Combined plane wave — Point source near-field far-field transformation for short measurement distances

The radiation behavior of an antenna can be characterized by a measurement in its radiating near field followed by a near-field far-field transformation. Many transformation algorithms utilize source expansions employing higher order Hankel functions. These Hankel functions are known to become singular for small arguments corresponding to short measurement distances or to a low frequency of the respective antenna excitation. In this paper a point source modeling approach is discussed which relates the measured field samples by direct evaluation of the Green's function. In this way the formulation remains stable even for very close measurements. In order to reduce the computational effort of the technique for larger problems it is combined with the plane wave based near-field far-field transformation algorithm, which handles those measurement points with sufficient separation from the antenna under test.