NF Accuracy Settings SBR+ Advanced Option

The NF Accuracy settings (NF Accuracy Controls for SBR+) provide access to methodology settings relating to cases where Tx antennas, Rx antennas, and near-field observation points are in proximity to the scattering geometry (i.e., the platform CAD model). When this feature is switched off, HFSS SBR+ uses default near-field accuracy settings that should be adequate for most situations, including close-proximity Tx/observer conditions that this feature is designed to tune.

After you enable the feature, the setting is available through the Solutions Setup for SBR+ solution types, Options tab, and HFSS with Hybrid and Arrays Solution Types, Solutions Setup, Hybrid tab, if the design contains SBR+ regions. Selecting the SBR+ Advanced Options button to display SBR+ Advanced Options.

Select Customize Near Field Accuracy Options to enable the NF Accuracy tab.

Tx Distance Ratio:

Fields change rapidly near the Tx antenna. When the Tx antenna is placed near a surface, HFSS SBR+ adaptively increases the ray density above the normal level, but only for the nearby surfaces. This ensures adequate sampling of the Tx radiation field by the rays.

For close-proximity surfaces, HFSS SBR+ further subdivides these sub-surfaces to maintain a minimum ratio between distance-from-Tx-to-surface and maximum-linear-dimension-of-surface. By default, this ratio threshold is set to 5. Normally, this setting is adequate. To increase the over-sampling, increase this ratio setting above 5. To switch off the over-sampling feature, set this ratio very low, say 0.01. Even when set very low, HFSS SBR+ will still shoot rays at a minimum density according to the Ray Density parameter in the Methodology node.

Rx/Obs-Pts Dist Ratio

This setting has the same geometric interpretation as Tx Distance Ratio, but instead controls the over-sampling of projected ray tube footprints for close-proximity observation points and receivers in the scattered field radiation integral. To switch off the over-sampling feature, set Rx/Obs-Pts Dist Ratio to zero. By default, the ratio threshold is set to 5, which is normally adequate, regardless of how close the observation point is to the surface.

(GPU plug-in only): For SBR ray footprints sufficiently near the field observation point or Rx antenna for over-sampling to occur, the scattering computation will not be GPU-accelerated. Instead, it will be performed on the CPU.

This setting has no impact on the computation of far-field patterns.