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International Journal of Antennas and Propagation
Volume 2012, Article ID 490327, 9 pages
Research Article

Modal Resonant Frequencies and Radiation Quality Factors of Microstrip Antennas

Department of Electromagnetic Field, Faculty of Electrical Engineering, Czech Technical University in Prague, Technick√° 2, 166 27 Prague, Czech Republic

Received 9 August 2011; Revised 10 January 2012; Accepted 13 January 2012

Academic Editor: Charles Bunting

Copyright © 2012 Jan Eichler et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The chosen rectangular and fractal microstrip patch antennas above an infinite ground plane are analyzed by the theory of characteristic modes. The resonant frequencies and radiation are evaluated. A novel method by Vandenbosch for rigorous evaluation of the radiation is employed for modal currents on a Rao-Wilton-Glisson (RWG) mesh. It is found that the resonant frequency of a rectangular patch antenna with a dominant mode presents quite complicated behaviour including having a minimum at a specific height. Similarly, as predicted from the simple wire model, the radiation exhibits a minimum too. It is observed that the presence of out-of-phase currents flowing along the patch antenna leads to a significant increase of the factor.