A method, suitable for investigation of ionospheric phenomena, is derived for computing the amplitude and phase characteristics of an electromagnetic wave after it has been perturbed by a phase distorting screen. Kirchhoff's integral' for diffraction is used to evaluate the Fresnel zone fields in terms of a field distribution which is assumed to exist over a plane surface just inside the screen. The perturbing screen is assumed to distort the front of constant phase in one dimension only. By approximating the actual curved wave front with plane wave segments, and with the use of the approximations normally used in diffraction pattern analysis, the fields are evaluated in terms of a sum involving the Fresnel sine and cosine integrals. Several examples are given.
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