wide-mesh scanning (PWMS) have been developed. They allow a remarkable measurement time saving with respect to that adopting the classical PR scanning, since their raster grid is characterized by meshes which become larger and larger as their distance from the scanning plane center increases. These NTFFTs have been obtained by applying the non-redundant sampling representations of the electromagnetic fields to the voltage detected by the scanning probe and adopting suitable AUT modellings for volumetric and quasi-planar AUTs. The evaluation of the AUT far field is then got by applying the PR NTFFT, whose input data are accurately recovered through optimal sampling interpolation expansions from the collected PWMS samples. In both the conventional and non-conventional scannings, the sampling points are reached through an x-y scanner. However, the finite resolution of the probe positioners and/or their imprecise control can prevent to exactly collect the near-field samples at the prescribed sampling points and imperfections in the mechanical rails driving the motion of the probe can cause a deviation from the considered measurement plane. Accordingly, 3-D positioning errors, which can be revealed via laser interferometric techniques, affect the acquisition. The aim of this work is to develop an effective NTFFT with PWMS from 3-D probe positioning error affected near-field measurements. To this end, the so named k-correction (Joy and Wilson, AMTA Proceedings 1982) will be used to compensate the positioning error related to the deviation from the considered measurement plane. Then, an iterative procedure (D’Agostino et al., International Journal of Electronics and Communications 2020) will be applied to retrieve the near-field samples at the points specified by the non-redundant sampling representation from those obtained at the previous step and affected by 2-D positioning errors. Numerical tests will show the capability of the procedure to fully compensate the 3-D positioning errors affecting the acquisition of the PWMS samples.

Reduced Distance OTA Testing Methodologies for Automotive Applications
Alessandro Scannavini, Francesca Mioc, Francesco Saccardi, Kim Rutkowski, Lars Foged, October 2022

With the growing of vehicular communication technologies, the need for performing radiated measurements accounting for the full vehicle is becoming increasingly important. In modern cars, antennas are an integral part of the vehicle which is too complex to be represented by a simple ground plane during the tests. 5GAA test report [1] unifies measurement procedures for vehicle mounted antennas for both passive (at the antenna level) and Over-the-Air (OTA - at the modem level) measurements. Both Far-Field (FF) and Near-Field (NF) measurement systems are considered for testing of the full vehicle. In NF systems the radiated signals are measured on a closed surface at reduced distance, and a NF-to-FF transformation is applied. Since the transformation requires phase coherence between the transmitter and the receiver, NF systems are suited for passive tests. On the other hand, FF ranges are more suited for OTA tests, but requires large measurements distances, and hence expensive testing environments. OTA testing at reduced distances offers several advantage including the possibility to consider smaller and cost-effective anechoic chambers and the reduction of the system path losses (improved dynamic range). Moreover, the use of multi-probe systems dramatically reduces the testing time. The possibility of performing automotive OTA tests in spherical multiprobe systems at a reduced distance will be investigated in this paper. Simulations of a realistic vehicle with antennas installed in different locations will be considered to assess the uncertainty introduced by the reduced measurement distance. Figure of merits like different partial radiated powers [1] will be considered. Experimental automotive OTA measurements of a monopole-like antenna, installed on the roof of a vehicle will also be presented. These measurements have been performed at LTE bands in a spherical multiprobe system with a 4m radius. The measurements will be analysed comparing direct OTA measurement with a two-stage method, where passive antenna measurements and a few sampled OTA measurement points are combined. The outcome of the simulated analysis and experimental tests will be used to preliminary assess the uncertainty of automotive OTA measurements at reduced distance considering metrics relevant to automotive technologies [1].

Design and Verification of Innovative Wideband Spherical Near Field Probes with High Modal Purity
Andrea Giacomini, Vincenzo Schirosi, Francesco Saccardi, Lars Foged, Jean-Marc Baracco, Anders Jernberg, Kazi Alam, Joseph Byström, Dan Karlsson, October 2022

Measurements of modern multi-service antenna systems require ever increasing bandwidths of the measurement equipment. The main bandwidth limiting factor of traditional Spherical Near Field (SNF) systems is mainly the probe as it should radiate only first-order azimuthal spherical modes to apply the first-order Probe Compensation (PC). Even though full PC techniques are becoming standard, enabling the use wideband antennas with more than 10:1 bandwidth as probes, high-purity first-order probes are still required in many applications, because of the simplification of data processing and calibration. Conventional dual-polarized first-order probes are based on Ortho-Mode Junctions (OMJ) with externally balanced feeding. The OMJ is fully symmetrical using two pairs of excitation pins fed by high precision 3dB, 0º/180º hybrid couplers to achieve good matching and maximize the cx-polar performance. Unfortunately, realistic couplers provide some excitation errors which are one of the main contributors of the generation of unwanted higher order spherical modes. Even a small unbalancing in amplitude or phase of the coupler will excite higher order modes at frequencies where these modes are allowed to propagate. Beside the possibility to compensate the effect of the higher-order modes in post-processing (e.g. full PC), the propagation of the spurious spherical modes can be controlled directly on the probe with improved designs of the feeding mechanism or considering ad-hoc designed hybrid couplers. In this paper, two innovative and high performance SNF probes will be presented. Both probes are based on an inverted quad-ridge waveguide technology. An advanced feeding mechanism allows the first probe to provide a high modal purity in the 617-960 MHz band, rejecting errors introduced by the external coupler. In the second one, a highly accurate coupler has been designed to minimize the higher order modes on a large bandwidth, 1427-4200 MHz. The two probes have been designed as part of the upgrade of a gantry arm system used to test modern base station antennas. The same measurement system has been used to calibrate the two probes and to verify the expected performance both in terms of radiation pattern and spherical modal content. The achieved measurement results will be shown in this paper.

Reinstatement of the NIST Field Strength Probe Calibration Service
Matthew Simons, Christopher Parks, Vincent Neylon, Galen Koepke, Christopher Holloway, October 2022

The Field Strength Metrology Project at the National Institute of Standards and Technology (NIST) in Boulder, CO has restarted field probe calibration services from 10 kHz to 40 GHz, after a renovation of ouranechoic chamber. WhileNISThas long served as the nation’s link to the SI for radiated field measurements, in 2014, the anechoic chamber used for generating standard electromagnetic fields from 0.5 – 40 GHz was renovated. The positioning system was upgraded with a new rail, motion control, and a robotic arm. New absorber was installed in the main section of the chamber. During the renovation, Field Strength services were unavailable. In order to resume operation in the chamber, several tests were done to validate the chamber. We show the results of a thorough comparison of three facilities, the anechoic chamber, a TEM cell and a GTEM cell. Measurements of electric field probes in the new chamber were also compared with past measurements in the chamber before renovation. The Electromagnetic Field Strength special test services are now operational.

Three-Antenna Polarization Measurements Again
Ronald Wittmann, Michael Francis, David Novotny, Allen Newell, October 2022

This paper is an extension of a 2020 AMTA paper [1] in which we simulated (with added noise) an older, and seemingly forgotten, technique for processing three-antenna polarization data that employs well known signal processing methods. In this paper we analyze actual measured data. Topics to be explored include: (1) Time-domain gating to mitigate antenna-antenna multiple reflection and room-reflection error signals, (2) Bi-directional S-parameter measurements, (3) a scheme [2] (based on the geometric mean of the S-parameters S_pq and S_qp) to mitigate calibration drift errors, (4) Fourier filtering. We plan to demonstrate a robust method that is effective and easy to implement. [1] R. C. Wittmann and M. H. Francis, "Three Antenna Polarization Measurement Revisited," Proc. AMTA, Virtual, pp. 3–6, Nov. 2–5, 2020. [2] D. R. Novotny, A. J. Yuffa, R. C. Wittmann, M. H. Francis, and J. A. Gordon, "Some advantages of using bi-directional s-parameters in near-field measurements," Proc. AMTA, Williamsburg, VA, pp. 327–332, Nov. 4–9, 2018.

Diffraction from Rotatin Absorber Array and Field_Probe Using Long Vertical Objects
Pax Wei, October 2022

Abstract. In order to characterize the Boeing 9-77 compact range, the empty chamber background was measured as a function of frequency, polarization, and the azimuth angle of the upper turn-table (UTT). The results exhibited a diffraction pattern with enlarged hot-spots on a 4-fold symmetry [1]. A 2-D FFT on the diffraction pattern yielded a mapping on the relative arrangement of the very weak absorber tips on the UTT [2]. Here, we take a closer look at the scattering geometry of the UTT as illuminated by the residual field above and beyond the quiet zone (QZ). The different responses in VV and HH are discussed. The enhanced diffraction due to a “blazed grating” condition is identified and analyzed. Some interesting physics are discussed. An extended long object usually gives rise to a strong reflection (glint) when viewed near its surface normal. To take advantage of this phenomenon, a discrete Fourier transform (DFT) on RCS measurements taken within a small angular range would yield a spectrum of incident wave distribution along that object [3]. Some results along the horizontal direction have been reported [4]. As a complementary, we present and discuss the results in the vertical direction. References [1]. P. S. P. Wei, A. W. Reed, and C. N. Ericksen, “Radar cross section measurements amid interfering backgrounds,” Proc. 22nd AMTA, pp. 99-104 (2000). [2]. P. S. P. Wei, “Scattering of the residual field above and beyond the quiet zone of a compact range,” Proc. 35th AMTA, Columbus, OH (2013). [3]. P. S. P. Wei, “Measurements on long and rigid objects for radar field probes" Proc. 34th AMTA, pp. 195-200 (2012); Also in ACES Journal 28, 1228-1235 (2013). [4]. P. S. P. Wei, “Measurements on extended objects for radar field probes," Proc. 41st AMTA, pp. 199-204 (2019); Also presented at ICECOM-2019 (23rd International Conf. on Applied Electromagnetics & Communications), paper S_16_3, Dubrovnik, Croatia, Sept. 30, 2019.

A New Handheld Sensor for Measuring Intrinsic Dielectric Properties at 100 to 1000 MHz
John Schultz, Ren Geryak, October 2022

Electromagnetic materials characterization at UHF and VHF frequencies is typically done with laboratory fixtures such as the coaxial airline or rectangular waveguide. These conventional methods require material specimens to be cut or machined to precision tolerances for insertion within the transmission line fixture. Measurement accuracy dictates there should be little or no air gaps between the specimen and the transmission line walls. Transmission line methods also require significant handling and multi-step calibration procedures to characterize a material specimen. This paper describes a new handheld measurement device that overcomes these limitations with a simple calibration and non-destructive measurement procedures. This new method applies an open-ended stripline sensor tuned to maximize measurement sensitivity in the 100 to 1000 MHz range. The sensor footprint is approximately 100 mm square and utilizes an integrated one-port vector network analyzer. It operates by measuring the amplitude and phase of the reflection coefficient when placed adjacent to a material specimen. While traditional transmission line methods employ analytical expressions to relate scattering parameters to intrinsic properties, The open-ended stripline sensor geometry and its interaction with the material cannot be easily modeled with an analytical approximation. Instead, it is modeled with a full-wave Finite Difference Time Domain (FDTD) code to develop the relationship between measured reflection and complex permittivity. This inversion method precomputes a translation table by iteratively modeling the measurement fixture across a range of complex permittivities and specimen thicknesses. From this inversion database, interpolation is then used to calculate the frequency dependent complex permittivity or sheet impedance of a given specimen. This paper provides details about the calibration and use of this new device as well as the material property inversion algorithm. Measurement examples of low-loss and lossy materials as well as resistive sheets are also presented and compared to more conventional transmission line results, and are discussed in relationship to measurement uncertainties.

Determination of the Number of Valid Scan Pairs in a Multielement Waveguide Simulator
Collin Wallish, Dejan Filipovic, October 2022

Modern design of phased array apertures typically begins with unit-cell design relying on an extensive use of full-wave simulations. The waveguide simulator is an equivalent, experimental simulator that allows for measurement of the active impedance of radiating elements at a prescribed pair {frequency, scan angle} in an infinite array environment. Therefore, the waveguide simulator offers a means of real-world verification of a unit-cell design before proceeding with finite array design or realization. In its simplest form, the waveguide simulator is constructed through placing an element within the walls of a rectangular waveguide. The natural imaging of the waveguide walls acts to emulates an infinite array environment. The multielement waveguide simulator described first by Gustincic (J. J. Gustincic, IEEE Trans. Antennas Propagat., vol. 20, no. 5, pp. 589–595, 1972), allows for experimental determination of the active reflection coefficient of an embedded array element for a discrete set of scan conditions corresponding to a given waveguide mode excitation. Though the theory behind the waveguide simulator is well documented in the literature, there is scant discussion of the effect of configuration on the number of and distribution of valid scan pairs. The number of valid scan pairs is proportional to the number of modes that are excited within a waveguide, which is set by the element spacing and size of the waveguide. It is desirable, for a given number of elements constituting a waveguide simulator, to maximize the number of valid scan pairs and simultaneously the information content that can be obtained from a single experimental setup. The number of valid modes for a square waveguide with half-wavelength element spacing is found to reduce to the well known Gauss circle problem. For the general case in which the element spacings are arbitrary and the waveguide is rectangular the problem is reduced to Hardy’s generalization of the Gauss circle problem (G. H. Hardy, Proceedings of the Royal Society of London. vol. 107, (744), pp. 623-635, 1925). The herto unrecognized connection to an existing and widely developed mathematical theory gives insight into the fundamental sampling limitations of the waveguide simulator.

RCS Compact Range Focal Plane Array Antenna Feed Design Concept
William Carter, Jerry Jost, Gabriel M. Rebeiz, October 2022

Diagnostic and verification testing of Low Observable (LO) platforms and components requires an Ultra-Wideband (UWB) Inverse Synthetic Aperture Radar (ISAR) imaging capability. A Compact Range (CR) is a test instrument that, when fitted with an instrumentation radar and target positioner, can efficiently produce ISAR images and other Radar Cross Section (RCS) data products required for LO research, design and production programs. Key limiting factors for the instantaneous radar imaging bandwidth of a CR is the feed antenna, where the criteria of a good feed is frequency bandwidth and illumination pattern shape. Maintaining a relatively constant reflector illumination characteristic typically requires several feeds with constant patterns functioning over smaller operating bandwidths, to be mechanically sequenced in the measurements. These feed limitations increase operational costs and complexity for LO measurements, driving a need for improved illumination sources providing constant reflector illumination for UWB collections. Focal Plane Arrays (FPAs) can be utilized to resolve these issues while increasing instantaneous bandwidth and measurement quality while reducing operational costs. This paper presents a procedure for defining complex weights of an FPA aperture to optimize radiation pattern matching to the reflector. A simulated plane wave arriving from the CR quiet-zone impinges on a model of the reflector. The FPA is placed in a region near the focal point and contained within the beam waist envelope, and the FPA weights are computed using a Computed Electromagnetic (CEM) techniques. The computational complexity of CEM simulations of electrically large CRs are usually prohibitive, however this method exploits the large focal lengths of CRs to sparsely model reflectors, and produces a tractable solution even at millimeter wavelengths. Practical aspects of FPA designs are presented and discussed as applied to the large outdoor CR at the US Army, Electronic Proving Ground (EPG), Fort Huachuca, Arizona.

Initial Development of Low-cost Custom Spherical Measurement Range
Songyi Yen, Ljubodrag Boskovic, Dejan Filipovic, October 2022

Measurements of antenna prototypes are a critical component of the development cycle for antennas, arrays, and other radiating structures. Benchtop tests to characterize the circuit performance of such devices are generally available to engineers and scientists, but the ability to capture the space (radiating) characteristics is often lesser available. This is not only due to the need for a vector network analyzer but also the necessity for mechanical infrastructure to sample the fields in a scan volume around the antenna (i.e., antenna range). Moreover, the software capable of any data manipulation is needed to obtain the far-fields either directly or from the sampled near-fields. Herein, we describe the initial exploratory development of a low-cost, bench-top, custom spherical range. The system consists of a phi-stage turntable where the antenna under test (AUT) is mounted, a theta-stage swing arm that sweeps the probe antenna in an arc about the center of rotation, and a polarization stage turntable on the probe antenna side. An adjustable scan radius of 30-40 cm is built into the theta-stage. The bulk of the range is fabricated using standard fused deposition modeling (FDM) 3D printing and inexpensive commercial off-the-shelf (COTS) components are used for the motors and controllers to keep cost of the system (excluding the network analyzer and RF cables) to around 500 US dollars, in accordance with the restrictions for an advanced antennas course class project. Development, fabrication, and assembly took place over the course of approximately a month. The drawbacks of the utilized materials, however, primarily manifest in the oscillations of the theta-stage due to the low-infill ratio (~10%) of the 3D printed plastic in conjunction with the weight of the probe antenna. Additionally, a basic spherical near-field to far-field transform code is developed. The measurement results of a wideband horn antenna are performed to validate the range performance and will be shown and discussed at the conference. Thoughts on future development and potential are also shared.

RCS Calculations and Measurements of a Spherical Drone Based Calibration Device
Spencer Wallentine, CJ Reddy, Joel Cannon, R. Jerry Jost, October 2022

Ultra-Wideband (UWB) calibration of RCS measurement radar systems, particularly outdoor, ground-to-air dynamic signature measurement radars, are conventionally accomplished using calibration devices (CD) attached to static towers, tethered from balloons, dropped from helicopters or other air vehicles, or with active RF repeater systems. These methods all contain errors from background-target interactions, or are operationally compromised, or are expensive. For high accuracy RCS radar calibration, a revolutionary methodology and architecture is mandatory to support demanding new radar metrology requirements. Within this paper, an update of ongoing efforts toward developing an autonomous, airborne drone-based CD is provided. The radar reflectivity of such a device must have a highly reproducible RCS, as manifested by a narrow, well defined probability distribution function (PDF), and should be independent of viewing aspect. Computational electromagnetic simulations were used to predict the RCS of a 60.9-cm diameter autonomous Spherical Passive/Active Calibration Device (SPARCS) with periodic, hexagonal “honeycomb” electromagnetic screens for inlet/outlet ports of the propulsion system. Three methods were used to predict the RCS, including Large Element Physical Optics (LE-PO), Physical Optics (PO) and Method of Moments (MoM) using the Adaptive Cross-Approximation (MoM-ACA). All methods show reduced cross section at angles centered on the periodic hexagonal RF screens. LE-PO resulted in a 30-fold decrease in computational expense relative to PO, but had a higher standard deviation. MoM-ACA calculations are ~57-fold more computationally expensive than PO results, but provide the full wave solution. PDFs determined from UWB RCS measurements have a narrow distribution and show reasonable agreement with calculations. These results validate the RCS signatures of the autonomous, airborne, spherical CD incorporating inlet/outlet RF screens as a valid calibration target.

Synthesis of a Phased Array with Planar Near-Field Techniques Based on Far-Field Measurements of a Sub-Array in a CATR
Bernd Gabler, Diego Lorente, L.G.T. van de Coevering, October 2021

Phased array antennas are often built from sub-arrays with identical or symmetrical layout. At an early project stage, performance verification measurements of the sub-array are valuable to proof the single module design. However, the characteristics of the final antenna are questionable without further processing. This work presents a concept that is based on far-field measurements of a sub-array in a Compact Antenna Test Range (CATR) in conjunction with planar near-field (PNF) processing to synthesize the entire phased array antenna characteristics. The procedure is explained with an example of a dual linear polarized L-band planar phased array antenna for an airborne synthetic aperture radar application. It is shown that the measured sub-array can be complemented by the synthesized twin to evaluate the characteristics of a final antenna that is not yet available in this form. The resulting performance of the synthesized entire phased array is presented and compared with simulations. The presented post-processing method would be beneficial to characterizing radiation patterns of large phased arrays by measuring only sub-arrays in a limited test-zone with any measurement principle.

Genetic Evolution of the Reflector Edge Treatment of a Single Offset-Fed Compact Antenna Test Range for 5G New Radio Applications
M. Dirix, S.F. Gregson, R. R. Dubrovka, October 2021

While the size of the parabolic reflector in general determines the usable area of the quiet zone of a compact antenna test range (CATR) inside which a pseudo plane-wave condition is produced, the reflector edge treatment also plays a significant role in terms of overall quality and electromagnetic field distribution & uniformity, and especially so at mm-wave frequencies. Using modern powerful digital computational simulation technology in combination with genetic optimization, the edge treatment can be evolved for a specific CATR application as part of the design process. This is crucial as it attempts to maximize the performance of a given solution while ensuring efficient use of the available space which correspondingly provides an economical implementation. This is particularly important in 5G production test applications where, in many instances, multiple systems are required to be collocated within a given host building and in which case, the savings become multiplicative. In this paper the novel design methodology is introduced for the genetic optimization (GO) of blended rolled edge single offset reflector CATRs. Several edge blends and treatments are considered with the genetically optimized design parameter. For each variation the quiet-zone performances are compared and contrasted.

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.

Examining and Optimizing Compact Antenna Test Ranges for 5GNR OTA Massive MIMO Multi-User Test Applications
Stuart Gregson,Clive Parini, November 2020

Direct far-field (DFF) testing has become the standard test methodology for sub-6 GHz over the air (OTA) testing of the physical layer of radio access networks with the far-field multi-probe anechoic chamber (FF-MPAC) being widely utilized for the test and verification of massive multiple input multiple output (Massive MIMO) antennas when operating in the presence of several users. The utilization of mm-wave bands within the 5th generation new radio (5G NR) specification has necessitated that since the user equipment should, preferably, be placed in the far-field of the base transceiver station (BTS) antenna, excessively large FF-MPAC test ranges are required or, the user equipment is paced at range-lengths shorter than that suggested by the classical Rayleigh criteria or, a modified compact antenna test range geometry must be developed and utilized. This paper presents a novel design for a new compact antenna test range (CATR) design that uses a parabolic toroid as the main reflector. The folded optics utilized within this design possesses superior pseudo-plane wave scanning capabilities than those available from equivalent, classical, point source offset parabolic reflector CATR designs. This wide-angle scanning capability is a crucial feature for successful over-the-air testing and measurement of mm-wave 5G NR Massive Multiple Input Multiple Output (MIMO) antenna systems within multi-user applications providing 60 degrees of azimuth scan and 15 degrees of elevation scan to the incoming plane wave at the AUT. CATR quiet-zone results are presented, compared and contrasted with more classical designs before results of the effects of the CATR test channel on a number of commonly encountered communication system figures of merit in wide scanning cases are presented.

Spherical Test-Zone Field Measurements of a Compact Antenna Test Range
Thomas Gemmer,Dirk Heberling, November 2020

A method to solve the far-field distance problem is the usage of reflectors in order to transform the spherical wave from the feed antenna into a plane wave which ultimately leads to the same far-field condition but in a more compact way. Therefore, these facilities are called compact antenna test ranges (CATRs). However, the finite size of the reflector(s), despite edge treatment, is the main cause of erroneous signals impinging into the test zone in which an antenna under test (AUT) is characterized. Especially at lower frequencies, every further structure inside the test chamber, although covered with absorbers, is an additional source of scattered signals. One method of correcting stray signals and to improve the AUT measurement accuracy is to compensate the non-ideal test-zone field (TZF) via spherical wave expansion (SWE). For this technique, a complete description of the TZF, i.e. measurements on a closed surface around the test zone, is required. The most convenient approach is to use a spherical scanning surface. In ranges with a roll-over-azimuth positioning system, the spherical scanning can be realized by an additional measurement arm. Using the chamber positioning system, thus, strongly reduces the required additional hardware and makes spherical scanning of the test zone a practical approach. With the knowledge of the incident unwanted field components, AUT measurements carried out in the corresponding test zone are correctable. Spherical near-field measurements of the test zone created by the CATR installed at the Institute of High Frequency Technology, RWTH Aachen University are performed at a frequency of 2.4 GHz using a simple scanning arm. Reliability of the results is ensured by comparing the measurements to full-wave simulations of the CATR. The radiation pattern of a base transceiver station antenna serves as a test case and is subsequently corrected for the erroneous signals using the SWE.
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