Directivity of an antenna does come from antenna geometry. If an
antenna is 100% efficient it will have a gain equal to its
directivity. Gain is simply the antenna directivity * efficiency.
Reductions in efficiency come from losses within the antenna
structure, losses within any feedpoint matching components AND high
VSWR. Increased VSWR reduces power delivered to an antenna because of
the reflections created at the antenna . This has the effect of
reducing gain since the total power delivered to the antenna is less
than the power incident at its input terminal.
73
Steve Best
steve wrote...
<big snip>
> So you can get high performance (gain) IN SPITE OF high swr.
this shouldn't be a surprise. but it sure bears repeating!
Yes, George, What gives an antenna gain has NOTHING to
do with the impedance of the antenna. The impedance
relative to the impedance at the end of the amateurs
transmission line out the the antenna is from where
vswr comes. Gain comes from the geometry of the beast.
73, Jim, KH7M
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