Dear Rik, LF Group,
An ideal "electric" monopole antenna has a uniform voltage at all points,
and a current distribution that tapers off along the wire, while a
"magnetic" loop antenna has a uniform current around the loop and a voltage
that tapers. It seems to me your antenna proposal is a hybrid of loop and
vertical, with both voltage and current non-uniform - the current in the
loop is non-uniform because some of the current returns to the feed point
via "displacement currents" flowing in the distributed capacity of the
antenna. In practice, this is true of any loop, since there is always a
finite voltage difference between different points on the loop, and a
finite distributed capacitance between them. The voltage on a practical
monopole will not be equal at all points either, since there is always a
finite distributed inductance which causes a potential difference when the
antenna current flows through it. So all real antennas will have at least
some hybrid electric/magnetic behavior - but what would be interesting to
know is if exaggerating this would result in a useful efficiency improvement.
As I understand it, whatever mode the antenna operates in, it is not
possible to create an E field without an H field existing at the same time
and vice versa, and also that feeding electrical energy into any generator
of E/H fields will inevitably result in some energy propagating away as
electromagnetic waves. The CFA people say that if E and H fields around the
antenna are arranged to be in a certain relation that the efficiency of
converting the incoming electrical energy into propagating e-m waves is
greatly increased. I think conventional antenna theory would expect the net
radiated signal from the antenna to be the superposition of the radiated
signals produced by both electric and magnetic modes - So if the radiated
signal was substantially different from the calculated level it would
support the idea that existing antenna theory is wrong.
Calculating what radiated signal this antenna should produce is another
matter - to work out what was being radiated in each mode, you would need
to measure the current distribution in different parts of the antenna -
this ought to enable you to work out the effective height for the electric
mode - since the current is non-uniform, you would also have to work out an
"effective area" of the loop in magnetic mode.
Cheers, Jim Moritz
73 de M0BMU
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