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.
Specular Wall Reflection
Meaning
Mirror-like bouncing of radio waves off the smooth surfaces of an anechoic chamber walls creates unwanted interference in the test zone. The presence of specular wall reflection prevents the chamber from simulating a free-space environment during antenna testing. This parameter must be controlled to ensure that the measured fields match the theoretical values.
Reflection Mitigation
Placement of high-performance foam absorbers at the reflection points prevents these echoes from reaching the test volume. The risk of specular wall reflection is highest on the side walls that lie directly between the transmitting antenna and the device under test. Lined sections of the chamber use thick foam cones to absorb the signal at these angles.
This treatment is verified by performing a path-loss sweep.
Ray Tracing
Geometric modeling is used to calculate the paths of the signals as they bounce off the walls of the room. This analysis of specular wall reflection enables the lab designers to place the absorbers only where they are needed. The simulation software maps the paths of the signals from the transmitter to the quiet zone.
This optimization reduces the cost of building the chamber by avoiding excess material. Knowing these paths helps in identifying the specific wall areas that require high-performance absorbers.
Accuracy Impact
Uncontrolled reflections distort the measured radiation pattern of the tested module. If specular wall reflection is too strong, the calculated gain of the antenna will be incorrect, leading to a false pass or fail. This uncertainty can delay the certification of the wireless assembly.