Electromagnetic Compatibility (EMC) testing refers to the ability of a device or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment. EMC design and EMC testing are complementary; the quality of EMC design is evaluated through EMC testing. Only by incorporating EMC design and testing throughout the entire product development process can compatibility be predicted and assessed, potential electromagnetic interference identified early, and necessary suppression and protective measures implemented to ensure system EMC.

Key points for EMC testing include:

1. Open Test Site (OTS)

   • Theoretical Basis: For high-frequency electromagnetic fields in the 30~1000 MHz range, emissions and receptions are entirely composed of the superposition of direct/space waves and ground-reflected waves at the receiving point.
   • Standards: ANSI C63.7, CISPR 16.
   • Requirements: An elliptical or circular test site with a flat, open, uniformly conductive, and reflective surface.
   • Technical Indicator for Site Quality: Normalized Site Attenuation (NSA) - the attenuation of the standardized site within the open test site.

2. Shielded Room

   • Definition: A specially designed, sealed room that attenuates radio frequency (RF) electromagnetic energy.
   • Function: Provides a controlled environment required for EMC testing.
   • Shielding Effectiveness (SE) Definition: The ratio of the electric field strength (E₀) or magnetic field strength (H₀) at a point in free space (without the shield) to the electric field strength (E₁) or magnetic field strength (H₁) at the same point inside the shielded enclosure.

3. Anechoic Chamber (often called "Dark Chamber" or "Silent Chamber")

   • Structure Types:
     1. Semi-Anechoic Chamber (SAC): Combines an electromagnetic shielded room with a reflective ground plane and absorber material on the walls and ceiling. It simulates the open test site environment.
     2. Fully Anechoic Chamber (FAC): Also known as a "Microwave Anechoic Chamber," it has absorber material covering all internal surfaces (walls, ceiling, and floor). Compared to other environments, it provides the most ideal anechoic (non-reflective) conditions, minimizing interference from external sources, ground reflections, and wall/ceiling reflections, and is unaffected by weather, allowing for 24/7 testing.