%  mie.m 
% SCATTERING FROM A PEC SPHERE USING THE MIE SERIES
% ARBITRARY (R,THETA,PHI) AND POLARIZATION.
% SPHERE RADIUS IS RD -- LOOP OVER RADIUS
      clear
      ka1=0.1;
      ka2=10;
      kainc=.1;
      sp2=sqrt(pi/2);
% SPECIFY KR,THETA,PH OF OBSERVATION POINT
      nmax=40;
      it=floor((ka2-ka1)/kainc)+1;
      for i=1:it     
        ka=ka1+(i-1)*kainc;     
        K(i)=ka;
        ska=sqrt(ka);
        spka=sqrt(pi*ka/2);
        a=ka/2/pi;
        area=pi*a^2; 
        sum=0;
% sum series for each value of ka       
        for n=1:nmax 
          hnm=besselh(n-.5,2,ka);     %Hn-1/2(ka)
          hnp=besselh(n+.5,2,ka);     %Hn+1/2(ka)
          hnpp=besselh(n+3/2,2,ka);   %Hn+3/2(ka)
          hpp=.5*(hnm-hnpp);          %d/dka(Hn+1/2)
% the "hat" functions
          Hnp=sp2*(ska*hpp+.5*hnp/ska);
          Hn=spka*hnp;
          sum=sum+(-1)^n*(2*n+1)/Hn/Hnp;             
        end    
        S(i)=abs(sum)^2/area/pi/4;
      end
     loglog(K,S),grid
     xlabel('ka'), ylabel('RCS/(pi*a^2)')