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AN/SPY-4 Volume Search Radar

The DDG-1000's AN/SPY-4 Volume Search Radar system was cancelled. The AN/SPY-3 was originally to be combined with the S-Band AN/SPY-4 under the designator "Dual Band Radar" on both the Zumwalt Class DDG-1000) destroyer and Ford Class (CVN-78) aircraft carrier. On 2 June 2010, Pentagon acquisition chief Ashton Carter announced that they will be removing the SPY-4 S-band Volume Search Radar from the DDG 1000's Dual-Band Radar to reduce costs as part of the Nunn-McCurdy certification process. Due to the SPY-4 removal, SPY-3 radar was to have software modifications so as to perform a volume search functionality. The VSR system was a 3-face, active, L-band phased array radar, intended to be deployed on new surface combatants, including DD(X), CV(X) and LPD(X). The VSR was paired with the SPY-3 MFR as the Dual-Band Radar Suite for the DD(X) and CVN 21. The VSR was based on solid-state, active array radar technology to provide target cueing to the Multi-Function Radar (MFR). MFR was planned for introduction in CVN-77/CVNX and DD-21 warships. The MFR/VSR suite supports new ship design requirement for reduced radar cross-section, reduced manning and total ownership cost reduction. Coupled with SPY-3, VSR supports ship self-defense for targets in the volume.

The primary mission of this system was to provide hemispheric volume surveillance to compile the total air picture. This requires the system to provide volume search/track-while-scan (VS/TWS) and precision track of threat targets. In addition, the VSR provides low elevation detection functionality in the stressing clutter and interference environments associated with littoral operation. The S-band VSR's phased array was designed to provide longrange detection of air targets.

It transmits and received pulses rapidly enough to track high-speed, low-altitude, stealthy or high-diving aircraft and missiles, and provides cueing for the SPY-3 to track and engage the targets. To meet performance requirements in these scenarios, the radar employs fast beam switching, low noise, active phased arrays, state-of-the-art dynamic range receive systems, adaptive digital matched filtering and Doppler processing for high sub-clutter visibility and interference suppression in a dense target environment.

Volume Search Radar Program

During deliberation of the Navy's fiscal year 2000 budget request, Congress provided the Navy with a $12-million plus-up to begin VSR development. Based on these program plans, the initial VSR prototype was to be available during fiscal year 2002 to coincide with MFR development testing.

Both DD 21 Industry Teams developed a VSR capability in the context of the design competition for that ship class. It was the Navy's intent that the MFR/VSR radar suite will be the radar suite for the CVN 77, and will replace the SPS-48E, SPS-49, and SPN-43 (air traffic control) radars currently on CVN-68 class ships. VSR was also a candidate for installation in LHD 8, CVN 70−76 (as a backfit), CVN(X), and LH(X).

Additionally, the Navy reviewed the LPD 17 combat system in 2001 to determine if changes in configuration are warranted. The costs and benefits of including the MFR/VSR suite in the LPD 17 combat system suite will be considered in this review.

An engineering and development model went through testing in fiscal 2006. The system's operational evaluation will coincide with testing of DD(X). Initial operating capability (IOC) was scheduled for 2013.

The Navy removed the Volume Search Radar (S-band) from the ships baseline design for cost reduction in compliance with an Acquisition Decision Memorandum of June 1, 2010.) Modification of the AN/SPY-3 Multi-Function Radar (X Band, horizon search radar) would provide the volume search capability that would have been provided by the Volume Search Radar.

L-band Digital Array Radar (DAR)

Transition roadmap was confirmed as the Technology Innovation Transition in PMO 02 NAVSEA PEO Theater Air Defense and Surface Combatants. The L-band Digital Array Radar (DAR) would be used for Volume Search Radar for DD21. The Digital Array Radar uses fully digitized T/R modules in a novel antenna array architecture. Advanced techniques and recent developments, (e.g. direct digital sampling, high rate, high dynamic range A/D converters, high-speed digital computation and digital fiber-optic interfaces) are employed. These technologies, leveraged from the commercial telecommunications, computers, and networking markets, combine to provide several orders of magnitude improvement in Navy radar system performance and promise low risk/cost for near-term acquisitions. One of the main risk areas was the accuracy of digital transceiver of arbitrary waveform, bandwidth at tens G Hz & beyond.

Early concepts of digital-array radar (DAR) began in the 1980s. As ADC, DAC, and wireless technologies began to improve in the mid 1990s, the DAR implementation was starting to become more realistic. In FY00, the Office of Naval Research (ONR) funded a new program to design, develop, and demonstrate a DAR test bed for a potential prototype for the Navy. Three organizations were involved in this initial effort: NRL, Massachusetts Institute of Technology (MIT) Lincoln Laboratory, and the Naval Surface Warfare Center (NSWC) in Dahlgren, Virginia. Digital processing encompasses the beam former and waveform generator entirely. Digital transmit waveforms and control are generated, converted to optical, and distributed optically to an array of digital/microwave transmit/ receive (T/R) modules behind the array antenna of N-radiating elements.

Future navy surface radars will need large Power-Aperture-Gain (PAG) products so as to perform challenging Air and Missile Defense functions. Oftentimes, these radars will operate in littoral regions, where their large PAG products will cause strong clutter returns. Unfortunately, radar equipment specifications can become stressed by the need to detect small targets in such strong clutter. Stressing hardware specifications include dynamic range, phase noise, system stability, isolation and spurs. Moreover, the additional desire for Low Probability of Intercept (LPI) radar operation will also influence radar hardware design. Hence, as radar PAG increases, it may become increasingly difficult to design conventional radar equipment to operate as desired in littoral regions. To partially address these issues, some future radar phased arrays (sometimes called "digital array radars") will employ high degrees of aperture digitization. Typically, this digitization was performed near each of the receive elements in the array, enabling faster search rates, increased dynamic range, and improved adaptive beamforming performance.

Naval operations are moving closer to shorelines in many regions of the world. Included in this environment are commercial and military communications, increasingly complex electromagnetic interference (EMI), and the need to detect both small moving targets embedded in severe clutter as well as other challenging targets (e.g., tactical ballistic missiles). This operational environment strains the performance of a number of current radar sensors onboard ships.

Shipboard array radars were largely analog-based. Despite the enhancements being made, they still are falling short of the potential performance improvements that could be embodied by fully digital adaptive arrays. New technologies are needed to support the development of higher performing shipboard radars. The success of the information technology (IT) market and other commercial technologies are leading the development of new digital components that could be incorporated in the design of high-performance digital array radar.

The wireless market, in particular, made great strides in improving the performance of digital cell phones and other technologies through smaller packaging, weight reduction, improved analog-to-digital (ADC) and digital-toanalog converters (DAC), and increased dynamic range of RF/microwave components. In addition, for rapidly configuring simple logic functions in an integrated chip and at a low cost, field-programmable gate arrays (FPGAs) have become an attractive alternative to application-specific integrated circuits (ASICs).

Strong land clutter, man-made sources of EMI (e.g., cell phone towers, other radars), and jamming signals coming from different directions are just a few of the factors that fleet radars must contend with. Extended land clutter that competes with small targets was a difficult problem. Many current shipboard radars have insufficient dynamic range (i.e., linearity) to pass the high-peak clutter levels without saturating the entire receiver. By digitizing analog radar data (i.e., through the use of an ADC) at the element level, the dynamic range can be enhanced.

Multiple jamming signals arriving from different directions pose a separate problem. As a ship navigates along coastal regions and scans the volume for targets, jammer energy can enter at any angle and strongly affect the ability of the array radar to form antenna beams for different targets. Analog beam formers are limited in terms of their performance since a single ADC was typically used at a summing point. The ideal solution to the jamming and clutter problem was to place an ADC at every radiating element in an array radar system and sum the contributions to form beams and nulls digitally with a digital beam former (DBF). Several benefits are derived from this solution: increased flexibility of forming array beams, improved time-energy management, enhanced dynamic range, and a potentially lower cost of implementation over time.

The ADC was critical to the performance of the digital beam former. The number of bits achievable by the ADC and the number of receive channels in the beam former impacts the dynamic range that can be obtained. Although their performance was steadily improving, the sampling rates of commercial ADC technologies are still not sufficient to support digital array radars. DACs have similar performance issues.


By 1998 Naval surveillance radars were expected by manufacturers to grow from the traditional rotating radar antennas to fixed-array radars and radars with long-range Infrared Search & Track (IRST) sensor. The development for naval surveillance radars evolved from the fixed array AN/SPY-1 S-band [E/F-band] phased array radar of the US Navy's Aegis combat system, although it still requires a rotating AN/SPS-49 2-D D-band volume search radar for long range volume search. The US Navy's proposed DD 21 destroyer program, meanwhile, was expected by senior European and US industry officials to pave the way for the development of the future non-rotating RF sensors, including the AN/SPY-2 long-range S-band [E/F-band] three-dimensional Multi-Function Radar (MFR) from Lockheed Martin Government Electronic Systems.

Raytheon applied the SPY-2 nomenclature to the High-Power Discriminator (HPD) X-band radar, but the SPY-2 designator hs also been used for the totally unrelated S-band Volume Search Radar. The Naval Institute Guide to Combat Fleets of the World by Eric Wertheim [2007] references "SPY-2 volume search radar and Raytheon SPY-3 target-detection radars". Some other sources reference a "AN/SPY-2 High-Power Discriminator (HPD)" but these do not seem to be authoritative.

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