Radiated Spurious Emissions Mitigation in Multi Radio System Design
Radiated spurious emissions in multi-radio designs demand aggressive board-level isolation and predictive intermodulation filtering to secure market approvals.
Faraday Boundary
Meaning
Conductive enclosures block external static and dynamic electromagnetic fields from interfering with sensitive internal electronic circuits. Establishing a faraday boundary involves creating a continuous electrical shield around the vulnerable components or the entire product assembly. The conductive barrier prevents external electric charges from creating field gradients within the enclosed region.
This shielding effect ceases to operate effectively if the openings in the conductive surface exceed the wavelength of the interfering radiation.
Electromagnetic Shielding
High-frequency attenuation depends on the skin depth of the selected material and the continuity of the seams. Attenuating incoming radio signals requires a low-resistance path that routes induced currents safely to the system ground. Gaps in the shield, such as display windows or cable entry points, alter the local impedance and allow leakage.
Physical Implementation
Designers employ conductive gaskets, metallic foils, copper sprays and shielding cans to maintain electrical continuity across mechanical joints. Sprayed conductive coatings inside plastic housings provide a lightweight alternative to sheet metal boxes. Spring fingers on printed circuit boards bridge the gap between the ground plane and the metal shield cans.
Fastener spacing must be close enough to prevent the material from bowing under thermal stress, which would otherwise break the electrical contact.
Performance Limit
The attenuation of magnetic fields at low frequencies presents a major design challenge because standard conductive materials cannot divert low-frequency flux. Special high-permeability alloys must be used to absorb and redirect these magnetic field lines. Apertures for ventilation or status indicators are sized to behave as waveguides below cutoff to preserve the integrity of the shield.