Helical Stirring for Enhanced Low-Frequency Performance of Reverberation Chambers

A novel class of volumetric mechanical mode stirring methods is introduced. One particular type, denoted as helical stirring, combines rotation and translation in a single motion. This technique is implemented, and its measured performance is compared to conventional circular stirring by the same paddle. It is observed that helical stirring can significantly increase the number of uncorrelated stir states at sufficiently low frequencies. Higher maximum- and lower minimum-to-average ratios of the magnitude and intensity of the received field are obtained that are traceable to a heavier tail of their probability density functions. While the helix pitch can be optimized per frequency, suboptimal values also yield considerable improvement. The use of a stir matrix facilitates the data analysis and estimation of ensemble statistics for arbitrary values of the helix pitch, beyond its experimentally realized discrete values.