low cost multifunction phased array radar concept

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*This work was sponsored by the FAA under Air Force Contract FA8721-05-C-0002. Opinions, interpretations,conclusions, and recommendations are not necessarily endorsed by the United States Government.Distribution A: Distribution unlimited.

Low Cost Multifunction Phased Array Radar Concept

J. Herd 1, S. Duffy 1, D. Carlson 2 , M. Weber 1, G. Brigham 1, C. Weigand 2 , D. Cursio 2 1MIT Lincoln Laboratory

244 Wood St. Lexington MA USA 02420

2M/A-Com Technology Solutions100 Chelmsford St. Lowell, MA USA 01851

Abstract - MIT Lincoln Laboratory and M/A-COM are jointly conducting a technology demonstration of affordableMultifunction Phased Array Radar (MPAR) technology forNext Generation air traffic control and national weathersurveillance services. Aggressive cost and performance goalshave been established for the system. The array architectureand its realization using custom Transmit and ReceiveIntegrated Circuits and a panel-based Line Replaceable Unit(LRU) will be presented. A program plan for risk reductionand system demonstration will be outlined.

Index Terms Radar, Phased Array, T/R Module,Multifunction, Low Cost.

I. INTRODUCTION

The U.S. Government currently operates seven distinctradar networks providing weather and air trafficsurveillance supporting air traffic control and homelanddefense missions. Many of these Systems are approachingend of life. A Multifunction Phased Array Radar (MPAR)system has been proposed as the next generation solutionfor the Nations weather and air surveillance needs (Fig 1 and Table 1). Full system implementation will result in the

deployment of approximately 350 radars. To effectivelycompete with current mechanically scanned solutions, theMPAR system must achieve an aggressive cost goal of $50k/m 2 of array face, while equaling or bettering current

performance metrics. To achieve the ambitious costtargets, highly integrated ICs and commercialmanufacturing practices are being implemented.

MIT Lincoln Laboratory and M/A-COM are jointlyconducting a technology demonstration of MPAR to: 1)define and retire technical risk, 2) establish measured

performance capability, and 3) provide realistic system costmodels.

Fig 1. Conceptual Drawing of Multifunction Radar.

Table 1 Top Level MPAR Definition

Active Array (planar, 4 faces)Diameter: 4 mT/R elements/face: ~ 5,000Dual polarizationBeamwidth: 1.2 (broadside)

2.0 (@ 45 )Gain: > 40 dB

Transmit/Receive ElementsWavelength: 10 cm (2.72.9 GHz)

Bandwidth/channel: 1 MHzPulse length: 80 s (1 s fill)Peak power/element: 8 W linear pol

16 W circular polArchitecture

Overlapped subarray beamformers: Number of subarrays/face: 24Maximum # concurrent beams/face: 24

II. SYSTEM REQUIREMENTS

The multi-mission requirement places unique performancespecifications on the radar system (Table 2). The aircraft

surveillance mode normally operates in single linear polarization. If there is heavy precipitation, a circularly polarized mode is preferred for aircraft surveillance tomitigate depolarization losses. The weather surveillancemode utilizes dual linear polarization. The dual

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simultaneous polarization components provide criticalinformation such as differential reflectivity, differential

phase, and cross-polarization correlation coefficients.These metrics are used to discriminate the scattering

properties of hail and rain, and enables the radar to rapidlyidentify severe flight hazards.

Table 2 Aircraft and Weather Surveillance Modes

Surveillance Type MaximumRange MaximumAltitude

PositionAccuracy MinimumSensitivity

UpdateInterval

Lateral Vertical

Aircraft 60 nm 20,000 600 600 1 m 2 < 4.8 s

Weather Microburst 5 nm Surface < 750 N/A 0 dBZ60 s

(surfacescan)

Gust Front 20 nm Surface < 750 N/A 0 dBZ60 s

(surfacescan)

StormStructure

60 nm 20,000 < 8500 < 8500 30 dBZ72 s

(volumescan)

Challenging time lines have resulted in the adoption of a beamforming architecture that provides multiplesimultaneous beam clusters. At the low elevation angles,the radar has no excess energy, and the surveillance is donewith single narrow beams, as shown in Fig. 2a. At thehigher elevation angles, the slant ranges to targets of interest becomes significantly shorter, and the radar hasexcess energy to utilize. By broadening the transmit beamand receiving with multiple simultaneous beam clusters, asshown in Fig. 2b, it is possible to greatly accelerate thevolume scan rate. With two independent beam clusters andselectable polarization for each cluster, it is possible tooperate the radar with two linear polarized beam clusters(24 beams) or dual linear polarization (12 beams).

Low Elevation

2

Aircraft(linear pol)

Weather (dual pol)

SpoiledTransmit

High Elevation

612

2

Aircraft(up to 24 linear pol beams)

Weather (up to 12 dual pol beams)

(a)

(b) Fig. 2. Overlapped Subarray Digital Beam Clusters.

The radar performs four simultaneous functions: AircraftTrack While Scan, Rapid Update Weather Scan, High

Fidelity Horizon Weather Scan, and High Fidelity 3DVolume Weather Scan. Each of these modes has a scanupdate interval set by the minimum revisit time. The timingdiagram in Fig. 3 shows an example of these three modesoperating simultaneously. The volume aircraft scan takes2.9 seconds, leaving 1.9 seconds in each period to be usedtowards the slower weather scans. In the future, it isexpected that adaptive scan strategies will reduce thesetimelines even further.

Function Scan Update Period (sec)

Aircraft Track While Scan 4.8

High Fidelity Horizon Weather Scan 60

High Fidelity 3D Volume Weather Scan 72

.32.9 1.6.32.9 1.6.32.9 1.6.32.9 1.6.32.9 1.6

Time, sec0 4.8 9.6 55.2 60 72

High fidelity horizon weather scan update period

Aircraft and rapid update weather scan update period

Mode scheduling example:

High fidelity 3D volume weather scan update period

Fig. 3. MPAR Mode Scheduling.

III. POLARIZATION RECONFIGURABLE T/RMODULE

The multi-mission requirement places unique performancespecifications on the radar system components. To achievethe required performance, a unique T/R modulearchitecture [1] with two independent transmit channelsand two independent receive channels with switchable

beamformer paths has been implemented (Fig. 4).

Fig.4. T/R Module Block Diagram.

H- V-

From TransmitTo Receive

HPALNA

TR

PhaseShifter

Antenna

Limiter

Attenuator

2:1split

SPDT

HPA

2:1 split

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The T/R Module block diagram has been partitioned into aRxIC, a TxIC, HPA, a switch IC, control IC and COTSfilters. The Tx IC, Rx IC and HPA are being realized inM/A-COMs PH4 high performance 0.5 m pHEMT

process. This process shares >80% of its process moduleswith M/A-COMs high volume commercial pHEMT

process while utilizing optical lithography for the 0.5 mT-Gate structure to achieve high performance whilemaintaining low cost. The process has been optimized for

power performance while maintaining good noise performance This process allows the integration of allrequired receive functionality: 6-bit phase shifters, 4-bitattenuators, limiter, switches and LNAs to form a singleRx IC. On the transmit side, the driver amplifiers, phaseshifter, and attenuator have been be integrated. An 8 WattHPA forms the final output stage of the Tx chain. Logiccontrol of the individual components will be accomplishedwith a CMOS ASIC. The use of CMOS for logic, whileincreasing the chip count compared to the integration of thelogic on the GaAs ICs has two compelling advantages: 1)

it lowers the current consumption of the T/R module and 2)dramatically lowers the cost of this functional block without sacrificing performance.

The RFICs, control IC and band pass filters are integratedonto a single multi-layer printed circuit board using bestcommercial practices. The layout of the T/R board isshown in Fig. 5

To aid in thermal management, an array of vias thermallyconnect the heat sink of the HPAs package to a COTS heatsink mounted on the backside of the board, Fig. 6. Solder

pads at the periphery of the T/R Board are used to connectto the next level assembly. The various solders used have

been selected to facility the multiple attachments whichmust be conducted to realize the full aperture board.

Fig. 6. Polarization Reconfigurable T/R Module.

IV. MULTIFUNCTION ARRAY PANEL

The T/R modules are integrated into an array panel, whichconsists of the radiating elements, the overlapped subarray

beamformer, and DC and RF distribution networks. Fig. 7shows the dual polarized stacked patch antenna. The patchradiator is fed with a balanced feed to provide a low cross

polarization response, which is required for accurate dual polarized weather radar measurements. The overlappedsubarray beamformer layout is shown in Fig. 8. The

beamformer is fabricated on multiple stripline layers, whichare integrated with the printed circuit antenna elements andthe RF and DC distribution networks to form the array

panel. Fig. 9 shows the assembled array panel under test inthe MIT LL near field test chamber.

Fig. 7 Dual Polarized Stacked Patch Antenna.

Fig. 8. Overlapped Subarray Beamformer.

16

Fig. 5. T/R Board Top Level Layout.

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Fig. 9. Assembled Array Panel in Near Field Chamber.

Figure 10 shows the measured elevation patterns (co- polarized and cross-polarized) on receive. A fullcharacterization of the panel on transmit and receive is in

progress. In future work, the aperture board will beintegrated with a heat exchanger and backplane PCB asindicated in Fig. 11. The heat exchanger will be air cooledfor simplicity and cost. The backplane PCB will contain allrequired power conditioning and may integrate the requireddigital receivers and wave form generators. This unit willform the building block for a highly scalable arrayarchitecture.

IV. SUMMARY

MIT Lincoln Laboratory and M/A-COM are collaboratingto demonstrate an affordable approach to realizing amultifunction phased array radar system. This approachleverages commercial RFIC manufacturing coupled with

Fig. 10. Measured Elevation Pattern (E-plane)..

Aperture PCB

Heat Exchanger

T/R Elements

DC/DC Converters

Backplane PCB

Ring Frame

Fig. 11. Line Replaceable Unit Conceptual Drawing

commercial PCB design and manufacturing to realize anaperture panel containing an array of 8x8 elements.

ACKNOWLEDGEMENTS

The MIT LL M/A-COM team would like to acknowledgeW. Benner, and G. Torok of the FAA for their ongoing

support of this program.

REFERENCES

[1] Technical Requirements Document for MultifunctionPhased Array Radar (MPAR) Multi-modeTransmit/Receive Module, V8, MIT LincolnLaboratory, August 2008.

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low cost multifunction phased array radar concept

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