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Yagi antenna design question
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 |
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