On Airborne Radar Main Lobe Clutter Adaptive Suppression Techniques Based On DPCA

In a look down airborne battlefield surveillance radar (ABSR), ground clutter is very strong. Effective ground clutter suppression is a major task of airborne radar signal processing. Owing to the radar platform motion, clutter returns in the airborne radar are Doppler shifted and have Doppler spectral spreading. Thus the ground clutter suppression is more difficult in airborne radars than in ground based radars. Conventional airborne radar clutter suppression techniques utilize the difference in Doppler frequency domain between clutter and target returns to suppress clutter, i.e. Doppler frequency domain one-dimension adaptive filtering, which usually used in main lobe clutter suppression. For slow targets whose Doppler frequencies fall into clutter Doppler band, the performance of frequency domain one-dimension filtering is seriously degraded. In an airborne radar, there is interdependence between the clutter Doppler frequency and spatial position. Space-time adaptive processing (STAP) utilizes this interdependence to suppress clutter and get perfect main-lobe and side-lobe clutter suppression. But STAP is too complex to be realized. This dissertation studies the ground clutter suppression of ABSR. Because low pulse repetition frequency (LPRF) and low side-lobe antenna are adopted, we focus on main-lobe clutter suppression. ABSR mainly used to detect the slow targets on ground whose Doppler frequencies are very close to clutter Doppler spectrum, or even fail into clutter Doppler band. Under this condition, frequency domain one-dimension filtering can not get satisfactory results, and STAP is too complex. So looking for a simple, effective and realizable method for main-lobe clutter suppression is the main task of this dissertation. Because multi channel receiver is adopted, adaptive displaced phase center antenna (ADPCA) has certain space-time two-dimensional filtering ability. ADPCA is better than frequency domain one-dimension filtering in main-lobe clutter suppression and slow targets detection, and is easier for realization than STAR So, this dissertation studies it in detail, and designed an ABSR main-lobe clutter suppression system based on ADPCA. Having done all these, this dissertation proposes two practical main-lobe suppression -3- methods and analyzes their realization. The main contents of this dissertation include: 1. Summarizes the main methods of airborne radar clutter suppression and analyzes their performances and characteristics. Chooses ADPCA as the study object, which is realizable under current technology condition and has satisfactory main-lobe clutter suppression ability. 2. Analyzes the echo characteristics of airborne radars in detail and constructs the airborne radar main lobe echo mode! for low PRF. Designs the echo simulation program which can sUnulates the time-space distribution characteristics of airborne radar main-lobe echoes. This is very important in studying the performances of various clutter suppression methods. 3. Analyzes the performance of ADPCA, especially its space-time filtering ability. Analyzes the reason that ADPCA performance degrades when the central Doppler frequency of main-lobe clutter is not equal to zero. Based on this, proposes a main-lobe clutter suppression method called main-lobe clutter frequency shift ADPCA. 4. Proposes a practical space-t...