Modified Wheeler cap method using a quarter-wave transformer

The Wheeler cap method was used to measure the radiation efficiency of antennas. The conventional method introduces errors in the measurement of radiation efficiency because a small loss resistance is difficult to measure. In this study, we propose a method that combines the Wheeler cap method with a quarter-wave transformer (QWT). The QWT is connected to the antenna to transform its impedance. Numerical validation confirmed that impedance transformation using QWT can transform a small loss resistance to a reasonable value. This would allow the proposed method to measure the radiation efficiency with a better accuracy.