Meaning
Boundary truncation effects in calculated far-field antenna patterns arise when near-field spatial sampling terminates before field intensity decays to negligible levels. Engineers evaluate truncation error to determine how finite scan planar boundaries affect reconstructed side lobe levels and directivity values. Truncating the scan plane removes high angle plane wave components from the measured spatial spectrum.
Spatial Boundary
Planar scanning grids cannot extend to infinity and must end at practical mechanical limits. Energy passing outside the physical scan area is omitted from Fourier transform integrations. Truncation severity depends on antenna directivity, scan plan size and clearance distance between antenna and probe.
Tapering windows applied to edge sample data mitigate sharp boundary discontinuities but broaden main beam width calculations.
Mathematical Artifact
Abrupt spatial data termination creates high frequency ripple in the transformed angular spectrum.
Field Distortion
Calculated radiation patterns exhibit artificial side lobes and inaccurate null depths beyond the valid angle defined by scan geometry. Increasing scan frame size captures more off-axis energy and reduces pattern distortion at wide angles. Mathematical correction techniques extrapolate edge field trends to reduce spectral leakage during transformation.
Minimizing truncation error is necessary for accurate side lobe level verification in high gain antenna arrays.
