The impedance of a dipole antenna in the ionosphere: 1. Experimental study

The impedance of a short electric dipole antenna has been measured from rockets in the ionosphere. The EIDI I experiment was launched in conditions where the plasma was expected to be nearly isotropic (operating frequencies 4.48 and 6.09 MHz, f₀F₂ ⋍ 9 MHz, f_H ⋍ 1 MHz). It was designed to detect and measure or to eliminate most of the unwanted effects which complicated the data reduction of previous experiments: outgassing, telemetry radiation, etc. The number of parameters measured simultaneously on board (impedances with variable bias and RF excitation level, resonance frequencies, T_e, dc current drawn by the antennas, vehicle potential) and from the ground or an overhead satellite was large enough to provide numerous cross checks and to determine the sheath dimensions. The impedance is very weakly spin-modulated over most of the flight; the collision frequency is very low (v/ω ⋍ 10^-5) unlike some of the previous experiments where collision losses were dominant. The measured values of the impedance are given as a function of X=f²_p/f² where the other parameters are known.