Oh, I would never make such an assumption that it applies to all antennas --
well maybe it did cross my mind!. My guess was that probably everybody knew
it anyway, but thought it was interesting. I have also noticed that the
phase of the current is constant over thin wire monopoles of less than a 1/4
wave

Regarding Richard's comments "Assuming the same currents". Not sure I
understand, since the feed-point current varies with constant power -- as
does the voltage. Also confused by the expression V=I/R.

73,

Frank



"Roy Lewallen" wrote in message
...
Ah, yes, that's one of those simple observations that lures people into
making false generalizations. I think you'll find that your observation
isn't true for any length, but only for lengths of a quarter wavelength
(for a monopole) and shorter. And only for an antenna consisting of a
single straight wire. Under those conditions, the phase of the current is
nearly constant along the wire, so the fields from the various parts of
the antenna add together in phase at a distant point broadside to the
wire. The maximum field strength is, therefore, proportional to the sum of
the fields from the individual segments which, in turn, is proportional to
the integral of the currents on the segments. Since the maximum field
strength (or gain) doesn't change much from a very short wire to a quarter
wavelength one, the integral of the current stays pretty constant. But
don't, for heaven's sake, think you've discovered a rule that applies for
all antennas. Not even all straight, single wire monopoles.

Roy Lewallen, W7EL

Frank wrote:
Concerning current distribution -- at least on a monopole above a
perfectly conducting ground. I have noticed that in any antenna, of any
length, inductively loaded, or not, the: Integral of I(z)dz (where the
units of dz are in fractions of a wavelength, and I(z) the current
distribution) is virtually a constant. Assuming the same input power in
all cases. Suppose it seems pretty obvious since the total radiated
power from any structure is also essentially constant. I must admit I
have not seen gain increasing, with decreasing size, but then I have not
seriously tried.

Regards,

Frank