The synthetic aperture radar in high frequency band

The possibilities of the synthetic aperture radar construction in high frequency (HF) band  are analyzed. The fields of application of such  radar are considered

Methods of studying the antennas synthesis problem in practical lessons

It is difficult to synthesize the antenna directly in practical lessons in general theory of antennas with students. The approximate method is proposed for solving the synthesis problem based on the minimization of the functional representing the distance in the functional space with a quadratic metric between the normalized desired antenna pattern (AP) and some normalized AP with unknown amplitude and phase distribution (APD) of the field in the aperture. In this case the AP does not necessarily have to relate to the class of realizable ones, and APD of the field, while functional is minimized, can be selected from the set of the functions suitable for implementation. Validity of the method is tested on the example of synthesis of a linear antenna with the APs for which the APD is accurately known. The recommendations for conducting practical lessons are given

Electromagnetic field of an antenna located near a sea tropospheric waveguide

The character of radio waves propagation when detecting low flying targets over a sea surface essentially depends on the distribution of temperature, pressure, humidity of air and hence on the height distribution of refractive index. Typical height dependences of the modified refractive index Mon height h above the Black sea measured by refractometer are shown in Fig. 1 for July (curve 1) and August (curve 2)

Measurement method of the object surface deflections using antennas theory

The method of remote measurement of object surface deflections using an artificially created system of secondary radiators located on this surface is considered. The physical basis of the method is a change of the pattern of radiators system due to their displacement under the loads influence. Radiators displacements which are included in the expression for the distorted antenna radiation pattern are determined by minimizing of the functional using a genetic algorithm. Reconstruction errors of radiators displacements are identified for different situations taking into account the ambiguity of the problem. The best conditions for the functioning of the method are recommended for the practical use

Low-height radiation field of the coastal radar antenna taking into account troposphere inhomogeneities

A procedure is considered for defining the presence of the tropospheric waveguide based on the shape of the phase-plane portrait, with which it is convenient to describe the behavior of all combinations of radio wave trajectories. A rough model of the spatial distribution of the troposphere refractive index n(x, z) near the sea coastline is given. The minimum information needed for model construction is from two separated vertical profiles of n(z) in the troposphere, which can be obtained by radio-acoustic sounding

Application of the computational electromagnetics methods for determining the radar characteristics of targets in the decametric wave band

The problem of target scattering analysis is very important for radars. In becomes considerably complicated for the over-the-horizon radar where a number of additional factors stipulated by the effect of ionosphere, earth surface, etc. appear. The sum of these factors can change the radar characteristics of the target (RCT) sich as the elements of polarization scattering matrix (PSM). RCT determination is realized either by experiments or by a physical and mathematical simulation. Experiments and physical simulation require considerable material and time expenses and can be carried out as a rule under a number of limiting conditions. The mathematical simulation of RCT has no such disadvantage. But the main aim: a high reliability of results must be achieved in this case, that puts strict requirements on a choice of mathematical model