EMC:

Radiated Emissions

A common component of EMC, radiated emissions testing measures the amount of electromagnetic interference (EMI) generated by the device under test (DUT). Most electronic devices emit some type of electromagnetic field under normal use, so the level of emission needs to meet a certain threshold to ensure it doesn't cause interference when used near other devices.

Measuring radiated emissions is accomplished using a certain set of equipment. The DUT is placed on a turntable which slowly rotates it to see whether radiated emissions are higher coming from a certain part of the device. Placed a certain distance away (1 meter, 3 meters, 10 meters, or 30 meters depending on the standard) is an EMC antenna which measures the DUT's radiated emissions. The antenna is mounted either on a tripod or a mast which is capable of moving it vertically. It is also important to know the antenna's factor, or the amount by which emissions change when moving through the antenna or its cable. This can be found in the antenna's datasheet.

The antenna is connected to anything from an EMI test receiver to a spectrum analyzer depending on whether compliance, pre-compliance, or simple troubleshooting is needed. The latter two can be performed with a spectrum analyzer or basic EMI receiver, while the former requires a CISPR-compliant EMI receiver such as the Rohde & Schwarz ESW44.

When examining emissions close to the device, a near field probe is used. Preamplifiers may also be necessary when looking for very small signal emissions, but many modern spectrum analyzers and EMI receivers have this function built in.

Below is our diagram of a common radiated emissions test setup.