[SI-LIST] Re: Do narrow ground areas on PCBs radiate?
- From: steve weir <weirsi@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Wed, 02 Jul 2014 13:28:14 -0700
"Ground" s only ground because currents can conduct along its
interconnect, ironically meaning that there are potentials along that
interconnect meaning that it is no longer an isopotential. Any patch
has resonant modes that can radiate. Skinny patches are more likely
than wide patches to have few or one stitch via lowering the resonant
frequency of the structure. Wide patches that aren't stitched can
radiate as well.
Steve
On 7/2/2014 10:55 AM, Joel Brown wrote:
> 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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