A cavity‐backed spiral antenna with an unbalanced feed system—analyses using FD‐TD and moment methods

Abstract

AbstractThe FD‐TD method and the moment method are used to analyze a two‐wire square spiral antenna backed by a conducting square cavity (SAC). The SAC is fed from a coaxial line without a balun circuit. First, the SAC is analyzed using the FD‐TD method. The SAC design is based on radiation characteristics of a two‐wire square spiral antenna backed by a conducting plane reflector (SAR). It is found that the frequency bandwidth for a 3‐dB axial‐ratio criterion is 12% (18% for SAR), with a gain of 7 dBi (8 dBi for SAR). Second, the moment method is used to analyze a wire‐grid model of the SAC. Grid sizes appropriate for the analysis are determined on the basis of the FD‐TD solutions. It is revealed that the grid size for the cavity side plates is 1.3 times larger than that for the cavity bottom plate. Third, a two‐SAC array is analyzed to reveal the mutual coupling. Calculation shows that the decoupling factor is larger than that for a two‐SAR array by approximately 3 dB. The computation time and memory size required for the analyses are compared between the two cases for the FD‐TD and the moment methods. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(1): 53–63, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10211