Tech Briefs Magazine - November 2021 - 43

TECHNOLOGY LEADERS Engineering Software
Optimizing Wireless Test Systems and
Antennas for High-Speed Communication
E
very year, consumers are dazzled
by the latest smartphones and
wireless devices that hit the market.
Before these upgraded
gadgets reach the shelves, there is an
extensive design and testing process that
goes into developing them. Antennas, a
paramount component of wireless de -
vices, are consistently updated to keep
up with advancing technology such as
5G and the Internet of Things (IoT).
They are expected to have greater bandwidth,
meet safety regulations, and be
small enough to fit into micro-designs.
To help engineers working with wireless
equipment, Bluetest (based in Gothenburg,
Sweden) has developed easy-to-use
reverberation test systems (RTS) that
measure the performance of wireless
devices and antennas. Today, Bluetest is a
market leader in over-the-air, multipleinput-multiple-output
(MIMO) testing.
The company uses simulation to ensure
that the components of their RTS designs
are optimized for performance.
Evolution of Reverberation Testing
Since the early 1940s, antenna performance
has been tested in anechoic
chambers, or microwave-absorbing rooms.
In this type of chamber, an antenna is
rotated and its radiated intensity is measured
in different directions. The data
gained from this testing method is relatively
easy to interpret but anechoic
chambers tend to be expensive and their
large size makes them unwieldy.
In the 1960s, a different type of chamber
was developed - the reverberation
chamber - that was originally used for
electromagnetic compatibility (EMC)
testing. Unlike anechoic chambers, reverberation
chambers reflect electromagnetic
waves (or sound for the acoustic equivalent)
instead of absorbing it. " You can
generate very high field intensities inside
this kind of chamber, which is a great feature
for testing immunity and how sensitive
a device is when it gets radiated with
high-power electromagnetic fields, " said
Robert Rehammar, chief technology officer
at Bluetest.
Tech Briefs, November 2021
Cov
Figure 1. An example of one of Bluetest's reverberation test systems, the RTS65. Bluetest currently has five different
RTS on the market.
In the late 1990s, people learned that
reverberation chambers can also be used
to test certain antenna parameters. For
example, a small antenna's most important
property is its efficiency, or the quotient
between the power you put into the
antenna compared to how much power
is actually radiated (typically measured in
dB). " What was realized is that you can
measure antenna efficiency in reverberation
chambers and it turned out that for
a small antenna, you can do it very fast
and accurately, " said Rehammar.
Toward the beginning of the reverberation
testing system's popularity, Per-35
-30
-25
-20
-15
-10
-5
500
Simon
Kildal, a professor of antenna systems
at Chalmers University of Tech -
nology in Sweden, started a research
project on reverberation chambers and
their ability to analyze antennas. After
studying these chambers, Kildal was
inspired to start a company based on his
findings and Bluetest was born. Around
2010, 4G - the fourth generation of
mobile systems (also known as LTE) -
was introduced, along with MIMO. As a
result, said Rehammar, " A lot of very
complicated questions popped up like,
'How are we going to test the perfor -
mance of these systems?' "
P1 A
P1 B
P1 C
P1 D
P1 E
P1 F
P1 G
P1 H
P2 A
P2 B
P2 C
P2 D
P2 E
P2 F
P2 G
P2 H
1000
1500
2000
Frequency [MHz]
Figure 2. Bluetest's first prototype of a Vivaldi antenna, simulated in COMSOL Multiphysics®
plot (right) shows the impedance matching characteristics up to 3 GHz.
www.techbriefs.com
ToC
. The S-parameter
2500
3000
43
Efficiency

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Tech Briefs Magazine - November 2021

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