function y = fbratio(ant,freq,w)
% y = fbratio(ant,f,w)
% Ratio of forward radiation against backward radiation.
% The forward gain is the maximum gain within the +x-half-space.
% The backward gain is the maximum gain within the -x-half-space.
% The antenna model must not contain groundproperties.
% The direction of main radiation must be the x-diection.
%
% ant  :  antenna description.  There are three options:
%         MATLAB expression :   description in MADL
%         string :   file with description in NEC-syntax
%         {string; p} : string = file with description in AAL-syntax; 
%                       p = antenna parameters
%
% freq :  frequency in MHz.
%
% w    :  conus angle around the negative x-axis for search of the 
%         backward maximum in degrees (default = 90)
%
% y = [fb,gn]  :  fb = forward/backward ratio in dB
%                 gn = maximum gain in dBi within any direction 
%                      in the +x-half-space.
