Extended edge wave diffraction model for near-field directivity calculations of horn antennas

The edge wave diffraction model for pyramidal horn antennas is extended to include the finite radii of curvature of the primary incident wave approximated by an astigmatic ray tube in determining the edge diffraction fields contributing to the radiated fields. The model is adapted to calculate the effective near-field directivity of a pyramidal horn antenna for generating standard electromagnetic field strengths for the calibration of field probes. The predicted directivity results for a range of standard gain antennas are verified with method of moments data and measured values obtained in a near-field antenna range.