Phase-Only Space-Time Adaptive Processing

• Published in: IEEE access Vol. 9; pp. 147250 - 147263
• Main Authors: Pallotta, Luca, Farina, Alfonso, Smith, Steven Thomas, Giunta, Gaetano
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: adaptive radar receiver; Antenna arrays; Beamforming; Clutter; Conjugate gradient method; Covariance matrices; Delay lines; Domains; Doppler radar; gradient descent method; Interference; Mathematical analysis; Optimization; phase-only adaptive nulling; phase-only STAP; Radar; Radar antennas; Radar signal processing; Signal to noise ratio; space time adaptive processing (STAP); Space-time adaptive processing; Spaceborne radar; Spacetime; Target detection; Toruses; Transversal filters
• ISSN: 2169-3536; 2169-3536
• DOI: 10.1109/ACCESS.2021.3122837

Space-time adaptive processing (STAP) is a well-known and effective method to detect targets, obscured by interference, from airborne radars that works by coherently combining signals from a phased antenna array (spatial domain) with multiple radar pulses (temporal domain). As widely demonstrated, optimum STAP, in the sense of maximizing the output signal to interference plus noise ratio (SINR), is a coherent, linear, transversal filter (i.e., tapped delay line), that can be synthesized by a complex-valued weight vector. This paper extends previous work that focused on adaptive spatial-only nulling; it derives the optimum phase-only STAP, namely, the optimal weight vector that maximizes the SINR subject to the constraint it belongs to the <inline-formula> <tex-math notation="LaTeX">N </tex-math></inline-formula>-torus of phase-only complex vectors, where <inline-formula> <tex-math notation="LaTeX">N </tex-math></inline-formula> is the number of spatio-temporal degrees of freedom. Because this problem does not admit a closed-form solution, it is solved numerically using the phase-only conjugate gradient method (CGM). The effectiveness of phase-only STAP is demonstrated using both SINR values and receiving beampattern shape, comparing it with the optimum fully-adapted STAP and the nonadapted beam former responses as well as other possible counterparts. Additionally, several analyses of practical utility also demonstrate the benefits provided by phase-only STAP.