Radiation efficiency measurement based on Wheeler method using 90-degree 3dB hybrid coupler and sliding short

In this paper, the proposed method using a 90-degree 3dB hybrid coupler is applied to the measurement of the radiation efficiency of a monopole antenna based on Wheeler cap method. And we show the uncertainty of the radiation efficiency measurement. Until now, the length of the sliding short is changed from 0mm to 75mm at intervals of 5mm, that is, the circle can be obtained by using 16 points on the reflection/transmission coefficient planes. In this paper, it is examined how the uncertainty is changed when the number of the points that are used to determine the circles is reduced.