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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.
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.
Jason Jerauld, Tarron Teeslink, Felix Yuen, Nathan Landy, Tom Driscoll, October 2023
We describe a planar near-field instrument capable
of measuring the non-linear response of an electronically
steered antenna (ESA) up to the third harmonic while requiring
only a single scan with a single probe. The system performs
phase-coherent measurements of the aperture near-field at the
fundamental frequency, second harmonic, and third harmonic
simultaneously, which are then transformed to the far-field. When
system losses are appropriately accounted for, these far-fields are
accurate representations of the harmonic patterns relative to the
fundamental. A broadband dual-polarized probe combined with
a specially-configured network analyzer is used to capture all
frequencies and both polarizations within a single scan. Using
a ultra-broadband probe introduces some limitations to the
measurement, but offers a significant increase in measurement
speed. In this paper we disclose various architecture and design
aspects of the instrument, discuss its advantages and limitations,
and compare non-linear PNF measurements with non-linear
array simulations and direct far-field measurements.
Jong-Hyuk Lim, Jungkuy Park, Dong-Woo Kim, Soon-Soo Oh, October 2023
This paper proposes the measurement technique for the
phase of 5G NR modulation signal using the fast spherical near-tofar
field measurements utilizing the multi-probe combing the
multi-receivers. The bandwidth of the 5G NR signal is 100 MHz at
28 GHz with 16-QAM (Quadrature Amplitude Modulation) or 64-
QAM TDD (time division duplexing). The reference receiver is
utilized since an absolute phase is changed every time. The relative
phase at each receiver was recorded, and the medium value was
calculated. It can be asserted that the middle value of phase could
be similar to the exact value with a little error even for the 5G NR
modulated signal.
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.
Compressive Sensing (CS) has been deployed in a
variety of fields including wideband spectrum sensing, active user
detection and antenna arrays. In massive MIMO arrays, CS has
been applied to reduce the number of measurements required to
verify the arrays excitation in a production environment. All
follow the general approach of creating the sparsity needed for
CS by subtracting the measured far-field or near-field of the test
array from that of a 'gold standard' array measured under
identical conditions. In a previous paper [1] the authors have
shown that using a Far-Field Multi-Probe Anechoic Chamber
(FF-MPAC) and an optimal sampling strategy CS can offer
accurate reconstruction of array excitation with a mean square
error (MSE) approaching -40dB using a sampling strategy of just
1.4% of the Nyquist rate. The approach assumed production
standard arrays with failure rates up to around 2%. In this paper
we extend the concept to using a planar near-field (NF)
measurement offering a much more compact test facility that is
more suited to the production environment for these antennas. In
our initial work the reconstruction of array excitation with a
mean square error (MSE) of -30dB was achieved for a 20 x 28
element array antenna at half wavelength spacing using just
1.5% (177 samples) of the samples needed for a conventional NF
measurement (12,100 samples) employing back projection to the
aperture. Critical to the performance is the realization that the
CS samples need to be confined to the central region of the NF
measurement plane which for a conventional NF to FF planar
antenna pattern measurement would offer a massive truncation
error. This paper addresses the optimal sampling strategy needed
for this NF approach and presents a statistical performance
analysis of the reconstruction accuracy.
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].
Papa Ousmane Leye, Adamo Banelli, Shaikha Aldhaheri, Chaouki Kasmi, Felix Vega, Islem Yahi, October 2023
The purpose of radar cross-section (RCS)
measurement is to determine the amount of scattering that
occurs when the radar signal illuminates the target. It is
generally performed to prove a design concept. RCS
measurement chamber requires a good signal-to-noise ratio
during the measurement. When the measurement is
performed in a non-controlled environment, coherent
background subtraction associated with time gating is
commonly used to improve the quality of the RCS data.
Although these techniques are usually effective, residual
clutter and background level still need to be removed to
accurately characterize the target’s RCS in highly cluttered
environments, such as semi-anechoic chambers. In this
paper, a four-step post-processing technique is presented.
In addition to the vector background subtraction and timegating
techniques implemented in our previous work, a
statistical algorithm called Principal Component Analysis
(PCA) is applied to the ISAR image of the target. It is an
extension of the PCA technique to RCS measurement. It is
shown that residual background and clutter can be reduced
by the statistical filtering method through eigenvalue
decomposition of the RCS data. The technique is presented
and evaluated through measurement of the RCS of a
dihedral corner reflector at the X-band in the semi-anechoic
chamber of the Directed Energy Research Center.
Ines Barbary, Luis Rolo, Eric Van Der Houwen, Mauro Bandinelli, Davide Bianchi, Dean Rowsell, Mike Royle, October 2023
The BIOMASS Calibration Transponder Antenna
(BCT) has been developed to track the BIOMASS satellite and to
send calibration signals to it. It has been measured in the ESAESTEC
HERTZ facility to ensure its performance before
installation. As this anechoic chamber has not been designed to
measure antennas at P-Band, its range of applications had to be
extended. To this end, spherical nearfield measurements were
carried out in order to minimize reflections and decrease
measurement uncertainties. Using an average of several
measurements, the very high requirements on gain accuracy,
crosspolar values, and group delay could be met. However,
certain effects in the phase patterns stemming from the chamber
that affect the calculation of the phase centre have been observed.
This work provides an account on the methods applied to extend
the usability of the HERTZ facility, discusses their effectiveness,
and infers some generalizations.
Bennett Gibson-Dunne, Greg Brzezina, Ken Oueng, Adrian Momciu, October 2023
Antenna measurements in the VHF band are
challenging because of the sensitivity to surroundings in both
outdoor and indoor ranges. The large size of the antennas involved
makes them difficult to manipulate and therefore more susceptible
to damage. In addition, the gain tables for standard gain antennas
at these low frequencies is often sparse, especially for older models.
This paper proposes to use the three-antenna gain method to
mitigate some of these problems by calculating the gains more
accurately than other gain calculation methods or the original
manufacturer’s datasheets. To this end, a new custom NSI2000
script was written and trialed with a trio of antennas commonly
used to test new devices for satellite and space related applications.
Using our newly refurbished large anechoic chamber with a nearfield
system, gain data calculated in the 200 – 325 MHz frequency
range shows notable differences relative to the datasheets. As
compared to other methods of gain calculation, the results for the
three-antenna method displayed smaller mean values and
standard deviations – indicating a reduction in the influence of any
single error on the overall outcome. The lessons learned from this
experiment can help improve measurement accuracy at these
frequencies.
This paper describes a new materials measurement
method that includes a sensor embedded within a ground-plane to
continuously measure complex permittivity of an adjacent
material. The sensor works with a 1-port vector network analyzer
(VNA) to collect amplitude and phase of the sensor reflection
signal, which is then converted to intrinsic dielectric properties or
sheet impedance. The complexity of the fields near this sensor
makes a conventional analytical method to relate reflection data to
dielectric permittivity impractical. Instead, this sensor uses a
computational electromagnetic (CEM) inversion method based on
finite difference time domain (FDTD) simulations to derive real
and imaginary dielectric properties from the amplitude and phase
of the measured reflection. This paper describes the sensor design
and inversion method. Additionally the sensor is demonstrated on
several material types including i) sheet materials that may be
manufactured in an in-line process and ii) concrete, which is a
material whose properties change as it cures.
Andrian Buchi, Ondrej Pokorny, Snorre Skeidsvol, Sigurd Petersen, October 2023
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.
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.
Henrik Jansen, Roland Moch, Dirk Heberling, October 2023
One of the main advantages of a robot-based antenna
measurement systems compared to traditional positioning
systems like roll-over azimuth positioners are the additional
degrees of freedom and, thus, the increased flexibility with respect
to the sampling grid and the placement of the antenna under
test (AUT). However, this flexibility also requires a precise alignment
of probe antenna and AUT to obtain accurate measurement
results. In this paper, an electrical alignment technique based on
a six term error model is introduced. The misalignment errors
are estimated from measurement of single θ-cuts of a reference
AUT, using a least-squares optimization approach. The estimation
results can be used subsequently to correctly align the probe
antenna to the physical position of arbitrary AUTs, independent
of the sampling grid. The technique is validated by measurements
in the mm-wave frequency range. Results show that the proposed
method allows a correction in the same order of magnitude as the
repeatability of the robotic system, therefore contributing to an
increased overall accuracy of the obtained measurement results.
The use of squat cylinders as both primary and
secondary calibration targets is commonplace within the radar
cross section (RCS) measurement community. Secondary
calibrations have become a best practice activity for ranges
seeking or maintaining certification. The calibration process, often
referred to by the measurement community as a “Dual-Cal,” uses
two squat cylinders of similar but unequal dimensions that provide
range operators with a broadband calibration vector and a
measurement uncertainty metric important to range certification.
Despite their popularity, the need to ensure resonance scattering
occurs below the desired measurement band results in physically
large cylinders at UHF. In addition, the need to access the test zone
for separate cylinder measurements may add substantial time to
the calibration process and require specialized equipment,
especially for large ranges.
In response to these issues, a 22.5-degree right dihedral has been
inserted into a squat cylinder form factor, creating a primary and
secondary calibration target within one body, each separated in
azimuth by 180 degrees. This two-target calibration device
removes the need to access the target zone twice and mitigates
errors associated with separate mounting schemes. The cylinder
aspect, now truncated by the imposition of a dihedral, has 50%
extended lower frequency coverage at UHF due to oblique edge
scattering at vertical polarization. At horizontal polarization, the
dihedral interruption of the cylinder creeping wave reduces its
contribution for ka<4. The dihedral aspect provides a full
polarimetric calibration, resulting in co-equal frequency responses
for each polarization in the high frequency limit. The design
parameters of the squat cylinder-dihedral device, its computed
full-wave frequency response, and relevant scattering features are
discussed.
Alejandro Antón Ruiz, Samar Hosseinzadegan, John Kvarnstrand, Klas Arvidsson, Andrés Alayón Glazunov, October 2023
In this paper, we propose quantifying the radiated
power of phased arrays or, in general, directive antennas, by
the Constrained-View Radiated Power (CVRP). The constrained
view shall be interpreted here as the Field-of-View (FoV) of an
antenna that defines a region in space where focusing the radiated
power is highly desired. In the limiting cases, we have that CVRP
equals the Total Radiated Power (TRP) when the FoV covers
the whole sphere, while, if the FoV reduces to a single point
in space, the CVRP equals the Equivalent Isotropic Radiated
Power (EIRP). We further present an analysis based on measured
radiation patterns of a 16-element, linearly polarized, millimeter-
Wave (mmWave), planar phased array antenna operating at 28
GHz. We compare the results to two ideal planar array antennas
with the same number of Huygens and cosine elements. The
evaluated figure of merit is computed for different scanning
angles, as well as for different malfunctions of antenna elements,
both for the real and simulated arrays. The results show that
the introduced figure of merit could be potentially used for the
detection of malfunctioning elements in antenna arrays as well
as to characterize the impact of scan loss. Furthermore, CVRP
is useful to straightforwardly and significantly characterize the
performance of a directive antenna in terms of the power radiated
towards a specific region in space.
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.
Donald Hilliard, Michael Emire, Long To, October 2023
This paper presents research results conducted at the Naval Air Warfare Center Weapons Division (NAWCWD) Radar Reflectivity Laboratory (RRL) to characterize RCS measurement quality of a compact range anechoic chamber using a small resonant sphere as a test probe measured over a 3.17-octave bandwidth, which covers the first half of the resonance region. Specifically, tests were performed on 1-inch and 12-inch diameter spheres over 2-18 GHz, which is a very prevalent test spectrum for RRL customers. The spheres were tested at the quiet zone center and the 1-inch was rotationally scanned over a 1- meter radial arc within the test zone. Spectral and spatial analysis was performed using techniques developed by Dr. Dean L. Mensa [1].
In a compact range when the antenna is used
for both transmitting and receiving in a monostatic
fashion, the wave packet senses everything within its
view. An extended long object usually gives rise to a
bright reflection (glint) when viewed near its surface
normal. To take advantage of this phenomenon, a
discrete Fourier transform (DFT) on RCS measurements
would yield a spectrum of incident wave
distribution along that object, provided the scattering
property is uniform along its length. Compared with
traditional field-probes which translate a sphere across
the test zone in horizontal and vertical directions, this
new method extends out from the usual quiet zone, and
is faster and less interfering to the field being probed.
Inspired by this idea, the progression to practical
innovation is discussed.
In General, theoretical RF attenuation in free space is
characterized according to the Friis equation in far field range The
equation says that the free space propagation of electromagnetic
waves is inversely proportional to the square of distance from
source It holds only in far field range. We investigate a
propagation characteristic of millimeter wave in all ranges of field.
The study provides measurement results of free space insertion
loss from 20GHz to 90GHz of frequency ranges, where the
separation between transmitting and receiving antennas is
increased from 1mm to 1400mm with 1mm step. The measurement
distances cover all range including the reactive and Fresnel ranges
as near field, and the far field too. The measuring values are fitted
in the free space path loss factor (λ/4πr)2. There are discrepancies
between theoretical and measuring values in near field ranges. We
added an extra terms to the formula in order to resolve the
difference in near field. The results calculated by new formula are
shown in good agreement at Fresnel range and also at some parts
of the reactive range. The new formula having the extra terms can
be also proposed for antenna gain measurements in the near
separation between antennas in the context of results according to
this study.
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