Microwave Holography for Analysis of Conformal Arrays,

The report describes a new method for determining the field near a radiating antenna, which may be planar or conformal. The method uses phase and intensity values that are measured by scanning a probe antenna over a spherical surface. The surface may be in the Fresnel or Fraunhofer regions in fact, it is chosen big enough to reduce antenna interactions but small enough to reduce reflections from the surroundings. The directive properties of the probe seem relatively unimportant because it is constantly pointed toward the antenna. The method computes the field at the antenna. The computations use the complex conjugate of the measured field so that the method is holographic. In physical terms the conjugation establishes sources that generated waves travelling inward from the measurement surface. Note that in this method the source antenna and the point at which the field is evaluated are inside the measurement surface. The authors deal with backward propagation. In contrast, other methods compute farfield patterns from data measured on a surface that separates the source from the field point.