Analysis of the Reflection Method for Measuring the Radiation Efficiency Using the Transmission Line Model

Nozomu ISHII  Yasuo KATAGIRI  Michio MIYAKAWA  

Publication
IEICE TRANSACTIONS on Communications   Vol.E90-B   No.9   pp.2394-2400
Publication Date: 2007/09/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e90-b.9.2394
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on 2006 International Symposium on Antennas and Propagation)
Category: Measurements
Keyword: 
radiation efficiency,  reflection method,  transmission line model,  waveguide,  sliding short,  

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Summary: 
The reflection method is an accurate and simple method for measuring the radiation efficiency of a small antenna. However, it takes too long and has the disadvantage of underestimating the efficiency due to resonance in the cavity formed by the straight waveguide and two sliding shorts. To reduce the measurement time, one sliding short can be fixed while the other one is moved. To improve the accuracy of this technique, we can set the antenna to be measured at the center of the two sliding shorts or at a local anti-node of the standing wave in the waveguide. When one of the sliding shorts is fixed, the measured efficiency becomes negative at certain frequencies. We examine these reductions in efficiency using an equivalent transmission line model for the reflection method. We also derive analytical expressions for the overall efficiency in the above cases and verify new procedures that enable measurements to be performed without any drops in the measured efficiency.