Fighter Radar in the 1990s

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NO SECTION, Japan

Date Posted: 01-Aug-1992

International Defense Review

FIGHTER RADAR IN THE 1990STEXT: a spectrum of progress

TEXT: The radar systems that are shortly to make their debut in the next generation of fighteraircraft will be far superior to their forebears of the 1960s and 1970s. Technology has in someways nearly reached the limits of development, since the fundamentals of wave propagation andtransmission cannot change due to the laws of phusics. The real revolution in radar systems hasbeen, and continues to be, in signal and data processing. Over the last decade, there has been atenfold increase in processing power for radar applications. Moreover, power generation efficiencyhas improved dramatically with a better conversion of raw to radiated power. This has improvedradar range capabilities, however, even this has limits: a doubling of range requires a sixteenfoldincrease in transmitter power.

Yet it is the numbercrunching advances that are delivering the quantum leap in system capability.Veryhighspeed integrated circuit technology, higher conductivity inb substrate materials (such asgallium arsenide), among other achievements, is allowing more useable data to be extracted fromradar returns, data that until recenlty was lost because of capacity limitations. finally, packagingadvances have allowed more system capability in smaller space, especially important whendesigning retrofit systems for older fighters.

One major difference in nextgeneration radars will be the use of electronicallysteered active andpassivearray antennas. Electronic arrays scan the radar beam without mechanical means such asa gimballed dish antenna. The array itself is comprised of hundreds of tiny transmit/receive (T/R)modules each functioning as a miniature radar in its own right. The triggering of these modules ina particular sequence provides beam steering. While not actually new, design complexity hasmade such units expensive, unreliable, and overly large. The first such equipment fielded in anoperational fighter was the Zaslon passivearray radar in the Russian MiG31 interceptor. WhileZaslon is a highpower unit with 200km range inlookdown mode, its design has been described as"technically inelegant" by some Western experts, and is said to embody chiefly 1960s technology.Speaking to IDR, one Russian aircraft designer said that CIS avionics currently have the samecapabilities as Western counterparts but not the same level of compactness. CIS design bureausare hoping to integrate Western avionics technology into future airframes in order to close thisgap.

Western efforts in electronic arrays have followed two paths: active arrays and passive arrays. Themain benefit of electronicallysteered beams is scanning agility, as the cone of radiated energy is

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not dependent on mechanical gimbals to steer it. Trackwhilescan mode is quicker for multipletargets, a wider frequency range is available, and graceful degradation is inherent bvecause of theindependent T/R modules. The main disadvantages of such antennas are that they suffer from alimited scan angle as the radar cone is narrower (although faster moving) and that overall systemreliability (other than the T/R modules) could be a problem, at least in firstgeneration designs.For the moment, cost is actually the largest stumbling block to fielding electronicallysteeredsystems. The European Fighter Aircraft (EFA) radar, the ECR 90 system developed by GECFerranti, FLAR, and INISEL, for instance, will still contain a mechanicallysteered planar array.Both the US F22 and the French Rafale, however, will use electronic arrays. The USAF has optedfor activearray technology in its radar while the French have pursued passivearray technologyinstead. No more ghosts Due to make its first flight in 1995, and to enter service around the endof the century, the USAF/Lockheed F22 Advanced Tactical Fighter (ATF) will have the first fighterradar to be based on an active electronically scanned array (AESA). Program officials say that allthe data continue to support the choice of the AESA, despite the technical and cost challenges ofsuch a radically new approach.

The USAF has pursued Xband AESA technology since the early 1980s for three main rasons:power/weight ratio, agility and reliability. With more than a thousand transmit/receive (T/R)modules, each capable of generating around 10W of power the F22 radar has a peak power inthe megawatt range, should that be required.

The agility of the beam its ability to change in direction or waveform is better than any othertype of radar. "We can do things with parallel processing that you simply cannot do with a movingantenna or a singletransmitter radar," says deputy ATF program director Tom Graves. The F22radar will operate in interleaved modes, switching from one to another so rapidly that they willappear concurrent to the avionics system. "It will act almost like two different radars," saysGraves.

Reliability is still the AESA's most important advantage. A physically fixed antenna eliminatescomponents such as rotary waveguide joints, "which cause a lot of nokidding failures," accordingto Graves. Because the array is physically locked into the aircraft, boresight angles and grazingangles with the radome cannot change in flight, so less time is spent "chasing ghosts," as Gravesputs it.

These advantages also apply to passive ESA like those on the B1B and MiG31, but, says Graves,research still shows superior reliability for the AESA. "We've done trade studies all the way from asingle travellingwavetube to the AESA, including a radar with 50 ganged transmitters that wasthe worst of all worlds," and the AESA comes out on top. Ultimately, a maintenancefree life of20,000h the lifetime of the aircraft is possible.

The F22 radar springs from several stages of development, starting with the USAF's Ultra ReliableRadar (URR) and Common Signal Processor (CSP) programs. The URR was an array only, withonly very basic radar performance; there were some plans to marry the URR and CSP for more

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complex radar tests, and even some ideas of installing them in an aircraft, but these did not takeplace.

URR team members Westinghouse and Texas Instruments were selected to build radars for bothATF Demonstration/Validation (Dem/Val) teams, using further improved T/R modules. Both teamstested the radars in the air, and performed some basic detection and tracking tasks.

Neither the URR nor the Dem/Val radars was anything like a prototype for the ATF radar. Rather,they showed that an AESA fighter radar could be made to work and could be controlled by acommon processor. The radar being developed in the engineering and manufacturingdevelopment (EMD) program is completely new.

Since the selection f the F22 in April 1991, the USAF and industry have been working to reducerisk in the development process and to make the resulting radar affordable. Like the rest of the F22 system, the radar is being subjected to a discipline known as "integrated product development"to ensure that every feature of the design supports the required operational capability of thesystem. "We need to make sure that we have a solution to every requirement, and that we don'tspend time on a solution for requirements that don't exist," says Graves.

At the same time, however, care is being taken to ensure that the design provides forimprovements to meet future requirements. This will be the focus of a design review later thisyear. This discipline has imposed some conservatism on the program. For example, the radar isnot required to have a much greater search range than the current F15 radar. "After a while, youget data or information overload" with increasing range, says Graves.

Originally, the ATF radar was to have included sidelooking auxiliary arrays to provide anextremely wide field of regard around the aircraft, but his feature was deferred in a 1989 reviewof the avionics requirements. "The operational advantage was not enough to justify the cost andrisk which we anticipated in making the switch between side and front arrays transparent to thepilot," says Graves.

However, space, weight, power, cooling and CIP capacity will still be reserved for side arrays the question, for the program managers, is how much. "We're trying to improve ourunderstanding of what the side arrays need to do and can do, whether you need to transmit andlisten on different antennas, and what kind of power they require," says Graves.

Most of the 17 baseline radar modes will be airtoair, says Graves, but the basic system will beable to do much more. Synthetic aperture radar (SAR), for instance, "is not in the baseline, butthe hardware can do it and we have an idea of what the software would need to be." The overalldesign reflects the need to incorporate SAR later in the program. Because SAR modes "are verysensitive to knowing what the antenna's doing," says Graves, the F22 inertial reference sysem ismounted on the back of the radar bulkhead, for the highest posible fidelity between the twosystems.

The critical element in controlling the cost of the F22 radar is the cost of the T/R modules. Thetarget set at the start of Dem/Val was $400 in baseyear (1985) dollars, but the USAF is nowpushing for $400 in thenyear dollars.

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The war on T/R module costs has been fought through a series of designproducetest cycles. Ineach cycle, TI has made enough modules to validate its predictions of manufacturing costs andyields. Then, the costs have been analyzed, says Graves. "We ask, where are the costs? Then weattack each area, to see if we can either design the cost item out of the module, or automate thetooling, assembly, or test processes."

Through this process, the USAF and TI found that they could remove a complex integrated circuitset from the T/R moudle and make it both cheaper and easier to test, without affecting itsoperational capability. Then, in the second EMD iteration, the modules were redesigned so thatthe transmit and receive components were physically separated, on opposite sides of the module.This means that the microwave monolithic integrated circuitry (MIMIC) on one side can becompleted and tested before the other side is built up, so that less work is lost on those which failthe test.

The decision not to use side arrays hurt the module program, because its costs are verydependent on numbers. However, says Graves, "we're still projecting good things on cost."

The first F22 is due to fly in August 1995, 48 months after the contract was awarded, but thesixth EMD aircraft, to fly in 1996, will be the first with radar. (The radar itself will make its firstflight in 1995, aboard the Boeing 757 used as the flighttest laboratory for Dem/Val.) Says Graves;"We recognized that it would take us five years or more to develop the radar."

The first four F22s, used for structural, performance and handling tests, "will have enoughavionies aboard to fly"; the fourth willb e the first twoseater. The fifth will have communications,navigation, and identification (CNI) avionics on board.

The seventh aircraft will have the Integrated EW System (INEWS), and the eighth F22 will be thefirst with complete mission avionics; the fifth and sixth aircraft will be retrofitted with full avionicsduring the test program. The ninth and tenth F22s will be used for integration and armamenttrials, and the eleventh EMD aircraft will be configured for radar crosssection tests. Rafale'spassive nature The RBE2 electronicallyscanned radar, developed jointly by ThomsonCSF andDassault Electronique (under the GIe Radar consortium), made its first flight on 10 July at theBretigny flighttest centre in France. The RBE2 will eventually equip both French air force andFrench navy variants of the Rafale fighter. This first flight took place according to schedule andonly three years after an order from the government to the consortium. The flight marked thebeginning of a series of tests of the RBE2 in flight on a Mystere 20 test aircraft specially equippedfor evaluation. First flight on a Rafale prototype is scheduled for May 1993.

The RBE2 is the first electronic sweep radar for fighters to have been developed in westernEurope, and will be one of the first in the world to be put into service. In comparison to currentradars, which use a mechanical sweep antenna, the RBE2 will offer the opportunity to fulfil avariety of functions simultaneously such as trackwhilesearch and terrain monitoring. The RBE2has the same sweep sector as most other military airplane radars, that is 120 degrees, but scanspeeds are 50 to 100 times faster than even the best mechanical antennas, whose speed is 100degrees/s. Direct comparison is misleading, however, since the beam does not sweep in the usual

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sense of the word, but literally jumps from one position to another within the sweep angle. Thisalso helps in maintaining radar discretion, as there is no steady sweep of the beam, it merelyjumps from point to point. The acquisition range of the RBE2 is in the order of 50nmi on nonstealth targets, and at least 35nmi on moderately stealthy contacts. Average power emission is onthe order of 1kW.

The radar differs from the US ATFbound system in that the beam is passively scanned through aradant or phaseshifter in order to steer it. A fixedbeam Xband antenna transmits a waveformdirectly into a threestage electronic "prism" (radant) that bends the beam in the desired direction.The first stage scans in the vertical plane, the second acts as a polarization rotator, and the thirdscans in the horizontal. While passive scanning is as technically sound as active scanning, thebenefit of graceful degradation is lost because a phaseshifter malfunction would mean a totalsystem failure.

The RBE2 is a fully multimode radar and its capabilities have been adapted to the wide range ofmissions that Rafale will be taksed with:

airtoair, to detect at longrange approaching aircraft, with multitarget tracking ability and trackwhilescan;

airtoground, ground target tracking and terrain avoidance with ordnance delivery despite groundclutter;

airtosea, to detect and track targets at longrange against surface clutter with effective ordnancedelivery.

In addition, to respond to the requirements of modern air combat, the functioning of "airground"and "airair" modes can be simultaneous. This, it is claimed, affords crews both a certain securityduring lowlevel air combat and the capability for selfdefense against interceptors withoutinterrupting lowlevel flight.

ThomsonCSF and GEC Marconi (lead contractor on the EFA ECR 90 radar) signed an agreement inMay 1991, to cooperate on research and development for the next generation of radar to equipthe successor or successors to Rafale and EFA. The new joint venture company, called GECThomson Airborne Radar, will concentrate on activearray antenna technology. The move is anindication of the expense of such research and shows European concern that such technology isnot lost to the US or Japan in the next decade. A prototype for the radar is not expected to makean appearance before 2005, and development costs are put at FFr5 billion (US$925 million) overthe next 12 years. The AngloFrench effort wants to eventually bring in a German partner.Benefits for the retrofit market While not all radar manufacturers are actively pursuing activearrays, the flurry of cuttingedge research is bestowing residual benefits for systems on the retrofitmarket. GECFerranti's work on the Iband Blue Vixen radar for the Sea Harrier FRS.2, has led to apowerful unit designed for a relatively confined space. Performance growth potential is already

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planned for with ample processing capability availabel for software upgrades without hardwaremodifications. One such benefit would be the addition of Doppler beamsharpening for very highresolution radar imaging. Moreover, work on the ECR 90, itself based to a large extent on BlueVixen, could be applied retroactively for Blue Vixen upgrades or perhaps even Blue Fox (on HarrierFRS.1 in Britain and India). One of ECR 90's features will be a superagile antenna pedestal toimprove scanning capability.

A more direct effort was recently announced by GECFerranti with the unveiling of its Blue Hawkprogram, a modular family of combat radars specifically developed for the retrofit market. BlueHawk, offered as a lightweight, lowcost system for fighters, is a multimode pulseDoppler radar.It will afford lookup and lookdown capability, ground mapping, and a high degree of missilecompatibility. Modular and air cooled, it consists of four LRUs plus the antenna unit.

Swedish manufacturer Ericsson, currently at work on the JAS.39 Gripen multimode radar, the PS05/A, is already looking at integrating the system into other airframes, although company sourceswould not elaborate. Ericsson has begun flight tests of the I/Jband radar in the Gripen andverification of specifications is expected to continue through mid1993. Ericsson is using anantenna platform gimbal from GECFerranti which is in turn using Ericsson exciter modules for theBlue Vixen radar. Ericsson's D80 signal processor (used in the PS05/A) had been a shortlistedcandidated for the ECR 90 radar but in the end was not selected by Ferranti. It is capable ofselecting low, medium, or high PRF modes depending on conditions and contact range andaltitude.

ThomsonCSF's multimode RDY radar, developed for export on the Mirage 20005, could now findits way into service with the French air force, if the proposed acquisition plans for the 20005 gothrough. The RDY could also be retrofitted to existing Mirage 2000 aircraft in French service. Withsuperior processing to the current RDM radar, the RDY also features a planar array, lowinertiaaperture antenna more capable than the RDM's that will eventually be replaced by anelectronicallyscanned one. These growth factors could make the RDY highly desirable to thesubstantial number of Mirage operators around the globe.

Elta Electronics Industries is a subsidiary of Israel Aircraft Industries, various divisions of whichhave experience of modifying and upgrading older aircraft. IAI maintains the third prototype ofthe nowcancelled IAF Lavi fighter program as a technology demonstrator. Tested on this platformis the Elta EL/M2032 multimode firecontrol radar, which can be customized to specificrequirements.

The 2032, one of the EL/M2000 family of radars, is tailored to fighter/attack aircraft. Because ofits modular hardware, MILSTD 1553B avionic interface and allsoftware control, it is suitable forthe F5, F4, and the Mirage, among other airframes. The EL/M2035 is for less specificallyoriented, multimission fighters, while the EL/M2011 is optimized for close air support operation,for advanced trainers and lightattack aircraft. All three basic radar configurations can be modified

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to specific needs.

For airtoair operation, the EL/M2032 has rangewhilesearch (RWS), trackwhilescan (TWS) andsingletargettack (STT) capabilities and ensures longrange target detection and tracking. Its aircombat modes are slewable, HUD, boresight and vertical scan, allied with automatic targetacquisition. For airtoground operation it has realbeam mapping with expand or freeze capability,ground movingtarget indication, airtoground ranging and terrainavoidance facilities, beacon andseasearch modes and Dopplerbeam sharpening. A twoaxis monopulse, pulseDoppler, allattitude, allaspect radar, its detection range for fighter aircraft in lookup mode is said to be30nmi, 25nmi in lookdown mode. Antenna size varies from 30 to 75cm according to platformrestrictions, and weight varies accordingly from 94 to 110kg.

Israel had the first operational lookdown/shootdown radar in service the 2001 for the Kfir inthe 1970s. This capability was not available to Russian aircraft until entry into service of the MiG29. The 2001B, a solidstate radar except for the travellingwave tube, is still available foroperation with singleseat tactical aircraft in both aittoair and airto ground modes.Though it has similar multimode and allaspect capability to the 2032, the 2011 does not physicallyresemble it and is more suited to the airtoground role. Antenna diameter for the 2011 is 33cmadaptable, power 1.5kW, and weight 67kg. Ranging capability in the airtoground mode is 150 15,000m with an accuracy of 30m (or 5 per cent). Detection range in the airtoair mode is 150m 8nmi with the 33cm antenna and a target size of 5m2 (probability of detection is 90 per cent).Certainly no newcomers to radar design, Italy's two radar houses, FIAR and SMA, are currentlyoffering very capable retrofit systems that are finding favour on the world market.

SMA has developed the SCP01 "Scipio" multimode radar in conjunction with Tecnasa of Braziland the Brazilian air force, to equip Brazilian AMX fighters. Now at the end of its developmentaltesting phase, the SCP01 offers three modes: airtoair, airtoground, and airtosea. A relativelycompact system, it consists of five line replaceable units and weighs only 73kg. Like the best ofthe current generation of fighter radars, it uses HOTAS controls and claims a high degree of ECMimmunity. SMA also claims a MTBF rate of better than 230h and a MTTR rate of 20min. While theFIAR Grifor radar equips Italian AMX aircraft, SMA hopes to acquire followon contracts for theItalian air froce and is eagerly awaiting the chance to bid on AMX's first export sale, possibly inAsia.

FIAR's fighter radar line is based around its Grifo family, of which the ASV variant equips Italian airforce AMX aircraft. The ASV, tailored to antiship missions, is a low PRF Xband system with apeak power output of 80kW. Grifo F/X plus is a lightweight pulse doppler system designedspecifically for the AMX in multirole missions (low, medium, and high PRF) but offered for the F5.FIAR also offers the GrifoM for Mirage retrofit and the Grifo7 for the MiG21/F7 fighter. Alloperate in the Xband, use pulse compression techniques, HOTAS control, offer good ECCM,

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flexible wide modular architecture,'and interface with a range of missiles (except Grifo7). TheGrifo7 has recently been sold to an Asian country, most likely India, to upgrade its Mig21 fleet.However, this report remains unconfirmed by FIAR. The extreme space constraints of the MiG21nosecone are a challenge for shoehorning in a capable multimode radar. The Grifo7 uses lowand medium PRF, and a 38cm circular planar antenna. FIAR is concentrating marketing efforts inAsia and South America, and is banking on the belief that developing nations will be holding ontotheir existing fleets for a long time. Grifo has already been sold to Singapore for its F5 upgradeand to New Zealand for its A4 Kahu.In the US, apart from work on ATF radar, manufacturers have been engaged in a series ofevolutionary upgrades to existing fighter radars, particularly for the F16 and F/A18 aircraft. TheHughes AN/APG73, based on the AN/APG65, offers increased processing speed and expandedmemory and will equip F/A18 fighters in the US, Canada, and inSwitzerland. Westinghouse hascaptured the lion's share of global F16 radar upgrades with its AN/APG68, first delivered to theUSAF in 1984. It offers enhanced ground mapping, BVR AMRAAM capability, and extendeddetection range, and will be in production throughout the 1990s. For other airframes,Westinghouse has launched its Modar 5000 family, a highperformance Xband pulse Dopplersystem built around common modules and offering over 600h MTBF.

In an F5 application, Modar 5000 would weigh about 68kg, feature an acquisition range out to80nmi, and would afford both airtoair and airtoground capability. The company's APG66system (developed for F16A/B) is getting a second lease on life as the BAeproposed solution forthe Hawk 200 light singleseat fighter. A new LRU signal data processor on the APG66H hasreduced packaging, increased reliability, and enhanced speed.

Both GE Aerospace and ESCO (formerly Emerson) offer retrofit systems, intended primarily for theF5. GE's multimode F5 radar, operating in the I/J band, features DBS ground mapping, lookupand lookdown tracking. Average acquisition range in search mode is 30nmi in lookup mode and19nmi in lookdown. MTBF is somewhat poor though, at 150h. ESCO's latest variant on thesuccessful AN/APQ159 series, the 159(V)7, provides an airtoground mode, a planar antenna,and a new programmable signal data converter. Again, MTBF is poor, around 127h. It has beenselected by CESELSA of Spain for the Mirage III modernization program. While these lattersystems fall at the low end of the modernization spectrum, they still afford a huge increase incapability over previous generation systems available to the airframes concerned. Even thesemodest radars are beholden to the great advances in processing, many of which are software andnot hardware driven.

CAPTION: Photograph: Improved signal processing allows more extracted return data to be used.Here, a GECFErranti Blue Vixen radar in airtosurface mode highlights targets in the North Sea ina decluttered display.

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Drawing: The ThomsonCSF/Dassault Electronique RBE2 radar uses a passive electronicallyscanned antenna. The Radant phase shifter that serves to steer the radar beam is comprised oftwo lenses (working in the vertical and horizontal planes) separated by a polarizing filter. Thebeam is instantaneously shifted from one point to another and is not swept as in mechanicallybased antennas.

Photograph:

Photograph: GECFerranti has announced a retrofit line of firecontrol radars, called Blue Hawk.The system provides reliable multimode pulse Doppler capability in a confined space.

Photograph: The FIAR Grifo F/X plus radar is amultimode, pulseDoppler system designedspecifically for smaller fighters such as the F5. Other Grifo variants are available for antisurfacemissions and for retrofit to other airframes. India is reportedly acquiring the Grifo7 radar for itsMiG21 fleet.

Photograph: The SMA/Tecnasa SCP01 system, nown going through qualification flight testing, isto be fielded by the Brazilian air force on the AMX fighter. Development of the system began in1989; the first operational prototype was isntalled on a HS125 testbed in 1991.

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FIGHTER RADAR IN THE 1990S

Fighter Radar in the 1990s

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