Summary
International Symposium on Antennas and Propagation
2012
Session Number:POS2
Session:
Number:POS2-20
Radiation Efficiency Measurement Based on Wheeler Method Using 90-degree 3dB Hybrid Coupler and Sliding Short
Hirofumi Iguchi,
pp.-
Publication Date:2012/10/29
Online ISSN:2188-5079
Summary:
A measurement technique of arbitrary reflection coefficient using 90-degree 3dB hybrid coupler and sliding short is proposed to reduce the uncertainty of the measurement. The measurement system is the same as that with 180-degree 3dB hybrid coupler and sliding short. In this method, a reference standard (RS) that the magnitude of the reflection coefficient of RS is constant but the phase of the reflection coefficient of RS can be varied is realized by a sliding short that is composed of a short connected with a variable-length coaxial line. The locus of the reflection coefficient of RS draws a circle on the reflection coefficient plane because the phase of RS can be changed by the sliding short. If well-chosen DUT and RS are connected into the hybrid coupler and transmission coefficient between unused two ports of the hybrid is measured, the locus of the transmission coefficient also draws a circle on the transmission coefficient plane. Then, the reflection coefficient of DUT can be obtained by determining the center and radius of the circles by means of the least square method. This technique can be applied to the measurement of the radiation efficiency of the antenna based on the Wheeler cap method. To evaluate the uncertainty of radiation efficiency measurement leads to the validity of the proposed technique. 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 points that are used to determine the circles reduced.