EMI Bites: Watch Out for Antenna-Like Structures in Your Layout
EMI Bites: Watch Out for Antenna-Like Structures in Your Layout
If you haven't done this before, start by checking your PCB layout for antenna-like structures, as they are one of the most common sources of EMI trouble.
Simple common issue?
Copper pours used incorrectly or as floating copper islands.
Why this causes problems:
- Floating copper areas (not connected to a solid reference) can act as antennas, picking up or radiating noisy signals.
- Even if they’re connected poorly, parasitic inductance and resistance can create voltage drops.
- These voltage drops can turn part of your "ground" plane into a radiator, depending on signal frequency and structure size.
Key Insight:
Every copper area in your layout should serve a clear purpose, or it may turn into an unintended antenna.
How to avoid antenna-like structures:
- Eliminate floating copper islands; tie all copper to a solid return & reference plane (RRP).
- Avoid narrow or weak connections between copper pours and RRP—they act inductively at high frequencies.
- Use multiple vias to ensure low-impedance paths between layers.
- Validate your copper fills during layout review, not just for coverage but for functionality.
- Don't use copper pours at all unless you can explain and back it up with (real) data on why you need them. They are often more trouble than benefit.
— Dario
P.S. Want more EMI control strategies to pass EMC?