Signal Processing Algorithm for Active Aperture Synthesis Systems

The real-time radar imaging of land cover over large areas is performed from aerospace carriers via imaging equipment operating in the optical, infrared and radio wavebands. The latter waveband allows to carry out the surveys regardless of weather and time of day. However, since radio waves are significantly longer (in comparison with optical and infrared ones), to achieve high-resolution images in spatial coordinates it is necessary to use antennas dozens, hundreds or even thousands of meters long. Naturally, it is rather difficult - and in most cases simply impossible - to implement this large antenna aperture. Therefore, since the middle of the XX century, specially synthesized systems consisting one or several antennas, which can be repositioned according to a given law, has been widely used. Signals recorded in different areas of space are accumulated and then processed altogether. This creates the effect of using large antennas. In this case, there are two main methods of signal processing implemented, respectively, in active radar systems with aperture synthesis and passive aperture synthesis systems. Traditionally, the viewing areas of these systems are correlated - the active systems form images within the range of angles ±(15°-50°) from the nadir, and passive systems within ±15° from the nadir. The physical essence of the images obtained at the outputs of these systems is also different complicating the image formation within the entire region of ±50° from the nadir. This report combines the features of signal processing in active and passive systems with the aperture synthesis proposing a system of active aperture synthesis. This allows to obtain radar images of high resolution in spatial coordinates within the monitored area that cannot be viewed by active radars, and the physical essence of the images themselves will be close to the essence of the images obtained by active radar systems with synthesized aperture.