IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 65, NO. 5, MAY 2017 1707
Miniaturized Millimeter-Wave Radar Sensor
for High-Accuracy Applications
Mario Pauli, Member, IEEE, Benjamin Göttel, Student Member, IEEE,SteffenScherr,Student Member, IEEE,
Akanksha Bhutani, Student Member, IEEE, Serdal Ayhan, Graduate Student Member, IEEE,
Wolfgang Winkler, and Thomas Zwick, Senior Member, IEEE
(Invited Paper)
Abstract—A highly miniaturized and commercially available
millimeter wave (mmw) radar sensor working in the frequency
range between 121 and 127 GHz is presented in this paper. It can
be used for distance measurements with an accuracy in the single-
digit micrometer range. The sensor is based on the frequency
modulated continuous wave (CW) radar principle; however,
CW measurements are also possible due to its versatile design.
An overview of the existing mmw radar sensors is given and the
integrated radar sensor is shown in detail. The radio frequency
part of the radar, which is implemented in SiGe technology, is
described followed by the packaging concept. The radar circuitry
on chip as well as the external antennas is completely integrated
into an 8 mm × 8 mm quad flat no leads package that is
mounted on a low-cost baseband board. The packaging concept
and the complete baseband hardware are explained in detail.
A two-step approach is used for the radar signal evaluation: a
coarse determination of the target position by the evaluation of
the beat frequency combined with an additional determination
of the phase of the signal. This leads to an accuracy within a
single-digit micrometer range. The measurement results prove
that an accuracy of better than ±6 µm can be achieved with the
sensor over a measurement distance of 35 mm.
Index Terms—Frequency modulated continuous wave
(FMCW) radar, high accuracy, millimeter-wave (mmw)
packaging, miniaturized radar sensor.
I. INTRODUCTION
T
HE highly accurate determination of distances and posi-
tions is ubiquitous in todays industry and is the basis
for highly precise machining systems, injection molding
machines, production and automation industry, and even for
construction machines. The need for high accuracy measure-
ments comes along with the trend to produce miniaturized
parts, produce more accurately, faster and, finally, cheaper with
increasing quality. One example in industry is micromachining
Manuscript received October 15, 2016; revised February 21, 2017; accepted
February 22, 2017. Date of publication March 23, 2017; date of current
version May 4, 2017. This work was supported in part by the Federal Ministry
of Economy and Technology, Germany, through AiF in context of the ZIM
initiative, and in part by the German Research Foundation in the context of
the SPP1476.
M. Pauli, B. Göttel, S. Scherr, A. Bhutani, and T. Zwick are with the
Institute of Radio Frequency Engineering and Electronics, Karlsruhe Institute
of Technology, 76131 Karlsruhe, Germany (e-mail: mario.pauli@kit.edu).
S. Ayhan was with the Institut für Hochfrequenztechnik und Elektronik,
76131 Karlsruhe, Germany. He is now with SEW Eurodrive GmbH & Co.,
KG, 76646 Bruchsal, Germany.
W. Winkler is with Silicon Radar GmbH, 15236 Frankfurt (Oder), Germany
(e-mail: winkler@siliconradar.com).
Color versions of one or more of the figures in this paper are available
online at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TMTT.2017.2677910
where the machined parts become smaller and smaller but the
size of the machines remains nearly the same. The reason is
that the machines have to be very stiff to reduce inaccuracies
in the traverse paths from tools and to eliminate inaccuracies
caused by mechanical actuators. If it is possible to measure
the distance directly to the tool (e.g., the drill, the grinder, or
the milling cutter) instead of measuring within the bearing, the
whole machine could be smaller, lighter, and less expensive
without reducing the accuracy. Other application examples
comprise the measurement of the flatness of steel plates,
plastic surfaces, or the eccentricity of drilling holes, cylinders,
shafts, and axes or vibration measurements [1]. Also, the
measurement of hot steel slabs and the distance to the liquid
steel surface in blast furnaces are requested as well as the
measurement of the piston position in hydraulic cylinders [2].
Generally, contact-free measurement systems are favored
for this kind of measurements, since they offer a higher
flexibility and are not prone to damage and wearing down
in harsh environments. Current state-of-the-art technology for
distance and position sensors comprises inductive, capacitive,
hall, ultrasonic, and laser sensors. Especially, in the micro-
machining industry, the glass scale is often used. Optical
sensors offer an unmatched accuracy [3] but their use is
limited in harsh, dusty, or foggy environment. Furthermore,
they cannot be used in a liquid media such as oil within a
hydraulic cylinder. Ultrasonic measurements show, in many
cases, similar drawbacks and are usually less accurate.
Millimeter-wave (mmw) radar sensors, on the other hand,
are able to measure even under bad environmental condi-
tions. The signals penetrate fog and dust easily and are not
affected by changing light conditions. Simultaneously, they
offer a high flexibility and robustness with a similar accuracy
at significantly lower costs compared with a laser sensor.
Also, high measurement repetition rates and the simultaneous
measurement of the velocity of the target are possible.
Although automotive radar sensors in the 24-GHz and the
77-GHz range have been on the market for more than 10 years,
mmw radars are still not widely used in industrial applications,
except for tank level measurement systems which also operate
mostly at 24 GHz [4]–[6]. One might ask why radar sensors
have not been used more often in industry despite their
advantages. One reason is the large size at lower frequencies,
which makes the sensor impractical for many applications. The
other reason is their high cost in frequencies in the millimeter
or even submillimeter range. Furthermore, the handling of
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