Software Analyzes
Complex Beam
Steering Antenna
ArraysRemcomState College, Pa.

A(a)(b)

Fig. 1 Patterns of a 1 x 8 linear array (a) and two, 1 x
4 linear arrays (b) of patch elements, simulated using thesuperposition feature in XFdtd.

s telecommunications standards
have shifted to higher frequencies, such as mmWave, systemdesigners have incorporated arrays of antennas into communication systems. These sophisticated arrays enablehigher gain and smaller beamwidth patterns
that can overcome the high path losses inherent at these frequencies, to deliver thehigher throughput promised by these newstandards. Even for small arrays with a few
elements, fully understanding the coverage
possible with different power and phasing
combinations can be difficult. When arrays
grow larger to contain tens or hundreds ofelements, advanced tools are required to
fully describe the operation and effectiveness of the design.
The latest release of Remcom’s XFdtd®
Electromagnetic Simulation Software contains analysis tools for rapidly characterizing
the performance of arrays of antennas for
beamforming and beam steering applications. Superposition enables the rapid synthesis of complex problems using basic datafrom an electromagnetic (EM) simulation,quickly overlaying the data in a linear space.
For example, consider multiple antennas
in a problem space. The requisite data—Sparameters, efficiency and far-zone—arecomputed once in an EM simulation for eachantenna of interest. These may be quickly
combined with complex scaling to yield theradiation pattern and associated active S-

Reprinted with permission of MICROWAVE JOURNAL® from the July 2020 issue.
©2020 Horizon House Publications, Inc.

ProductFeature
Fractional Area

1.0
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parameters and efficiency for any
desired antenna power and phasing
combination. For situations wherespecific port power and phasing
options are known, the resulting farzone pattern can be computed immediately in post-processing.
A second situation is where thespecific beam directions are known
in advance, and the power andphasing of the ports is desired tomaximize the effective isotropic radiated power (EIRP) in those directions. Using statistical analysis, thecoverage provided by the array for
all possible directions may be determined by calculating the cumulative distribution function (CDF) ofthe EIRP, which shows the percentof the spherical far-zone volume
with positive gain for a given input
power.
To illustrate, we consider a 1 × 8
array of 28 GHz patch antenna elements, where the phasing between
elements is swept using the superposition feature from -90 to +90
degrees in 30 degree steps. Seven
unique beams will be created, which
focus a fan beam between -30 and+30 degrees (see Figure 1a). Alternatively, if the array is used in a configuration with two adjacent 1 × 4
subarrays, the superposition featurecan be used to generate separate
patterns for each subarray (see Figure 1b).
Alternatively, where the desired
beam directions are known and theport settings are desired, an array
optimization feature is available. Alarge, two-dimensional array, suchas an 8 × 8 patch array at 28 GHz,
will create narrow beams that canbe swept over a broad range of(23, 0.10718)

0.20Fig. 2 Patterns of an 8 x 8 array ofpatch elements, simulated using thearray optimization tool in XFdtd.

(23, 0.34371)

0.4510152025
EIRP (dBmW)Left SideRight SideTopBottom
Left Side + Top
Right Side +Bottom

Fig. 3 Patterns of an 8 x 8 array ofpatch elements structured as four 4 x 4independent subarrays, simulated using
the array analysis tools in XFdtd.

30

Left Side + Bottom
Right Side + Top
Left Side + Right SideTop + Bottom
All Four Arrays

Fig. 5 EIRP CDFs of the patch arraysin the mobile phone.

Fig. 4 Four, 1 x 4 patch arrays
distributed in a mobile phone to enablewide spatial coverage.

directions above the array. Figure
2 shows the “max hold” patterncreated with the array optimization
tool, where the beams are desired
at every 15 degrees in the azimuth
direction and an elevation angle 30
degrees down from normal. Following the calculation, the required
port power and phasing requirements for the elements to form eachbeam are available.
A large array may also be operated as a set of smaller subarrays
functioning independently. Figure
3 shows the same 8 × 8 array configured as four, 4 × 4 arrays, eachwith their own unique power andphasing to communicate with four
receivers. Using the array analysis
tools, the subarrays are defined andtheir operating characteristics canbe explored.
Multiple arrays on a single device
are used for spatial diversity, to provide coverage over a wider rangeof angles—more than a single array
could produce. An example of thisis a 5G mobile phone incorporating
multiple arrays around the edge ofthe phone. Figure 4 shows four arrays located on the sides, top andbottom of the phone case. Eachare four element patch arrays thatcan produce a steerable beam covering a wide region normal to thearray. When used in combination,
the arrays can provide coverage in
multiple directions, which is best
demonstrated with the CDF of theEIRP. This one-dimensional function
describes the percentage of the farfield sphere covered by an array fora given input power. In Figure 5,
the CDF of EIRP is plotted for different combinations of the four arrays
along the edges of the phone. The
single arrays used individually provide positive gain for about 66 percent of the directions (i.e., 1–0.34
from the CDF plot), assuming atypical 23 dBm input power to eacharray. The coverage improves toabout 90 percent when two arrays in
one of the corners are used in combination, and full coverage results
when the arrays on opposite sidesof the phone are used together.
As device performance is pushed
to new levels by the increasing demands of 5G mmWave systems, theneed for more comprehensive analysis tools for complex antenna systems grows. XFdtd’s new features
simplify the process of understanding device performance by providing efficient ways to analyze andvalidate array coverage.
RemcomState College, Pa.
www.remcom.com