Development Design and Demonstration of Very High-Speed Multi-Antenna Digital Receiver

The authors present initial results from the fourth-generation receiver for the Manastash Ridge radar, which is a distributed passive radar system used for ionospheric physics and engineering studies. This receiver permits simultaneous access to the high-frequency (HF), very HF (VHF), and ultra HF (UHF) spectrum by sampling at speeds up to 5 billion samples/s on multiple antennas. This system has large aggregate bandwidth; it can simultaneously collect the entire VHF FM broadcast band as well as several UHF DTV broadcasts. The receiver adopts direct sampling architecture; therefore, high dynamic range is achieved with decimation for narrowband signals. Most of the analogue signal path is eliminated, yielding excellent linearity, and high-speed digital signal processing in the field programmable gate array (FPGA) yields low-latency real-time operation. The authors also discuss algorithms to make effective use of the FPGA. For example, the sampler runs 16 times faster than the FPGA, so initial FPGA processing requires parallel algorithms. In the authors design, the downconverter passband centre frequencies and spectral widths are selectable at run time, and can be changed in a few milliseconds. The authors FPGA computes in fixed point math, which presents both opportunities and challenges in managing precision during the signal processing for networking and for subsequent signal processing.