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A study of near-field data handling and probe design techniques
Abstract
The ability to fully characterize a probe antenna using a near-field range is demonstrated subject to the conditions that two identical probes are available. A completely general three antenna approach, requiring no such assumptions, appears feasible. Some questions with respect to uniqueness of solution of the three antenna approach remain. Experimental results indicate that at wide angles (approx. 77 deg), considerably below the apparent geometric limit, the planar near-field approach suffers a notable loss of accuracy. Improvements in both hardware and software-techniques to increase the data handling ability of the near-field facility are described.
... Aiming at gain measurements, the two-antenna method [21], [22], originally defined for measurements in the FF and working with two unknown but identical antennas, has been developed and, later, extended to NF measurements [23, pp. 93-98] [24], [25]. However, and as pointed out in [5], it can neither be considered a rigorous, complete, nor reliable approach. ...
... Second, the P matrices from (25) to (28) are inserted into (24) leading to z for ∈ {1, ..., ( A − 1) P } at the expense of solving ( A − 1) P linear systems of equations. Third, we compute C ∋ [b] = b T z ∀ . ...
... This can be seen as a generalization of the two-antenna method [21] known from FF measurements and which has later, with restrictions, been generalized to NF measurements [23, pp. 93-98] [24], [25]. By enforcing the AUT and probe to be identical, one would hope for a less ill-posed inverse problem and mitigated requirements on the necessary measurement diversity. ...
p>According to the electromagnetic uniqueness theorem, the radiation behavior of an antenna under test (AUT) can be recovered from measurements of two tangential components of its radiated fields on an enclosing surface. In practice, measurements conducted in the radiating near-field (NF) of an AUT utilize probe antennas of finite size. Thus, instead of discrete field values, spatially blurred probe signals are acquired. The probe influence can be compensated, however, this commonly requires precise knowledge about the probe antenna. In this work, the concept of NF far-field (FF) transformations (NFFFTs) with full correction of the influence of unknown probe antennas is introduced. Two nonconvex and two convex formulations are presented and their relation to the similar task of phase retrieval is highlighted. Simulation and measurement results illustrate the validity of the concept, shed light on the required complexity of measurement setups, and illustrate limitations of the approach. Special attention is paid to the case of high practical relevance when AUT and probe are identical.</p
... Aiming at gain measurements, the two-antenna method [21], [22], originally defined for measurements in the FF and working with two unknown but identical antennas, has been developed and, later, extended to NF measurements [23, pp. 93-98] [24], [25]. However, and as pointed out in [5], it can neither be considered a rigorous, complete, nor reliable approach. ...
... Second, the P matrices from (25) to (28) are inserted into (24) leading to z for ∈ {1, ..., ( A − 1) P } at the expense of solving ( A − 1) P linear systems of equations. Third, we compute C ∋ [b] = b T z ∀ . ...
... This can be seen as a generalization of the two-antenna method [21] known from FF measurements and which has later, with restrictions, been generalized to NF measurements [23, pp. 93-98] [24], [25]. By enforcing the AUT and probe to be identical, one would hope for a less ill-posed inverse problem and mitigated requirements on the necessary measurement diversity. ...
According to the electromagnetic uniqueness theorem, the radiation behavior of an antenna under test (AUT) can be recovered from measurements of two tangential components of its radiated fields on an enclosing surface. In practice, measurements conducted in the radiating near-field (NF) of an AUT utilize probe antennas of finite size. Thus, instead of discrete field values, spatially blurred probe signals are acquired. The probe influence can be compensated, however, this commonly requires precise knowledge about the probe antenna. In this work, the concept of NF far-field (FF) transformations (NFFFTs) with full correction of the influence of unknown probe antennas is introduced. Two nonconvex and two convex formulations are presented and their relation to the similar task of phase retrieval is highlighted. Simulation and measurement results illustrate the validity of the concept, shed light on the required complexity of measurement setups, and illustrate limitations of the approach. Special attention is paid to the case of high practical relevance when AUT and probe are identical.
... Aiming at gain measurements, the two-antenna method [21], [22], originally defined for measurements in the FF and working with two unknown but identical antennas, has been developed and, later, extended to NF measurements [23, pp. 93-98] [24], [25]. However, and as pointed out in [5], it can neither be considered a rigorous, complete, nor reliable approach. ...
... Second, the P matrices from (25) to (28) are inserted into (24) leading to z for ∈ {1, ..., ( A − 1) P } at the expense of solving ( A − 1) P linear systems of equations. Third, we compute C ∋ [b] = b T z ∀ . ...
... This can be seen as a generalization of the two-antenna method [21] known from FF measurements and which has later, with restrictions, been generalized to NF measurements [23, pp. 93-98] [24], [25]. By enforcing the AUT and probe to be identical, one would hope for a less ill-posed inverse problem and mitigated requirements on the necessary measurement diversity. ...
p>According to the electromagnetic uniqueness theorem, the radiation behavior of an antenna under test (AUT) can be recovered from measurements of two tangential components of its radiated fields on an enclosing surface. In practice, measurements conducted in the radiating near-field (NF) of an AUT utilize probe antennas of finite size. Thus, instead of discrete field values, spatially blurred probe signals are acquired. The probe influence can be compensated, however, this commonly requires precise knowledge about the probe antenna. In this work, the concept of NF far-field (FF) transformations (NFFFTs) with full correction of the influence of unknown probe antennas is introduced. Two nonconvex and two convex formulations are presented and their relation to the similar task of phase retrieval is highlighted. Simulation and measurement results illustrate the validity of the concept, shed light on the required complexity of measurement setups, and illustrate limitations of the approach. Special attention is paid to the case of high practical relevance when AUT and probe are identical.</p
... Aiming at gain measurements, the two-antenna method [21], [22], originally defined for measurements in the FF and working with two unknown but identical antennas, has been developed and, later, extended to NF measurements [23, pp. 93-98] [24], [25]. However, and as pointed out in [5], it can neither be considered a rigorous, complete, nor reliable approach. ...
... Second, the P matrices from (25) to (28) are inserted into (24) leading to z for ∈ {1, ..., ( A − 1) P } at the expense of solving ( A − 1) P linear systems of equations. Third, we compute C ∋ [b] = b T z ∀ . ...
... This can be seen as a generalization of the two-antenna method [21] known from FF measurements and which has later, with restrictions, been generalized to NF measurements [23, pp. 93-98] [24], [25]. By enforcing the AUT and probe to be identical, one would hope for a less ill-posed inverse problem and mitigated requirements on the necessary measurement diversity. ...
p>According to the electromagnetic uniqueness theorem, the radiation behavior of an antenna under test (AUT) can be recovered from measurements of two tangential components of its radiated fields on an enclosing surface. In practice, measurements conducted in the radiating near-field (NF) of an AUT utilize probe antennas of finite size. Thus, instead of discrete field values, spatially blurred probe signals are acquired. The probe influence can be compensated, however, this commonly requires precise knowledge about the probe antenna. In this work, the concept of NF far-field (FF) transformations (NFFFTs) with full correction of the influence of unknown probe antennas is introduced. Two nonconvex and two convex formulations are presented and their relation to the similar task of phase retrieval is highlighted. Simulation and measurement results illustrate the validity of the concept, shed light on the required complexity of measurement setups, and illustrate limitations of the approach. Special attention is paid to the case of high practical relevance when AUT and probe are identical.</p
Expressions that relate the signal-to-noise ratio in the near field to
the signal-to-noise ratio in the far field are developed. The
expressions are then used to predict errors in far-field patterns
obtained from near-field data. A technique for measuring the noise in
the calculated far-field pattern by calculating the spectrum in the
evanescent region from a single-dimensional oversampled scan is also
described.
A methodology that is a combination of analysis, computer
simulation, component certification, self-tests, and comparison tests is
presented for the accuracy qualification of near-field antenna
measurement ranges. The analysis uses closed-form equations to establish
upper-bound far-field determination errors due to near-field measurement
errors. Computer simulation is used to model the specific near-field
measurement errors associated with the near-field measurement system
components. The closed-form equations and computer simulations are used
to form a near-field error budget for each of the near-field measurement
system components. A near-field system component certification is
undertaken to measure the near-field measurement system component error
and establish that they are within the error budget
The activity of the Georgia Institute of Technology in the
development of the near-field measurement technique is reviewed. The
work conducted during the years 1967-73 is given primary importance, and
the major near-field developments in the 1973-80 time period are also
described
A procedure used by the US National Bureau of Standards (NBS) for
accurately determining the plane-wave receiving parameters of both
single- and dual-port linearly polarized probes is described. Examples
are presented, and the effect of these probe receiving characteristics
in the calculation of the parameters for the antenna under test is
demonstrated using the required planar near-field theory. The planar
near-field theory necessary to accomplish probe correction and to
formulate probe parameter errors is presented in a concise and
meaningful way to help understand when probe correction is or is not
needed
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