[SI-LIST] Do narrow ground areas on PCBs radiate?
- From: Joel Brown <joel@xxxxxxxxxx>
- To: SI-List <si-list@xxxxxxxxxxxxx>
- Date: Wed, 2 Jul 2014 10:55:27 -0700
I was once told by an EMI consultant not to have a narrow ground area on
PCB that did not have stitching vias along its length. The theory behind
this I think is that an ungrounded metal area will act as a monopole
antenna if its length is greater than 1/20 of the wavelength of signals
that might couple to it. For example an narrow ungrounded area of 1 inch
might radiate signals up to 285 MHz. This is probably more true of a wire
that is perpendicular to the PCB which would form a true monopole. But how
about a trace on the PCB that is parallel to and 5 mils away from a solid
ground plane? Can it still radiate, perhaps signals that are lower in
frequency than 1/20 of wavelength?
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