Measuring Polymer Radome Transmission Loss at Millimeter Wave Frequencies
Polymer radome transmission loss at mmWave frequencies depends on dielectric loss tangent and wall thickness precision to maintain regulatory EIRP compliance.
Oblique Incidence Reflection
Meaning
Electromagnetic waves striking a boundary at an angle away from the perpendicular exhibit complex behavior compared to a straight on impact. This effect called oblique incidence reflection causes the amount of reflected energy to vary based on the angle of arrival and the polarization of the wave. It is a major factor in the design of stealth coatings and high performance antenna enclosures.
Polarized Response
The behavior of the signal differs notably between the electric field components that are parallel or perpendicular to the plane of the interface. Under conditions of oblique incidence reflection, the transverse electric and transverse magnetic waves follow different mathematical rules for their reflection coefficients. This divergence means that a surface might be highly reflective for one orientation while being almost transparent for another.
Designers use this knowledge to optimize the orientation of sensors behind a plastic cover.
Angular Sensitivity
Small changes in the arrival path of the signal can lead to large fluctuations in the reflected power. As the angle increases, the phase shift at the interface also changes, which can disrupt the timing of a multi antenna array. Calculations for oblique incidence reflection must be performed across the entire expected range of movement for a mobile device.
Shielding Effectiveness
Metal enclosures rely on reflecting waves away from sensitive electronics to prevent interference. Effectiveness of a shield decreases as the signal moves toward an oblique incidence reflection path. Gaps in the housing or seams in the metal are more likely to leak energy when the waves hit them at an angle.