Richard Fry wrote:
Followup -- the link below compares the relative current distribution,
directivity and radiation efficiency of a helical and a linear radiator
system when the helical radiator described in my earlier post is
operating at the frequency of its first self-resonance, and the linear
monopole height is set for its first self-resonance at that same frequency.

It is interesting to note that linear form has better performance than
the helical form.

http://i62.photobucket.com/albums/h8..._Resonance.gif


One antenna is physically larger, though, right: 5.535m vs 3m?

How is radiation efficiency calculated here? Integral over hemisphere of
radiated power vs applied power Seems like that would be
12.17/(10+12.17) vs 36/(10+36), so you're really just seeing a
manifestation of the different feedpoint impedance vs ground losses
(which you've assumed fixed..)

I'm not sure the assumption of fixed ground losses is reasonable here.
(Actually, now that I think about it, it might actually be worse for the
shorter element, in real life)


The other thing is that the shorter radiator is going to have a "lower
directivity" pattern vs the longer. That is, a shorter one will tend
towards the "Hertzian infinitestimal dipole" with 1.6dBi while the
longer will be closer to the 2.15dBi.