The performance of a rectangular
patch antenna design is controlled by
the length, width, dielectric height,
and permittivity of the antenna. The
length of the single patch controls the
resonant frequency, whereas the width
controls the input impedance and the
radiation pattern. By increasing the
width, the impedance can be reduced.
However, to decrease the input impedance
to 50 Ohms often requires a very
wide patch antenna, which takes up
a lot of valuable space. Larger widths
can also increase the bandwidth, as
does the height of the substrate. The
permittivity of the substrate controls the
fringing fields with lower values, resulting
in wider fringes and therefore better
radiation. Decreasing the permittivity
also increases the antenna’s bandwidth.
The efficiency is also increased with a
lower value for the permittivity.
Designing a single patch antenna
or array is made possible through the
use of design software that utilizes EM
analysis to accurately simulate and
optimize performance. NI AWR Design
Environment includes AXIEM 3D planar
and Analyst™ 3D finite element method
simulator. These simulators not only
simulate antenna performance such as
near and far-field radiation patterns,
input impedance, and surface currents,
they also co-simulate directly with VSS,
automatically incorporating the antenna
simulation results into the overall radar
system analysis without the need to
manually export/import data between
EM simulator and system design tools.
Both AXIEM and Analyst take the
user-defined physical attributes of the
antenna such as patch width and length,
as well as the dielectric properties such
as material and substrate height, to
produce the electrical response. AXIEM
is ideal for patch antenna analysis,
whereas Analyst is best suited for 3D
structures such as modeling of a coaxial
feed structure or finite dielectric (when
proximity to the edge of a PCB would
impact antenna performance) (Figure 9).
Figure 10 shows a patch antenna
array with corporate feed and 167 k unknowns
solved in less than 6.5 minutes
with a quad core.
To determine the physical attributes
that will yield the desired electrical
response, antenna designers can use NI
AWR software’s AntSyn™ antenna synthesis
and optimization tool (Figure 11).
AntSyn enables users to specify the electrical
requirements and physical size constraints
of the antenna and the software
explores a set of design configurations
mmWave Design
and determines the optimum structure
based on proprietary genetic optimization
and EM analysis. The resulting antenna
geometry can then be imported in a
dedicated planar or 3D EM solver such
as AXIEM or Analyst for verification or
further analysis/optimization.
Planar elements can easily form array
structures by combining very simple
elements such as microstrip patches.
Patches can be configured in a series
such as the 1 x 8 patch array, where each
element is connected serially by a “tunable”
section of transmission line. In this
AXIEM project, the lengths and widths of
each array element and the connecting
transmission lines were defined with variables
to allow optimization of the overall
array performance.
The 1 x 8 array can be further expanded
into an 8 x 8 array for a highgain
fixed-beam design replicating the 8
x 8 element array reported in 3.
Within NI AWR Design Environment
arrays can be represented in VSS as a
system behavioral block using the proprietary
phased-array model that enables
designers to
specify the array
configuration
(number of elements,
element
spacing, antenna
radiation
pattern, impaired
elements,
gain tapering,
and more) for
a high-level
understanding
of array
requirements
for desired
performance
such as gain
and side lobes.
This approach
is best for largescale
arrays
(thousands of
elements) and
system designers
developing
basic requirements
for the
antenna array
team.
The array
could also
be modeled
in AXIEM or
Analyst with
the detailed
physical array,
specifying individual port feeds as in
Figure 12 or a single feed if the feed
network is also implemented in AXIEM/
Analyst, Figure 13.
This approach enables the design
team to investigate the interaction
between the beam angle and the input
impedance of each individual element,
allowing RF front-end component designers
to account for impedance loading
effects on transceiver performance.
This capability highlights the importance
of having RF circuit, system, and
EM co-simulation to accurately investigate
circuit/antenna behavior before
fabricating these complex systems.
MIMO AND BEAM-STEERING
ANTENNA TECHNOLOGIES
For road vehicles, a radar will receive
unwanted backscatter off the ground
and any large stationary objects in
the environment, such as the sides of
buildings and guardrails. In addition to
direct-path reflections, there are also
multipath reflections between scatterers,
which can be used to mitigate the
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OCXO
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OeXO® Series a proven performer in:
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www.Pletronics.com
or call (425) 776-1880
www.mwee.com November - December 2017 MW 19
