On Sun, 4 Feb 2007 15:39:49 +0100, "Antonio Vernucci"
wrote:

I wonder whether anyone can formulate a convincing answer to the following
question.

Let us assume you wish to design a 3-element Yagi antenna for good performances,
but with NO REGARD AT ALL TO ITS IMPEDANCE (i.e. assume that you anyway intend
to have a matchbox at the antenna terminals, so that the antenna impedance is of
no concern at all for you).

Hi Tony,

That is a good start for discussion, but you abandon this care-free
attitude almost immediately:

...that we here assume to be e.g. 30 ohm.

Chances are it will be much less, possibly 5 Ohms. So, you see, you
have already introduced a constraint, and you continue adding mo

At this point you change your mind and, instead of using a 30-to-50 ohm
matchbox, you decide to match the antenna to the cable using the well known
hairpin technique, ...

Which leads to another constraint:

Doing so the radiator length will result to be shorter ...

As you are using a modeler from the beginning, you should also use
these constraints from the beginning.

Perhaps you are thinking of this as a two step process starting with
no constraints and then adding them. That works too and it requires
you to perform successive refinement. You can not escape this anyway.

If the change is confirmed, we would inevitably also come to the conclusion that
the antenna radiation characteristics depend on the technique which is adopted
to match the antenna to the cable (e.g. matchbox or hairpin). This would sound
real odd!

The change could be small. The question is how much change makes it a
"real odd" result?

73's
Richard Clark, KB7QHC