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=== Short Dipole Sources ===

A short dipole is the simplest type of radiator, which consists of a short current element of length Δl, aligned along a unit vector û and carrying a current of I Amperes. The product IΔl is often called the dipole moment and gives a measure of the radiator's strength. A short dipole in the free space generates an azimuth-symmetric, almost omni-directional, far field. However, the radiated fields of a short dipole above a layered planar background structure are greatly altered by the presence of the substrate layers. Note that the electric and magnetic field radiated by a short dipole in the presence of a layered background structure are indeed nothing but the dyadic Green's functions of that structure: