S-Parameter Analysis for Balanced and Unbalanced Modes Corresponding Dissipated Power of a Small Antenna

Takashi YANAGI
Naofumi YONEDA

IEICE TRANSACTIONS on Communications   Vol.E103-B    No.7    pp.780-786
Publication Date: 2020/07/01
Publicized: 2020/01/15
Online ISSN: 1745-1345
DOI: 10.1587/transcom.2019EBP3112
Type of Manuscript: PAPER
Category: Antennas and Propagation
balanced mode,  unbalanced mode,  S-parameter,  self-balancing,  measurement,  

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In this paper, an analysis method for calculating balanced and unbalanced modes of a small antenna is summarized. Modal condactances which relate dissipated power of the antenna are directly obtained from standard S-parameters that we can measure by a 2-port network analyzer. We demonstrate the validity and effectiveness of the proposed method by simulation and measurement for a dipole antenna with unbalaned feed. The ratio of unbalanced-mode power to the total power (unbalanced-mode power ratio) calculated by the proposed method agrees precisely with that yielded by the conventional method using measured radiation patterns. Furthermore, we analyze a small loop antenna with unbalanced feed by the proposed method and show that the self-balancing characteristic appears when the loop is set in resonant state by loading capacitances or the whole length of the loop is less than 1/20th the wavelength.