On Aug 31, 6:53*am, Richard Fry wrote:
On Aug 30, 9:23*pm, Art Unwin wrote:

Exactly because it takes a WL or multiple there of to attain
equilibrium

Art -- how, then, do you account for the fact that a 1/4-wave monopole
and r-f ground system used by many AM broadcast stations produces
radiated fields that have been measured to be within a few percent of
the maximum possible for the applied power?

If "equilibrium" takes a WL or multiple thereof, why are such
fractional wavelength radiators so efficient?

RF

One time response
Most hams are aware there are two basic resistances or impedances
involved in any antenna. The d.c. wire resistance is a constant
whether it is above ground or not.
Radiation resistance only occur when radiation is allowed to take
place which usually is considered above ground. When the circuit
cannot radiate such as in a ground plain or similar then the circuit
does not encounter radiation resistance thus the only resistance
encountered is the dc resistance which means it draws less power from
the source.
Thus for a half wave with ground plain it will draw 1/2 the power from
the source that a full wave will. So when talking about efficiency per
unit of energy supplied the only difference
between the two is the wire resistance that is not accompanied by
radiation which is extremely small. So overall efficiency changes of a
radiator is so small it really is of zero significance. What is
important is the ability of an antenna to radiate maximum strength
where you want and the ground plain applies a limitation which many
can live with.
The importance of efficiency is that one is accounting for all forces
that impact it where you enter a different mathematical areana which
opens up clues to the formation of radiation
and possibly other scenarios that can be of benefit in other areas.

A case in point. If one has a vertical then the radiation pattern is
donut shaped ie it has a hole that is devoid of radiation which is not
so good for military servalance. This is because the radiator is
oriented opposite to the gravitational force only. If one wants to
account for ALL forces involved then one must include with gravity the
Corriolis force without which NOTHING can be stable on Earth. One must
include it when considering the Earths forces within a arbitrary
boundary to achieve equilibrium. Thus to be in equilibrium a radiator
must be tipped to include the Coreolis force which then allows for a
spherical radiation pattern ala Poynting's vector where the forces
within the boundary equals ( and opposite) that outside the boundary
and is in a state of equilibrium Thus when a radiator is tipped it now
fills up the hole in the donut to obtain radiation that is equal in
all directions( equilibrium) which is what a military installation
would prefer as possible observation is 100 %. Thus starting with a
single radiator that is in equilibrium you are starting from a
different point to a planar mode when proceeding with array designs
which then becomes educational with respect to possible occurances
that are not available to systems outside that of the equilibrium.
NUFF SAID