Spherical Test-Zone Field Measurements of a Compact Antenna Test Range

Every antenna measurement is subject to errors since undesired signals enter the test zone and are received by the antenna under test. However, by measuring the test-zone field on a spherical surface and thereby, gaining knowledge about the incident spherical waves, the unwanted field components are correctable. To apply the so-called test-zone field compensation to a compact antenna test range, spherical near-field measurements of its test zone are carried out by using a scanning arm which is mounted onto the roll-over-azimuth positioner. Accurate probe alignment is ensured by a robust arm design. By using a directive probe, the effects of the rotating elements which are not considered by the theory are minimized. Blockage of the positioning system, however, still causes measurement errors. Via spherical wave expansion, the measuring probe which is characterized beforehand is corrected and reliability of the method is demonstrated by a comparison to full-wave simulations.