Increasing efficiency of over-the-horizont surface wave radars for detecting surface objects based on the antenna system aperture

Nowadays, over-the-horizon surface wave radars are used to solve the problems of monitoring the situation on the water surface adjacent to the border areas of the land. The main advantage of these means is the ability to detect surface objects beyond the optical horizon due to the propagation of an electromagnetic wave along the sea surface in the diffraction zone. However, the accuracy characteristics of such observations turn out to be extremely low due to the small signal-to-noise ratios of the reflected signal, which in turn are caused by the wide directivity pattern of the existing antenna systems.
It leads to the prevalence of background reflection in the irradiated region over the radio echo of the target object. For the same reason, stationary targets are undetectable, for which there is no Doppler frequency shift in the reflected signal spectrum. The only way to increase the signal-to-noise ratio is to narrow the radiation pattern in the direction of the detected target (an increase in the antenna system directivity. The article proposes a solution for the described problem by the method of sequential accumulation of reflected signals and their summation according to the principle of optimization of the selection of phase relationships for adjacent pulses (synthesized apertures) corresponding to the eventual front of electromagnetic waves focused in the direction of the hypothetical target.
The solution of this problem will significantly narrow the antenna directional pattern, which leads to the achievement of direction finding accuracy that meets the requirements for some navigation systems. In this case, there is no need to change the design of the antenna arrays. Computer simulation of the synthesized antenna array was performed and its directional pattern was constructed. A quantitative assessment of the increasing the angular resolution was performed in comparison with the potentially possible one determined by the Rayleigh criterion. This circumstance allows us to consider the possibility of using coastal over-the-horizon surface wave radars to detect stationary objects «invisible» by existing radars.