The Far Zone Reference Settings allow users to set the reference point for computing radiated fields. This analysis is used when the phase difference between antenna elements requires careful design, such as an antenna array or radar.

Background

XF performs a surface integral over the fields near the boundary of the FDTD space and it applies a near to far field transformation in order to arrive at the radiated fields. This is an application of the surface equivalence theorem and the surface integral requires a reference point.

Reference point for simulations.
Reference point 1 (red), 2 (green), 3 (blue).

Consider the two projects in the first image. Project A has a half-wave dipole centered in the FDTD simulation space, and project B has a half-wave dipole offset λ/8 from the center. A 2-D far zone sensor is defined around the azimuth (XY) plane of the dipole in both projects and three simulations are run:

  1. Project A is simulated with the reference point set to the center of the space (co-located with dipole A).
  2. Project B is simulated with the reference point set to the center of the space (λ/8 offset from dipole B).
  3. Project B is simulated again with the reference point offset from the center of the space by λ/8 (co-located with dipole B).
Phase results for three simulations.
Far zone phase for the three simulations.

The second image shows the far zone phase for each simulation. When the reference point is co-located with the dipole, a constant phase is computed, but when the reference point is offset λ/8, the phase has a difference of 45° (138.3° - 93.3° = 45°) at 90° (along the Y axis). At 0° (along the X axis) there is no difference in the far field phases.

Controls

The Far Zone Reference Settings are accessed by right-clicking on the Far Zone Sensors item in the Project Tree. The settings consist of an editor across the top of the Geometry window where users can select a Mode option, which applies to all of the Far Zone Sensors in the project.

Screenshot of properties tab. Center of Space is XF's default setting that determines the reference point based on the bounding box of the grid. This location may change between simulations if the the grid's size changes due to parameterized geometry or other settings.
Screenshot of properties tab. Single Position specifies a constant location for use as the reference point. Users can type values in the X, Y, Z boxes or use the three picker tool icons to the right in order to select a point based on geometry.
Screenshot of properties tab. Per Active Source sets a unique phase reference point per feed when there are multiple feeds in a project. When using this mode, XF expects only one active feed per Simulation : Run—as is the case when S-parameters are requested.