Ian White, G3SEK wrote:
Now if you measure the complex (R-X) impedance of an antenna across a
very wide range of frequencies, and plot it on the Smith chart, you will
typically find that it goes in a series of orbits around the chart.

For resonance not to occur at minimum SWR, the orbit must not be a
circle centered on the pure resistance line. The 'R' in the R+jX
impedance looking into my transmission line changes much faster
around resonance than does any SWR circle.
--
73, Cecil http://www.qsl.net/w5dxp