Understanding Radar Signal Processing
Radar signal processing is a critical aspect of radar systems, responsible for separating targets from clutter based on signal amplitude, Doppler information and other characteristics.
Signal Processing Components
The signal processor is a vital part of the radar system that performs the task of target-clutter separation. In modern radar sets, after intermediate frequency (IF) amplification and phase-sensitive detection, the radar signals are converted to digital form. At this stage, the signals are referred to as radar video signals, typically having a bandwidth ranging from 250 KHz to 5 MHz. According to the Nyquist–Shannon Sampling Theorem, the appropriate sampling rates therefore fall between 500 KHz and 10 MHz, well within the capabilities of modern analogue-to-digital converters (ADCs).
The signal processor can consist of the following components
I&Q Phase Detector: This component extracts the in-phase (I) and quadrature-phase (Q) components from the radar signals. These components play a crucial role in determining the Doppler content and phase information of the targets.
Moving Target Indication (MTI): MTI techniques may be employed to distinguish moving targets from stationary clutter by exploiting the Doppler shifts in the received radar signals. For example, the signal processor can use MTI processing to filter out stationary clutter and focus on targets moving above speeds of interest.
Constant False Alarm Rate (CFAR) Detection: CFAR techniques ensure a consistent detection threshold that adapts to varying clutter levels. By maintaining a constant false alarm rate, the signal processor achieves robust target detection while minimizing false alarms caused by clutter fluctuations.
Plot Extraction and Processing
Plot extraction and processing form the final stage in the primary radar sensor chain. This stage involves processing the raw waveform to generate plots representing possible targets of interest.
The key components of plot extraction and processing include:
Plot Extractor or Hit Processor: The plot extractor translates the hits generated by the signal processor into individual plots. This component correlates the hits to form coherent plots that represent individual targets detected by the radar system, extracting valuable information, such as target positions and energy levels.
Plot Filtering: The plot processor analyses the blob information to reject plots based on criteria such as minimum and maximum sizes, strengths and other parameters, to minimise false or unwanted plots.
Plot Merging: The plot combiner considers closely spaced blobs to determine whether they represent a single target or multiple targets, merging them into a single plot report if appropriate.
Additional Radar Data Chain Devices
Apart from the primary components mentioned above, the radar data chain may include the following devices:
Radar Tracker: The radar tracker integrates multiple plots of a target from a single sensor to form a coherent track. By associating plots over time, the tracker reduces false alarms and provides continuous and accurate target tracking information, including velocities and other dynamic values. Missed detections can be handled by coasting the track based on the last known position and velocity, providing an estimated position of the target even when not visible to the signal processing chain.
Multiple Sensor Fusion: This device combines tracks from multiple radar and other sensors, enabling the integration of information from different sources. By leveraging data from various inputs, multiple sensor fusion improves overall target detection capabilities and situational awareness.
Further Reading on Radar Signal Processing
Radar Terminology
Radar Scan Conversion: The Hows, Whys and Where Nexts?
Understanding ACP and ARP Radar Signals
RadarTutorial.eu - The Radar Signal Processor