Space Time Adaptive Processing
Published on Dec 12, 2015
Space-Time Adaptive Processing (STAP) refers to a class of signal processing techniques used to process returns of an antenna array radar system. It enhances the ability of radars to detect targets that might otherwise be obscured by clutter or jamming.
. The output of STAP is a linear combination or weighted sum of the input signal samples .The "adaptive" in STAP refers to the fact that STAP weights are computed to reflect the actual noise, clutter and jamming environment in which the radar finds itself. The "space" in STAP refers to the fact that STAP the STAP weights (applied to the signal samples at each of the elements of the antenna array) at one instant of time define an antenna pattern in space.
If there are jammers in the field of view, STAP will adapt the radar antenna pattern by placing nulls in the directions those jammers thus rejecting jammer power. The "time" in STAP refers to the fact that the STAP weights applied to the signal samples at one antenna element over the entire dwell define a system impulse response and hence a system frequency response.
STAP is a multi-dimensional adaptive signal processing technique over spatial and temporal samples. In this approach, the input data collected from several antenna sensors has a cubic form. Depending on how this input data cube is processed, STAP is classified into Higher Order Post-Doppler (HOPD), Element Space Pre-Doppler, Element Space Post-Doppler, Beam Space Pre-Doppler, and Beam Space Post-Doppler.
STAP consists of three major computation steps. First, a set of rules called the training strategy is used to select data which will be processed in the subsequent computation. The second step is weight computation. It requires solving a set of linear equations. This is the most computationally intensive step. Finally, thresholding operation is performed after applying the computed weights. In HOPD processing, Doppler processing (FFT computations) is followed by solving least square problems (QR decompositions).
Introduction To Radar
Radar is an electromagnetic system for the detection and location of objects. RADAR is nothing but Radio Detection And Ranging. It operates by transmitting a particular type of waveform and detects the nature of the echo signal. An elementary form of radar consists of a transmitting antenna emitting electromagnetic radiation generated by an oscillator of some sort, a receiving antenna, and an energy detecting device or receiver .
A portion of the transmitted signal is intercepted by a reflecting object (target) and is reradiated in all directions. It is the energy reradiated in the back direction that is of prime interest to the radar. The receiving antenna collects the returned energy and delivers it to a receiver, where it is processed to detect the presence of the target and to extract its location and relative velocity.
The transmitter may be an oscillator such as magnetron, which is pulsed by the modulator to generate a repetitive train of pulses. The waveform generated by the transmitter travels via a transmission line to the antenna where it is radiated into space.
A single antenna is generally used for both transmitting and receiving. The receiver must be protected from damage caused by the high power of the transmitter. This is the function of the duplexer. The duplexer also serves to channel the returned echo signals to the receiver and not to the transmitter. The receiver is usually of the superhetrodyne type.
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