matlab-基于MATLAB的LFM线性调频信号产生仿真-源码

clc; clear; close all; warning off; addpath(genpath(pwd)); B = 30.0e6; % Set the bandwidth of the chirp T = 42e-6; % Set the time duration of the chirp time_B_product = B * T; if(time_B_product < 5 ) fprintf('************ Time Bandwidth product is TOO SMALL ***************') fprintf('\n Change B and or T') return else end % Compute alpha mu = 2. * pi * B / T; npow = nextpow2(5 * B * T + 1); npoints = 1*(2^(npow)); % Determine sampling times delt = linspace(-T/2., T/2., npoints); M = length(delt); % Compute the complex LFM representation Ichannal = cos(mu .* delt.^2 / 2.); % Real part Qchannal = sin(mu .* delt.^2 / 2.); % Imaginary Part LFM = Ichannal + sqrt(-1) .* Qchannal; % complex signal SNR = 15; w_n = randn(1,M) + i*randn(1,M); w = (10^(-SNR/10))*w_n; % Additive white noise LFM = w+LFM; % Compute the FFT of the LFM waveform LFMFFT = fftshift(fft(LFM)); % Plot the real and Inginary parts and the spectrum sampling_interval = T / npoints; freqlimit = 0.5 / sampling_interval; freq = linspace(-freqlimit,freqlimit,npoints); figure(1) subplot(4,1,1) plot(delt,Ichannal,'k'); axis([-T/2 T/2 -1.5 1.5]) grid xlabel('Time - seconds') ylabel('Units of Waveform') title('Real part of an LFM waveform') subplot(4,1,2) plot(delt,Qchannal,'k'); axis([-T/2 T/2 -1.5 1.5]) grid xlabel('Time - seconds') ylabel('Units of Waveform') title('Imaginary part of LFM waveform') subplot(4,1,3) plot(freq, abs(LFMFFT),'k'); grid xlabel('Frequency - Hz') ylabel('Amplitude spectrum') title('Spectrum for an LFM waveform') % Chirp detection method % Computer delay and multiply of chirp with itself delay = 2000; chrp_d = real(LFM(delay:end)) ; chrp = real(LFM(1:length(chrp_d))); output_ch = abs(fftshift(fft(chrp_d.*chrp))).^2; y = output_ch/max(output_ch); fs = 1/sampling_interval; f = (fs/length(y))*(-(length(y)/2):(length(y)/2)-1); % Plot delay and multiple result subplot(4,1,4) plot(10e-6*f,10*log10(y),'k'); grid xlabel('Frequency (MHz)') ylabel('Normalized Amplitude (dB)') title('Chirp Detection Tone Plot') ylim([-75 0])