FR-4 dielectric is quite lossy, comparable to the copper
loss. Making the trace wider neither increases nor decreases
dielectric loss, but it does spread the heat over a larger
area. What many designers do is print the trace on the
bottom of the PC board in an area with no ground plane
and then use the chassis underneath the PC board as the
ground plane. This eliminates most dielectric loss
(there is still a little fringing within the FR-4).
Dielectric loss is proportional to frequency while
copper loss is proportion to the square root of frequency.
Having air dielectric also approximately halves the copper
loss.
Rick N6RK
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