Further Experimental Study of Plasma Sheath Effects on Antennas

Abstract

In the case of semi-infinite and finite-extent homogeneous plasma sheaths, the radiation pattern and the impedance characteristic are investigated with regard to the geometry of the discontinuity and its proximity to the slot antenna. It is found that the radiation pattern is unaffected by the discontinuity as long as the ratio of the distance between the source and the discontinuity to the sheath thickness is of the order of 20 or greater. When the sheath is made finite in extents with a discontinuity on each side of the slot, the resulting pattern is seen to be a superposition of the effects of each discontinuity acting separately. The input impedance of the slot exhibits only small variations when the ratio of the discontinuity separation to the sheath thickness is of the order of 4 or greater. For smaller separations, the impedance exhibits significant variations, strongly dependent on the geometry of the discontinuity. The effects produced Ly inhomogeneities are found to be similar to those of a homogeneous sheath with a certain equivalent dielectric constant.For both the homogeneous and inhomogeneous sheaths, favorable comparison with the available theory is obtained.