Beam position monitoring in the 100-MHz to 500-MHz frequency range using the log-ratio technique

A logarithmic-ratio beam position monitor (BPM) circuit has been designed that operates directly from radio frequency signals in the 100-MHz to 500-MHz frequency range. The circuit uses four logarithmic amplifiers, a pair for each channel. One amplifier per channel receives its signal input directly from a BPM electrode, while the second amplifier receives the same signal attenuated by 7-dB. The two outputs of each channel are summed together and the composite video outputs are applied to a differencing amplifier. The net result is the logarithmic-ratio position measurement derived from the two input RF signals. Paralleling the pairs of outputs from the amplifiers provides measurement accuracy that is comparable to other circuit techniques used for position measurement