Radiated Emission Measurement Step by Step: From Scan to Final
How the noise a product radiates is measured in a semi-anechoic chamber, with the pre-scan, maximization and final measurement steps.
3 min readNovember 11, 2026
An Unbroken Ground Plane
Every signal current returns to its source through a return path. At high frequency, that return current wants to flow in the ground plane right under the signal trace. When the plane is split, the current has to detour and a large loop antenna forms.
On multilayer boards, dedicating at least one layer to an unbroken ground plane is the single most effective EMC step you can take. Fast signals should be routed on layers adjacent to this plane.
Keep Fast Signals Short
Clock lines and fast data buses are the board's strongest noise sources. The shorter these traces, the less they tend to behave like antennas. Not making edge rates faster than necessary is another important gain.
Fast traces should be kept away from the board edge and connectors. A trace near the edge makes it easier for the field to spill off the board and couple noise onto cables.
Zoning and Filtering
The board should be divided into power, digital, analog and I/O zones, with noisy sections placed away from sensitive ones. The high-current loop of the switching power supply should be kept as small as possible.
Every line leaving the board should be filtered close to the connector. The filter components' ground connection must be short; a long ground path makes the filter useless at high frequency.
Connectors and Testing
Bonding cable shields to the enclosure through the connector with full 360-degree contact should be seen as part of the board design. If this connection is weak, even the best board layout can't stop noise radiating from the cable.
The way to be sure the rules are followed is to measure. In-house pre-testing from the first prototype lets you catch the problems we listed among the reasons products fail EMC tests at the design stage.
Frequently Asked Questions
Can EMC be achieved on a two-layer board?
It's hard but possible. The bottom layer should be largely a ground pour and fast signals kept short.
Should we split the ground plane into analog and digital?
In most cases it's better not to. Placing sections in separate zones over a single unbroken plane is safer.
Does simulation software replace measurement?
Simulation is a useful guide, but it can't fully capture cable and enclosure effects; it should be verified by measurement.
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