There is a large
family of antenna simulation programs of NEC
like EZNEC, MMANA, 4NEC2, NEC-2, NEC-4 etc.
These programs can produce excellent results in designing and
optimizing of beams and similar antennas.
Personally, I made very good experience by optimizing the well
known Spiderbeam. The results of the simulation proved to be
fully correct in the practical field tests.
However, there are many cases where the simulation with NEC
programs is failing.
You even may obain results indicating efficiency of over 100% !
This is not the discovery of a "perpetual motion machine", it is
an error of computer simulation ..., or the results may become
very inaccurate if there are varying diameters, different
The NEC programs are designed primarily for wire
constructions and can be used for other constructions only
under specific conditions.
Regarding my RoomCap antenna the question was rised many
times, how the NEC simulation would look like.
Here I can say very simply: This construction can not be defined
by the existing NEC programs.
Especially the central element, the Varylink, can not be defined
by NEC. Conversation with the well known NEC expert L. B. Cebik,
W4RNL have revealed, that a way will be searched to include
such elements in later editions of the programs.
This example shows once more, that the usual way of antenna
development with simulation, as is done mostly today, is not
the optimum way, as finding of new constructions is prevented
by the many limitations of the simulation programs.
The programs are good at schools to show the students
the behaving of changing parameters, but are not the way
of the inventing engineer.
To find new ways and concepts, one depends on the
profound knowledge, the experience, and the mental force
of the engineer, together with experiments in the field.
The computer is a very helpful tool in many aspects, but
one may not expect much novelties by "experimenting"
with simulation. At least not, until big improvements are
made to these programs.
Felix Meyer HB9ABX