DETERMINING THE DISTANCE TO THE TARGET IN PASSIVE RADAR OF SURFACE OBJECTS

Subject and Purpose. While outperforming active radar methods for range, stealth, and energy consumption, passive radar has a significant disadvantage: it cannot determine the target distance and coordinates when only one reference receiving point is available. We seek to develop a passive radar method and technical means for its implementation to establish the target distance over the sea surface with a single reference receiving point. Methods and Methodology. The idea behind the proposed passive radar method for determining target distance is to use a floating radio-beacon buoy beyond the radio horizon. The buoy is equipped with a transmitter that poses no radiation hazard to coastal areas. A ground-based receiver is installed on the shore to catch both the direct signal from the buoy and the signal reflected from the waterborne target. The performance of the system is evaluated through numerical modelling and analysis. Results. The mechanisms of radio wave propagation beyond the radio horizon have been thoroughly analyzed. Based on this analysis, a functional diagram of the proposed passive radar, which employs a surface radio buoy equipped with a transmitter and an amplifier-repeater, has been developed. In this scheme, an additional radio wave propagation path emerges from the target to the amplifier-repeater and then to the ground-based receiver on the shore. The time delay between the radio beacon signal and the main signal from the target has been determined, as well as the angle between the target and radio-beacon directions. The difference in signal path lengths along the main and additional paths has been established. For the practical implementation of the proposed scheme, the operation principle of passive radar has been supplemented with algorithms for determining the surface target distance. The operation of the devices has been described in detail. Conclusion. A method has been developed to construct an over-the-horizon passive radar system that determines the target distance using, among others, an amplifier-repeater mounted on a radio beacon buoy beyond the radio horizon. The algorithm for finding the surface target distance has been validated through mathematical modeling of radar propagation paths.