Image Overview
3D Spatial Filtering Applications in Spherical Near Field Antenna Measurements
The equivalent source approach has been presented recently as an advanced antenna diagnostics tool. The equivalent source approach is a true 3D approach as opposed to traditional methods based on plane wave expansion using hemispherical field information. This method is therefore highly suitable for diagnostics on low and medium directivity antenna and even allows the possibility to isolate, identify and filter unwanted effects close to the antenna from the measurements such as cable interactions.
Spatial filtering is used in spherical near field measurements through the truncation of the mode spectrum. From knowledge of the minimum sphere enclosing the Antenna Under Test (AUT) the minimum number of spherical modes needed to represent the antenna can be determined and information resident in the higher order modes are eliminated as associated to sources outside the spatial domain of the source. Due to the nature of the spherical waves, spatial filtering truncation cannot be performed too close to the physical minimum sphere enclosing the antenna.
