Dielectric Classification
High-frequency printed circuit boards used in automotive driver-assistance systems require base materials with exceptionally low insertion loss and extremely stable permittivity at millimeter-wave frequencies. A 77 ghz radar substrate satisfies these criteria by utilizing polytetrafluoroethylene or thermoset hydrocarbon resins loaded with ceramic fillers to minimize signal attenuation. The material governs the propagation velocity and phase consistency of radar signals across the operating temperature range.
It maintains these properties up to ninety gigahertz, beyond which dielectric dispersion begins to compromise signal integrity.
Transmission Loss
Signal attenuation is primarily controlled through the surface roughness of the clad copper foil and the dissipation factor of the resin matrix. In a 77 ghz radar substrate, very low profile or rolled copper is specified to reduce skin effect losses at high frequencies. This minimizes the risk of signal degradation in the microstrip feed lines and patch antennas.
Dimensional Stability
Thermal and moisture behavior dictates the long-term reliability of these high-frequency assemblies under harsh automotive hood environments. Moisture absorption must be kept below one tenth of a percent to prevent shifts in the center frequency of the radar sensor. Consequently, the chosen resin system must resist environmental humidity during extended field exposure.
