To perform clutter filtering, we can use a high-pass filter (e.g., Butterworth) to suppress low-frequency clutter (stationary/slow-moving objects) while preserving high-frequency Doppler shifts from moving targets.
Follow these steps to create a radar clutter filtering program using Doppler extraction:
1. Define radar and simulation parameters
numRangeBins = 128; % Number of range bins
numPulses = 64; % Number of pulses in one coherent processing interval (CPI)
prf = 1e3; % Pulse Repetition Frequency (Hz)
fc = 10e9; % Radar carrier frequency (Hz)
c = 3e8; % Speed of light (m/s)
2. Simulate raw radar data Including clutter and targets
data = complex(zeros(numRangeBins, numPulses));
clutterAmplitude = 5;
data = data + clutterAmplitude * (randn(numRangeBins, numPulses) + 1i * randn(numRangeBins, numPulses));
targetRanges = [30, 90]; % Target positions (in range bins)
targetDopplers = [0.25*prf, -0.2*prf]; % Target Doppler frequencies
targetAmplitudes = [1, 0.8]; % Signal strength of targets
for idx = 1:length(targetRanges)
rangeBin = targetRanges(idx);
t = (0:numPulses-1)/prf;
dopplerPhase = 2 * pi * targetDopplers(idx) * t;
data(rangeBin, :) = data(rangeBin, :) + targetAmplitudes(idx) * exp(1i * dopplerPhase);
end
3. Design a High-Pass Filter to suppress clutter
filterOrder = 5;
normalizedCutoff = 0.1; % Normalized to Nyquist (0.1 = 10% of PRF)
[b, a] = butter(filterOrder, normalizedCutoff, 'high');
4. Apply clutter filter
filteredData = zeros(size(data));
for rangeBin = 1:numRangeBins
filteredData(rangeBin, :) = filter(b, a, data(rangeBin, :));
end
5. Perform doppler FFT for target extraction
fftPoints = 1024; % Number of points in Doppler FFT
dopplerAxis = linspace(-prf/2, prf/2, fftPoints); % Doppler frequency axis
% Compute Doppler spectra (FFT across slow-time dimension)
originalFFT = fftshift(fft(data, fftPoints, 2), 2);
filteredFFT = fftshift(fft(filteredData, fftPoints, 2), 2);
6. Visualize the results
figure('Position', [100, 100, 1200, 800])
tiledlayout(2, 1, 'TileSpacing', 'tight', 'Padding', 'compact');
% (a) Original Range-Doppler Map
nexttile
imagesc(dopplerAxis, 1:numRangeBins, 20*log10(abs(originalFFT)))
xlabel('Doppler Frequency (Hz)'), ylabel('Range Bin')
title('Original Range-Doppler Map')
colorbar, clim([0 50]), axis xy, grid on
% (b) Doppler Spectrum at a Selected Range Bin
nexttile
rangeBin2Plot = targetRanges(1);
plot(dopplerAxis, 20*log10(abs(originalFFT(rangeBin2Plot, :))), 'b', 'LineWidth', 1.5);
hold on
plot(dopplerAxis, 20*log10(abs(filteredFFT(rangeBin2Plot, :))), 'r', 'LineWidth', 1.5);
xlabel('Doppler Frequency (Hz)'), ylabel('Magnitude (dB)')
title(['Doppler Spectrum at Range Bin ', num2str(rangeBin2Plot)])
legend('Original', 'Filtered', 'Location', 'best')
xlim([-prf/2, prf/2]), grid on
You can refer to the following documentation pages for more information:
