Meaning
Mathematical framework used to represent the electromagnetic radiation field of an antenna as a infinite sum of spherical vector wave functions. For wireless product development, spherical wave expansion is applied to reconstruct the far-field antenna pattern from near-field measurements taken on a spherical surface. This method is bounded by the minimum radius of the sphere that encloses the antenna and all its structures.
Data Interpolation
Measuring the radiated field at every point in space is impossible due to test chamber constraints. By utilizing spherical wave expansion, engineers can calculate the field from a finite set of measured samples. This interpolation allows for the rapid creation of high-resolution radiation patterns.
Diagnostic Value
Analyzing the coefficients of the expanded wave functions provides valuable insights into the behavior of the antenna system. When a design fails to meet its gain targets, the spherical wave expansion coefficients can help identify which mode is causing the degradation. This diagnostic capability is useful for troubleshooting complex multi-antenna arrays that are integrated into compact enclosures.
Standard Workflow
Anechoic chambers often implement this mathematical method to speed up the certification process. The test software captures the near-field amplitude and phase on a spherical scan surface and then performs the calculation to generate the far-field pattern. This automated process provides the required regulatory reports with a high degree of repeatability, which helps ensure the product is approved on schedule.
It also allows the engineering team to compare the physical measurements with the simulated antenna model to verify that the assembly meets the design specifications.
