ABSTRACT The subject paper dis- cussed the merits of applying infrared imaging technologies, in association with advanced digital processing tech- niques, as a system health diagnostic tool to (1) enhance readiness and (2) reduce the cost of ownership associ- ated with phased array radar systems that are used throughout the military services. The planned project shall establish a field-level diagnostic tool that can rapidly assess deployed phased array radar antenna performance, using infrared (IR) imaging techniques and that can isolate deficient radio fre- quency (RF) solid state emission devices (radiator elements). Infrared imaging of RF emissions from an air- craft-installed phased array radar sys- tem (APG-63 used in F-15 aircraft) has been conceptually demonstrated; how- ever, full scaleup was never achieved nor other potential technology applica- tions evaluated because of funding con- straints. Today, solid state phased array technology is used pervasively in air and in ground/surface-based radar sys- tems. Table 1 identifies representative ground/surface-based radar systems that incorporate phased array antennas in their system architecture.

The ability to conduct operational “end-twnd” testing of phased array antennas will enable deployed verifica- tion of detected performance degrada- tions, facilitate field-level replacement of faulty RF emission devices, and help reduce the overall logistics burden asso- ciated with dismantling and transport- ing bulky radar systems for return to depot. In addition, the proposed capabil- ity could be used as a preliminary diag- nostic tool, augmenting existing depot capabilities, to help facilitate the acceler- ated identification/confirmation of required depot-maintenance actions. IR imaging has the potential to catalyze a fundamental shift, comparable to the introduction of automated testing in support of avionics, in the basic approach to phased array antenna maintenance.

Infrared Imaging of Phased Array Radar Antenna Emissions

Introduction

round-based radar system mission criticality has increased signifi- cantly in recent years, because of the need to accurately detect and track theater launched missiles (SCUDS). Enhanced radar preci- sion, increased power levels, and reduced side lobes, achieved

through solid state phased array technology, have enabled radar systems to breech the envelope in their ability to detect fast moving and/or low signature threats characteristic of tactical ballistic missiles. Advances in antenna design have made radar systems more complex, which has compounded their main- tenance burden. For example, the TPN-25 is populated with 824 individual elec- tronic radiator elements (phase shifters) that operate in a controlled fashion. Some advanced phased array antennas have in excess of 5000 radiator elements.

Antenna performance is usually not significantly impacted if supporting radi- ator elements fail in a random pattern as opposed to more localized radiator fail- ures that degrade specific performance capabilities/parameters (e.g., detect extended left quadrant threats). In either case, incurred side lobe and beam width degradations will impact radar performance. Detection of these degra- dations is difficult to achieve through internal self-test diagnostics, because they do not measure radiated power performance. A major need associated with all radar systems is the ability to verify overall installed system perfor- mance through an “end-to-end” system assessment. Improved built-in-test capabilities have enhanced line repairable unit (black box) confidence checks; however, installed antenna performance verification remains the weak link in determining overall radar system health.

Measuring emitted RF energy is the only known method for determining total radar system performance. At the depot/original manufacturer level, cal- ibrated indoor/outdoor antenna ranges provide the enabling measurement capabilities. However, they must be remotely located/isolated and require expert technicians and a sizable capital investment. Such an approach is not feasible for field purposes; however, advances in infrared imaging have estab lished a lowcost, alternative approach for accurately measuring RF emissions. The advocated concept involves placing a radiation sensitive screen in front of a phased array antenna (see Figure 1) to collect and convert its emitted RF energy into thermal energy, establishing the media for IR diagnostic imaging that is directly linked to individual radiator element performance.

State-of-the-art infrared imaging technology, coupled with a matched com- puter system, is then used to analyze (Figure 2) radiator alignment and power characteristics via collected thermal patterns. Established analysis capabilities, tailored to specific systems under test, assess collected imaging data to facili- tate the identification of deficient/marginal radiators that cannot be detected through conventional field testing.

The Air Force Sacramento Air Logistics Center (SM-ALC) recognized in the mid-1980s that IR imaging capabilities, established in support of mobile depot

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lnlrared lmapinp 01 Phased Array Radar Antenna Emissions

Representative Ground/Surface-Based Phased Array Radar Systems System Service Mission Status Total Units

MK23TAS Navy

ANISPY-1 Navy

MPQ-53 Army

GBR-X ArmylBMDO

MPQ-64 Army

TPS-59 Marine Corp

ARSR-4 Air ForcelFAA

GPN-22 Air Force

TPS-43/70/75 Air Force

TPN-25

Sea Sparrow Missile System

Fleet Defense (Multi Functional-AEGIS)

Patriot Antiaircraft and Tactical Ballistic Missile Defense (BMD)

Theater Missile DefenselUpper Tier BMD

Forward Air Defense (Low-Level Detection)

SurveillanceTTacticaI Missile Defense

Joint SurveillancelNationaI Air Defense

Precision Approach Radar

Surveillance

Deployedlln Production

Deployedlln Production

Deployedlln Production

DemonstrationNalidation Engineering and Development

Low-Rate Production Began January 1995

Deployed/Tactical Missile Defense Upgrade w/HAWK

Developmenthitial Production- First Delivery December 1994

Deployed: Mobile (GPN-22) and Fixed Based (TPN-25)

Deployed/-67 Units Upgraded to -75 Configuration

a7 (Produced)

47 (Produced)

104 (Produced)

1 (DemNal)

154 (Potential)

12 (Deployed)

42 (Original

Production)

40 (Produced)

213 (Produced)

antenna maintenance teams, would enhance the perfor- mance of on-site radar maintenance. In 1993, an Air Force repair technology project, using an F-15 aircraft radar system with known antenna performance anomalies, ver- ified phased array antenna IR imaging concept validity. In 1995, the SM-ALC generated a formal technology need, later validated as a high-priority support and industrial operations requirement by the Air Force Materiel Com- mand, for the establishment of IR imaging test capabili- ties in support of ground-based radars. Follow-on need analysis revealed that the other services have compara- ble requirements and that a common IR imaging tech- nology demonstration effort, involving ground/surface- based radars, could enhance readiness and reduce maintenance support costs.

Table 2 identifies representative unscheduled mainte- nance workload cost data for the GPN-22 and/or TPN-25 ground-based phased array radar systems, managed by the SM-ALC, that are contractor maintained (depot level). Approximately seven antenna units are returned annually to the contractor for unscheduled maintenance. An additional eight units (average) are returned each year for scheduled maintenance (5year rotation cycle). Each return incurs approximately 1300 hours total test time, using serial test methodologies, because each radi- ator element (824 total elements in the TPN-25) populat- ing the array requires independent performance evalua- tion to determine individual element serviceability and total system health. IR imaging technology offers the opportunity to establish a field-level diagnostic test

capability that would (1) eliminate return of premature failures, (2) retard “normal” field-incurred array degra- dation, (3) extend the interval between scheduled main- tenance, and (4) determine actual radar system perfor- mance through “end-toend” test capabilities vs. reliance on detected operational anomalies. IR imaging technol- ogy insertion into the depot-maintenance environment should reduce test diagnostic times for the reference sys- tems to under one-tenth of the 1300 hours now being incurred, establish a paradigm shift in phased array test methodologies, and minimize dependency on highcost antenna ranges. The ability to rapidly isolate deficient radiator elements while they are installed in the antenna array will accelerate product velocity through the depot- level repair cycle, minimize required spares, and reduce depot-support costs currently being incurred because of an excessive test time burden.

Other projected payoffs from establishing an IR imag- ing diagnostic test capability in support of ground/sur- face-based phased array radar maintenance include the following:

Enabling the field to assess generated radiation pat- terns-assured mission readiness Establishing expanded on-site test/maintenance capabilities Reducing cost of ownership Enabling enhanced documentation/communication of field-incurred discrepancies Equipping field and depot with comparable diagnostic test capabilities

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Infrared Imaflinfl 01 Phased Array Radar Antenna Emissions

F I G U R E 1 . IR Imaging Technology Concept

rn Minimizing Could Not Duplicate (CND) situations Critical Factors between field and depot Reducing technician skill level requirements

rn Enhancing mobile maintenance

Objective The proposed demonstration targets achieving four sequential goals: (1) verifying that an IR imaging diag- nostic test capability established in support of ground/surfacebased radars, is mission beneficial and can generate a substantial return on investment (enhanced readiness and cost avoidance); (2) establish- ing the optimum methodology for imaging ground- and/or surface-based radars within existing design and/or installation constraints; (3) deploying an IR imag- ing diagnostic prototype, generated in support of a selected system, that is capable of catalyzing a revolu- tionary shift in ground/surface-base radar maintenance concepts; and (4) identifying IR imaging diagnostic test accommodations that should be incorporated into future antenna designs.

The suggested prototype capability must be deployable and have the inherent agility to be affordably tailored to support diverse radar configurations. The established prototype must be affordable; have light-weight portable characteristics, minimum ancillary support require- ments; and be able to image the selected test-bed radar antenna while it is operating at full power and in diverse modes. As a minimum, the established prototype must be capable of measuring phase, beam steering, and amplitude performance characteristics. The established capability is intended to (1) augment existing diagnostic capabilities, (2) perform rapid field-level performance assessments that can accurately determine total antenna performance health, (3) isolate deficient radiator ele- ments and facilitate their replacement under field condi- tions, and (4) extend the duration that an antenna remains in the field before requiring depot overhaul. The prototype must be affordable and able to achieve a sub stantial return on original investment (minimum 12:l). Demonstrated imaging capabilities must facilitate bene-

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F I G U R E 2 . IR Imaging Concept

ficial reductions in depot-level test times, achieved through rapid/simultaneous radiator elements screen- ing, in pursuit of accelerating field-returned assets through the maintenance pipeline.

APPROACH Analysis of the completed APG 63 IR (F-15 aircraft radar) imaging effort indicates that the demonstrated theo- retical capabilities are transferable to supporting ground/surface-based radar requirements; however, design characteristics, installation features and power level differences present potential constraints that must

Representative Contractor Maintenance Incurred support costs

Unscheduled Maintenance Workload Data (GPN-22 and/or TPN-25 Antennas)

TASK AVERAGE UNIT COST

Antenna CheckoutfRepair 5638K Shipping S127K TOTAL 5765K

be assessed before commencing full concept demonstra- tion activities. A prudent, two-phased approach is con- sidered the optimum approach to ensure the established prototype is capable of achieving the required return on investment and that the actual demonstration risks are known before committing scarce technology investment resources.

The suggested two-phase demonstration effort would use affordable, commercial off-the-shelf equipment that has the inherent features to support prototype require ments; however, an imaging screen must be designed and tailored to the radar system type under test (assess- ment). Other prototyping efforts would include the estab lishment of an agile (tailorable) radar system diagnostic software package capable of assessing collected IR images against known baselines and of generating spe- cific instructions for correcting detected anomalies.

Emphasis would be placed on risk reduction and per- formance metrics identification before an actual IR imag- ing demonstration capability is established. Preliminary analyses indicate that the proposed capability would be capable of achieving a minimum 12:l return on invest- ment. The established prototype capability must have the inherent flexibility to be modified to support diverse antenna requirements and to achieve previously attained benefits. The selected test-bed radar system used in sup

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IR Imaging Funding Requirements (Two-Phase Effort) PHASE FYXl FYX2 FYX3 TOTAL

I b250K b250K II b800K $900K 61700K TOTAL S1950K

port of the proposed demonstration effort would be r ep resentative of military radar systems to ensure technol- ogy exportation is feasible. The first phase shall assess (1) array failures that necessitated depot maintenance to determine which returns could have been avoided, if the associated field activity had been equipped with IR imag- ing diagnostic test capabilities and (2)determine what benefit IR imaging would have at the depot level. This analysis shall help determine the optimum IR imaging capability, ensuring the established prototype is able to support maintenance requirements and shall verify that IR imaging is a viable diagnostic test tool. The second phase shall involve demonstrating a prototype capability in support of field requirements.

In addition to determining cost avoidance contribu- tions, the proposed effort would quantify any incurred impacts on mission readiness. The proposed “end-to- end” IR imaging diagnostic test tool shall enable the field to periodically assess and record, using established IR imaging test methodologies, on-site operational radar performance.

Funding Requirements Identified in Table 3 is the required funding to support this proposed two-phase effort.

If the suggested two-phase demonstration is success- ful, a separate follow-on effort is required to insert the

demonstrated technology into all phased array mainte- nance concepts (existing and future). Emphasis would be placed on generating a cultural shift in the perfor- mance of phased array antenna maintenance. In addi- tion, the recommended effort would identify antenna design/installation accommodations that would enhance expanded IR imaging technology exploitation.

Conclusions IR imaging technologies present a tremendous opportu- nity to move away from burdensome infrastructure sup port capabilities, required to support phased array radar antenna performance evaluations, towards a more agile approach that is capable of performing rapid perfor- mance characterization. 4-

Mr. Pat Sisson Mr Sisson has 30 years aerospace experi- ence. Operationally, he served as a line and research pilot. He served as a n Assistant Professor of Electrical Engineering and directed R&D activity for both the Air Force and as a n Indus- try researcher He possesses extensive experience with the Air Force Research Laboratory Sensors Directorate working advanced electronics issues. He currently serves as the Divi- sion Manager for the Sensors Business Area for Anteon Corpo- ration, Dayton, OH. MT. Bruce Long is a 30year aerospace professional, serving 20 years in the United States Air Force, and for the past nine years has been employed by Anteon Co@oration, Dayton, Ohio. Military assignments relevant to this symposium include duty as an avionics maintenance officer at the Warner Robins Air Logistics Center Avionics Technology Repair Center and as the B-IB Defensive Avionics Program Manager during the initial weapon system acquisition. Since leaving active duty in 1990, Mr Long has directly supported the Air Force Sustainment, managed by the Air Force Research Laboratory’s Materials and Manufacturing Directorate. As a 10-year Anteon employee, M7: Long has supported diverse defense activities, including the DOD Sustainment Readiness Working Group. M r Long earned his BA degree from Whitman College and has an MSfrom Georgia College.

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