Testing bumper material for installation of automotive radar sensors

Automotive radar sensors are usually installed behind vehicle bumpers. In order for the sensors to function reliably, the bumper material and paint layers where they are installed must be sufficiently transparent and homogeneous. The ¸QAR automotive radome tester provides information about the RF characteristics of the bumper material at the push of a button. The R&S®QAR enables users to optimize the material characteristics during development and verify them in production.

Your task

Lateral radar sensors are currently being deployed in vehicles as blind spot, lane change and cross traffic assistants. Radars that sense the surrounding area are key components for future autonomous vehicles. For aesthetic reasons, the sensors are usually installed behind the vehicle bumpers where they can't be seen.Error-free radar sensing of the surrounding area is especially important for autonomous driving. Bumpers can impair the transmission of the radar signals, with the result that objects are detected too late, in the wrong place or not at all. Bumpers are usually injection molded from plastic in one piece and then coated with several very thin layers of paint. Inhomogeneous bumper material as well as too thick or unevenly applied paint layers can strongly attenuate the radar signal or change its transmission angle and prevent the radar sensors from functioning properly. Car manufacturers and their suppliers need new measurement methods that allow them to quickly and reliably assess the radar compatibility of bumpers during development and in production.

QAR with the QAR-Z60 reference reflector behind the bumper
Fig. 1: The R&S®QAR with the R&S®QAR-Z60 reference reflector behind the bumper
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The Rohde & Schwarz solution

The R&S®QAR is currently the only available solution that can test, at many points simultaneously and in just a few seconds, the material characteristics of the bumper area where the radar is installed. The R&S®QAR features a large panel containing several hundred transmit and receive antennas operating in the automotive radar frequency range from 76 GHz to 81 GHz. To measure the transmission loss, the bumper is placed between the panel and the R&S®QAR-Z60 reference reflector (Fig. 1).

The QAR-Z60 reference reflector's 102 metal pins create a defined diffuse reflection.
The R&S®QAR-Z60 reference reflector's 102 metal pins create a defined diffuse reflection.
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The rectangular reference reflector consists of an absorbent layer (Fig. 2: 1) on which 102 metal pins with a length of 50 mm are mounted (Fig. 2: 2). The length of the pins was chosen to make them clearly distinguishable from the absorbent layer during measurement. The specially formed ends of the pins reflect the signal from the transmit antennas and create a defined diffuse reflection (Fig. 3), which allows the entire reflected power to be captured by the receive antennas. Instead of a time-consuming series of tests, for example with a vector network analyzer, the R&S®QAR determines its results in a one-shot process like a camera.

Results of reference measurements
Fig. 3, left: result of reference measurement without the bumper; right: with the bumper; shows excessive signal attenuation in some places
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Application

To visualize how the bumper influences the radar signal, the reference reflector is initially placed in front of the R&S®QAR panel without the bumper. A reference measurement is started by pressing a button. The result is visible in just a few seconds (Fig. 3, left). Since the metal pins almost fully reflect the signal without any loss, the pins appear as white spots. The absorbent area between the pins is black. Now the bumper is mounted in front of the reference reflector. A new reflection measurement gives the result shown on the right in Fig. 3. The darker areas in the reflection image indicate significant signal attenuation. Areas highlighted in red indicate pronounced inhomogeneities in the bumper material. The average attenuation over the entire area is shown in dB. The way the R&S®QAR visualizes the measured values allows even non-techies to immediately judge the quality of the DUT.

Rohde & Schwarz service concept for minimum downtime
Rohde & Schwarz service concept for minimum downtime
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Rohde & Schwarz service concept for minimum downtime: To minimize downtime in the event of a defect, four different service levels are offered for the R&S®QAR to meet various customer requirements. For more information, please contact your local Rohde & Schwarz sales representative.