Paul Burridge wrote in message . ..
....
I'm simply trying to establish the radiation resistance of a non-ideal
antenna so I can reasonably match it to the output impedance of the
transmitter PA stage. The figure is likely to be very low, given that
this antenna is highly non-ideal. I'm not interested in plotting polar
patterns of the radiation distribution!

Then you want to know the feedpoint impedance, not the radiation
resistance.

You can measure that with any of a variety of impedance-measuring
devices. You need to be careful to not disturb the antenna with your
measurement, and to properly couple the measurement device to the
feedpoint, taking into account the effect of the coupling on the
measurement. For example, like Wes said, if you measure it through a
length of feedline, you need to accout for the impedance
transformation performed by that line, or calibrate your measurements
at the end of that line.

You can generally get a fairly accurate number through a simulation of
the antenna, too.

Cheers,
Tom