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Jorge L. Salazar-Cerreno, Luis Felipe Moncada, Edgar Alexis Oblitas, Caleb Nelson, October 2024
This paper presents an overview of the induced ripples observed in the far-field antenna patterns of the Antenna Under Test (AUT) when measured with an open-ended waveguide antenna probe in a near-field planar system. The author hypothesized that induced ripples in far-field patterns are primarily originated by diffracted fields on the ground plane that supports the collar absorber. This study systematically evaluates the effects of absorber size and quality. Numerical simulations and experimental measurements are employed to validate the author’s hypothesis, providing insights into the relationships between these parameters and their influence on the induced ripples in far-field patterns. Results indicate that collar absorbers with reflectivity better than -30 dB are optimal for achieving accurate element characterization of phased array antennas.
Amedeo Capozzoli, Claudio Curcio, Angelo Liseno, October 2024
We address the generation of complex near-field (NF) wavefronts through a two-step process involving the determination of an equivalent radiating panel and its practical implementation as an array. Our novel approach discretizes 2D radiating panels using an optimized, nonuniform 2D quadrature rule. The optimized quadrature nodes determine the array element locations, while the excitation coefficients are obtained using the Singular Value Decomposition (SVD). Numerical results demonstrate the effectiveness of the method in accurately generating NF waveforms.
Eros Ciccarelli, Florindo Bevilacqua, Amedeo Capozzoli, Claudio Curcio, Angelo Liseno, October 2024
We discuss an approach to represent the electromagnetic field radiated/scattered by oblong objects. The field representation exploits Vector Prolate Spheroidal Wave Functions (VPSWFs) which are computed by a stable and accurate numerical scheme and take into account the a priori information about the geometry of the radiator/scatterer.
The presented numerical results highlight the satisfactory accuracy and the convenience of the approach against the classical representation by spherical harmonics.
Domenic Belgiovane, Justin Dobbins, Afifeh Khatabi, Andrea Giacomini, Francesco Saccardi, Lars J. Foged, October 2024
This is a continuation of the work presented at the AMTA 2022 symposium to assess the accuracy of on-axis antenna gain with commercially available computational electromagnetic (CEM) solvers [1]. Common practice for computing antenna gain normalization via the gain-transfer technique is to use the on-axis NRL gain curve of a pyramidal standard gain horn (SGH) derived by Schelkunoff and Slayton [2], [3]. Due to approximations in this formulation, Slayton assessed an uncertainty of ±0.3 dB for typical SGHs operating above 2.6 GHz. Since this uncertainty term is often one of the largest terms in the range measurement uncertainty budget for AUT gain, it is highly desirable to reduce it. Many studies in the past have attempted to improve upon Slayton’s expressions for SGH gain, but none have achieved widespread use. The previous investigation demonstrated the use of several commercially available solvers, including HFSSTM, CST Studio Suite®, and FEKO® to model the on-axis directivity and gain of a commercial off-the-shelf (COTS) X-band SGH [1]. In that work, the CEM simulation results from multiple solvers in HFSSTM, CST Studio Suite®, and FEKO® are shown to be within ±0.0075 dB of each other. This work is an extension to study how closely the simulation models match recent measurements of gain for the same MVG SGH820 horn discussed in previous paper. These measured and modeled results are compared with the international intercomparison results of a similar SGH [4], in conjunction with a best-estimated simulation model of the original dimensions from [4]. To capture the differences of the physical as-built antenna versus the simulation model, a simple tolerance study in simulation is performed based on the build tolerances of the antenna to provide an uncertainty estimate of the simulation results.
For many applications, one needs to know the accurate in-situ response of complex antennas mounted on complex platforms. To accomplish this objective, modern numerical EM simulation software apply the equivalence theorem and Huygens' principle to construct equivalent electrical and magnetic sources within an arbitrarily chosen antenna volume from measured antenna data on a finite ground plane. These sources are then used to perform on-platform simulations to estimate in-situ antenna performance. However, these measured far-field data are often contaminated by additional scattering from the ground plane. This paper studies the application and effectiveness of a processing method for removing such contaminations directly from the far- filed data by employing spherical wave modes filtering. A simple patch antenna and an array of patch antennas tuned to 1.575 GHz are used for this study. A full-size simplified C-12J Huron aircraft model is used as the target platform. The performance of the proposed method is compared against the reference gain pattern data obtained from directly solving the method of moments (MoM) integral equations (HFSS-IE) with antennas mounted on the target platform.
We present on a novel gain extrapolation antenna range, the Compact Homodyne Extrapolation System (CHEXS), that can achieve absolute antenna gain measurements with uncertainties of +/-0.1 dB or better with as few at 10 data points and is significantly more compact, up to six times shorter than conventional gain extrapolation ranges. This compact gain extrapolation range achieves these beneficial attributes by measuring the homodyne signal that occurs naturally between two directional antennas that often exhibit strong third order mutual coupling at close proximity. The design and operation of the CHEXS is presented along with gain measurements of NIST reference standard gain antennas which are shown to be equivalent to those obtained using a conventional gain extrapolation range.
Satoru Kurokawa, Michitaka Ameya, Masanobu Hirose, October 2024
We have newly developed a millimeter-wave vector measurement system for an oscillator-integrated antenna using a time-domain measurement setup. The measurement system consists of two mixers, one for the antenna pattern measurement and one for the phase reference measurement. In this paper, we show the developed W-band millimeter-wave measurement system configuration. In addition, we show the measurement results in the time domain and the estimated magnitude and phase in the frequency domain for a FMCW automotive collision detection radar.
The extrapolation method is widely used for antenna absolute far field gain calibration. The technique involves measuring responses between precisely aligned antenna pairs across varying distances. Previous studies have suggested that how one measures the separation distance—whether from aperture face to face or from phase center to phase center—doesn't influence the resulting far-field gain. However, our present study demonstrates that this assumption is incorrect. The choice of reference points for measuring separation distance can indeed impact the computed far-field gains. Our investigation shows that using the distance from the phase centers provides the most accurate far-field gain. Through numerical experiments and measurement data, we illustrate the discrepancies in the far-field gains caused by different distance definitions. Since the phase center of the antenna under test is usually unknown in practice, finding the phase center separation distances to apply to the extrapolation calculation isn't straightforward. To address this, we introduce a novel searching algorithm that varies an offset distance during polynomial fitting. This generates various convergence curves with different trends and rates, allowing for the accurate determination of phase center separation distances. The proposed algorithm not only enhances the accuracy of the antenna gain extrapolation method but also provides the phase center information of the antenna under test, all without requiring additional measurements.
Edgar Alexis Oblitas, Jorge L. Salazar-Cerreno, October 2024
This paper presents a novel design for a multi-probe antenna array for continuous measurement in a planar near- field system. This design reduces scanning time while maintaining accuracy compared to conventional methods used in near-field planar systems. The work introduces the design of the irregular probe array and discusses its trade-offs and functionality. It includes a comparison of the results from the two methods mentioned and analyzes the time durations associated with each approach. Additionally, the paper provides projections based on previous data to estimate scan durations for a large number of sampling points, considering the impact of the velocity of the linear positioners.
This paper presents the design, simulation, and experimental validation of a compact full-polarimetric antenna module for short-range radar sensors. Existing radar modules often use same-polarized antennas, potentially missing cross-polarized signals. While polarimetric radar systems offer superior polarization diversity, they are typically costly and complex. Research on radar polarimetry for short-range radar sensors is limited, and a compact antenna design is desirable for seamless integration and flexible placement in modern sensors. Additionally, collecting full-polarimetric data with a small sensor is crucial for developing realistic channel model tailored to short-range sensors. Developing a radar sensor with full-polarimetric operation is challenging due to size limitations and design complexity. This study introduces a 24-GHz full-polarimetric radar system utilizing a novel compact antenna module that captures both co- and cross-polarized signals. The well-designed antenna module, combined with generalized calibration techniques (GCT) demostrated outstanding performance in simulations and experimental validation. Both results closely aligned with ideal target scattering matrices. The proposed module's accuracy and reliability were confirmed through the successful characterization of various targets. These findings highlight the potential of the proposed antenna module for advanced radar sensors applications.
Luis Felipe Moncada, Jorge L. Salazar-Cerreno, October 2024
This paper presents an analysis of the truncation errors of co-pol and cross-pol data by comparing a far-field pattern obtained from simulation, with different patterns obtained from the near-field to far-field transformation for different scan area sizes. It is shown how these errors are reduced when the scan area is larger, the reason being that more significant fields are being captured by the probe; however, the improvement comes at the expense of longer measurement time. From this problem, a new method is proposed where the system makes sure to measure all the significant fields and avoid the insignificant ones, reducing the measurement time and increasing the accuracy.
B. Ohana, Z. Menachem, Amir Gamliel, M. Haridim, October 2024
The feasibility and radiation properties of the nullifier-based monopole array antenna are studied and analyzed. Since this antenna does not require grounding, arrays of this antenna are less prone to mutual coupling, at least to the part stemming from mixing currents in a common ground plane. Simulations results for the performance of a 2-element array of the nullifier-based monopole antenna and the mutual coupling between the elements are presented and compared with those of a similar array of conventional monopole. The proposed array of nullifier-based monopole can be used in wireless communication systems such as RADAR and IoT applications.
Industrial robotic arms offering high speed, precise positioning repeatability, and a high degree of freedom in motion, are an attractive alternative positioning solution for supporting a wide variety of scan geometries using a single antenna measurement system. For multi-function and production antenna measurement applications, this makes them a cost-effective solution compared to custom designed positioner stack-ups. However, motion is not the only consideration when implementing a multi-functional measurement system. The RF system design needs to be equally flexible to accommodate different measurement topologies and operating modes. Ideally, the solution should be flexible enough to also provide a clear upgrade path to accommodate future requirements. This paper discusses the use of commercial modular multi-port Vector Network Analyzer products in the implementation of a distributed RF system for a 14-axis robotic antenna measurement system that supports multiple antenna measurement geometries with minimal manual reconfiguration. This novel RF system design has the capability of simultaneously measuring multiple antenna test ports and can be easily reconfigured to support a variety of measurement configurations and other applications.
Cosme Culotta-López, Snorre Skeidsvoll, Andrian Buchi, Joakim Espeland, October 2022
Unmanned aerial systems (UASs) enable the in situ diagnostic of antennas operated in outdoor environments. Additionally, their flexibility introduces the possibility of performing several diagnostic methods. In this overview work, the challenges of performing outdoor measurements with UASs are discussed and some of the possibilities they introduce are outlined.
The main diagnostics tool when performing outdoor far-field measurements with UASs is the so-called raster scan. This is the two-dimensional scanning of a limited portion of the measurement sphere about the main lobe. From the information raster scans provide, it is possible to retrieve antenna parameters critical for the deployment of large antennas, such as the Side Lobe Level (SLL) in all directions, as well as the First Null Level. Additionally, assuming a fine scan, i.e., sufficient resolution, the interpolation of any 1D cut for diagnostics is possible. Once a problematic cut is interpolated and assessed, it can be measured using the UASs and increasing the measured angular range for further assessment.
Assuming the measured large antennas are reflector antennas, the finding of a higher-than-expected SLL may point to a problem with the positioning of the feed. Measuring with UASs allows for an iterative measurement-and-adjustment process directly in situ, which guarantees that the antenna’s performance is within the boundaries required by either the application or regulations.
Additionally, the flexibility of UASs provide further advantages, such as the assessment of the impact of environmental reflections in the radiation characteristics by flying along the radial component of the measurement sphere and assessing the measured ripple, using a method similar to the Voltage Standing Wave Ratio (VSWR) method used for the characterization of anechoic chambers. With this technique, the impact of the environment of candidates for an antenna deployment site can be assessed before the antennas are installed, thus supporting the choice process, and reducing the risk of malfunction.
The discussion of the introduced techniques is supported by measurements, and future possibilities and advantages are studied.
Andrea Giacomini, Domenic Belgiovane, Justin Dobbins, Francesco Saccardi, Lars Foged, October 2022
When using the gain substitution method with a pyramidal standard gain horn (SGH), it is common practice to use the on-axis NRL gain curves derived by Schelkunoff and Slayton [1]. Due to approximations in this formulation, Slayton assessed an uncertainty of ±0.3 dB for typical SGHs operating above 2.6 GHz. Since this uncertainty term is often one of the largest terms in the range measurement uncertainty budget for AUT gain, it is highly desirable to reduce it. Many studies in the past have attempted to improve upon Slayton’s expressions for SGH gain, but none have achieved widespread use. With the advent of high-performance computing (HPC), antenna simulations with computational electromagnetic (CEM) full-wave solvers are now capable of solving complex, electrically large models with high accuracy. This paper investigates the use of several commercially available solvers, including HFSS, CST, and FEKO to model the on-axis directivity and gain of a commercial off-the-shelf (COTS) X-band SGH. Relevant modeling techniques are described in detail and are shown to employ best practices as well as conformance with the IEEE 1597.1 and 1597.2 “Standards for Validation of CEM Modeling and Simulations” and “Recommended Practice for Validation of CEM Computer Modeling and Simulations,” respectively. The challenges and trade-offs of each CEM solving technique used, as well as their limitations, are discussed. Simulation errors are quantified via the IEEE standards, and other practical limitations of SGH manufacturability and measurement are discussed. Finally, the results from the CEM simulations are compared with the NRL gain curve and measured on-axis directivity and gain of the COTS SGH. Based on the compiled results of multiple simulations and measurements, this simulation methodology could be applied to other models of COTS SGH antennas to provide more accurate on-axis gain predictions.
[1] W. T. Slayton, “Design and calibration of microwave antenna gain standards,” US Naval Res. Lab., Washington, DC, Rep. 4433, Nov. 1954.
Recent papers have addressed making far field measurements at much less than the traditional far field distance, particularly for 5G MIMO test articles. These papers have focused on main beam measurements only, such as Total Radiated Power (TRP) and have stated that other normal antenna pattern metrics, such side lobe level measurements are not appropriate for this shortened distance. These papers have addressed fixed error levels acceptable for this quasi far field technique. This paper will present a sliding scale of main beam error versus measurement distance that can provide a more precise evaluation for the practitioner on selecting this technique. In addition, the paper will present a trade study in terms of chamber size, measurement durations and measurement methods between the quasi far field, compact range, and spherical near-field approaches. This trade study will cover three representative test articles in the C, Ka, and V frequency bands for 5G applications. A case study for a particular test article will provide an evaluation example.
Christopher Howard, Kenneth Allen, Bill Hunt, October 2022
The precise characterization of the complex permittivity, particularly loss tangent, in low-loss dielectric samples at microwave frequencies usually employs resonant cavity methods, where the quality factor of some resonance is determined by a precisely dimensioned sample of the material placed inside the cavity. In order to characterize materials over a broad set of frequencies, a separate measurement fixture and sample is required for each frequency, a tedious and expensive endeavor. In response, one may turn to a single broadband measurement system, such as the focused beam system, but simple transmission and reflection measurements suffer from poor loss tangent sensitivity. In this work, a hybrid approach is investigated whereby a highly resonant periodic metallic array adjoined to a dielectric sample is measured in a broadband focused beam system. A frequency selective surface (FSS) is designed to be placed against a planar dielectric sample to create a transmission or reflection response that is sensitive to the loss tangent of the material under test. This sandwiched structure is illuminated by the focused beam system to approximate plane-wave-like incidence, and scattering parameters measured. It is shown that the magnitude of response at the resonant frequency is linearly dependent on the loss tangent of the material under test for a certain range of loss tangents, and sources of error that limit sensitivity at lower loss tangents are explored. The effect of various FSS design parameters on loss tangent sensitivity is investigated, including sample thickness, FSS substrate thickness and complex permittivity, and FSS element pattern. Techniques for extracting complex permittivity from the scattering parameters of the focused beam measurement are presented, along with measured permittivity data from the FSS against a variety of well-known materials.
Van Atta Arrays are antennas with uniquely configured beamforming networks (BFNs) that allow for innate retrodirection of incident signals. While useful for a range of applications, their characterization has typically necessitated the use of radar crosssection (RCS) ranges. Our work proposes an alternate method that uses conventional array characterization, specifically element patterns and scattering matrix measurements, to synthesize both bistatic and monostatic RCS patterns for Van Atta arrays. This method is demonstrated theoretically and experimentally first with a cross-polarized dipole array followed by a counterwound octafilar helix antenna array. The benefits of the proposed synthesis method include fast design studies and trades of the Van Atta BFN enabling retrodirective operation. Among other things, this allows for broader access to experimental research on this topic. The significance of the structural radar cross-section is also discussed.
Nicolas Mezieres, Benjamin Fuchs, Michael Mattes, October 2021
The characterization of the radiation performances is a necessary step in the conception of any wireless system. These systems require always more demanding radiation performances that calls for time consuming characterizations. This duration can be reduced by the decrease of the number of field samples. By enclosing the antenna in a Huygens’ surface, we can build a radiation matrix that maps equivalent surface currents to the radiated field. A singular value decomposition of this matrix enables to build a compressed representation of the antenna measurement and more specifically a reduced basis of the radiated fields. By harnessing the outer dimensions of the antenna, the number of field samples can be reduced as compared to spherical wave expansion techniques. This number is shown to be connected to the area of the convex equivalent surface enclosing the AUT, as hinted by previous analytical works for canonical enclosing surfaces. The whole antenna characterization procedure is validated by simulations and experiments.
Bj”rn M”hring,Bernd Gabler,Markus Limbach, November 2020
Antenna placement or antenna in-situ performance analysis on large and complex platforms such as ships, airplanes, satellites, space shuttles, or cars has become even more and more important over the years. We present a systematic investigation of different antenna types for space applications in G- and S-band on an experimental aircraft. In this process, the individual antennas are measured with the help of a dual reflector compact antenna test range (CATR) under far-field conditions in various configurations. These results are validated and compared utilizing a finite element method (FEM) based solver simulation model. At first, the antennas are simulated and measured alone without any supporting or mounting structure. Subsequently, the effect of mounting structures on the overall radiation performance is added by analyzing the antennas over a large conducting ground plane, on top and the side of winglets, and on top of a cylinder body with dimensions on the order of the actual aircraft. For the detailed in-situ investigations, a second method of moments (MoM) based simulation tool is employed which works on measured sources. These measured sources are obtained from the CATR measurements of the isolated antennas. By means of a spherical wave expansion (SWE), they are transformed into a near-field source for the simulation model. These measured data based results are again compared and validated with the full FEM simulation for the complete aircraft setup and the simplified cylinder body. By this means, the expensive design and measurement of a full-scale electromagnetically equivalent mock-up of the aircraft could be saved. Furthermore, the pure simulation of the installed antenna performance often suffers from the limited availability of exact antenna design parameters. In some cases, the antenna design data remains undisclosed deliberately due to IP reasons. The presented results reveal the influence of physical structure on the radiation characteristics and demonstrate the benefits of working with measured data in simulation tools.
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