Modified radiation pattern prediction for small aperture horn antennas

The overall performance of an antenna system is often judged by its far-field pattern and/or its gain. In radar system design, these fundamental parameters generally determine the type and size of antenna to be used. Accurate radiation pattern and gain formulae are obtained when the aperture is large in terms of a wavelength, but break down as the dimensions of the aperture become small. The deficiency is attributed to the neglected fringe currents at the edge of the aperture. We present modified far-field and gain formulae for small-aperture horn antennas incorporating the fringe currents on the edge of the aperture, and comparison is made with measured data to quantify the accuracy of the modified formulas. The modified formula for the radiation pattern agrees well with the measured data.