Lightning-Induced Transients on Buried Shielded Transmission Lines

This paper is primarily concerned with the analysis of induced transient current and voltage surges on buried shielded transmission lines due to earth-conduction effects of nearby lightning discharges. An analytical method is presented in this paper to model the conductive coupling mechanisms in the earth and to determine the amount of coupling between a lightning discharge to ground and an earth-return transmission line. The transmission line is assumed to be a long straight horizontal coaxial cable with an inner shield and an outer armor, terminated on both ends with typical communication-equipment load impedances. The general case is considered here, in which the outermost conductor is not necessarily in perfect contact with the conducting earth, but has a contact impedance with the earth, as in cables with an outer dielectric covering for corrosion or water protection. Average lightning-channel conditions and a representative buriedcable geometry are examined. The results are conveniently displayed via several graphs of the time histories of the resulting transient current and voltage surges.     

Measurement of the electrical constitutive parameters of materials using antennas

A general technique is presented for measuring the electrical constitutive parameters of a material using a monopole (dipole) antenna. A normalized impedance that is only a function of the dimensionless parameterkh(wavenumber length) is defined for the antenna. The normalized impedance is expressed as a rational function, and the coefficients in this function are determined from a measurement of the impedance in a standard medium. The impedance measured in a material with unknown constitutive parameters is used with the rational function to form a polynomial inkh. The constitutive parameters of the medium are determined from a root of this polynomial. The measurement technique is implemented for a rational function of order three. The constitutive parameters of the alcohol 1-butanol and saline solutions were measured over a range of frequencies using the technique with cylindrical and conical monopole antennas. The measured constitutive parameters are in good agreement with those determined by previous investigators.     

Alteration of the Surface Current on a Missile by the Presence of an Exhaust Plume

This paper presents an analysis of a missile with an exhaust plume when exposed to an incident electromagnetic plane wave at an arbitrary angle of incidence. Both homogeneous and axially inhomogeneous plumes are considered. For the inhomogeneous case, the AeroChem low altitude plume program is used to provide realistic values of the electrical properties along the length of the plume. In the analysis, the missile and the plume are assumed to be thin when compared to the length of the missile and the wavelength of the incident radiation. Conventional numerical methods developed for thin-wire antennas are used to determine the current in the missile and the plume, and the effect the plume has on the current is examined. Field patterns for aperture coupling at specific points on the missile are also presented. A limited comparison with measured results is presented.