Tech Briefs Magazine - September 2021 - 34

Communications
Atom-Based Radio Communications
An atom-based sensor can determine the direction of an incoming radio signal.
National Institute of Standards and Technology, Gaithersburg, Maryland
esearchers demonstrated an atombased
sensor that can determine the
direction of an incoming radio signal,
another key part for a potential atomic
communications system that could be
smaller and work better in noisy environments
than conventional technology.
The capability to measure a signal's
" angle of arrival " helps ensure the accuracy
of radar and wireless communications,
which need to sort out real messages
and images from random or deliberate
interference. A true atom-based
com munication system would benefit
5G and beyond.
Two different-colored lasers prepare
R
by the atoms. An atom-based " mixer "
takes input signals and converts them
into different frequencies. One signal
acts as a reference while a second signal
is converted or detuned to a lower frequency.
Lasers probe the atoms
to
detect and measure differences in frequency
and phase between the two signals.
Phase refers to the position of
electromagnetic waves relative to one
another in time.
gaseous cesium atoms in a tiny glass flask,
or cell, in high-energy (Rydberg) states
that have novel properties such as ex -
treme sensitivity to electromagnetic
fields. The frequency of an electric field
signal affects the colors of light absorbed
The mixer measures the phase of the
detuned signal at two different locations
inside the atomic vapor cell.
Based on the phase differences at these
two locations, researchers can calculate
the signal's direction of arrival. To dem -
onstrate the approach, the team measured
phase differences of a 19.18-Gig -
ahertz experimental signal at two locations
inside the vapor cell for various
angles of arrival. They compared these
measurements to both a simulation and
a theoretical model to validate the new
method.
Atom-based sensors in general have
many possible advantages including
measurements that are both highly ac -
curate and universal; that is, the same
everywhere because the atoms are iden -
tical. Measurement standards based on
atoms include those for length and
time.
With further development, atombased
radio receivers may offer many
benefits over conventional technologies.
For example, there is no need for tra -
ditional electronics that convert signals
to different frequencies for delivery be -
cause the atoms do the job automatically.
The antennas and receivers can be
physically smaller, with micrometerscale
dimensions. In addition, atombased
systems may be less susceptible to
some types of interference and noise.
For more information, contact Laura Ost
at laura.ost@nist.gov; 303-497-4880.
Researchers determined the direction of an in -
coming radio signal based on laser measurements
at two locations in this sensor filled with
a gas of cesium atoms. (Credit: NIST)
34
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