MATLAB Examples

# Figure 14. Example clutter ridges with velocity misalignment, for Doppler-ambiguous clutter.

## Contents

Coded by Ilias Konsoulas, 16 Dec. 2014. Code provided for educational purposes only. All rights reserved.

clc; clear; close all; 

## Radar System Operational Parameters.

fo = 450e6; % Operating Frequency in Hz fr = 300; % PRF in Hz Tr = 1/fr; % PRI in sec. c = 299792458; % Speed of Light in m/sec. lambda = c/fo; % Operating wavelength in meters. d = lambda/2; % Interelement Spacing % Azimuth angle in degrees: phi = -180:0.5:180; Lphi = length(phi); fd = zeros(1,Lphi); 

## Platform Parameters.

beta = 1.5:0.5:3; % Beta parameter values. ha = 9e3; % Platform altitude in meters. Rc = 13e4; % (clutter) range of interest in meters. psi = asin(ha/Rc); % Grazing angle at the clutter patch in rad (flat earth model). theta = psi; % Depression angle to ik-th clutter patch (flat earth model). phia = [30 45 60 75]; % Velocity Misalignment angle in degrees. 

## Clutter Spatial Frequency of ik-th Clutter Patch.

fsp = d/lambda*cos(theta)*sin(phi*pi/180); 

## Plot Normalized Doppler Frequency vs Spatial Frequency.

figure('NumberTitle', 'off','Name', ... 'Figure 14. Example clutter ridges with velocity misalignment, for Doppler-ambiguous clutter.', ... 'Position', [1 1 1150 1250]); for i1=1:length(beta) for i2 = 1:length(phia) % Platform Velocity for various beta parameter values: va = beta(i1)*d*fr/2; % Doppler Frequency from ik-th Clutter Patch fd = 2*va/lambda*cos(theta)*sin(phi*pi/180 + phia(i2)*pi/180); % Eq. (82) % Normalized Doppler Frequency: omegac = fd*Tr; for k=1:Lphi if omegac(k)>0.5 && omegac(k)<=1.5 omegac(k) = omegac(k) - 1; elseif omegac(k)<-0.5 && omegac(k)>=-1.5 omegac(k) = omegac(k) + 1; end if omegac(k)>1.5 && omegac(k)<=2.5 omegac(k) = omegac(k) - 2; elseif omegac(k)<-1.5 && omegac(k)>=-2.5 omegac(k) = omegac(k) + 2; end if omegac(k)>2.5 && omegac(k)<=3.5 omegac(k) = omegac(k) - 3; elseif omegac(k)<-2.5 && omegac(k)>=-3.5 omegac(k) = omegac(k) + 3; end end front = zeros(1,Lphi); back = zeros(1,Lphi); for k=1:Lphi if abs(phi(k)) <= 90 front(k) = omegac(k); else back(k) = omegac(k); end end zeroindfront = find(front==0); zeroindback = find(back==0); front(zeroindfront) = NaN; back(zeroindback) = NaN; i3 = 4*(i1-1)+i2; subplot(4,4,i3); plot(fsp,front,'.'); hold on; plot(fsp,back,'r.'); title(['\beta = ', num2str(beta(i1)), ', \phi_a = ',num2str(phia(i2)),'\circ']); if i3==1||i3==5||i3==9||i3==13 ylabel('Norm. Doppler Freq. \omega_c'); end ylim([-0.5 0.5]); xlim([-0.5 0.5]); grid on; if i3==16 legend('front','back','Location','Best'); end if i1==4 xlabel('Spatial Frequency \vartheta_c'); end end end tightfig;