5G – Antenna Design
MIMO Dual-Band WiFi Antenna Using NI AWR Software,
Optenni Lab, and Premix PREPERM Materials
By Jaakko Juntunen, Optenni Ltd; Jan Järveläinen, Premix Group;
Derek Linden, AWR Group, NI
INTRODUCTION
Multiple-in-multiple-output (MIMO)
antenna technology is regarded as a
key technology enabler for mobile radio
services because of its ability to multiply
the capacity of a radio link using
multiple transmit and receive antennas,
thus exploiting multipath propagation.
A dual-band WiFi antenna was recently
developed through the collaborative
efforts of three companies specializing
in electronic design automation (EDA)
software and dielectric materials.
This article describes the design of
an electrically-small antenna project for
WiFi applications using the NI AWR Design
Environment platform, specifically
the AXIEM 3D planar electromagnetic
(EM) analysis simulator, as well as the
AntSyn™ automated antenna design,
synthesis, and optimization tool, along
with Optenni Lab™ RF design automation
platform for the antenna system
optimization, and Premix Group’s
PREPERM dielectric plastic materials
for the antenna and its feed network. To
minimize the losses at higher frequency
bands, a high-quality dielectric material
was first selected. The design process
is shown in Figure 1.
DESIGN FLOW
A dual-band MIMO Wi-Fi antenna and
associated matching circuitry operating
at 2.4 GHz and 5 GHz was designed,
the purpose being to exercise materials
and techniques to demonstrate antenna
designs at S and C bands that could
be leveraged and scaled for future millimeter
wave (mmWave) stationary and
mobile platforms at higher frequencies.
PREPERM PPE370, which has a dielectric
constant (εr) = 3.7 was used for the
antennas. The associated matching circuitry
was designed on PREPERM 255
with εr = 2.55. The PPE370 contains
more ceramic filler than PREPERM
255 in order to obtain a higher dielectric
constant. The substrate size was
90 mm x 50 mm (≈ 3.5 x 2 inches) and
the nominal frequencies were 2.4 GHz
and 5 - 6 GHz. To enhance isolation, a
decoupling network was designed between
Figure 1: Example of prototyping with Premix PREPERM and NI AWR software.
Figure 2: The antennas were synthesized using AntSyn according to the
specifications.
the two antennas. An overall efficiency
of -2 dB or better was achieved.
Efficiency is defined as:
where Rrad is the radiation resistance
and Rloss denotes loss resistance which
includes loss in the antenna structure
and loss in the matching circuit Rloss.
The initial designs (Figure 2) were
developed using the AntSyn antenna
synthesis module, which has a unique
capability to synthesize antenna geometries
to a given specification.
The performance metrics used were
pattern efficiency and impedance match.
No specific gains were given as the
antenna size was electrically small, thus,
the pattern was more or less omnidirectional
by default. The emphasis on each
metric was balanced in the optimization
process, however, the better the impedance
match, the better the efficiency
would tend to be, so in reality the two
criteria were highly related and mutually
cooperative.
With a dual-band requirement, not
only was the optimization process more
complicated, but also each run took
longer to complete. However, while a
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