Pedram Yazdanbakhsh1, Markus Fester2, Ralph Oppelt3, Andreas Bitz4, Oliver Kraff4, Stephan Orzada4, Mark E. Ladd4, Klaus Solbach1
1High Frequency Technique, University Duisburg-Essen, Duisburg, NRW, Germany; 2Siemens Medical Solutions, Erlangen, Germany; 3Siemens Corporate Technology, Erlangen, Germany; 4Erwin L. Hahn Institute for Magnetic Resonance Imaging, Essen, Germany
Butler matrix networks are used for the excitation of phase modes of MRI coil arrays. The standard excitation method is to connect each power amplifier output to one of the (input) mode ports of a Butler matrix. This allows all phase modes of the coil array to be excited at equal power level. However, not all modes are equally useful, since the lowest-order CP mode is the dominant mode, while higher modes are less important to excite and CP- modes may be completely unnecessary to excite. In this work an eight-channel variable power combiner has been designed and fabricated using an 8×8 Butler Matrix network to excite the coil array in a 7 T MRI system.
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