Radiation from a vertical dipole in a warm plasma--Part II

Abstract

A numerical evaluation of the integrals that constitute the formal solution of the problem of a vertical dipole, which is situated in a homogeneous, warm plasma half-space above a perfectly conducting plane, is considered. An asymptotic series expansion is obtained for these integrals by the double saddle point method of integration. The dominant terms of the solution in the far field are shown to consist of a surface wave, which arises from the residue of a pole, and a space wave, which is the leading term of the saddle point contribution. The space wave is identified as the geometrical ray approximation to the solution. It is demonstrated that the surface wave can propagate when the source frequency is either above or below the plasma frequency. The transfer of power from an incident acoustical ( p ) mode to a boundary-generated electromagnetic ( e ) mode, and from an incident e mode to a boundary-generated p mode, is investigated at a plasma-conductor interface. It is evident in both situations that only a small percentage of the incident power is transformed into the boundary-generated mode. In the case of a vertical dipole, however, it is shown that, at source frequencies which are near to the plasma frequency, the power in the incident p mode is much larger than that in the e mode. Thus, the boundary-generated e mode, which is due to the incident p mode, is as large as the reflected e mode due to an incident e mode. As a result of this effect, it is pointed out that one can represent the reflected e mode by two image sources.