Calculation of the field radiated by horn-antennas using the mode-matching method

Methods employed for evaluating fields radiated by horn antennas, like the aperture field method and the spherical wave expansion, have not taken into account the contribution by fields existing outside the horn aperture (e.g., along the outer walls of the horn). The use of the mode-matching technique for analyzing the transition from horn antenna to free space makes it possible to include in the analysis even those fields which exist outside (e.g., behind) the horn aperture when determining the far as well as the near field. Furthermore, the effects of the finite wall thickness and the discontinuity caused by the transition from waveguide to free space are also taken into account. A suitable development of the fields at the transition of the conical/corrugated horn to free space using the mode-matching technique is presented. Two different convergence diagrams, depending on the kind of modes excited in the horn antenna, are given. They show the results from extensive convergence investigations. With the help of these diagrams, a reliable evaluation of the fields radiated by horn antennas is guaranteed. Practical measurements of the fields radiated by horn antennas confirm the field distributions gained through analysis