AbstractThis article presents the design and realization of 8 × 8 and 16 × 16 Butler matrices for 7 T MRI systems. With the focus on low insertion loss and high amplitude/phase accuracy, the microstrip line integration technology (microwave‐integrated circuit) was chosen for the realization. Laminate material of high permittivity (εr = 11) and large thickness (h = 3.2 mm) is shown to allow the best trade‐off of circuit board size versus insertion loss, saving circuit area by extensive folding of branch‐line coupler topology and meandering phase shifter and connecting strip lines and reducing mutual coupling of neighboring strip lines by shield structures between strip lines. With this approach, 8 × 8 Butler matrices were produced in single boards of 310 mm × 530 mm, whereas the 16 × 16 Butler matrices combined two submatrices of 8 × 8 with two smaller boards. Insertion loss was found at 0.73 and 1.1 dB for an 8 × 8 matrix and 16 × 16 matrix, respectively. Measured amplitude and phase errors are shown to represent highly pure mode excitation with unwanted modes suppressed by 40 and 35 dB, respectively. Both types of matrices were implemented with a 7 T MRI system and 8‐ and 16‐element coil arrays for RF mode shimming experiments and operated successfully with 8 kW of RF power. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.