Comparison of a direct low-pass filtering technique with spherical modal filtering applied to the suppression of range reflections in antenna measurements

In this paper, two filtering techniques for the suppression of range reflections in antenna measurements are compared based on simulated and measured data. The spherical modal filtering is based on the expansion of the measured field in spherical wave functions. Range reflections are suppressed by removing unwanted modes before transforming back to the far-field. The direct low-pass filtering technique employs the band limitation of the radiation pattern function directly. Range reflections are suppressed by removing higher order components of the angular spectrum. Both methods require a modal or spectral separation between the wanted and unwanted part of the radiation pattern to be effective. The direct low-pass filtering technique is computationally simpler than the modal filter and has a number of additional advantages. In contrast to the modal filter it can be applied to a single cut. Furthermore the method is less sensitive to geometrical position errors and window functions may be applied to reduce the effect of angular truncation.