B. Agrawal

Ionosphere effects on navigational and positioning signals full-wave solutions

Full-wave, numerical, and analytical solutions are obtained for navigational signals reflected or transmitted through an inhomogeneous anisotropic layer such as the ionosphere. The transfer functions used in these solutions are obtained by using a nonsingular transformation matrix to convert Maxwells equations (for the transverse electromagnetic field components) into a set of loosely coupled first-order differential equations for the forward and backward traveling ordinary and extraordinary wave amplitudes. These transformation matrices which are also suitable for critical coupling regions (characterized by strong reflections or coupling between the ordinary and extraordinary waves) are constructed through the use of generalized characteristic vectors. Analytical and numerical techniques are used to obtain the signal distortions and instantaneous phase anomalies due to the medium. These are used to determine the time of the third zero crossing, which is generally regarded as the effective arrival time of the signal.

Transmission of horizontally polarized waves and trapped waveguide modes in inhomogeneous media

A generalized Wentzel-Kramer-Brillouin (WKB) approach is used to obtain full wave solutions for horizontally polarized waves in inhomogeneous media when no closed form analytic solutions are known. This approach is suitable for complex permittivity profiles with critical coupling regions even when the permittivity gradient approaches zero. The transmission and reflection coefficients and the characteristic surface impedance for inhomogeneous layers of finite thickness are computed for several permittivity profiles. Excitation of propagating and evanescent waves is considered and the results are shown to satisfy the realizability and reciprocity relationships in electromagnetic theory. Sinusoidal permittivity profiles for which closed form analytical solutions are known are also considered to provide an additonal check on the generalized WKB solutions. For permittivity profiles with several spatial periods, transmission windows with very narrow beamwidths are found to exist. When conditions for total internal reflection in the inhomogeneous dielectric layer are satisfied, the reciprocal of the reflection coefficient vanishes and propagating waves are trapped in the layer. For these trapped waveguide modes the inhomogeneous dielectric is characterized by a surface reactance.

Propagation of EM waves in inhomogeneous anisotropic media

Maxwells equations for the transverse ( x , y ) components of the electromagnetic field are solved numerically for horizontally stratified inhomogeneous anisotropic media using a Fortran IV program

Horizontally polarized waves in inhomogeneous media--Energy conservation and reciprocity relationships

Full wave solutions for the electromagnetic fields of a horizontally polarized wave propagating through an inhomogeneous ionized medium are derived using a generalized WKB method. Both the electron density and the collision frequency of the horizontally stratified media are assumed to vary and special attention is given to permittivity profiles with critical coupling regions. The reflection and transmission coefficients and the characteristic surface impedance for an inhomogeneous layer of finite thickness are computed as functions of the transverse wave number for various permittivity profiles. Excitation of both propagating and evanescent waves are considered. For some special permittivity profiles considered, closed form analytical solutions for the electromagnetic fields are known. Computations derived from these solutions are in good agreement with those obtained using the generalized WKB method. The results are also shown to satisfy energy conservation and reciprocity relationships in electromagnetic theory.

Generalized characteristic functions applied to propagation in bounded inhomogeneous anisotropic media—reciprocity and energy relationships

Abstract The problems of radio wave propagation, in bounded inhomogeneous anisotropic media, can be expressed as sets of four simultaneous first order differential equations with variable coefficients. A nonsingular transformation matrix which consists of generalized characteristic vectors is introduced to diagonalize the coefficient matrix even when two or more of its characteristic values are equal. Thus, the original set of differential equations for the transverse electromagnetic field components are converted into loosely coupled generalized characteristic functions. These generalized characteristic solutions are suitable for regions where there is strong coupling between the upward and downward traveling ordinary and extraordinary waves. In this work, numerical solutions are presented for the transmission and reflection scattering coefficients that characterize a bounded inhomogeneous plasma in an arbitrarily oriented magnetic field. These numerical solutions for arbitrary excitations are shown to be consistent with the adjoint reciprocity conditions for dissipative anisotropic media and also with energy conservation for nondissipative media.