Proprietary - Felton Electronic Design
A New Approach for Intelligence Gathering
Radar systems typically obtain intelligence information through the signal processing of RF energy, reflected from an electrically conductive target. The signal processing of this detected energy has become highly sophisticated due to the significant available computing power. A major deficiency of this approach is that, because it utilizes high power RF transmitters to illuminate the targets of interest, long term radar surveillance of large numbers of suspected threat areas is not practicable. A second deficiency is that these systems are relatively less effective at detecting structures that are largely non-conductive.
- Bistatic systems, in which the transmitter and receiver(s) are not co-located, are often used. Modern weather radars make use of multiple receivers to facilitate creation of 3-dimensional maps of precipitation1.
- Some effort has been made to use existing radio frequency transmitters (e.g., commercial broadcasting stations) as illuminators to create "passive" radar systems2. Because these transmitters broadcast over large angles, the power delivered on target is usually small.
- Additional effort has been made to utilize low and very low frequencies to allow the radar to see beyond the horizon. VLF has the potential for radar imaging well beyond the horizon and even to significant depths in the ocean and the earth's mantle. VLF attenuation in the atmosphere is relatively small so that use at long distances is feasible, even though the atmospheric noise levels are high. The phase stability of VLF signals is extraordinarily high.
- There exist several large time/frequency standard transmitters around the world. These sources are generally fairly powerful, more stable than commercial broadcast stations and also provide precise timing information. Some of these are LF stations. There is also a network of VLF stations used for submarine navigation/communication.
- Large scale geologic features, such as faults and conducting rock units, are routinely mapped using the magnetic component of reflected/refracted waves initially radiated by the VLF transmitters used for submarine navigation/communication3. This mapping provides structural data to depths of a few 10s of meters in most soils.
- The interaction of RF with non-conductive structures (dielectrics) is more accurately characterized as refraction (not reflection). Current radar systems are not optimized for detection of these targets. Phase detection is probably more useful for detection and classification of dielectrics and poor conductors, - Use of existing LF and/or VLF transmitters as illuminators, combined with low noise phase detection, may provide the basis for a "passive" radar system that can detect and identify both reflective and refractive targets at useful range.
With sufficient development, we believe that existing LF and VLF transmitters, in combination with specially designed detectors/receivers, can be used to provide useful radar data/imagery. Such a system could be the basis for covert surveillance of suspected threat areas. Targets of interest could include missile plumes, underground bunkers, and equipment movement.
PROOF OF CONCEPT:
The feasibility of a "passive" radar system can be explored on a relatively small scale by utilizing existing transmitters and by designing, fabricating, and testing special detectors/receivers. The purpose of this effort will be to determine if the basic approach can detect and discriminate, to some level, different stationary and moving targets at useful ranges. The fabricated equipment will be sufficiently small to be truck mobile, so that experiments can be performed at varying ranges from the transmitter.
An appropriate proof of concept illuminator is the Department of Commerce time and frequency standard station, WWVB (60 kHz) in Ft. Collins, Colorado.
The following tasks will be performed:
- Fabricate and test two low noise phase detectors
- Fabricate and test two prototype receivers
- Purchase storage/display/processing system (COTS computer)
- Develop initial display software
- Perform initial tests with stationary and moving targets
- Develop simplified signal processing algorithms/software
- Perform additional tests/demonstration using real-time signal processing
- Write final report
The receiver will be coupled to the display system through an analog-to-digital (A/D) converter. Perturbations in the 60 kHz RF field, due to several stationary and moving targets will be examined. Signal processing software, similar to that used for imaging of precipitation by weather radar systems will be acquired/modified to allow near real time display of target information. Because there is no known prior experience with the processing of phase detector outputs at these frequencies, appropriate signal processing is probably a large development effort, beyond the scope of this investigation. Only very simplified processing is envisioned for this task.
This effort can be performed for $470k and will require 18 - 20 months for completion.
1. For example, see A Bistatic Multiple-Doppler Radar Network: Part 1, Theory, Wurman, Heckman, and Boccippio, National Center for Atmospheric Research
2. Target tracking using television-based bistatic radar, P. E. Howland, IEE Proc.-Radar, Sonar Navig., Vol. 146, No. 3, June 1999
3. Commercial equipment to perform this function is manufactured by, for example, RMS Instruments, Canada. Website: [http://www.rmsinst.com/dshtvlf.htm]
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