www.pudn.com > programradarsystemdisign.zip > clutter_rcs.m

function [sigmaC,CNR] = clutter_rcs(sigma0, thetaE, thetaA, SL, range, hr, ht, pt, f0,... 
    b,  t0, f, l,ant_id) 
% This function calculates the clutter RCS and the CNR for a ground based radar. 
clight = 3.e8; % speed of light in meters per second 
lambda = clight /f0; 
thetaA_deg = thetaA; 
thetaE_deg = thetaE; 
thetaA = thetaA_deg * pi /180; % antenna azimuth beamwidth in radians 
thetaE = thetaE_deg * pi /180.; % antenna elevation beamwidth in radians 
re = 6371000; % earth radius in meter 
rh = sqrt(8.0*hr*re/3.); % range to horizon in meters 
SLv = 10.0^(SL/10); % radar rms sidelobes in volts 
sigma0v = 10.0^(sigma0/10); % clutter backscatter coefficient  
tau = 1/b; % pulse width   
deltar = clight * tau / 2.; % range resolution for unmodulated pulse 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
range_m = 1000 .* range;  % range in meters 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
thetar = asin(hr ./ range_m); 
thetae = asin((ht-hr) ./ range_m); 
propag_atten = 1. + ((range_m ./ rh).^4); % propagation attenuation due to round earth 
Rg = range_m .* cos(thetar); 
deltaRg = deltar .* cos(thetar); 
theta_sum = thetae + thetar; 
% use sinc^2 antenna pattern when ant_id=1 
% use Gaussian antenna pattern when ant_id=2 
if(ant_id ==1) % use sinc^2 antenna pattern 
    ant_arg = (2.78 * theta_sum ) ./ (pi*thetaE); 
    gain = (sinc(ant_arg)).^2; 
else 
    gain = exp(-2.776 .*(theta_sum./thetaE).^2); 
end 
% compute sigmac 
sigmac = (sigma0v .* Rg .* deltaRg) .* (pi * SLv * SLv + thetaA .* gain.^2) ./ propag_atten; 
sigmaC = 10*log10(sigmac); 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
figure(1) 
plot(range, sigmaC) 
grid 
xlabel('Slant Range in Km') 
ylabel('Clutter RCS in dBsm') 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
% Calculate CNR 
pt = pt * 1000; 
g = 26000 / (thetaA_deg*thetaE_deg); % antenna gain 
F = 10.^(f/10); % noise figure is 6 dB 
Lt = 10.^(l/10); % total radar losses 13 dB 
k = 1.38e-23; % Boltzman’s constant 
T0 = t0; % noise temperature 290K 
argnumC = 10*log10(pt*g*g*lambda*lambda*tau .* sigmac); 
argdem = 10*log10(((4*pi)^3)*k*T0*Lt*F .*(range_m).^4); 
CNR = argnumC - argdem; 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
figure(2) 
plot(range, CNR,'r') 
grid 
xlabel('Slant Range in Km') 
ylabel('CNR in dB')