Distributed Adaptive Control and Metrologyfor Large Radar Apertures

Principal Investigator: James Lux, P.E. (337)Dr. Elaine Chapin (334), Samuel Li (337), Luis Amaro(337), Ofelia

Quintero(337)

Poster No. 05 - 003

Project Objective:

Develop and demonstrate method of self-calibrating large (>100 m2) phased array radar antennas without requiring a centralized metrology system.

FY05 Results:

Defined set of validated radar performance requirements• Significant driving requirement is sidelobe performance• Sidelobes < -30dB requires overall phase control to 1° rms• Performance budget requires calibration to 0.1° rms

Developed distributed calibration technique• Uses mutual coupling between elements and beacon(s) for

synchronization and frequency/phase reference.

Demonstrated calibration technique with 3 active elements.• Extended FY04 breadboard to 1.26 GHz radar frequencies• “Antenna simulator” simulates interelement coupling• Breadboard captures data, postprocessed with Matlab®

Produced 25 element antenna array for testing• Square array (5x5) dual polarization patches• Configuration allows testing nearest neighbor, cross

polarized, 2 elements away, etc.

Benefits to NASA and JPL:

Future Earth Science missions contemplate the use of radar antennas tens of meters in extent and hundreds of square meters in area with tens of thousands of active elements.

Accurate control of phase and amplitude for each element is required to meet overall performance requirements, particularly for sidelobes. Effects such as aging, radiation, and temperature change the phase & amplitude characteristics of the element electronics. The changes must be measured and calibrated out, after the radar is deployed in orbit.

The method developed here is very scalable, without the limitations imposed by the use of centralized metrology systems, which have limits on the number of elements that can be calibrated at once. Self calibration may allow relaxed component performance specifications, reducing parts, ground testing and calibration cost.

5x5 patch array for testing(3 elements used, others terminated)

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Power Spectrum of Received Signals from Self, Beacon, & Other Elements

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Coupling between elements is quite stable,can be modeled accurately, and “factored out”

Measuring a calibration signal transmitted from one element and received by adjacent elements can be used to calculate the properties of the electronics.

Need >2 elements in “Cal group” to be able to distinguish between Tx side and Rx side.

Cal signals are low power and compatible with radar waveforms, so many groups can calibrate simultaneously, and will not interfere with the radar operation. E.g. 1% of elements are calibrated at any given time, and the other 99% do the radar work.

Self Calibration Method

PC Serverfor control and data collection

Breadboard with 3 Elements

Synchronization “pulse”

All nodes reset.Signal from Node 4Signal from Node 3 2 Beacon Tones

Net RF signalgeneratoras beacon

Own transmitter

1.26 GHz RF sectionSingle-board PC + IF radio

Single Board PC with"sound card" interface

DDS controlledtransceiver

1.26 GHzreceiver chain

1.26 GHztransm it chain

T/RSwitchMatrix

PatchAntenna

5x5 Test Array

Rel

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owe

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1.26 GHz RF sectionSingle-board PC & IF radio

Single-board PC

Wireless Network

DDS IFRadio

1.26GHz Rx

1.26GHz Tx

10 MHzRef Osc

T/R switch