I didn't say that RF current in a ground plane wasn't "well-behaved",
whatever that means. I said that it wasn't uniform, as in uniform
density. It's not.
73,
Dave AB7E
On 8/7/2013 2:10 AM, Jim Brown wrote:
On 8/6/2013 8:49 PM, David Gilbert wrote:
Currents most certainly do not flow uniformly in ground planes, and
coupling effects can be real whenever significant gain is involved.
Actually, what happens is that a trace above an ideal "ground plane"
(the ground layer) forms a transmission line, with the return current
flowing in the ground plane directly below he trace -- UNLESS the
ground plane below the trace is broken, for example, by the circuit
board layout guy realizing he left something off the main layer, and
putting on the ground layer instead. In which case there is no longer
a transmission line, the return current flows wherever it can.
inductance is added to the path, which causes magnetic coupling to
other circuits, and it forms an antenna, so it can radiate, into other
circuitry, or outside the box, or both.
So the RF current in a ground plane is VERY well behaved and
predictable. The problems arise when the PC layout guy doesn't
understand the function of the ground plane, and that it CANNOT be
interrupted without consequences. Like zipper noise on tuning in the K3.
73, Jim K9YC
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