Correcting Ray Field Failures Caused by Focusing in an Inhomogeneous Duct: A Critical Look at the Gaussian Beam Method,
NEW JERSEY INST OF TECH NEWARK DEPT OF ELECTRICAL ENGINEERING
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Ducting due to an inhomogeneous refractive index profile affects the propagation of electromagnetic signals in various regions of the earths environments. At high frequencies ray methods afford a versatile, and numerically easily implementable, method for predicting the field at the receiver. However, when ducting occurs, multiple refractions of the confined rays cause field enhancement due to focusing, and when there is an abrupt change in the ducting profile, critically incident and glancing rays cause diffraction and shadowing. The ray algorithm fails in these transition regions. To repair these deficiencies, one may eliminate the troublesome ray fields and fill the spatial spectral interval vacated thereby with guided modes and remainder fields. This technique has previously been incorporated in a hybrid ray-mode theory, which accomplishes the desired objective and also furnishes important physical insight into the associated propagation phenomena, but its implementation requires calculation of the relevant guided modes and remainders, which may be inconvenient. By a new alternative approach, first introduced into seismology, we explore here the effectiveness of filling the transitional spectral intervals with Gaussian beams. Gaussian beam fields, because of their smoothed profile, do not experience the violent transitional behavior of ray fields.
- Radiofrequency Wave Propagation
- Atmospheric Physics