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CR5CBCC User Manual
Budapest
10 June 2021
Page 11 of 17
Report
CR5CBCC_User_manual.docx
6.2
Fascia design guidelines
Material
Material with low dielectric constant (
r
) and low dielectric loss factor tan
δ
at 77 GHz should be
used. Recommended are materials based on polypropylene (PP) and polymethyl methacrylate
(PMMA), while materials like polycarbonate (PC) and acrylonitrile butadiene styrene (ABS) are
still ok. The material shall be homogenous, compounds including glass fiber, carbon fiber or
metal particles are not recommended.
The fascia shall be designed for radar transparency. The thickness shall be a multiple of the
half wavelength (in the material) to minimize the influence of the fascia. The quality criteria of
radar transparency is the reflection coefficient of the radome/fascia. Tolerances of the overall
thickness and the dielectric constant of the used material influence the amount of reflection at
the radome/fascia. Additional influence occurs due to curvature of the fascia. Therefore the
radius has to be as large as possible. With sharp edges the negative influence will increase
significantly. Not allowed are ribs, structures and steps changing the thickness of the
radome/fascia.
Painting
The layer structure of the painting, typically made of three painting layers consisting of primer,
base coating and clear coating, will increase the effective permittivity value
r,eff
and dielectric
loss factor tan
δ
of the painted plate used as fascia.
Fascia Classification (CR5CB)
The two-way radar loss caused by fascia should be as low as possible. High losses decrease
the sensor performance regarding range and angle estimation. Therefore it is recommended to
achieve a two-way radar loss below 4 dB in the ranges [-20;+20]° and [+/-60;+/-75]° and 3 dB in
the range [+/-20,+/-60]° t.b.c..
4 dB attenuation corresponds to a loss of about 20% of sensor range.
