Meaning
Physical law describes the change in direction of a wave as it passes from one medium to another with a different refractive index. Snellian refraction determines how radio signals bend when they encounter the radome or the housing of a wireless device. Integration engineers calculate these angles to ensure that the internal antenna is correctly aligned with the aperture of the enclosure.
The ratio of the sines of the angles of incidence and refraction equals the ratio of the phase velocities.
Refractive Transition
Relative permittivity of the plastic or composite material dictates the severity of the beam deviation. For a device relying on snellian refraction, a high-permittivity cover will cause a sharper bend in the signal path. Selecting a material with a low dielectric constant minimizes this effect and preserves the intended radiation pattern.
Radome Interaction
Geometric properties such as the curvature and thickness of the enclosure wall must be accounted for during the placement of the antenna. The effects of snellian refraction are most pronounced when the signal hits the surface at an oblique angle. Adjusting the geometry of the interior mount compensates for the predicted shift in the main lobe.
Path Calculation
Energy loss occurs through reflection at the boundary between the air and the enclosure. By applying the principles of snellian refraction, the total transmission coefficient is calculated to determine the impact on the range of the device. This calculation is a standard part of the mechanical and electrical co-design process.
