SPC has been involved in measurements of 
atmospheric reentry measurements for both the NASA Space Shuttle
and the CNES Ariane 5 launch programs. In 1990, SPC fielded three VHF radars in Hawaii to observe
the reentry and breakup of the STS-31 external fuel tank. These systems consisted of dipole and co-linear
antenna arrays, 50kW transmitters, receivers, O-scopes, and analog tape recorders. In 1999, SPC developed
a more flexible, airborne version of the VHF system to measure the reentry of the main cryogenic stage (EPC)
of the CNES/Arianespace Ariane 5 rocket. In order to achieve the mobility necessary to observe reentries over
the open ocean, SPC worked with the US Army Big Crow Program Office (BCPO) to incorporate the radar on a KC-135
aircraft. This new system used the same transmitters as the STS-31 system, but employed COTS-based multifunction
I/O cards and PCs to provide pulse control, real-time data processing, and digital data collection. The PC-based
radar control and real-time processing systems are described below and in a 1Mb downloadable PDF file.
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Versatile Inexpensive Pulsed Radar (VIPR) |
SPC's Radar Physics Group has developed a low cost, rapidly deployable PC-based control station for
instrumentation radars. The Versatile Inexpensive Pulsed Radar (VIPR) provides pulse control, sampling,
real-time processing, and display functions. The system was originally developed to observe atmospheric
reentry but is flexible enough to be useful for a variety of applications. VIPR is comprised entirely of
commercial-off-the-shelf (COTS) hardware and custom-built software, contained in ruggedized, rack-mountable
computer chassis. The system acts as a flexible, versatile, and compact back end, and, when configured
with suitable transmitters, receivers, and antennas on the front end, functions as a substantially
well-featured radar system. Continuous digital data storage is achieved by using SPC's accompanying
Analog/Digital Data Recorder (ADDR).
Operation
The main component of the VIPR processor station is an industrial PC with one or two PCI multifunction I/O
boards inside. The I/O board currently employed uses twin 20MHz counters for transmit brackets and an
analog-to-digital converter that can sample analog signal returns on up to four channels in phase at up to
5MHz. In typical operation, the two counters produce a pulse bracket and a transmitter bracket which are
cabled to the transmitter. Down-converted video signals from the receiver are then sampled using a triggered
acquisition starting at the transmit bracket. A number of range gates are then sampled, as governed by the
user-specified sampling rate, and then the card is reset for another pulse. All pulse timing and sampling
rates are controlled from the main display screen and can be stored in setup files.
The feature that sets VIPR apart from ordinary "pulse generator and O-scope" radars is the onboard real-time
analysis and display. Currently the system performs matched filter analysis for range walk trace and range
history waterfall plots, coherent integration to create a range-Doppler-intensity graph, instantaneous range
walk and Doppler spectrum displays, a Doppler-time-intensity waterfall plot, and two types of displays for
amplitude comparison monopulse tracking in two dimensions (azimuth and elevation). Each system also uses a
GPS/IRIG time card to synchronize events with a universal time reference.
Software
- Radar Control Features
- Programmable number of simultaneous receive channels (up to 4)
- Real-time waveform modification
- Pulse Repetition Frequency (PRF)
- Pulse Width
- T/R Bracket Width
- Sample Rate
- Setup files allow for simple configuration of parameters
- Waveform sequencing option allows "round-robin" sequencing of multiple waveforms
- Real-time Processing and Display Features
- Displays
- Range-Amplitude Traces
- Range-Time-Intensity (RTI) plots
- Range-Doppler-Intensity (RDI) plots
- Doppler-Time-Intensity (DTI) plots
- Doppler Spectra
- Processing Options
- Doppler Processing
- Matched Filtering
- Windowing (Hanning, Hamming, Blackman)
- Platform Interface Features
- Antenna pointing/GPS/INS data strings can be read via TCP/IP messaging
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Hardware
- Ruggedized rack-mountable computer chassis
- System drop-tested up to 3 feet
- PCI Multifunction I/O cards
- Provides two digital transmit/receive (T/R) brackets
- Up to 5MHz analog-to-digital sampling on up to 8 input channels simultaneously
- Triggered acquisition ensures that sampling starts at transmit bracket
- GPS/IRIG Time card
- Allows computer to run from an external time source
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Components
- Rack-mountable PC chassis
- Rack-mountable BNC connector box
- Rack-mountable monitor/keyboard
Specifications
- A/D Sampling
- Number of Channels: 4 or 8 (2 or 4 IQ pairs)
- Maximum Sampling Rate: 5 MHz per channel
- Sampling Resolution: 12 bit
- Timing/Pulse Forming
- Number of Counters: 2 (one pulse, one bracket)
- Pulse Width Resolution: 1microsec steps
- Maximum Pulse Repetition Frequency: 1MHz
- Upgrade Options
- Number of Channels (with lower maximum sampling rate): Up to 64
- Sampling Resolution (with lower maximum sampling rate): Up to 16 bit
- Customized Realtime Data Processing (FFTs, Beam Steering on Receive, etc.)
- Customized Positioner Interface (TCP/IP, GPIB, serial, ARINC)
- Frequency Control with Synthesizer (parallel, GPIB, PCI)
