Profiles calculated from the FFT amplitude for RF1 and RF2 at the same power (−27 dBm). The black data show the profile when the phase of RF2 is 40° and the blue for 220°. The green and yellow markers highlight the displacement of the maxima, as shown in the upper-left inset from 0 to 360°. In the upper-right inset, the remaining propagating content in the SSAWs, determined by fits to the FFT profiles (e.g. black and blue line in the main panel), is plotted as a function of the relative phase. The red line in the inset results from a mathematical simulation using the application described in the supporting information.