High Speed Passive Radar Receiver with Application to Digital Television Signals
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In this dissertation we present initial results from the fourth generation receiver for the Manastash Ridge Radar (MRR), which is a distributed passive radar system used for ionospheric physics and engineering studies. This receiver permits simultaneous access to the HF, VHF, and UHF spectrum by sampling at speeds up to 5 billion samples per second on each 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 digitizers have eight-bit precision. The wide bandwidth sampling (oversampling) means that it is possible to accurately sample narrowband signals whose amplitude is much less than the least sampling quantum. Most of the analog signal path is eliminated, yielding excellent dynamic range, and high speed digital signal processing yields low-latency real time operation. We also present initial data from such a receiver used to support passive bistatic radar experiments. We discuss in detail algorithms to make effective use of the FPGA. For example, the sampler runs 8 or 16 times faster than the FPGA, so initial FPGA processing requires parallel algorithms. In our design the downconverter passband center frequencies and spectral widths are selectable at run time, and can be changed in a few milliseconds. The FPGA operates in fixed point, which presents both opportunities and challenges in managing precision during the signal processing, for networking, and for subsequent signal processing. Data is sent off the receiver via one or more 10 GbE ports. In our current implementation system performance is limited primarily by network bandwidth. For radar application, the signal to clutter ratio is dominant for radar system performance. DTV signals have a known structure which permits recovery of the original transmitted waveform from imperfect reception. With such a nearly ideal reference signal, we are able to map the multipath and also improve the instantaneous dynamic range to over 100 dB with one-second coherent processing, and thus detect the weak echoes from targets of interest, such as aircraft or ionospheric field-aligned irregularities, and pave the way for AoA estimates or interferometric imaging of these scatterers.
- Electrical engineering