Electromagnetic near-field scanner (NFS
) is a
measurement system
A system of units of measurement, also known as a system of units or system of measurement, is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defi ...
to determine a spatial distribution of an electrical quantity provided by a single or multiple field probes acquired in the
near-field region of a device under test possibly accompanied by the associated numerical post-processing methods enabling a conversion of the measured quantity into
electromagnetic field
An electromagnetic field (also EM field) is a physical field, varying in space and time, that represents the electric and magnetic influences generated by and acting upon electric charges. The field at any point in space and time can be regarde ...
.
Depending on a signal receiver detecting the probe signal,
voltage
Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...
as a function of time or frequency is a typical measured quantity. It should be underlined that as the DUT may be considered any object ''radiating or storing'' electromagnetic field energy intentionally or unintentionally, e.g. the antenna radiation excited beyond its
resonance frequency
Resonance is a phenomenon that occurs when an object or system is subjected to an external force or vibration whose frequency matches a resonant frequency (or resonance frequency) of the system, defined as a frequency that generates a maximu ...
. The voltage pattern is usually mapped on
planar
Planar is an adjective meaning "relating to a plane (geometry)".
Planar may also refer to:
Science and technology
* Planar (computer graphics), computer graphics pixel information from several bitplanes
* Planar (transmission line technologies), ...
,
cylindrical
A cylinder () has traditionally been a Solid geometry, three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a Prism (geometry), prism with a circle as its base.
A cylinder may ...
or
spherical
A sphere (from Ancient Greek, Greek , ) is a surface (mathematics), surface analogous to the circle, a curve. In solid geometry, a sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three ...
geometrical surfaces as a collection of a finite number of spatial samples.
Antenna near-field scanner
First scanners were built in the 1950s to map probe signal variations in front of microwave antennas. Determination of a far-field radiation pattern constitutes the primary application of antenna near-field scanners. This novel technique offered an attractive alternative to conventional open area test sites for measurements of high gain, electrically large antennas or antenna arrays (gain > 20 dBi, diameter > 5λ) in an indoor, controlled and all-weather capability environment. Among well recognized and analyzed errors of the near-field measurements, multiple reflections between an antenna under test (AUT) and an electromagnetically non-transparent field detection system (scatterer) belong to the most contributing errors when the AUT has a high gain. Therefore, the scanning surface is recommended to be located ''outside the reactive near-field region'' of the AUT.
EMI near-field scanner
In EMI applications, the main focus of a scanner system is on locating real electromagnetic interference (EMI) sources distributed in a device under test, the DUT. Accordingly, the scanning surface is located ''in the highly reactive region'' of the DUT to enable a precise spatial localization of the electric charges and current surface densities directly from the mapped pattern of probe signals. Typically the separation between the scanning surface and the DUT is much smaller than the largest physical dimension of the DUT. Typical distances are 1 mm for scanning of PCBs and 30 μm for scanning of integrated circuits on a die level. In order to quickly localize field emission in the frequency domain, time domain detection techniques together with signal processing based on fast Fourier transform could be employed, e.g. utilizing a digital storage oscilloscope as a signal receiver.
Further reading
References
{{Reflist
Measuring instruments
Electromagnetic radiation meters