Estimation of Required Characteristic Modes for Stirrers in a Reverberation Chamber

This paper investigates an approach for assessing stirrer performance in a reverberation chamber (RC) using characteristic mode analysis (CMA). In the design of a reverberation chamber, evaluating stirrer performance is crucial; however, it is considered challenging to assess it independently. In this study, we focus on evaluation based on the number of characteristic modes and clarify the quantitative relationship between electric field uniformity and the number of characteristic modes through RC analysis of 117 configurations. For the 117 cases obtained, non-parametric estimation was performed to model the data without assuming any physical relationships. The findings suggest that the stirrer’s influence on field uniformity stabilizes when its characteristic mode count reaches 40 to 60, aligning with the cavity mode density at the lowest usable frequency (LUF). The derived criterion also meets the IEC’s “medium” field anisotropy requirement. Additionally, comparison with geometric parameters in the IEC standard indicates that conventional metrics, such as stirrer length, can distinguish performance variations by up to 33.3%, whereas the characteristic mode-based evaluation improves this distinction to 66.7%. In addition, CMA-based evaluation can reduce design time by 27%.