sci.physics.electromag

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On Fri, 14 Sep 2007, Bill Miller wrote:

> "Szczepan Bia=B3ek" < @ > wrote:
>>
>> It is sufficiently close. I try to be precise. My claim is that OPEN
>> CIRCUITS radiate off their ends (called antenas).
>> Closed circuits also radiated something.
>
> If by your definition, the open circuits are the "wires" that stick up in
> the air, then we are in agreement. So far...
>
> But this is only a partial explanation by example, since LOOP antennas al=
so
> radiate nicely, and these are -- by definition -- CLOSED CIRCUITS. In
> addition, there is a third class (sort of) that can be represented by
> devices like the folded dipole. In this configuration, at the dipole ends=
,
> the "wire" doubles back toward the center -- spaced a short distance from
> the "outbound wire. If we do this at both ends, the doubled back wires me=
et
> at the centre, and there is now a CLOSED CIRCUIT. But this antenna also
> radiates with high efficiency and with a pattern that is essentially
> identical to that of a concentional dipole.

Consider two short dipoles next to each other, half-wave out of phase - do=
=20
they radiate?

One can say that that is effectively two capacitors right next to each=20
other (and even if driven by "separate" circuits, that'll couple the two=20
of them nicely). Why doesn't each plate of a parallel plate capacitor=20
radiate (unlike, say, a single-sphere capacitor, which we could call a=20
monopole antenna instead)? Easy to say mathematically, harder to say=20
physically. And one can ask whether a circuit with a capacitor is a=20
"closed" circuit.

(Why does the existence/non-existence of "displacement current" receive so=
=20
much more attention than the existence/non-existence of "magnetic=20
displacement current" - why should the lack of a magnetic conduction=20
current so affect the status of dB/dt?)

--=20
Timo Nieminen - Home page: /people/nieminen/
E-prints: /view/person/Nieminen,_Timo_A..html
Shrine to Spirits: /timo_nieminen/

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