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Experimental evidence based on ionospheric scintillation observations has revealed the importance of multiple scattering at a frequency as high as gigahertz. In most cases, even though the scattering is intense, the scattered energy is concentrated mainly in the forward direction. Making use of these observations, a scattering theory is developed in this paper that takes into account both multiple scattering and Fresnel diffraction. It shows that both of these effects will reduce the backscattered power when the irregularity spectrum is Gaussian, but will leave the backscattered power unaltered, except for a 3-dB enhancement, when the irregularity spectrum follows a power law. This enhancement of radar returns subtends a narrow cone centered in the backward direction. Numerical investigations show that the width of the enhancement cone is controlled by the intensity of multiple scattering, i.e., a change of parameter to increase multiple scattering will decrease the width of the enhancement cone.