What are the challenges and solutions for achieving high-resolution radar imaging of moving targets?

1 Challenge 1: Range ambiguity

One of the challenges for radar imaging of moving targets is range ambiguity, which occurs when the radar receives echoes from multiple targets at different distances but with the same delay. This can happen when the radar pulse repetition frequency (PRF) is too low or the target range is too large. Range ambiguity can cause confusion and errors in the radar image, especially when the targets have similar velocities or cross each other.

2 Solution 1: Range coding

One of the solutions for range ambiguity is range coding, which involves modulating the radar pulses with different codes or patterns to distinguish them from each other. The codes can be binary, phase, or frequency modulated, and they can be matched or mismatched to the radar receiver. Range coding can increase the effective PRF and reduce the range ambiguity, but it also requires more complex signal processing and may reduce the signal-to-noise ratio (SNR).

3 Challenge 2: Doppler ambiguity

Another challenge for radar imaging of moving targets is Doppler ambiguity, which occurs when the radar receives echoes from multiple targets with different velocities but with the same Doppler frequency. This can happen when the radar PRF is too high or the target velocity is too large. Doppler ambiguity can cause distortion and blurring in the radar image, especially when the targets have different ranges or angles.

4 Solution 2: Doppler coding

Another solution for Doppler ambiguity is Doppler coding, which involves modulating the radar pulses with different frequencies or phases to distinguish them from each other. The frequencies or phases can be linear, nonlinear, or random, and they can be coherent or noncoherent to the radar transmitter. Doppler coding can increase the effective bandwidth and reduce the Doppler ambiguity, but it also requires more complex signal processing and may reduce the SNR.

5 Challenge 3: Clutter suppression

A third challenge for radar imaging of moving targets is clutter suppression, which refers to the elimination or reduction of unwanted echoes from stationary or slow-moving objects, such as terrain, buildings, or vegetation. Clutter can interfere with the detection and identification of moving targets, especially when they are close to or embedded in the clutter. Clutter can also affect the range and Doppler resolution, as well as the SNR.

6 Solution 3: Clutter filtering

A third solution for clutter suppression is clutter filtering, which involves applying different techniques to separate the moving target echoes from the clutter echoes. The techniques can be based on spatial, temporal, or spectral characteristics of the signals, and they can be adaptive or nonadaptive to the clutter environment. Clutter filtering can improve the contrast and clarity of the radar image, but it also requires more computational resources and may introduce artifacts or errors.