Abstract
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 $N$ -torus of phase-only complex vectors, where $N$ 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.
Highlights
R ADAR space-time adaptive processing (STAP) is a powerful technique used in airborne systems to detect a target embedded in interference potentially comprising clutter, jamming and noise [1]–[5]
It should be observed first that in analyzing the detection capabilities of a radar system it is essential to take into account the signal to interference plus noise ratio (SINR) which provides a measure of the radar strength to distinguish the useful component with respect to the interferences in the received signal
All the above-mentioned research papers are essentially based on the computation of the weight vector, that for the optimum adapted radar STAP is essentially described by a number of complex quantities that would be multiplied to the received signal samples in the receiving filter
Summary
R ADAR space-time adaptive processing (STAP) is a powerful technique used in airborne systems to detect a target embedded in interference potentially comprising clutter, jamming and noise [1]–[5]. All the above-mentioned research papers are essentially based on the computation of the weight vector, that for the optimum adapted radar STAP (i.e., that maximizing the SINR) is essentially described by a number of complex quantities that would be multiplied to the received signal samples in the receiving filter. In several practical implementations, the radar receiver could comprise only phase shifters not-always sharing amplitude tuners, it would be interesting to implement complex weights having a constant modulus, namely to derive a phase-only weight vector This problem has been addressed in [35], where the optimum phase-only adaptive array has been designed formalizing the problem as a SINR maximization constraining the weight vectors to belong to the phase-only space. [A, B] between matrices A and B is the Lie bracket or commutator product defined as AB − BA
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