Ed's one meter vertical over a large conductive ground plane has an
effective height of close to 0.5 meters up to something like 20 MHz. With
an amplifier at the base of the vertical that has high input impedance and
some tailored feedback, one can have a system that can be used to measure
field strength with very little frequency dependence.
I use a miniaturized version of such an antenna as a probe in a TEM
cell.

I have seen the use of resistively loaded (short) dipoles connected to
resistively loaded transmission lines used by the NBS (as it was then
called) to measure field strength with minimum disturbance to the field.

These are all receiving antennas with essentially uniform performance
over very large frequency spans.

My feeling is that to have a small variation in transmitting gain over
more than something like five to one will require an adaptive antenna
system. (I am assuming antennas with an "average" gain that is close to
one - no resistive loading.) 73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Fractenna" wrote in message
...
I regularly use an active 41" monopole to accurately measure electric
field
strength over the range of 10 kHz to 30 MHz. That's a ratio of 3000:1,
and
that is 25-year old technology.

--
Ed
WB6WSN


And your variation of gain, excluding mismatch, is...?

73,
Chip N1IR