Direct Band-Pass Analog-to-Digital Conversion
Navy SBIR 2015.1 - Topic N151-057
NAVSEA - Mr. Dean Putnam - dean.r.putnam@navy.mil
Opens: January 15, 2015 - Closes: February 25, 2015 6:00am ET

N151-057 TITLE: Direct Band-Pass Analog-to-Digital Conversion

TECHNOLOGY AREAS: Sensors, Electronics, Battlespace

ACQUISITION PROGRAM: PEO IWS 2, Above Water Sensors

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with section 5.4.c.(8) of the solicitation. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Develop direct band-pass analog-to-digital conversion capability for Navy rotating air surveillance radar systems to improve performance capability and reduce costs.

DESCRIPTION: The U.S. Navy is seeking research and development in band-pass sampled digital downconversion technologies for use with rotating air surveillance radar systems. Current radar systems designed in the 1990s utilize two or three analog frequency downconversions and other signal processing operations prior to the conversion to digital inphase signal (I) and quadrature phase signal (Q) data. With multiple mixers, filters, and local oscillators, these systems have variable performance over time requiring manual adjustments to maintain optimum performance. As these systems age and require technical refreshing (tech refresh), an opportunity to simplify the system and reduce the cost of the tech refresh becomes available. A tech refresh for radar systems covering all below-deck electronics is actively being pursued. Operational availability for the system is well below the Navy benchmark and maintenance costs are increasing due to parts obsolescence.

According to James Alter and Jeffrey Coleman at the Naval Research Laboratory, "band-pass sampling is a powerful tool that allows a relatively high frequency signal to be sampled by a relatively low-performance digitizer, which can result in considerable cost savings" (Ref. 1). If the band-pass sampling downconversion process is successfully demonstrated, then significant cost savings could be realized by a large reduction in required parts.

Communications systems are using this technique on multiple channels; however, no examples of this approach are currently available for an 850-950 Megahertz (MHz) radar system (Ref. 2). To successfully demonstrate the technology in this frequency range, a pulse-Doppler radar system with pulse compression is required.

The cost and performance is a major factor of a band-pass sampling approach that can be achieved by developing band-pass sampling, direct analog-to-digital conversion for the 850-950 MHz band for a pulse-Doppler radar system with pulse compression. This approach must support 90- 1 MHz bands of nonlinear frequency-modulated signals that yield a 1.5 microsecond (s) compressed pulse from a 32 s transmitted pulse. It is anticipated that the new system will have fewer parts. As a result, the new system should have both reduced maintenance costs and more cost-effective tech refreshes.

This effort requires an assessment of the feasibility of a receiver that can take in synthesized radio frequency (RF) radar return signals and output baseband I and Q in real-time with a demonstrated noise figure of less than 3.5 decibels (dB).

PHASE I: The company will define and develop a concept for a Band-pass Sampled, Digital Down conversion System that meets the requirements as stated in the topic description. The company will demonstrate the feasibility of the concept in meeting Navy needs and will establish that the concept can be developed into a useful product for the Navy. Material testing and analytical modeling will establish feasibility. The concept development effort should assess the importance of several factors, such as sampling rate, guard band size, and non-minimum sampling rates (Ref. 3). Evidence of design optimization and of these parameters as well as a comparison between model predictions and measured performance are required.

PHASE II: Based on the results of Phase I, the company will develop a prototype system for evaluation. The prototype will be evaluated to determine its capability in meeting performance goals and Navy requirements for the Band-pass Sampled, Digital Downconversion System. System performance will be demonstrated through prototype evaluation and modeling or analytical methods over the required range of parameters including numerous deployment cycles. Evaluation results will be used to refine the prototype into a design that will meet Navy requirements. The system should include filtering as required to reduce potential alias input. Documentation should include analysis comparing sampling rates, analog downconversion, noise figure, calculation of data throughput and recommendations for data handling/reduction. The company will prepare a Phase III development plan to transition the technology to Navy use.

PHASE III: The company will support the Navy in transitioning the technology for Navy use. The company will develop a Band-pass Sampled, Digital Downconversion System according to the Phase III development plan for evaluation to determine its effectiveness in an operationally relevant environment. The company will support the Navy for test and validation to certify and qualify the system for Navy use and transition the downconversion system to its intended platform.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Direct digital downconversion has application to the commercial radar market as well as additional military applications. The proliferation of small solid-state radars for remote sensing and navigation benefits from cost-saving digital technologies that drive affordability and consequently expand the market even further. The commercial market is typically quick to adopt technology that enhances performance while controlling cost. The technology developed under this effort will facilitate a shift from expensive RF analog receiver circuitry to receivers based on commercial microprocessor technology. Even complex commercial radars such as weather radar can benefit from this technology, as digital processing is inherently scalable, allowing radars of various size and complexity to achieve improved performance at reduced cost.

REFERENCES:
1. Skolnik, M. RADAR Handbook. New York: McGraw-Hill 2008.

2. Tseng, Ching-Hsiang, Chou, Sun-Chung. "Direct Downcoversion of Multiple RF signals Using Bandpass Sampling." IEEE Paper, 0-7803-7802, April, 2003.

3. Vaughan, Rodney, Scott, Neil, White, Rod. "The Theory of Bandpass Sampling." IEEE Transactions on Signal Processing, VOL. 39, NO. 9, September 1991: p 1973.

KEYWORDS: band-pass sampling; direct RF conversion; radar band-pass sampling; digital receiver design; digital signal processing; band-pass sampling coherent detection

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