Pulse-Doppler signal processing

Small fast moving objects can be identified close to terrain, near the sea surface, and inside storms.

Other signal processing strategies, like moving target indication, are more appropriate for benign clear blue sky environments.

In a hostile environment, there can be millions of other reflections from slow moving or stationary objects.

The same tone that is used to generate the transmit pulses is also used to down-convert the received signals to baseband.

The process of digital sampling causes ringing in the filters that are used to remove reflected signals from slow moving objects.

Sampling causes frequency sidelobes to be produced adjacent to the true signal for an input that is a pure tone.

The digital filter produces as many frequency outputs as the number of transmit pulses used for sampling.

Constant false alarm rate processing is used to examine each FFT output to detect signals.

This is an adaptive process that adjusts automatically to background noise and environmental influences.

The area surrounding the detection is examined to determine when the sign of the slope changes from

Detections for a single ambiguous range are sorted in order of descending amplitude.

For monopulse radar, signal processing is identical for the main lobe and sidelobe blanking channels.

This identifies if the object location is in the main lobe or if it is offset above, below, left or right of the antenna beam.

Range and speed of the target are folded by a modulo operation produced by the sampling process.

The received signals from multiple PRF are compared using the range ambiguity resolution process.

Invalid reflections include things like helicopter blades, where Doppler does not correspond with the velocity that the vehicle is moving through the air.

Invalid signals include microwaves made by sources separate from the transmitter, such as radar jamming and deception.

This means the feedback loop must be opened for objects like helicopters because the main body of the vehicle can be below the rejection velocity (only the blades are visible).

Doppler velocity feedback must be disabled in the vicinity of the signal source to develop track data.

The XYZ velocity is multiplied by the time between scans to determine each new aiming point for the antenna.

The antenna must be aimed at the position which will paint the target with maximum energy and not dragged behind it, otherwise the radar will be less effective.

Distance error is a feedback signal used to correct the position and velocity information for the track data.

The amplitude and phase for the signal returned by the reflector is processed using monopulse radar techniques during track.

Users are generally presented with several displays that show information from track data and raw detected signals.

The plan position indicator and scrolling notifications are automatic and require no user action.

The remaining displays activate to show additional information only when a track is selected by the user.