Calculating Volumetric Site Voltage Standing Wave Ratio in Hybrid Chambers
Volumetric site voltage standing wave ratio in hybrid chambers isolates 3D quiet zone reflections by converting normalized spatial field ripples into linear ratios.
Spatial Field Ripple
Meaning
Variation in electromagnetic field intensity across a designated region in an anechoic chamber indicates the presence of multipath interference. High levels of spatial field ripple corrupt the measurement of antenna patterns by introducing artificial fluctuations in the recorded signal power. This parameter must be mapped during the commissioning of the test facility.
Interference Cause
Scattering from the chamber floor or poorly aligned antennas generates constructive and destructive interference patterns. In this environment, the spatial field ripple represents the peak-to-peak variation in the field strength across the quiet zone. This issue is resolved by adjusting the positions of the absorber tiles.
This adjustment ensures that the reflections from the chamber walls are minimized.
Measurement Technique
Continuous sweeps with an isotropic antenna along several parallel tracks are used to map the field variation. This analysis of spatial field ripple requires high-precision robotic positioners to maintain the antenna path. The recorded voltage is analyzed to calculate the deviation from a theoretical flat field.
This dataset is compiled into a report that is used to validate the quiet zone of the chamber. Performing this test annually ensures that any degradation in the absorber performance is detected early.
Test Repeatability
Consistency between test runs on different days is only possible if the test volume has a stable field distribution. If the spatial field ripple exceeds the allowed limit, the tested wireless module might pass or fail based on its physical position on the rotation table. This variation makes the test results unreliable for regulatory approvals.