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Absorber treatment for an anechoic range is designed to attenuate the potential reflections from the walls, ceiling, and floor and to keep a certain level below the direct path between the range antenna (or probe) and the quiet zone (or minimum radiated sphere for spherical near-field ranges). There are, however, some antenna measurement systems where the range changes or moves as the data is acquired. In some cases, the probe moves around the antenna-under-test (AUT) along a section of circle supported by an arch or a gantry. In other ranges, the multiple probes are switched on and off; these probes are supported by an arch. Because the direction of the range moves with respect to the walls, ceiling, and floor, it is a bit more complex to arrive to an optimal absorber layout, as well as locating the preferred placements for the instrument rack, door, and vents in the range.
In this paper, a higher-order-basis-function method of moments approach is used to model a gantry-supported probe as it moves around the location of the AUT. The power density at the walls as the probe moves is analyzed to arrive to an optimal absorber layout that will provide adequate levels of reflections for measuring an antenna. The paper looks at a gantry that moves from +135° to -135° with the AUT rotating 180° and for a gantry that moves from 0° to +135° with the AUT rotating 360°. The latter will require a smaller range with one of the walls closer to the location of the antenna under test.
A series of recommendations based on the electrical size of the absorber at different areas of the range are provided.

Fernando Rodriguez Varela, Manuel Sierra-Castañer, Francesco Saccardi, Lucia Scialacqua, Lars Foged, October 2023

The reduction of acquisition time in planar near field
systems is a high interest topic when active arrays or multi beam
antennas are measured. Different solutions have been provided
in the last years: multi-probe measurements systems and the
PlanarWide Mesh (PWM) methodology, which implements a non
redundant sampling scheme that reduces the number of samples
required for the far-field transformation, are two of the most
well known techniques. This paper proposes the combination
of both approaches to derive a multi-probe PWM grid which
reduces the measurement times to the minimum. The method is
based on treating the near-field to far-field transformation as an
inverse source problem. The multi probe PWM is designed with
a global optimization process which finds the best measurement
locations of the probe array that guarantee a numerically stable
inversion of the problem. A simulated measurement example with
the VAST12 antenna is presented where the total number of
samples is reduced by a factor of 100 using a 4×4 probe array

Zhong Chen, Stuart Gregson, Yibo Wang, October 2023

Mode filtering has been shown to be very
effective in suppressing spurious reflections in antenna
measurements. Specifically, it has been well documented
that in the quasi-far-field, the two polarizations are
decoupled, making it possible to apply standard cylindrical
near-field theory on the amplitude and phase data acquired
from a single polarization measurement on a great circle cut
[1]. The method was further extended to allow data
collected from an unequally spaced angular abscissa by
formulating the solution as a pseudo-inversion of the
Fourier matrix [2]. This formulation, however, can be
prone to spectral leakage because of nonorthogonality of the
Fourier basis on an irregularly sampled grid, especially
when the positions deviate significantly from the regular
grid [2]. In this paper, we propose to use Compressed
Sensing (CS) to compute the Cylindrical Mode Coefficients
(CMCs), which improves the signal to noise ratio, allowing
more accurate recovery of the prominent modes. The CS
recovery is tenable because with the coordinate translation
of the measurement pattern to the rotation center, the
Maximum Radial Extent (MRE) of the antenna under test
is greatly reduced, making CMCs quite sparse in the mode
domain. The novel application of CS presented in this
paper further expands the generality of the mode filtering
method, which is now applicable to under-sampled data (at
below the Nyquist rate) acquired on positions that grossly
deviate from the equally-spaced regular grid.

Rostyslav Dubrovka, Robert Jones, Clive Parini, Stuart Gregson, October 2023

In this paper, the full-wave computational
electromagnetic simulation of the production test, measurement,
and calibration of a 5G, 24 elements, C-band, active, planar
array antenna together with a representative open-ended
rectangular waveguide probe with, and without, absorber collar
were evaluated using a large computing cluster and a proprietary
full-wave solver. In this way, various components within the
measurement could be carefully and precisely examined
providing a framework for further measurement optimization.
Particular attention has been paid to the presence of the standing
waves in the simulated near-field measurement. This is a crucial
feature of most practical measurements, but is omitted from the
vast majority of simulations due to the computational effort
required to evaluate it, and which is absent from the standard
near-field theory. Here, the presence and impact of this
phenomenon has been carefully examined with a range of
intensive simulations being harnessed to quantify their impact, as
well as enabling various methods for their minimization to be
explored in a convenient and highly controlled fashion.

Benoit Derat, Thorsten Liebig, David Schaefer, Winfried Simon, October 2023

This paper proposes a fast human exposure Absorbed
Power Density assessment approach, based on a combination
of over-the-air radiative field measurements and fullwave
electromagnetic simulations. This so-called augmented OTA
technique relies on the computation of an equivalent source or
digital twin, which reproduces the radiation properties of the
device under test. At short separation distances, the interaction
between the human model and the device is however not
negligible. A novel solution to model the influence of multiple
reflections is introduced, where the inside of the equivalent source
box is filled with a perfect electric conductor, thereby creating a
reflective digital twin model. Simulation results demonstrate the
relevance of this approach for enabling accurate absorbed power
density evaluations.

Yibo Wang, Zhong Chen, Dennis Lewis, Wayne Cooper, October 2023

Extrapolation method is regarded as one of the most
accurate methods for obtaining the absolute far-field gain of an
antenna. This paper will compare the efficacy of several data
processing techniques for calibrating low frequency antennas with
long ring down time. Traditionally, measurement data are preprocessed
to remove ripples from multipath reflections before a
curving fitting is applied. We will first investigate two traditional
data processing techniques. The first technique is to apply time
domain gating to the vector response vs. frequency data at each
separation distance. Then the gated data as a function of distance
is fitted to the polynomial equation. The second technique is
spectrum domain filtering. The vector response as a function of
distance is transformed to k domain at each frequency. A band
pass filter is applied in k domain to keep only the direct antenna
response. In this study, we propose a new approach - the
magnitudes of the antenna response as a function of distance
including the ripples is fitted to a more complete generalized
antenna response equation with the antenna-to-antenna multiple
reflection terms included. This paper will compare the three
techniques using a set of measurement data on double-ridged
waveguide horn antennas in a fully anechoic extrapolation range.

The success and efficiency of many classical iterative
plane-to-plane based phase retrieval algorithms is to a large
extent dependent upon the fidelity of the initializing, i.e. guiding,
phase estimation [1], [2]. This is especially so when using these
techniques to recover the phase of active electronically scanned
array antennas such as those employed within beam-steering
mm-wave Massive MIMO antenna systems intended for 5G New
Radio applications where the performance of the algorithm, and
its ability to not become trapped within one of the (possibly
many) local minima, is particularly dependent upon the quality
of the initializing guess where access to a phase reference is not
always convenient, or even possible. Many traditional phase
recovery iterative Fourier methods employ simulation or passive
measurement supported phase initialization [1], however this
information is not always readily available, or in the
measurement may require a destructive, invasive, examination of
the device under test (DUT). In this work we address this issue by
presenting a proof of concept which employs a machine learning
based neural network [3] to estimate the initializing phase
function based on the assessment of the measured amplitude only
near-field pattern. Here, we show that there is sufficient
information contained within the difference between the two
near-field amplitude only scans to be able to determine the
antenna beam steering characteristics. A simplified beam
steering case with electronic scanning in one, or more, scanning
axes is demonstrated and verifies the power of the novel method,
as well as illustrating its inherent resilience to noise within the
amplitude only measurements, and verification of the robustness
of the approach thereby extending the range of measurement
applications for which this class of iterative Fourier algorithms
may be successfully deployed [4].

Sangdong Kim, Bong-seok Kim, Jonghun Lee, Tarun Chawla, Greg Skidmore, Ram Narayanan, October 2023

This paper proposes a range-Doppler imaging method
based on FFT-MUSIC method for FMCW radar systems. With the
growing significance of vehicle and human motion recognition in
automotive radar, the accuracy of conventional deep learning
network-based recognition methods is reduced because it depends
only on distance, speed, and angle information provided by
conventional radars. Therefore, various types of imaging radar
methods have recently been proposed. Among them, the range-
Doppler imaging algorithm is widely used. This algorithm can
simultaneously analyze both distance and velocity characteristics
of a vehicle or person. However, conventional range-Doppler
imaging based on the FFT algorithm has limited resolution, which
cannot obtain detailed information on the target. Although the
FFT algorithm is widely used in many applications, its lowresolution
characteristics can limit its ability to provide detailed
information. In particular, improving velocity resolution often
requires the extraction of a significant amount of data. To address
this issue, a range-Doppler imaging method based on FFT-MUSIC
is proposed in this paper. This technique has been simulated using
Remcom’s WaveFarer® software package. The proposed
algorithm is effectively able to distinguish between two moving
vehicles in several cases in which the ranges and velocities are too
close to be resolved by conventional FFT methods. We can observe
that the proposed algorithm enhances the velocity resolution by
approximately twice as much as the conventional algorithm.
Additionally, in indoor environments, the proposed algorithm
provides a detailed representation of the indoor multipath,
outperforming conventional algorithms. The high-resolution
radar imaging offered by the proposed method will enable
improved target recognition and thus enhance overall
performance in practical applications.

Sangdong Kim, Bong-seok Kim, Jonghun Lee, Tarun Chawla, Greg Skidmore, Ram Narayanan, October 2023

This paper proposes a range-Doppler imaging method
based on FFT-MUSIC method for FMCW radar systems. With the
growing significance of vehicle and human motion recognition in
automotive radar, the accuracy of conventional deep learning
network-based recognition methods is reduced because it depends
only on distance, speed, and angle information provided by
conventional radars. Therefore, various types of imaging radar
methods have recently been proposed. Among them, the range-
Doppler imaging algorithm is widely used. This algorithm can
simultaneously analyze both distance and velocity characteristics
of a vehicle or person. However, conventional range-Doppler
imaging based on the FFT algorithm has limited resolution, which
cannot obtain detailed information on the target. Although the
FFT algorithm is widely used in many applications, its lowresolution
characteristics can limit its ability to provide detailed
information. In particular, improving velocity resolution often
requires the extraction of a significant amount of data. To address
this issue, a range-Doppler imaging method based on FFT-MUSIC
is proposed in this paper. This technique has been simulated using
Remcom’s WaveFarer® software package. The proposed
algorithm is effectively able to distinguish between two moving
vehicles in several cases in which the ranges and velocities are too
close to be resolved by conventional FFT methods. We can observe
that the proposed algorithm enhances the velocity resolution by
approximately twice as much as the conventional algorithm.
Additionally, in indoor environments, the proposed algorithm
provides a detailed representation of the indoor multipath,
outperforming conventional algorithms. The high-resolution
radar imaging offered by the proposed method will enable
improved target recognition and thus enhance overall
performance in practical applications.

Mark Ingerson, Vince Rodriguez, Daniel Janse van Rensburg, Anil Tellakula, October 2023

Absorber fences have been used on compact ranges since their first implementations. The purpose of this fence is to hide the feed positioner and reduce the direct coupling between the feed and the device under test (DUT). A known problem caused by such a fence is that it diffracts the plane wave generated by the reflector, creating an interfering ripple on the illumination of the DUT in the quiet zone. Traditionally, fences have serrated edges to direct this diffracted signal away from the quiet zone. However, this redirection is not always achievable or even repeatable from one facility to the next. Often low frequency requirements drive absorber physical size, leading to very large absorbing surfaces that cannot be optimized to reduce this interfering signal. In this paper, the fence design presented in a recent publication [1] is further optimized by modifying its shape and absorbing material parameters. The performance of this new design is compared with traditional fences.

Francesco Saccardi, Andrea Giacomini, Lars Foged, October 2023

The spherical wave expansion-based transmission
formula allows to accurately evaluate the coupling (or S21
parameter) between a transmitting and a receiving antenna. Its
use as tool for probe corrected spherical near-field to far-field
transformation is well accepted and documented. On the other
hand, its direct use in the evaluation of antenna measurement
performance has been exploited only in recent years. In this paper
we will show how measurement performances predicted with the
transmission formula compare with actual measurements. Taking
as examples relatively complex antenna measurement systems like
spherical near-field, plane wave generators and CATR, we will
focus on the prediction of the accuracy of the measured radiation
patterns, also including the approximation of reflections from the
test environments, and on the evaluation of link budgets.

Florindo Bevilacqua, Francesco D'Agostino, Flaminio Ferrara, Claudio Gennarelli, Rocco Guerriero, Massimo Migliozzi, October 2023

This communication provides an effective two-steps strategy
to compensate for known 3-D probe positioning errors occurring
in the non-redundant (NR) cylindrical near-to-far-field (NTFF)
transformations. As first step, a phase correction, here denoted as
cylindrical wave correction, is employed to perform the correction
of the positioning errors relevant to the deviations of the measured
NF samples from the nominal scanning cylinder. Then, an iterative
procedure will be applied to retrieve the NF samples at the points
specified by the adopted sampling representation from those obtained
at the previous step and affected by 2-D positioning errors.
Finally, after properly reconstructing the correctly distributed cylindrical
samples, the data necessary to apply the classical cylindrical
NTFF transformation can be restored in accurate way by employing
a 2-D optimal sampling interpolation (OSI) formula. It should be
noticed as, to derive the NR sampling representation, as well as the
OSI scheme, it is necessary to provide a proper modeling of the antenna
under test. This modeling has been got by shaping the source
with a prolate spheroid. Numerical tests will show the capability of
the procedure to compensate these 3-D positioning errors.

Francesco D'Agostino, Flaminio Ferrara, Claudio Gennarelli, Rocco Guerriero, Massimo Migliozzi, October 2023

This work aims to propose and optimise a non-redundant
spherical spiral near-to-far field (NTFF) transformation for elongated
AUTs from spiral near-field (NF) data acquired over the upper
hemisphere due to the presence of an infinite perfectly electric conducting
(PEC) ground plane. Such a technique properly exploits the
principle of image and the theoretical foundations of spiral scan
for non-volumetric AUTs to develop the non-redundant representation
along the sampling spiral in presence of PEC ground plane
and to synthesise the voltage NF data which would be acquired
over the spiral wrapping the lower hemisphere. Once these voltage
NF data have been synthesised, then an efficient 2-D optimal sampling
interpolation scheme allows the recovering of the NF data required
by the classical NTFF transformation. In the hypothesis that
the AUT and its image exhibit a predominant dimension as compared
to the other two ones, a prolate spheroidal source modeling is
here adopted. Numerical tests show the accuracy of the developed
non-redundant spherical spiral NTFF transformation.

Jon Kelley, Kurt Norris, Brian Mackie-Mason, Brody Barton, David Chamulak, Scott Schaeffer, Mark Martin, Kendall Crouch, Clifton Courtney, Ali Yilmaz, October 2023

—Cylindrical hubs with fan blades are inserted
into a pipe inside a modified camera box—a recently
introduced structure intended to host differently-shaped
ducts behind an aperture. The resulting structures increase
the reproducibility of commonly used simplified jet-engine
inlet models and are designed to serve as precisely-defined
radar cross section (RCS) benchmarks with reliable
reference results. The design, manufacturing, and assembly
of the measured structures are detailed; the RCS measurement setup, data collection, and post processing are
documented; and the uncertainty in measured RCS data is
quantified with the help of simulations. Results show that the
fields scattered by the structures, while highly sensitive to
geometric and material perturbations, can be both measured
and simulated accurately even at frequencies with many
propagating modes inside the pipe.

Francesco Saccardi, Andrea Giacomini, Lars Foged, Nicolas Gross, Thierry Blin, Per Iversen, Kim Hassett, Roni Braun, Lior Shmidov, Meng He, Chen Chen, Xavier Bland, October 2023

The application of multi-probe (MP) technology in
near-field (NF) measurement scenarios is well-known for its ability
to significantly reduce test time. This is achieved by electronically
sampling the radiated field using different probes in the array,
eliminating the need for mechanical probe movement. However, in
planar near-field (PNF) measurements, the accuracy is contingent
on probe correction (PC) during post-processing. Characterizing
the pattern of each individual sensor in a PNF MP system presents
an additional challenge, often being impractical or impossible.
Previous publications have explored various approaches to
address this challenge and achieve an accurate characterization of
the MP equivalent pattern. In this paper, we focus on the average
probe pattern (APP) technique, which involves the experimental
determination of the MP pattern. To validate the effectiveness of
the APP technique, we conducted experiments on a large PNF MP
system equipped with a 4.65m probe array. Our measurements
focused on an electrically large 1.5m diameter reflector antenna
(MVG SR150 reflector, fed by a quad-ridge horn) operating in the
1.8–6.0 GHz frequency range. The validation process involved the
comparison of MP measurements processed with the APP
technique and conventional open-ended waveguide (OEW) PNF
measurements. To ensure the reliability of the validation, we
conducted the comparative tests within the same frequency range
and test setup. This minimized the impact of measurement errors,
enabling a robust and accurate comparison between the
techniques. By validating the APP technique's effectiveness, we
aim to establish its suitability for improving accuracy in PNF MP
system measurements.

There are several applications that require the Fourier transformation from data obtained on a regular polar grid to a regular sine-space grid, and one of these is the processing of plane-polar near-field data. The most common approach to this task is to interpolate from the polar grid to an X-Y grid and then use the conventional 2D Fourier transform.
This paper revisits an alternative algorithm, referred to herein as the polar-coordinate Fourier transform (PCFT), for doing the same transformation from polar input to a regular sine-space output grid. This PCFT has some advantages when processing data undersampled in their angular phi spacing, and appears to offer the possibility of probe correction without having to counter-rotate the probe.
The process of the PCFT is similar to that of the conventional 2D Fourier transform. These two processes are compared.
Rather than interpolating the polar data to the X-Y grid, the PCFT starts with a 1D transform along each diametric spoke of the polar wheel. Each spectral output is then rotated by the corresponding phi angle and interpolated to a common sine-space output grid. If probe-pattern correction is needed for a probe with no extra roll axis, then a notional approach is also described.

In this contribution a simple algebraic approach is
discussed on the minimum of required sample points for either a
nearfield or a farfield configuration to calculate the antenna’s
current distributions to accurately reconstruct the antenna’s
radiation pattern anywhere in space. The proposed algebraic
approach comprises a Gaussian quadrature sampling scheme for
a set of Hertzian dipoles with unkown amplitudes representing
the antenna current distribution. The algebraic equation system
with the number of unknown amplitudes then suggests the
minimum of required sample points in the radiated field. In this
initial study simulation examples of a dipole antenna and a horn
antenna are presented validating the proposed algorithm.

Christopher Howard, Kenneth Allen, Bill Hunt, October 2023

In this work, a tunable frequency-selective surface
is designed with a center frequency that can be varied with
an applied DC voltage. An equivalent circuit representation
of the FSS is derived from a finite-difference time-domain
(FDTD) simulation of the passive FSS, allowing tuning circuits
for the FSS to be designed in common circuit simulation tools
such as SPICE. A comparison between the spectral response
obtained from FDTD and equivalent circuit modeling (ECM)
in SPICE shows that under certain conditions, ECM provides
good agreement with full-wave analysis, is less computationally
intensive, and provides physical insight. The ECM technique
enables rapid design and analysis of various trade-offs, such as
those between resonant frequency tunability and bandwidth. The
ECM-designed circuit is then validated with full-wave analysis of
the designed structure with active components using an FDTDSPICE
hybrid co-simulator. Finally, applicability of the chosen
active FSS topology as a metasurface for free-space dielectric
material characterization is discussed.

Vikass Monebhurrun, Satyajit Chakrabarti, Richelieu Quoi, October 2023

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.

Vehicular wireless power transfer (WPT) systems
conforming to the SAE J2954 standard are thought to operate
as inductive WPT systems. As such, they should be able to
be accurately represented by a magnetic multipole source. For
example, the magnetic field of the “circular” coupler, which
is described in the SAE standard, can be represented by a
combination of a vertical, linear magnetic quadrupole and a
horizontal magnetic dipole. However, it has been recently shown
that a significant conservative electric field exists in such a
WPT system due to the multi-turn windings. This can lead
to a significant electric multipole contribution, predominantly
a vertical linear electric quadrupole for the circular coupler. In
fact, the circular coupler electric field (not the magnetic field) is
somewhat similar to that of a coaxial aperture. Here, we carry
out a detailed analysis of the electric multipole representation of
the “DD” coupler which is also described in the SAE standard.
The analysis of the electric multipole of the DD coupler is more
complex than that of the circular coupler. Because the DD coupler
is composed of two side-by-side spiral windings, it is possible to
obtain two different electric multipoles from configurations that
produce nominally the same magnetic multipole and the same
magnetic performance. Fortuitously, the configuration used in the
DD coupler very nearly cancels the conservative electric field, the
associated electric multipole, and the attendant emissions.

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