mmWave Design
automotive radar for ACC, the velocity
and distance information would be used
to alert the driver or take corrective action
(such as applying braking).
MULTI-BEAM/MULTI-RANGE DESIGN
A typical ACC stop-and-go system
requires multiple short and long-range
radar sensors to detect nearby vehicles.
The shorter range radar typically covers
up to 60 m with an angle coverage
up to ±45°, allowing the detection of the
vehicle’s adjacent lanes that may cut into
the current travel lane. The longer range
radar provides coverage up to 250 m
and an angle of ± 5° to ±10° to detect
vehicles in the same lane, further ahead.
To support multiple ranges and scan
angles, module manufacturers such as
Bosch, DENSO, and Delphi have developed
and integrated multi-range, multidetection
functionality into increasingly
capable and cost sensitive sensors using
multi-channel transmitter (TX)/receiver
(RX) architectures, as shown in Figure 7.
These different ranges can be addressed
with multi-beam/multi-range radar by employing
radar technology such as FMCW
and digital beamforming with antenna
array design.
ANTENNA DESIGN
A multi-modal radar for an ACC sys -
tem2 based on an FMCW radar driving
multiple antenna arrays is shown in
Figure 8. This multi-beam, multi-range
radar with digital beam forming operates
at both 24 and 77 GHz, utilizing
two switching-array antennas to enable
long range and narrow-angle coverage
(150 m, ±10°) and short range and
wide-angle coverage (60 m, ±30°). This
example illustrates the use of multiple
antenna-array systems, including
multiple (5 x 12 element) SFPAs for long
range, narrow-angle detection (77 GHz),
a single SFPA (1 x 12 elements designed
for 24 GHz) for short, wide-angle
detection, and four (1 x 12) SFPAs for
the receiver that were required for this
type of system.
Radar performance is greatly influenced
by the antenna technology, which
must consider electrical performance
such as gain, beam width, range, and
physical size for the particular application.
The multiple, fixed TR/RX antenna
arrays in the example radar were optimized
for range, angle, and side-lobe
suppression. A patch antenna is relatively
easy to design and manufacture and
will perform quite well when configured
into an array, which results in an increase
of overall gain and directivity.
Figure 10: 8 x 16 patch antenna array (128-element) with corporate feed (singlefeed
port) and 167 k unknowns (1.88 GHz) solved in ~6.5 minutes with quad core.
Figure 11: a) AntSyn antenna synthesis specification interface and library of antenna
types, and b) simulated results based on user-specified antenna requirements.
Figure 12: 4 x 4 patch antenna array with individual ports for each element
enables the feed structure (lower left) to be defined and co-simulated at the
circuit/system level to monitor the changing antenna input impedance per element
and control beam steering through the RF feed network.
18 MW November - December 2017 www.mwee.com
