Investigations to extend the lower frequency limit of reverberation chambers

As the use of reverberation chambers for electromagnetic effects testing increases there is a growing interest in lowering the minimum useable frequency in a specific chamber. This paper describes a series of measurements to investigate the field uniformity of reverberation chambers in the frequency region below which they have been considered useable. The measurements are part of a continuing program to characterize the overall field uniformity of reverberation chambers as a function of frequency. Measurements were taken using the large reverberation chamber (10.82 m/spl times/5.18 m/spl times/3.96 m) at the Naval Surface Warfare Center, Dahlgren Division at frequencies from 80 MHz to 200 MHz. The commonly accepted guideline yields a lowest useable frequency of 110 MHz for the large chamber. Measurements were also obtained using a small reverberation chamber (1.8 m/spl times/1.2 m/spl times/0.8 m) over 100 MHz frequency bands starting at 300, 400 and 730 MHz. The predicted lowest frequency for the small chamber is 556 MHz. The results suggest that the commonly accepted guideline for defining the lowest useable frequency needs to be revised. A performance based criterion using measured uniformity data appears to have merit for defining the lowest useable frequency for typical operations. The results also suggest that useful testing can be conducted at frequencies below the minimum useable frequency as defined by the commonly accepted guidelines.