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.
Moisture Absorption Loss
Meaning
Water molecules entering the microscopic pores of a dielectric material increase the dissipation of electromagnetic energy into heat. This phenomenon known as moisture absorption loss is a primary concern for high frequency circuit boards and antenna housings exposed to humid air. It results in a lower signal to noise ratio and can cause a system to fail its performance specifications over time.
Permittivity Shift
Water has a very high dielectric constant compared to most industrial polymers and ceramics. As a substrate experiences moisture absorption loss, its effective permittivity increases and shifts the resonant frequency of the traces. This change detunes the filters and antennas, leading to a mismatch that reflects power back to the source.
Engineers must account for these shifts by selecting materials with very low water uptake for outdoor deployments.
Material Degradation
Persistent exposure to high humidity can lead to the breakdown of the polymer chains or the delamination of the copper layers. Beyond the immediate moisture absorption loss, the structural integrity of the assembly may be compromised. Some plastics swell when they take on water, which introduces mechanical stress into the solder joints and leads to premature failure.
Environmental Testing
Qualification of a new design involves placing the module in a chamber with controlled temperature and humidity for several hundred hours. Measuring the moisture absorption loss after this exposure confirms if the chosen enclosure provides an adequate seal. These tests ensure that the connectivity remains stable across the intended lifecycle of the product.