green's function question

hello,

the green's function in free space is very well known (exp(j*k*R)/(4*pi*R)). however, for very small distances (R) the result becomes infinite. how can these problems be solved? is there a specific green's function for small distances (e.g. 1e-6*lambda)?

best regards.

The Green'sfunction must become infinite because it is the fields due to an infinitely small dipole with infinite current. However, to get the fields of a real patch of current, you always integrate the Green's function over the area of the patch of current. This integral exists...except where the fields are infinite. If you have a real patch of current, the fields will always exist. If you have a theoretical patch of current that cannot really exist, then the fields might also be infinite. For example, the E fields of a roof-top function are infinite at the peak and eaves of the rooftop. Fortunately, even where the fields are infinite, the integral of the fields is no problem. Thus, we can deal with finite voltages (voltage is the integral of the e field).