dihedral_rcs_f.m

这是计算各种形状的散射程序

% dihedral_rcs_f.m
% ==============================================================
% MATLAB code for the calculation of
%  frequency Response of the Polarization Scattering Matrix 
% of dihedral corners near boresight, by using PO approximation,
% with consideration of single-bounce and double-bounce 
% contributions.
% Syntax:
% 		[dhh,dvv,dhv]=dihedral_rcs_f(a,b,l,beta,tau,fmin,fmax,phi,nf)
% Input:
%		a,b -- lengths of the sides of the dihedral corner (cm)
%		l -- Height of the dihedral corner (cm)
% 		tau-- angle tilted above the local horizontal (deg.)
%		beta -- the angle between the two faces (deg.)
%		fmin -- minimum frequency (MHz)
%		fmax -- maximum frequency (MHz)
%	 	phi -- azimuthal angle (-50=<phi<=50 deg.)
%		nf -- No. of frequency samples
% Output:
%		dhh -- complex RCS for H-H polarization 
%		dvv -- complex RCS for V-V polarization
%		dhv -- complex RCS for H-V polarization (dhv=dvh)
% Conditions when holding accuracy: 
%		a,b,l>= several wavelengths
% ==============================================================

function [dhh,dvv,dhv]=dihedral_rcs_f(a,b,l,beta,tau,fmin,fmax,phi,nf)


c=300.0;  % (m/s)
a=a/100.; %(m)
b=b/100.; %(m)
l=l/100.; %(m)
beta0=beta/2.; %(deg.)
phi=phi*pi/180.; %(rad.)
fstep=(fmax-fmin)/(nf-1);
j=sqrt(-1);

for i=1:nf
   freq=fmin+fstep*(i-1);
	wavelength=c/freq;  % (m)
	k=2*pi/wavelength;
   
% calculation of sa,sb
   ka=k*a;
   kb=k*b;
   beta=beta0*pi/180.;
   beta3=beta*3.;
   
   x=ka*cos(beta+phi)/pi;
   sa=-j*ka*l/wavelength*sin(beta+phi)*exp(-j*ka*cos(beta+phi))*sinc(x);
   
   x=kb*cos(beta-phi)/pi;
   sb=-j*kb*l/wavelength*sin(beta-phi)*exp(-j*kb*cos(beta-phi))*sinc(x);
   
% calculation of sab,sba
   gama=atan2(b*sin(2.*beta),a-b*cos(2*beta));
   alpha=pi-beta3;
   
   if phi<=-alpha
      aa=0.0;
   elseif phi>=gama-alpha
      aa=b*sin(beta-phi)/sin(beta3-phi);
   else
      aa=a;
   end
   
   if phi>=alpha
      bb=0;
   elseif phi<=gama-beta
      bb=a*sin(beta+phi)/sin(beta3+phi);
   else
      bb=b;
   end
   
 %e-plane
   x=k*bb*cos(2*beta)*cos(beta+phi)/pi;
   sin3=sin(beta3+phi);
   sab=-j*k*bb*l/wavelength*exp(-j*k*bb*cos(beta*2)*cos(beta+phi))*sinc(x);
   sabe=sab*sin3;
   
   x=k*aa*cos(2*beta)*cos(beta-phi)/pi;
   sin3=sin(beta3-phi);
   sba=-j*k*aa*l/wavelength*exp(-j*k*aa*cos(beta*2)*cos(beta-phi))*sinc(x);
   sbae=sba*sin3;
   
 %h-plane
   sin3=-sin(beta-phi);
   sabh=sab*sin3;
   
   sin3=-sin(beta+phi);
   sbah=sba*sin3;
   
%Total e&h-plane fields
   tvv(i)=(sa+sb+sabh+sbah)*wavelength/pi;
   thh(i)=(sa+sb+sabe+sbae)*wavelength/pi;
end

dhh=thh*cos(2*tau*pi/180.);
dvv=tvv*cos(2*tau*pi/180.);
dhv=-thh*sin(2*tau*pi/180.);

%Graphics
gresult=dihedral_graph(dhh,dvv,dhv,fmin,fmax);


% Graphics for dihedral_rcs
% -------------------------------------------------------------
function gresult=dihedral_graph(dhh,dvv,dhv,fmin,fmax)

np=max(size(dhh));
pstep=(fmax-fmin)/(np-1);

figure

i=1:np;
p=((i-1)*pstep+fmin);

thha=20*log10(abs(dhh)+eps);
thhp=atan2(imag(dhh),real(dhh))*180/pi;
thhamin=max([min(thha),-75]);
thhamax=max([max(thha),-75]);

subplot(321)
plot(p,thha,'b-')
axis([fmin fmax thhamin-5 thhamax+5])
grid on
title('RCS Magnitude of the Dihedral (HH)')
%xlabel('Frequency (MHz)')
ylabel('RCS (dBsm)')

subplot(322)
plot(p,thhp);
axis([fmin fmax -180 180]);
grid on
title('RCS Phase of the Dihedral (HH)')
%xlabel('Frequency (MHz)')
ylabel('Phase (deg.)')

tvva=20*log10(abs(dvv)+eps);
tvvp=atan2(imag(dvv),real(dvv))*180/pi;
tvvamin=max([min(tvva),-75]);
tvvamax=max([max(tvva),-75]);

subplot(323)
plot(p,tvva,'b-')
axis([fmin fmax tvvamin-5 tvvamax+5])
grid on
title('RCS Magnitude of the Dihedral (VV)')
%xlabel('Frequency (MHz)')
ylabel('RCS (dBsm)')

subplot(324)
plot(p,tvvp);
axis([fmin fmax -180 180]);
grid on
title('RCS Phase of the Dihedral (VV)')
%xlabel('Frequency (MHz)')
ylabel('Phase (deg.)')

thva=20*log10(abs(dhv)+eps);
thvp=atan2(imag(dhv),real(dhv))*180/pi;
thvamin=max([min(thva),-75]);
thvamax=max([max(thva),-75]);

subplot(325)
plot(p,thva,'b-')
axis([fmin fmax thvamin-5 thvamax+5])
grid on
title('RCS Magnitude of the Dihedral (HV)')
xlabel('Frequency (MHz)')
ylabel('RCS (dBsm)')

subplot(326)
plot(p,thvp);
axis([fmin fmax -180 180]);
grid on
title('RCS Phase of the Dihedral (HV)')
xlabel('Frequency (MHz)')
ylabel('Phase (deg.)')

gresult=1;