% This is receiver plane focusing parameter, radius of curvature of Gaussian beams - 23.04.2012
clear;clc;clf;warning off MATLAB:divideByZero;close all
lamda = 1.51e-6; k = 2*pi/lamda;zarr = 1:0.1e2:5e3;

Fs = 100;alfas = 1.2e-2;alfa = 1./(k*alfas^2) + j./(2*Fs);

%%%% Beam size expression in terms of alpha_s and F_s
Fr = -(k^2*alfas^4*Fs^2 - 2*k^2*alfas^4*Fs*zarr + 4*Fs^2*zarr.^2 + k^2*alfas^4*zarr.^2)./(4*Fs^2*zarr - k^2*alfas^4*Fs + k^2*alfas^4*zarr);
%Fr = - (k^2*alfas^4 + 4*zarr.^2)./(4*zarr);
figure(1)
plot(zarr/1e3,Fr/1e3,'-k','LineWidth',3);
%semilogy(zarr/1e3,Fr/1e3,'-k','LineWidth',2);
set(gcf,'Renderer','Zbuffer');set(gcf,'Color','White');set(gca,'FontSize',14);grid on;
axis ([min(zarr/1e3)*1 max(zarr/1e3)*1 -6 0]);
ylabel('\itF_r \rm\bf in km - Radius of curvature','FontSize',16,'FontWeight','bold');
xlabel('\itz\rm\bf in km - Propagation distance','FontSize',14,'FontWeight','bold')