i am considering building two movable (concrete base with wheels) non metallic poles with hooks every ten centimeters or so, in order to test wire dipoles of various sizes at various heights with an antenna analyzer, far from obstacles (let's say in a field).

Do you think it's better to use non conductive masts to avoid parasitic influence on the measurement or is it overkill? Is there anything else on antenna metrology I should know for this project?

Under ideal conditions you should strive to keep all conductive materials that are not part of the antenna system out of the near field of the antenna. This generally means non-conductive supports.

As a practical matter, if you are supporting horizontal dipoles, there is very little current at the open end of each leg so very little radiation occurs in this region. There is generally high voltage present, however, due to the standing waves on the antenna. If the ends of the antenna are properly insulated and spaced reasonably (e.g. >1/10 $\lambda$) away from the supports, this should not cause problems - particularly if the only source of excitation is a fractional watt antenna analyzer. The spacing also serves to minimize capacitive coupling with the supports.

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