Dynamic X-Y Crosstalk / Aliasing Errors of Multiplexing BPMs

Multiplexing Beam Position Monitors are widely used for their simplicity and inherent drift cancellation property. These systems successively feed the signals of (typically four) RF pickups through one single detector channel. The beam position is calculated from the demultiplexed base band signal. However, as shown below, transverse beam motion results in positional aliasing errors due to the finite multiplexing frequency. Fast vertical motion, for example, can alias into an apparent, slow horizontal position change.