I. I. Salnikov, M. N. Chernyshev

It is hard to determine intruder-s characteristics when protection zone is large. False alarm rate could be decreased using devises which can measure some dimensions and velocity of intruder. The article is devoted to solving this problem by means of transmission function determining based on electromagnetic complex amplitude value measured by receiver of protection system. We use Fresnel-Kirchhoff equation as dependence of complex amplitude on intruder-s coordinate x0 to determine intruder-s dimensions. Series expansion of this equation about a point x0 with truncation all terms starting with quadratic gives Fraunhofer diffraction. Truncation all terms starting with cube gives Fresnel diffraction. It is possible to determine transmission function using reversed transformation in both cases. Equation which reconstructs transmission function in the line of x-axis has been derived. This equation requires less limitation than Fraunhofer and Fresnel ones. Noises produced by signal interaction with ground, growth or blanket of snow, results in inaccuracy of intruder-s dimension measurements. Noise analysis shows that low-frequency component predominates. In addition there is high-frequency component, which produces low-amplitude short fluctuation. Algorithms, decreases false alarm probability, have been discussed. Methods, which allow determining intruder-s velocity, using additional receiver also has been described in this article.