I am trying to understand why the so-called reflector has to be longer than the
driven element and the so-called director has to be shorter than the driven
element for the standard configuration Yagi. I have been reading antenna books
and also trying to rationalize what is going on. Secondly, I am trying to
rationalize why the longer element is called a reflector and the shorter
element a director. I posted this to Towertalk perhaps two years ago and only
got simplistic (?) answers. Hopefully some of the great gurus here can provide
an explanation.
I think that I understand the fundamental principle of the Yagi i.e. the
induced currents in the parasitic elements cause a re-radiation in all
directions. For compass bearing points around the array, the currents in all
of the elements are vectorially added. In some directions the vectors will
add, but in other directions the vectors will subtract.
What bothers me is that the currents at the end of the elements are low so I
would think that the ends would not have much effect on the pattern?
I think that I have the answer for my second question. For a resonant driven
element, a longer parasitic element will have vectors on the side facing the
driven element that will add to the vectors from the driven element. Hence the
"reflector" appears to reflect the wave. For a shorter element the vectors on
the side away from the driven element will add to the vectors from the driven
element. Hence the "director" appears to direct the wave.
k7puc
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