Cables as Antennas: Why Geometry Beats Component Choice

In a significant number of MIL-STD-461G failures, the root cause is not the electronic circuitry but the external cabling. Cables frequently dominate electromagnetic coupling paths because their physical dimensions and routing allow them to interact strongly with both conducted and radiated fields.

Cable length, routing, separation from structure, and termination geometry often determine how energy enters or leaves a system. Even when internal circuitry is well designed and adequately shielded, cables can act as efficient antennas that collect, radiate, or redistribute electromagnetic energy. Unintended loops formed by cable routing and return paths further amplify this effect by creating low impedance coupling structures.

A system can contain a well-designed printed circuit board housed in a sealed enclosure and still fail susceptibility testing if the cables connected to it are poorly managed. Shield terminations that rely on pigtails, inconsistent bonding at connectors, or uncontrolled routing can negate otherwise effective internal design measures.

This is why test laboratories place so much emphasis on cable layout during MIL-STD-461G evaluations. Experience has shown repeatedly that cable geometry, not component choice, is often the decisive factor between passing and failing.