Tech Briefs Magazine - November 2021 - 44

TECHNOLOGY LEADERS Engineering Software
Measuring Antenna
Performance
Bluetest's reverberation systems
(Figure 1) perform passive
and active tests to determine
whether or not a device
is optimized. Passive tests predominantly
measure antenna
efficiency, while active tests
measure the total radiated
power and total
isotropic
sensitivity in the device un -
der test's (DUT) transmitter
and receiver, respectively.
During active tests, the transmitter
and receiver in the
DUT are powered on. Active
measurements help give an
overview of how the DUT
performs as a whole. Both
tests help ensure that the
device, such as a mobile
phone, meets regulations and
customer requirements.
All of Bluetest's reverberation
test systems and products
are designed and produced in
Gothenburg. The RTS contains
a wide variety of components,
such as walls made of
reflective material, a reference
antenna, four to 16
measurement antennas with
different polarizations, mode
stirrers, RF interfaces, and
more. When the production
process is complete, the system is packaged
in a large wooden cradle and sent to
customers around the world.
ings, they were able to simulate
an im proved Vivaldi antenna by
im plementing Bézier curves into
their model (Figure 2).
Bluetest also simulated, de -
signed, and tested the efficiency
of a wideband monopole antenna
for ultra-wideband operating
from 6 GHz to 67 GHz. This type
of antenna is used in their RTS
for 5G measurements;
it also
helps provide the system with
more versatility because it can
be used during a measurement
without switching the standard
test antenna.
The use of simulation is not
limited to antenna designs. To
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enhance the performance of the
reverberation chamber, Bluetest
not only investigated the resonance
eigenmodes of a customized
cavity but also developed
circuit-to-waveguide transitions.
Keeping Up with the
Advancement of Technology
At Bluetest, Rehammar believes
Figure 3. Fabricated antennas designed using simulation.
Design, Fabrication, Test, and Validation
Bluetest is in the process of designing
new technology to use in their RTS for
millimeter-wave applications, including
the 5G mmWave band, where the center
frequency is an order of magnitude
higher than that of conventional mi -
crowave applications. High-speed communication
relies on a wide bandwidth,
which is provided by a high carrier frequency.
One
of the most popular antenna
designs for wideband applications is the
Vivaldi antenna - a tapered slot antenna.
" When it comes to antennas, we
need to be able to test anything from the
low cellular bands around 650 MHz up
to over 40 GHz, " said Rehammar.
44
Cov
The wavelength in millimeter-wave
device designs is much smaller than the
microwave wavelength and any minor
physical distortion due to thermal-structural
effects or fabrication tolerance error
would undesirably impact its perfor -
mance. Therefore, it is critical to validate
the performance of such devices using
simulation. Bluetest used COMSOL
Multiphysics® simulation to optimize
their antenna and circuit designs including
the Vivaldi antenna.
The first prototype of the Vivaldi
antenna design was modeled in FR4 substrate
(a composite material made up of
woven fiberglass and epoxy resin) with a
thickness of 1.6 mm. Simulating the first
iteration of this antenna allowed Reham -
mar and his team to see that there were
a few issues relating to its mounting, size,
stability, and efficiency while operating at
low frequencies. Thanks to these findwww.techbriefs.com
ToC
that
simulation technology and
measurement technology complement
each other completely.
" At the beginning stages of building
a design, you need simulation,
and to confirm your physical
device is working properly,
you have to do measurements, "
said Rehammar. Bluetest's systems are consistently
being updated to keep up with
the advancement of wireless technology,
especially within the mobile phone development
industry.
" Before 5G, mobile systems operated
up to about 2.6 GHz and now you have
5G systems that can run up to 40 GHz, "
said Rehammar. To stay on track with
this advancing field, Bluetest has been
working on supporting as many frequency
bands as possible. With the help of
simulation, Bluetest can focus on
improving their RTS test time and measurement
accuracy, while keeping the
testing complexity at a high level.
This article was written by Rachel Keatley,
Content Writer at COMSOL, Burlington, MA.
For more information, visit http://info.
hotims.com/79419-122.
COMSOL Multiphysics is a registered trademark
of COMSOL AB (www.comsol.com).
Tech Briefs, November 2021
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Tech Briefs Magazine - November 2021

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