Inverse Synthetic Aperture Radar Imaging With MATLAB Algorithms, 2nd Edition

Appendix

In this appendix, we present some useful Matlab functions that are used by the Matlab codes given in the chapters of this book.

Matlab code A.1 Matlab file “stft.m”

function [B,T,F]=stft(Y,f,BW,r,d)
%STFT Calculates the Short Time Fourier Transform of Vector Y
 
% Inputs:
% Y : signal in the frequency domain
% f : vector of frequencies [Hz]
% BW : bandwidth (same unit as F) of the sliding window
% f : desired dinamic range of the display
% d : additional delay [s] (if desired)
%
% Outputs:
% B : stft of vector Y
% F : frequency vector [GHz]
% T : frequency vector [ns]
 
% The window used is a Kaiser window with beta=6.0 
 
df = f(2)-f(1); % frequency resolution
Ws = round(BW/df); 
if (Ws<2),
 Ws=2;
end;
 
W = kaiser(Ws,6); % window is a Kaiser with beta=6.0
N = max(size(Y)); % find length of Y
 
% Spectrogram
[B,T,F] = specgram((Y.*exp(-j*2*pi*f*d))',N,1/df,W,Ws-1);
F = F+((Ws-1)/2)*df+f(1); % set frequency axis
T = T-d; % set time axis
 
% Treshold the image to the dynamic range
bmax = max(max(abs(B)));
ra = bmax/(10^(r/20));
B = B.*(abs(B)>=ra)+ra*ones(size(B)).*(abs(B)<ra);
 
% Display the STFT
colormap(jet(256)); %set colormap
imagesc(T*10^(9),F*10^(-9),20*log10(abs(B')/bmax))
axis xy; % change origin location
xlabel('Time [ns]'), 
ylabel('Frequency [GHz]');

Matlab code A.2 Matlab file “cevir2.m”

function out=cevir2(a,nx,ny)
% This function converts a 1D vector to a 2D matrix
 
% Inputs:
% a : 1D vector of length (nx*ny)
% nx : column length of ...