E-Band VNA for Automotive Market: Bumper and Emblem Measurements
■This application note, developed in conjunction with vendors in the automotive market, will present a configuration used to test and measure the transmission and reflection characteristics of materials (emblems and bumpers) placed in front of automotive radars. The configuration explained below will make it possible to provide clear and accurate measurements for companies working in the automobile market. These will be precise and repeatable measurements given in dBs for transmission and reflection characteristics.
★Introduction:
■A radar placed behind an emblem or bumper of a car must transmit its signal with minimal interference. Specifications of the materials are required by the car manufacturers to ensure the proper operation of the radars. To test the emblem or the bumper, a ShockLine MS46522B vector network analyzer (VNA) with option 83 (5 meter E-band) is used to provide the necessary frequency range coverage, measure all S-parameters (S11, S12, S21, and S22), and characterize the behavior of the material. In this case, instead of using a conducted setup, where the signals are transmitted through a transmission line like a coaxial cable, two antennas are attached to both ports of the ShockLine MS46522B-083 VNA to transmit and receive the signals. The model of antenna used must be defined according to the test configuration, always considering a plane wave must be present in the surface to be measured (working in the E-band [60 to 90 GHz], this should not be an issue). Specific antennas with lens or dielectric will be chosen to form the wave.
■For this test, the shape of the material under test (MUT) is something that must also be considered as it can affect the results depending on the width, paint, manufacturing process, etc. Another question that arises is whether it is better to use a single, large beam on the whole surface to be tested or a smaller beam and to do it in two or three tests.
■It is important to note that during these tests the radiation environment was not ideal to characterize a MUT and that some care had to be taken. The most important issue is reflections. In the open environment used, reflections could happen and ruin the measurements. To avoid reflections there are two options that could be used that are not exclusive of each other. The first requires placing an absorbent material all around the room, however, this can complicate the setup even more. The second is the use of the gating process in the ShockLine VNA. In this case, a gate is defined around the test distance range to exclude any external interference.
■The test results were quite precise and consistent, getting measurement accuracies in the order of a few hundredths of a dB. When conducting these measurements, the ShockLine VNA did not seem to be the most critical element affecting the accuracy of the measurement, rather it was the actual position of the tested sample for the reflection measurement. This measurement was influenced by the angle between the direction of the transmission and the plane of the sample. A small longitudinal displacement of the sample has little affect on the transmission measurement and for the reflection it is on the order of ± 0.2 dB for ± 1 mm.
■The measurements on the bumpers gave values around 0.7 dB for the transmission and –9 dB for the reflection. These values, of course, being affected by the thickness and paint used.
■Although traditional E-band measurement systems, which are much larger and more expensive, can yield sufficiently accurate results, we must also consider how those systems would fair in a production environment. The lower cost and smaller "plug-and-play" form factor of the ShockLine MS46522B model is perfectly suited for this type of production use.
■Today, radars used by automotive manufacturers are critical elements in their safety systems. In the future, these systems will be considered even more critical for the autonomous car. At the output of the production line, all bumpers and emblems must be measured to ensure that they comply with safety standards and the results will be saved to maintain traceability. One must be able to leverage a quick and easy-to-use VNA system that can be placed in a production plant environment.
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Application note & Design Guide |
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Please see the document for details |
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English Chinese Chinese and English Japanese |
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2020-03 |
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Rev. B |
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11410-01181 |
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2.2 MB |
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