MATLAB Examples

# Figure 7. Clutter Loci for Different Platform Velocities.

## Contents

clc; clear; close all; 

fo = 450e6; % Operating Frequency in Hz Pt = 200e3; % Peak Transmit Power 200 kW Gt = 22; % Transmit Gain in dB Gr = 10; % Column Receive Gain in dB B = 4e6; % Receiver Instantaneous Bandwidth in Hz Ls = 4; % System Losses in dB fr = 300; % PRF in Hz Tr = 1/fr; % PRI in sec. % M = 18; % Number of Pulses per CPI: Tp = 200e-6; % Pulse Width in sec. N = 18; % Number of Array Antenna Elements Gel = 4; % Element Gain in dB be = -30; % Element Backlobe Level in db Nc = 361; % Number of clutter patches uniformly distributed in azimuth. 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:.5:180; Lphi = length(phi); 
va = 50; % Platform velocity in m/sec. ha = 9e3; % Platform altitude in meters. beta = 0:0.5:7; % Beta parameter values. 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). % Clutter Spatial Frequency of ik-th Clutter Patch: fsp = d/lambda*cos(theta)*sin(phi*pi/180); 
figure('NumberTitle', 'off','Name', ... 'Figure 7. Clutter Loci for Different Velocities of Side Looking Airborne Radar (SLAR) ', ... 'Position', [50 50 1150 700] ); for i=1:length(beta) % Platform Velocity for various beta parameter values: va = beta(i)*d*fr/2; % Eq. (71) % Doppler Frequency from ik-th Clutter Patch % fd = 2*va/lambda*cos(theta)*sin(phi*pi/180); % Normalized Doppler Frequency: % omegac = 2*va*Tr/d*fsp; omegac = beta(i)*fsp; % Eq. (70) % This loop simulates the fold-over of the Clutter ridge (i.e. brings omegac % back into the [-0.5 0.5] interval) when clutter is Doppler-ambiguous (β>1). 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 % Plot Normalized Doppler Frequency vs Spatial Frequency. subplot(3,5,i); plot(fsp,omegac,'.'); title(['v_a = ',num2str(round(va)),' m/sec, \bf\beta = ',num2str(beta(i))]); if i==1 || i== 6 || i==11 ylabel('Norm. Doppler Frequency \omega_c'); end if i>10 xlabel('Spatial Frequency \vartheta_c'); end ylim([-0.5 0.5]); xlim([-0.5 0.5]); grid on; end tightfig;