Conclusion and Outlook

The FFTS has been in routine operation since May 2005 at the APEX. The backend has been proven extremely reliable and robust, even under the harsh environmental conditions at this remote facility. The potential advantages of FPGA-based FFT spectrometer can be summarized:

• High bandwidth (1 to a few GHz in the future) with up to 16K spectral channels (32K channels in preparation at MPIfR) in a single FPGA chip.
• Full signal sampling with 8-bit, no additional calibration by means of implicit total power measurements, thus higher sensitivity and stability in comparison with autocorrelators and acousto-optical spectrometers. In addition, this multi-bit sampling provides a higher dynamic input-range, so a less sophisticated autogain control is needed. Consequently, the IF processor is less complex, making the system more stable.
• Very high stability via pure digital signal processing.
• Modular design with calibration-free digitizer / analyzer boards, thus simple reproducibility.
• Low space and power requirements, thus safe to use at high altitude (e.g. APEX at 5100 m) or well as on satellites.
• Low price compared to traditional spectrometers through use of commercial parts.

Our novel FPGA-based FFTS development offers exciting perspectives for high-resolution broadband spectrometers. The new class of high-speed ADCs and the advantages of FPGA, with their wide availability, decreasing costs (both based on the large commercial interest) and increasing processing capability (Moore's Law), makes it very likely that FFTS can be pushed to broader bandwidths in the near future.