Echo Reduction by Modal Filtering Technique in Advanced Near Field Antenna Measurement

Spurious error signals from absorbers and other structures in the measurement set-up can significantly decrease the measurement accuracy in standard antenna measurement configurations. Most near field antenna measurements are performed in shielded anechoic chambers to simulate free-space conditions. High-quality absorbing materials are generally used on all surrounding surfaces that otherwise would interfere with the measurement by transmitting energy toward the test region through a combination of reflections and/or diffractions.

In the majority of measurement cases with well-designed anechoic chambers, the measurement uncertainty contribution from these additional error signals named echo(s) or echo pollution in the following discussion can be considered negligible. However in special measurement conditions and/or when very high precision measurements are needed, the above consideration is no longer valid.