if you could make a 500nm antenna (or around that size)
could it emit visible light? no smartalecks talking about light
bulbs, those aren’t antennae.
I suppose in theory, it could, but you’d have a hell of a time building a circuit to produce the necessary 600 million MHz signal to drive it.
Why?
Well, if nothing else there is the formula for resonant frequency for, say, an LC tuned circuit: F = 1 / (2 x pi x L x C). Examination of the formula will show you that really, really small of values of L and C are needed to give the required frequency, and in the real world, these values would be impossible to attain.
Really what it boils down to is that at the circuit values that would be required, leakage (or stray) inductance and capacitance would have values greater than the actual circuit values!