Single-pass bunch position measurement for S-band beams
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Single-pass bunch position measurement for S-band beams - Principles

Based on the pioneering work of Robert E. Shafer at Los Alamos Laboratory, the Log-Ratio BPM derives beam position from logarithm of the ratio of opposite pickup signals: Log(A/B).

Position measured by this method is more linear, over a wider range, than difference-over-sum.

Main features

  • Resolution X & Y is pickup aperture radius / 10'000
  • Dynamic Range > 50 dB
  • Operating Frequency of 2.856 GHz and 2.999 GHz



User's manual

Technical notes

Current price list

Signal processing

Signals from the pickups are stretched to produce bursts. This is essential to measure the single pass of a bunch. Four parallel logarithmic amplifiers detect the burst envelopes.

Amplifiers’ response is log of amplitude. Logs of opposite pickups are subtracted.

If pickups are rotated, axes are translated to obtain X and Y positions. The process is all-analog, wideband.

Front-end Filter / Amplifier FEFA

Front-end Filter / Amplifier FEFA

One Front-end Filter / Amplifier is required for every BPM pickup electrode.
It is tuned to the beam RF or an harmonic and powered from the S–BPM module via the coaxial cable linking them together.

S-BPM FEFA must be installed close to the BPM pickup block, e.g. 1 meter.


  • The S-band / L-band Beam Position Monitor (S-BPM) is an electronics module for fast analog processing of beam pickups signals.
  • Single-pass bunch and macropulses can be measured thanks to parallel processing of inputs.
  • Macropulses and single bunches up to 2MHz repetition rate can be measured individually. X and Y coordinates are memorized until the next macropulse or bunch.
  • CW beam can be measured continuously. X and Y coordinates are available permanently. Beam position motions up to 5MHz can be observed.
  • X and Y outputs are strong analog ±2V signals.
  • S-band / L-band BPM is compatible with other Bergoz’ BPM. They can be plugged in the same chassis.
  • Precise phase matching of input signals is not required.