function s = polygon(a,d,m)
% s = polygon(a,d,m)
% Polygon of linear wires or tubes
% a :  Matrix n*[ax ay az] of wire end coordinates
% d :  Wire diameter in m  (default = 0.002 m).
% m :  Vector of n numbers of segments.
%      If a scalar value is given it will be applicated to all wires.
% s :  Resulting antenna structure 
