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Larger low-observable targets are being mounted onto RCS pylons. In many cases not only Azimuth rotation of the target, but a degree of movement in elevation is desired. This requires in many cases a large number of positioning cables to run from the base of the pylon to the tip where the rotator is placed. At the same time the low-observable qualities of the target call for pylon ogives with higher ratios to minimize the background RCS of the pylon that supports the target. The higher ratios call for very thin structures that cannot handle the weight of the rotator or have not enough space for the control and power cable to be fed to the rotator. A way of solving this problem is to have a variable ratio pylon, where the ogive at the tip is different from the ogive on the main body of the pylon. To analyze these pylons a higher-order basis-function method of moments (HOBFMoM) approach has been used in the past [1]. To conform the quadrilateral flat patches to the round geometry of the pylon, patches smaller than 0.3λ were used. While this was still an advantage over the typical 0.1to 0.05λ patches it placed limits on the highest frequencies that could be analyzed give the available computational resources. In this paper the authors present an approach to the meshing of the structure that allows for computing the monostatic RCS at frequencies in the x-band for a 2.4 m tall pylon. In addition, the effects of the non- physical absorber terminations are further analyzed.
In this paper we introduce a novel technique for the efficient production test and measurement of 5G, Massive MIMO array antennas for the purpose of verification, diagnostics, and fault detection that drastically reduces the number of measurements required and the associated acquisition time needed. The technique utilises compressive sensing and sparse sampling combined with a total variation measurement approach that enforces the requisite sparsity on the problem. In this paper, we compare this new spherical near-field total-variation based acquisition approach with the authors existing, analogous, planar technique. Extensive performance comparisons are presented which aggregate results across many test cases which is a necessity, and a consequence of the statistical nature of the compressive sensing technique that is imposed by virtue of the requirements of the Restricted Isometry Property (RIP). Crucially, this paper identifies and addresses a fundamental flaw within the application of many total-variation based methods and especially when used with the difference field between a reference antenna and a production test antenna. This extends the use of a novel analysis process that incorporates an l0 based minimisation strategy to overcome this problem thereby restoring the CS process to very nearly the levels of performance attained in our prior work.
Planar near-field (PNF) acquisition always samples a limited or truncated subset of the infinite plane in front of an antenna under test (AUT). That truncation of the sampled field has two primary impacts: Power radiating to or from angles beyond the probing boundary is not fully captured and thus not included and erroneous ripple is injected throughout the pattern when the transformation algorithm sees by default a sudden drop to zero power beyond that boundary. The topic of truncation mitigation in the PNF geometry has been addressed with a variety of algorithms. This paper introduces a new algorithm that is similar to, yet distinct from, some that have come before. The new algorithm makes use of the recently introduced holographic PNF filter [1][2][3], treating the truncation effects like stray signals. Where the most common technique [2][4] uses the known planar-AUT bounds (2D) and a computed “valid region” of the plane-wave spectrum as truth through iterative transformations, this algorithm treats as truth the known AUT volume (3D) and the measured PNF data. The new algorithm is evaluated herein by retruncating a large set of measured PNF data.
The impact of receiver internal leakage on planar near-field measurement uncertainty is significantly influenced by the selection of near-field parameters. Understanding how specific scan parameters affect the far-field leakage level is essential for effective mitigation. This paper establishes quantitative relationships between near-field parameters and the far-field peak amplitudes of both leakage and the antenna under test (AUT), as well as the mean noise level in the far-field pattern, based on empirical results. Systematic scans were performed by altering only one or two specified near-field setup parameters per measurement, and graphical comparisons are provided. Practical approaches for mitigating receiver leakage are demonstrated through a case study involving receiver leakage on a planar scanner with a maximum scan area of 3.6 m x 3.6 m (12 ft x 12 ft). Additionally, a method for estimating the far-field receiver leakage level relative to the beam peak is discussed.
In this work, an effective procedure to compensate for 3-D mispositioning errors of the probe, occurring when characterizing a long antenna through a non-redundant (NR) near to far-field (NTFF) transformation with helicoidal scan, is developed. The pro- posed technique involves two steps. The former allows the correction of the mispositioning errors, caused by the deviation of each sampling point from the nominal measurement cylindrical surface, using a phase correction technique called Cylindrical Wave correction. The latter restores the samples at the sampling points required by the NR representation along the scan helix from the previous ones affected by 2-D mispositioning errors, via an iterative scheme. Finally, the compensated near-field samples are effectively interpolated via an optimal sampling interpolation (OSI) formula to accurately recover the input data required to perform the traditional cylindrical NTFF transformation. The OSI representation is here developed by assuming a long antenna under test as enclosed in a cylinder terminated by two half spheres (rounded cylinder), in order to make the representation effectively non-redundant. Numerical results, assessing the effectiveness of the proposed technique, are reported.
In this work, an efficient two-step algorithm to compensate for 3-D probe positioning errors, which occur in a near-field–far-field transformation (NF–FFT) using a minimum number of spherical NF measurements, is developed and numerically assessed. Firstly, a so called spherical wave correction is exploited to correct the phase shifts caused by the deviations from the nominal spherical surface. Then, an iterative technique is employed to recover the NF samples at the exact sampling points from those, altered by 2-D mispositioning errors, attained at the previous step. Once the correctly positioned samples have been retrieved in such a way, an optimal sampling interpolation formula is used to accurately determine the massive input NF data for the classical spherical NF–FFT. Numerical tests will be shown to prove the capacity of the devised method to correct even severe 3-D positioning errors.
The objective of this paper is to provide some guidelines about the measurement uncertainty of Spherical Near Field (SNF) ranges when they are used to derive near field figure of merits instead of more conventional far field-based metrics. One of the main advantages of the SNF ranges is their flexibility. Indeed, from the NF scanning, the spherical wave expansion is applied, and it can be used as a powerful, accurate and efficient propagation tool, able to evaluate figures of merits at (almost) any distance from the device under test. This feature is particularly useful in the testing of modern antenna systems intended to operate in specific regions of space instead of conventional far field scenarios. Examples are Plane Wave Generators (PWG) which create a uniform field distribution in the proximity of the device, or more generic field synthesizer devices. Despite the flexibility of SNF systems, the evaluation of their uncertainty budgets is normally limited to far field-based metrics. Understanding under which conditions and in which measurement scenarios such uncertainty budgets are applicable to more generic near field metrics is the main topic addressed in this paper.
One of the major contributions to the measurement uncertainty of antenna measurements are multiple reflections between antenna under test (AUT) and probe antenna. In the case of spherical near-field (SNF) measurements, multiple reflections are typically estimated and compensated for by conducting full SNF measurements at different radii and averaging the transformed far-field results. However, the need for several measurements leads to a multiplication of the measurement duration, and subsequently to an increase in costs. Another option is to increase the measurement radius, which might not be possible depending on the positioning equipment. Therefore, a technique to reduce multiple reflections between AUT and probe antenna by intentionally tilting the latter is presented. The technique is evaluated with a robotic antenna measurement system, the flexibility of which allows to almost arbitrarily tilt the probe antenna and perform a spherical measurement in this tilted configuration. It is shown that the magnitude of the reflections can be reduced significantly with this approach, even for small tilt angles. A comparison with the conventional averaging technique indicates that the presented approach reduces the error to a similar level, but at a fraction of the measurement time.
Classic methods for extracting material characteristics typically demand rigorous calibration, multiple samples, precise location measurements, etc. A recent research effort led by Zhao Caijun, Jiang Quanxing, and Jing Shenhui utilized a simple transmission/reflection method to extract high accuracy permittivity results from a Coaxial Line system. This method uses two uncalibrated scattering parameter measurements: one of the empty fixture and one of the sample at a single position. This paper extends the method to produce accurate permittivity results from a Rectangular Waveguide system once corrected for detector mismatch.
Spherical Near-Field antenna measurements are broadly used for vehicular measurements, which almost always include several antennas. Due to the large size of vehicles and the reduced size of near-field ranges, it is often impossible to displace the vehicle so that the desired Antenna Under Test (AUT) be in the center of the measurement sphere - and when it is possible, it is highly impractical to repeatably displace the vehicle for each of the antennas. Nevertheless, it is often required to retrieve the radiation characteristics of the AUT as if it were centered. In this work, Parallax-based methods for the correction of near-field acquired data are discussed, and a novel method based on the correction of the probe’s relative view angle and distance to the offset AUT is introduced. This method, additionally, does not require any matrix (pseudo)inversion for the calculation of the Spherical Wave Coefficients (SWCs) and can be solved with classical FFT-based Near-Field-to-Far-Field Transformations (NFFFT) based on the Wacker transmission formula.
Transceiver satellites with a ”bent-pipe” payload are commonly used in communication systems. Accuracy of measurement of their main End-to-End (E2E) parameters, such as Saturating Flux Density (SFD), Gain flatness (G/F), Equivalent Isotropic Radiated Power (EIRP) and Gain over Temperature (G/T) depends not only on the test setup, but also on the accessibility of different test points in the payload. In this work, we focus on the error budget for different accessibility levels when the payload is tested in Planar Near-Field (PNF).
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.
In the 2013 revision of the IEEE Standard for Definitions of Terms for Antennas [1], multiple new terms were added to describe active antenna systems. One such term is receiving efficiency, which was added to describe the behavior of either a passive receiving antenna or an active receiving antenna system. The definition of receiving efficiency contains other new terms such as isotropic noise response and isotropic noise response of a noiseless antenna. These new terms and definitions may cause some confusion for individuals responsible for antenna design and measurement. We attempt to demystify a few of the terms added to IEEE Std 145-2013, especially those terms that relate to receiving efficiency. In addition, we propose a measurement technique for measuring the receiving efficiency of an active receiving antenna system.
After a five-year renovation of the National Institute of Standards and Technology (NIST) Boulder, CO, antenna measurement facility, the Antenna On-Axis Gain and Polarization Measurements Service SKU63100S was reinstated with the Bureau International des Poids et Mesures (BIPM). In addition to an overhaul of the antenna facility, the process of reinstatement involved a comprehensive measurement campaign of multiple international check-standard antennas over multiple frequency bands spanning 8 GHz to 110 GHz. Through the measurement campaign, equivalency with 16 National Metrology Institutes (NMIs) and continuity to several decades of antenna gain values was demonstrated. The renovation process, which included implementing new robotic antenna measurement systems, control software, and data processing tools is discussed. Equivalency results and uncertainties are presented and compared to checkstandard historical values.
This paper presents a new test procedure to asses and validate key performance indicators for NGSO antennas, and serves to introduce said methodology to the antenna measurement community to foster a discussion on future evaluation procedures for modern day ground segments. Beyond introducing the proposed test methodology we also present results highlighting the actual accuracy of a UAV based measurement system enabling the proposed measurement procedure. The paper is intended to be viewed as an initial proposal for a qualification methodology.
This paper extends the time-domain gated response isolation scheme for full polarimetric calibration with a modified Thru-Reflect-Match procedure for network analyzer selfcalibration where precise knowledge of the metrology standards is not required. Cross-polarization contributions from the measurement setup are neglected to simplify the procedure. A simulated cascade analysis is included to demonstrate the relative scattering parameter error of the sample under test when the measurement setup cross-polarization level is neglected. The featured calibration analysis leverages a 4x4 scattering parameter matrix notation to capture the polarimetric scattering at each cascaded stage and develops a 16-term error correction factor model to account for cross-polarization scattering contributions from the measurement sample. Finally, a wire-grid polarizer is used as a modified Match standard where a series of interrogations at multiples orientations, in combination with Thru and Reflect measurements, enables cross-polarized scattering channels to be characterized. This polarimetric self-calibration approach uses physically realizable metrology standards and accounts for all error terms for precision focus beam system measurements.
The IEEE Std 1720™, "Recommended Practice for Near-Field Antenna Measurements," serves as a dedicated guideline for conducting near-field (NF) antenna measurements [1]. It serves as a valuable companion to IEEE Std 149-2021™, "IEEE Recommended Practice for Antenna Measurements," which outlines general procedures for antenna measurements [2]. IEEE Std 1720 was originally approved in 2012 as a completely new standard by the IEEE Standards Association Standards Board. It holds significant importance for users engaged in NF antenna measurements and contributes to the design and evaluation of NF antenna measurement facilities. With its tenyear term coming to an end in 2022, the standard will no longer remain active. Nonetheless, a "minor revision" of the existing standard is in progress and is expected to be completed in 2023. The objective of this paper is to provide insights into the ongoing activities surrounding the revision and to explore the proposed changes. It aims to facilitate a discussion on the modifications to and their implications for modern NF antenna measurements.
The reflectivity of foam absorber materials is governed by the correct loading and mixture of carbon and other supplicants such as fire retardants. In order to assess the reflectivity of the absorbers various measurement setups are applied, each having different advantages and disadvantages in terms of frequency coverage and RF performance. The measurement setups are used both in the quality control (QC) as well as for product development. Especially for the product development case, it is important to understand limits of these setups as the lower the reflectivity gets, the more difficult it becomes to detect minute differences between different variants of the absorbers. For reflectivity measurements of microwave absorbers, the available dynamic range and calibration-quality of the setup plays a vital role in this respect. By determining the uncertainty of the measurement setups, a clear assessment can be made to the quality of the measurement and the product to insure consistent QC, as well as plan for the product development.
The IEEE Std P2816 recommended practice for computational electromagnetics applied for the modeling and simulation of antennas is currently being developed by the IEEE Antennas and Propagation Standards Committee (APS/SC), sponsored by the IEEE Antennas and Propagation Society (APS). The document provides guidance on the numerical modeling of antennas deployed in free space using commonly adopted computational electromagnetics (CEM) techniques such as the finite element method (FEM), the finite difference time domain (FDTD) method, the Method of Moments (MoM), the finite integral technique (FIT) and the transmission line matrix (TLM) method. Benchmark models and comparisons of numerical simulation results are included for potential users of the standard to better understand the uncertainties and limitations of these techniques. A biconical antenna was previously proposed as a benchmark model. The numerical simulation results showed a good overall agreement among the participating laboratories and against the analytical solution. Herein, a 5G New Radio (NR) FR1 ultrawide band (UWB) antenna is proposed as another benchmark model for the development of IEEE Std P2816. In addition to the comparison of the numerical simulation results obtained from the participating laboratories, the simulation results are confronted with preliminary measurement results.
The existing IEEE-STD 1128 on “Recommended Practice for RF Absorber Evaluation in the Range of 30 MHz to 5 GHz” was published in 1998. The standard has been referenced frequently and used as a guide for RF absorber evaluations. The document has several aspects which need updating, including the frequency range of coverage, requirements for newer test equipment, advances in test methodologies and material property evaluation, measurement uncertainty considerations, and absorber high power handling and fire testing requirements. The working group is divided into task groups and is in the final stage of collecting inputs from these subgroups. The next step is to consolidate the inputs and produce a draft standard for a wider distribution before being submitted for balloting. The subgroup contributions can be found on the IEEE imeetcentral website (https://ieeesa. imeetcentral.com/p1128). The sections which have received substantive updates include bulk material measurements, instrumentation, absorber reflectivity measurements, and power handling test. In this paper, we will provide some detailed discussions on the planned updates from these contributions. For areas which did not receive sufficient input, the working group plan to table those topics for future considerations.