Development of high performance tuners for mode-stirring and mode-tuning applications

Reverberation chambers may be operated in either the mode-stirring or mode-tuning configuration. For mode-stirring, the primary requirement for the tuner is to provide a low flutter continuous rotation, while mode-tuning requires minimal vibration after stepping via fast dampening of timer motion. The tuner(s) must also be electrically large with respect to the enclosure and for the intended lowest usable frequency. This paper details the evolutionary steps in recent tuner design to both reduce testing time in the mode-tuning configuration and improve moding performance for meeting standards-mandated isotropy and field homogeneity at the low end of the desired test frequency range. Boundary change effectiveness versus tuner dimensions, and test time reductions as a function of tuner settling time, are demonstrated. Requirements for suitable stepper drive systems are discussed.