Determination of Horn Antenna Phase Centers by Edge Diffraction Theory

The edge diffraction method of analysis utilized in the past to determine amplitude patterns is extended in this paper to predict the radiation phase center of pyramidal horn antennas. A series of extensive phase and amplitude measurements were performed on these antennas to determine the validity of the theoretical results. The measurements were performed over a frequency range of 7.5 to 10.5 GHz in the E plane of the antennas. The phase measurements were accurate to ±0.2 electrical degrees, so that the phase center locations relative to the horn apertures were repeatably determined to better than 0.010 inch for horn apertures as large as 7 inches. The results of the measurements indicate that excellent agreement is obtained with the theory in predicting the phase center location of the larger horns (kRE > 50). For the smaller horns, however, there is a large discrepancy between the theory and measurements. The measured phase centers of the smaller horns exhibit a large variation with frequency which cannot be explained with the existing theory. Several reasons for the discrepancy are presented, and it is concluded that a more rigorous approach involving higher order modes has to be developed for the smaller horns.