M.A. Astashkin

The problem of detecting low observable targets is very serious for radio wave security systems. As in our country and abroad radio-wave system are widespread. There are single station and two-way radio-wave security systems. Some systems are the two emitting coaxial cable laid under the ground parallel to each other. The first cable is receiving antenna, the other is transmitting. The principle of operation of most systems are based on the Doppler effect, so there are some limitations of parameters of detected intruder. For domestic systems, the lower limit of the range of detectable velocity of 0.1 m / s, weight not less than 50 kg, height not less than 1 meter. Systems to overseas rates 0.02 ÷ 0.025 m / s; mass 30 ÷ 37 kg. In this article we consider the case when the electrical dipole antenna located in free space by an insulator at a distance. For such a case is the transmission coefficient, reflection coefficient. Based on these results there was found input impedance of the antenna. Input resistance may serve as an informational parameter for the construction of single-position alarm system. To describe the layered structure is used the equivalent circuit - the cascade-connected two-port system. Interest in the problem under consideration, among other things is that on the basis of the results can be described by a model radio wave security system consisting of two mutually-parallel dipoles located on opposite sides of the insulator.