Experimental investigations on the impedance behavior of a cylindrical antenna in a collisional magnetoplasma

An experimental study of the input impedance of a short cylindrical antenna immersed in a laboratory magnetoplasma is reported. The antenna is fixed in length and is aligned with its axis parallel to the dc magnetic field. Of particular interest is its impedance behavior in the vicinity of the resonance and cut-off conditions of the magnetoionic medium. Independent measurements are made to determine the electron density from the ion-current characteristics of a spherical Langmuir probe and the strength of the applied magnetic field with a Hall-effect probe. Measured impedances are compared with Balmain's theory. Essential features observed experimentally are a peak in the antenna input resistance near the upper hybrid resonance frequency and a peak in the antenna conductance near the cyclotron frequency. An additional small increase in the input resistance is observed near the plasma frequency when the plasma frequency is not close to either the upper hybrid resonance frequency or the cyclotron frequency. These results suggest the possibility of using a short cylindrical antenna as a diagnostic probe for measuring properties of a magnetoplasma such as the electron density and collision frequency.