Reg Edwards wrote:
Antennas and transmission lines are not just analogues - Antennas
ARE transmission lines with controlled 'leakage'. In fact, as people
forever complain on these walls, it is impossible to prevent a transmission
line FROM leaking.

The reason they are considered separately is that their functions are
different. Steps are taken to minimize transmission line 'leakage'.
Steps are taken to maximize antenna 'leakage'.

I was surprised that, for the purpose of a ballpark conceptual analysis,
Kraus considers the reflected current on a dipole to be equal to the
forward current. But then I remembered 50% of the power can be radiated
while the current drops by only 29.3%.

Here's what Kraus says: "It is generally assumed that the current
distribution of an infinitesimally thin antenna is sinusoidal and
that the phase is constant over a 1/2WL interval ... A sinusoidal
current distribution may be regarded as the standing wave produced
by two uniform (unattenuated) traveling waves of equal amplitude
moving in opposite directions along the antenna."

Exactly the same thing can be said about a lossless unterminated
transmission line. If lumped circuit analysis doesn't work on
transmission lines with reflections, why should it be expected
to work on antennas with reflections?
--
73, Cecil http://www.qsl.net/w5dxp



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