Characteristics of electric wire antennas onboard scientific spacecrafts [plasma wave observations]

For observation of plasma waves by a scientific spacecraft, we usually use wire dipole antennas for AC electric field and dipole probes for DC field measurement. An accurate value of effective length of the antenna (h_eft) is required to calculate absolute intensities of the electric fields from the output voltage of the antennas , and it is known as L/2 for wire dipole antennas and L for dipole probes. In this paper, we try to clarify the transition of h_eff from L to L/2 with frequency. At first, we report the result of a "rheometry experiment" which measures the frequency dependence of h_eff directly, and then theoretical calculations by using its equivalent circuits. The result clearly explains why the effective length transits.