[Antennas] Another Look at Efficiency

[Robert Lay (W9DMK)]

It would appear that the efficiency of the multi-conductor antenna is not,
as a result, higher. After looking it up in the only references that I have,
it would appear that the true radiation resistance, as other contributors
have pointed out, does not increase in fact (relative to ground and other
losses) but is simply transformed to a higher value as seen at the feed
point.

I would have to presume from that, that the ground loss term appearing in
the total real part of the impedance would also be transformed by the same
amount.

The ARRL Handbook says that the folded dipole "has the same ... total
radiation resistance as an ordinary dipole."

So, thanks for the correction.

It is also interesting to note that the RSGB Radio Communication Handbook
seems to contradict that, if we take their use of the term "radiation
resistance" as being the same as ours. Quoting from page 12.33:

"Since half the current flows in each wire, the radiation resistance
referred to the centre of either is four times that of a simple dipole, ie
300 ohms approximately, which is particularly convenient for matching to
standard ribbon feeder, though the higher impedance and wider bandwidth of
an open-wire line greatly eases the problems of resonant feed lines, and
this can be exploited to good effect for the development of multiband beams
as discussed later."

73 de W9DMK (Bob Lay in Dahlgren, VA
http://www.qsl.net/w9dmk