Hello Felix,

Regarding antennas that are very small with respect to wavelength.

With regards to your example, no correction to antenna theory is
necessary. Small antennas can be efficient radiators, but the smaller
the antenna, the more difficult to achieve reasonable efficiency.

Antenna theory is well established. When you know the current
distribution in a structure, one can calculate (mathematically or
numerically) how much power is radiated (and also how much power is
dissipated in the structure). This approach is used by virtually all
Antenna Design software packages.

All electrically small antennas have one thing in common, the usable
bandwidth is small. The Q-factor of a lossless electrically small
structure is proportional to
about 0.05*lambda^3/Volume.

For example a small loop of thin material with infinite conductivity
has higher Q-factor than a loop of same diameter, but made of very wide
strip (with infinite conductivity). The last one occupies more volume
and therefore has lower natural Q. The Q-factor of practically small
antennas can be that high that the bandwidth may by just a few kHz.

The problem is in the matching. Matching, for example 0.8 Ohms in
series with a reactance of 2800 Ohm (Q=3500), to 50 ohms is not easy.
The Q-factor of the components is not high enough, some or most power
is dissipated in the additional components, or even the antenna wire
itself. So in the end your antenna may have an overall efficiency of
5% (-13 dB). Also voltages can be that high that power is lost by
corona effects. Often, due to the high local E- and H-fields, power is
lost in nearby constructions.

About the practical use of small antennas. In many cases received
signal levels are in the S9+20 dB range. As the noise level is far
below this, loosing 13 dB (so your signal level will be S9+7 dB), is
acceptable. If not, you may increase the input power. In the end, the
small inefficient antenna is at least better then no antenna.

So in my believe, a nice QSO over 600 km with a small antenna, doesn't
prove that antenna theory has to be revised.

I'm very curious to see the construction details.

Best regards,


Wim
PA3DJS.